研究者総覧

郭 新宇 (カク シンウ)

  • 沿岸環境科学研究センター 教授
Last Updated :2020/11/10

研究者情報

学位

  • 博士(工学)(愛媛大学)

論文上での記載著者名

  • Xinyu Guo

ホームページURL

J-Global ID

研究キーワード

  • 沿岸海洋学   東シナ海   環境変動   瀬戸内海   長江   海洋科学   渤海   三峡ダム   栄養塩   栄養塩輸送   気候変動   低次生態系モデル   南水北調   黄河   ラニーニャ   振り分け潮   資源変動予測   駿河湾   黒潮蛇行   黒潮   栄養塩濃度   海洋物理・陸水学   熱輸送   黒潮変動   水産資源   物質循環   マアジ   北赤道海流の分岐緯度   惑星地衝流モデル   エネルギー論   資源管理   

研究分野

  • 環境・農学 / 環境動態解析
  • 自然科学一般 / 大気水圏科学
  • ライフサイエンス / 水圏生産科学

経歴

  • 2014年08月 - 現在  愛媛大学沿岸環境科学研究センターCenter for Marine Environmental Studies教授
  • 2007年04月 - 2014年07月  愛媛大学 沿岸環境科学研究センターCenter for Marine Environmental Studies准教授
  • 1999年11月 - 2007年03月  愛媛大学 沿岸環境科学研究センターCenter for Marine Environmental Studies助教授
  • 1997年10月 - 1999年10月  地球フロンティア研究システム研究員
  • 1997年04月 - 1997年09月  東京大学海洋研究所COE研究員

学歴

  • 1994年04月 - 1997年03月   愛媛大学   理工学研究科   生産工学
  • 1991年03月 - 1994年03月   青島海洋大学   海洋物理学専攻
  • 1988年09月 - 1991年01月   哈爾浜船舶工程学院   海洋流体力学専攻
  • 1984年09月 - 1988年07月   天津大学   工学部   船舶工学

研究活動情報

論文

  • Mingyu Zhong, Jianhui Tang, Xinyu Guo, Chao Guo, Fei Li, Huifeng Wu
    Science of The Total Environment 741 140434 - 140434 2020年11月 [査読有り]
     研究論文(学術雑誌)
  • Chao Zhang, Jingyi He, Xiaohong Yao, Yingchun Mu, Xinyu Guo, Xiaokun Ding, Yang Yu, Jinhui Shi, Huiwang Gao
    Science of the Total Environment 739 2020年10月 [査読有り]
     研究論文(学術雑誌) 
    © 2020 Elsevier B.V. Dust deposition can supply nutrients that affect marine phytoplankton, but changing trophic statuses of the surface ocean increase the complexity of interpreting the process. In this study, four onboard incubation experiments amended with various nutrients and dust were performed in the Kuroshio Extension (KE) and Kuroshio–Oyashio transition (TR) of the northwest Pacific (NWP), which are characterised by lower and higher trophic statuses, respectively. According to the nutrient-addition experiments, phytoplankton were limited by nitrogen (N) in the KE, and limited by iron (Fe) or co-limited by Fe and phosphorus (P) in the TR. Dust additions supplied a considerable amount of N and Fe but negligible amount of P to stimulate phytoplankton growth, as indicated by chlorophyll a (Chl a) concentration. In the KE incubations, dust additions enhanced the shift of phytoplankton size structure towards larger cells from dominantly pico-sized (0.2–2 μm) Chl a to comparable contributions from each size class (i.e. pico-, nano-: 2–20 μm, micro-: >20 μm). On the basis of the large shift of size structure towards nano- or micro-phytoplankton in the unamended control treatments in the TR, dust additions furtherly promoted the shift towards micro-phytoplankton becoming the dominant contributor to the total Chl a. The collective analysis of the data from experiments in both regions revealed that, the extent of phytoplankton growth stimulation and the shift towards larger cells were enhanced gradually with increasing amounts of nutrient uptake (including N, P, and silicon). The nutrient uptake ratios of phytoplankton converged towards the Redfield ratio in comparison to the wider range of nutrient ratios in the dust-amended seawater. This study suggested consistencies in the dynamic of phytoplankton growth, shift of size structure, and nutrient uptake following dust additions in the KE and TR, although the trophic status and limiting nutrient varied between these two regions.
  • Xiaojie Yu, Xinyu Guo, Huiwang Gao
    Journal of Geophysical Research: Oceans 125 10 2020年10月 [査読有り]
     研究論文(学術雑誌)
  • Xiaokun Ding, Xinyu Guo, Chao Zhang, Xiaohong Yao, Sumei Liu, Jie Shi, Chongxin Luo, Xiaojie Yu, Yang Yu, Huiwang Gao
    Chemosphere 254 2020年09月 [査読有り]
     研究論文(学術雑誌) 
    © 2020 Elsevier Ltd The Water Sediment Regulation Scheme (WSRS) is a unique engineering measure that has been regularly performed to reduce reservoir sedimentation and increase the flood capacity of the Yellow River in China since 2002. As a side effect, the WSRS greatly increases the monthly input flux of nutrients to the Bohai Sea (BHS) in summer, potentially exacerbating eutrophication levels therein and subsequently affecting the growth of phytoplankton. However, its influence on the Chlorophyll-a (Chl-a) dynamics over the BHS is still poorly understood. In this study, two approaches were adopted to investigate it: 1) long-term in-situ observations and satellite-derived data of surface Chl-a were used to study its seasonal variations before and since 2002, and 2) one 1D physical-biological coupled model was developed to evaluate the impact of WSRS on seasonal Chl-a. The results showed that the surface Chl-a exhibited two peaks in spring and autumn until 2002, but has exhibited only one peak in spring-summer since 2002. Satellite-derived Chl-a concentrations in spring-summer since 2002 have increased by 56% compared to those until 2002. The simulated results showed that the change in Yellow River discharge induced by the WSRS has resulted in the appearance of high concentrations of Chl-a in summer over the Central Bohai Sea since 2002. The WSRS increased the ratio of added Chl-a owing to the riverine nutrients to total Chl-a by 19% compared to that until 2002. Overall, WSRS greatly affects the seasonal cycling of Chl-a in the Bohai Sea, and the side effect needs to be considered.
  • Toru Kobari, Taiga Honma, Daisuke Hasegawa, Naoki Yoshie, Eisuke Tsutsumi, Takeshi Matsuno, Takeyoshi Nagai, Takeru Kanayama, Fukutaro Karu, Koji Suzuki, Takahiro Tanaka, Xinyu Guo, Gen Kume, Ayako Nishina, Hirohiko Nakamura
    Biogeosciences 17 9 2441 - 2452 2020年05月 [査読有り]
     研究論文(学術雑誌) 
    © 2020 Author(s). The Kuroshio Current has been thought to be biologically unproductive because of its oligotrophic conditions and low plankton standing stocks. Even though vulnerable life stages of major foraging fishes risk being entrapped by frontal eddies and meanders and encountering low food availability, they have life cycle strategies that include growing and recruiting around the Kuroshio Current. Here we report that phytoplankton growth and consumption by microzooplankton are stimulated by turbulent nitrate flux amplified by the Kuroshio Current. Oceanographic observations demonstrate that the Kuroshio Current topographically enhances significant turbulent mixing and nitrate influx to the euphotic zone. Graduated nutrient enrichment experiments show that growth rates of phytoplankton and microheterotroph communities were stimulated within the range of the turbulent nitrate flux. Results of dilution experiments imply significant microzooplankton grazing on phytoplankton. We propose that these rapid and systematic trophodynamics enhance biological productivity in the Kuroshio.
  • Lei Lin, Dongyan Liu, Xinyu Guo, Chongxin Luo, Yao Cheng
    Journal of Geophysical Research: Oceans 125 5 2020年05月 [査読有り]
     研究論文(学術雑誌) 
    ©2020. American Geophysical Union. All Rights Reserved. Water export rate of shelf seas is a pivotal factor impacting the global carbon cycle. Tides have important impacts on shelf hydrodynamics but are excluded in many climate models. To assess the effect of tides on export rates of shelf water, this study used a regional hydrodynamic model and a water residence time (WRT) adjoint model and examined model runs with and without tides for the eastern shelf seas of China. The results show that the average WRTs in the Bohai, Yellow, and East China seas were 11.60, 4.95, and 0.39 years, respectively. When tides were excluded, the WRTs decreased by >70% in the Bohai and Yellow seas and by ~10% in the East China Sea, indicating a significant acceleration in the shelf water export due to the absence of tides. The tidal effect has spatial variability associated with the water depth. Sensitivity experiments suggest that the tidal effect on the mean WRT was stronger than the effect of other dynamical factors (winds, rivers, and boundary currents). In the model with tides, tides weakened the wind-driven coastal current by intensifying the bottom resistance and thus slowed water export in the inner and middle portions of the shelf, compared to the model without tides. Parameterization of the tidal bottom friction in the model without tides could significantly improve the WRT result. This study highlights the crucial role of tides on the long-term transport of shelf seas and the significance of parameterizing the effect of tidal friction in climate models.
  • Fei Ji, Xinyu Guo, Yucheng Wang, Katsumi Takayama
    Climatic Change 159 4 601 - 618 2020年04月 [査読有り]
     研究論文(学術雑誌)
  • Yang Yu, Shu Hua Chen, Yu Heng Tseng, Xinyu Guo, J. I.E. Shi, Guangliang Liu, Chao Zhang, Y. I. Xu, Huiwang Gao
    Journal of Physical Oceanography 50 3 633 - 653 2020年03月 [査読有り]
     研究論文(学術雑誌) 
    © 2020 American Meteorological Society. The impacts of diurnal atmospheric forcing on the summer salinity change in the East China Sea are investigated using the Regional Ocean Modeling System, forced by the hourly and daily reanalysis of wind and insolation. The differences between the forcing of these two frequencies reveal a dipole pattern of salinity change with a positive salinity deviation (1–2 psu) offshore of the Yangtze River estuary, and a negative deviation (from-1 to-0.5 psu) along the Jiangsu Coast. Further dye tracking experiments confirm that diurnal forcing strengthened the northwestward longshore freshwater transport (NLFT) of the Yangtze River by 5.2 x 109 m3 and reduced the mean water age of 7 days. Sensitivity experiments using different forcing combinations suggest that the diurnal wind, that is, the land–sea breeze, is the key to developing the dipole pattern of salinity change and the NLFT. Through the experiment, the land–sea breeze induced a mean clockwise circulation offshore of the Yangtze River estuary. The above changes resulted from both the nonlinearity of wind stress averaging (i.e., the square nature of wind stress) and the baroclinic adjustment related to the diurnal salinity variation, which is directly connected to the diurnal swing of the Yangtze River front. The baroclinic adjustment generated a dipole pattern of vorticity changes offshore of the Yangtze River estuary and a coherent northwestward jet current strengthening the NLFT. These processes developed the summer dipole pattern of the salinity change.
  • Jie Shi, Qian Leng, Junying Zhu, Huiwang Gao, Xinyu Guo, Xinyan Mao
    Sustainability 12 6 2020年03月 [査読有り]
     研究論文(学術雑誌) 
    © 2020 by the authors. A marine ecosystem box model was developed to reproduce the seasonal variations nutrient concentrations and phytoplankton biomasses in Jiaozhou Bay (JZB) of China. Then, by removing each of the external sources of nutrients (river input, aquaculture, wastewater discharge, and atmospheric deposition) in the model calculation, we quantitatively estimated its influences on nutrient structure and the phytoplankton community. Removing the river input of nutrients enhanced silicate (SIL) limitation to diatoms (DIA) and decreased the ratio of DIA to flagellates (FLA); removing the aquaculture input of nutrients decreased FLA biomass because it provided less dissolved inorganic nitrogen (DIN) but more dissolved inorganic phosphate (DIP) as compared to the Redfield ratio; removing the wastewater input of nutrients changed the DIN concentration dramatically, but had a relatively weaker impact on the phytoplankton community than removing the aquaculture input; removing atmospheric deposition had a negligible influence on the model results. Based on these results, we suppose that the change in the external nutrients sources in the past several decades can explain the long-term variations in nutrient structure and phytoplankton community. Actually, the simulations for the 1960s, 1980s, and 2000s in JZB demonstrated the shift of limiting nutrients from DIP to SIL. A reasonable scenario for this is the decrease in riverine SIL and increase in DIP from aquaculture that has reduced DIA biomass, promoted the growth of FLA, and led to the miniaturization of the phytoplankton.
  • Miho Ishizu, Yasumasa Miyazawa, Tomohiko Tsunoda, Xinyu Guo
    Climatic Change 2020年 [査読有り]
     研究論文(学術雑誌) 
    © 2020, The Author(s). Here, we investigate the seasonal variability in the dissolved inorganic carbon (DIC) cycle in the Northwest Pacific using a high-resolution biogeochemical and carbon model coupled with an operational ocean model. Results show that the contribution to DIC from air–sea CO2 exchange is generally offset by vertical mixing at the surface at all latitudes, with some seasonal variation. Biological processes in subarctic regions are evident at the surface, whereas in the subtropical region these processes take place within the euphotic layer and then DIC consumption deepens southward with latitude. Such latitudinal differences in biological processes lead to marked horizontal and vertical contrasts in the distribution of DIC, with modulation by horizontal and vertical advection–diffusion processes.
  • Xinyan Mao, Xinyu Guo, Taishi Kubota, Yucheng Wang
    Progress in Oceanography 179 2019年12月 [査読有り]
     
    © 2019 Elsevier Ltd The snow crab Chionoecetes opilio is an important fishery species in Japan. Hydrodynamics are vital to the distribution, recruitment and settlement of crab larvae in nursery areas. In this study, we developed a survival and transport model of snow crab larvae to investigate the interannual variability in larval settlement in three fishing areas: west of Toyama (region A), west of Niigata (region B) and west of Hokkaido (region C). We found that the female crab stock abundance determined the modeled number of zoea in regions A and B, whereas water temperature played a major role in the initial number of zoea in region C. As for larval settlement, the ocean current impacted settlement in region B, and water temperature was vital to settlement in region C. Both female crab abundance and hydrodynamics contributed to variability in settlement in region A. The results revealed contrasting recruitment patterns in the three fishing areas. Self-recruitment was the primary form in regions A and C, whereas both self-recruitment and recruitment from upstream sources were important in region B.
  • Jing Zhang, Xinyu Guo, Liang Zhao
    Progress in Oceanography 176 2019年09月 [査読有り]
     研究論文(学術雑誌) 
    © 2019 Elsevier Ltd Nutrients (dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP)) in the East China Sea (ECS) have four external sources, namely the Kuroshio, Taiwan Strait, rivers, and the atmosphere. In order to evaluate the contribution of each source of nutrients to the nutrient inventory and primary production over the ECS shelf, a tracking technique was applied to all the state variables in a low-trophic ecosystem model. Each source of nutrients has strong seasonal variations in the spatial distribution that depends closely on circulation, mixing, and stratification. The primary production supported by each source of nutrient is under the control of a combination of nutrients, temperature, and light. As a mean state over the entire ECS shelf, the Kuroshio contributes 72% of DIN input and 84% of DIP input, 57% of DIN inventory and 78% of DIP inventory, 50% DIN-based primary production and 61% DIP-based primary production and therefore is the dominant one among four sources. However, the contributions of four external nutrients have strong spatial dependence: the riverine nutrients and the atmospheric DIN dominate the inner shelf (0–50 m), the nutrients from the Taiwan Strait dominate the southern part of the middle shelf (50–100 m), and the nutrients from the Kuroshio dominate the outer shelf (100–200 m). The production efficiencies of the nutrients from the Kuroshio are low, while those from the atmosphere and Taiwan Strait are high. The riverine DIN is inefficient but DIP is efficient. The nutrient limitation, light and water temperature at the location of the nutrients determine the production efficiency of each specific sources.
  • Yucheng Wang, Xinyu Guo, Liang Zhao, Jing Zhang
    Progress in Oceanography 176 2019年09月 [査読有り]
     研究論文(学術雑誌) 
    © 2019 Elsevier Ltd Based on a three dimensional low-trophic ecosystem model, we revaluated budgets of nutrients and biogenic particles (phytoplankton and detritus) in the East China Sea (ECS), a continental shelf sea with high productivity that is affected by a large river (Changjiang River) and a western boundary current (Kuroshio). Following careful comparison of model results with available observation data, we calculated the monthly inventories of the nutrients and biogenic particles in the ECS and the fluxes of the nutrients and biogenic particles through the lateral and vertical interfaces of the ECS. As an improvement over previous nutrient budget calculations that treated the ECS as one box, we divided the water column into two layers: upper and lower layers corresponding to different light condition. Seasonal variations in inventories of nutrients and biogenic particles in both upper and lower layers are apparent but present different features, which are related to opposite contributions of biological processes and physical processes in the two layers. Our calculation shows the necessity of evaluating not only the horizontal fluxes of nutrients and biogenic particles into and out of the ECS through lateral boundaries with adjacent seas but also the exchange fluxes of nutrients and biogenic particles between the upper and lower layers because the latter is larger than the former. Our calculation also reveals two major export pathways of biogenic particles generated locally in the ECS: from the ECS to the Japan/East Sea through the Tsushima Strait and from the ECS to the Kuroshio region through the shelf break (200 m isobath). The export amount of biogenic particles is larger through the Tsushima Strait than through the shelf break in the water column. The depth for the biogenic particles exporting through the shelf break of the ECS is the middle layer (from ~60 m to ~160 m).
  • Rui Bao, Meixun Zhao, Ann McNichol, Ying Wu, Xinyu Guo, Negar Haghipour, Timothy I. Eglinton
    Journal of Geophysical Research: Biogeosciences 124 8 2582 - 2594 2019年08月 [査読有り]
     研究論文(学術雑誌) 
    ©2019. American Geophysical Union. All Rights Reserved. To assess the influences of carbon sources and transport processes on the 14C age of organic matter (OM) in continental margin sediments, we examined a suite of samples collected along a river-shelf-deep ocean transect in the East China Sea (ECS). Ramped pyrolysis-oxidiation was conducted on suspended particulate matter in the Yangtze River and on surface sediments from the ECS shelf and northern Okinawa Trough. 14C ages were determined on OM decomposition products within different temperature windows. These measurements suggest that extensive amounts of pre-old (i.e., millennial age) organic carbon (OC) are subject to degradation within and beyond the Yangtze River Delta, and this process is accompanied by an exchange of terrestrial and marine OM. These results, combined with fatty acid concentration data, suggest that both the nature and extent of OM preservation/degradation as well as the modes of transport influence the 14C ages of sedimentary OM. Additionally, we find that the age of (thermally) refractory OC increases during across-shelf transport and that the age offset between the lowest and highest temperature OC decomposition fractions also increases along the shelf-to-trough transect. Amplified interfraction spread or 14C heterogeneity is the greatest in the Okinawa Trough. Aged sedimentary OM across the transect may be a consequence of several reasons including fossil OC input, selective degradation of younger OC, hydrodynamic sorting processes, and aging during lateral transport. Consequently, each of them should be considered in assessing the 14C results of sedimentary OM and its implications for the carbon cycle and interpretation of sedimentary records.
  • Takashi Mano, Xinyu Guo, Naoki Fujii, Naoki Yoshie, Eisuke Tsutsumi, Rui Saito
    Journal of Oceanography 75 4 359 - 374 2019年08月 [査読有り]
     研究論文(学術雑誌) 
    © 2019, The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. We found a good linear relation between the mean volume backscattering strength measured using a scientific echo sounder and the distribution density of moon jellyfish recorded simultaneously by an underwater video camera in small bays (Hokezu Bay and Mikame Bay) in Japan. This relation held in all of the surveys carried out in recent years (2013–2016), although the regression coefficient varied slightly from year to year due to the existence of ambient organisms. Using this relation and high-resolution echo sounder scan surveys across the bay, we obtained the spatial structures of moon jellyfish aggregations and categorized them into either patchy, layered, or wavy aggregations. We also examined possible physical mechanisms responsible for the moon jellyfish aggregations. In particular, passive particle tracking simulations of several idealized internal wave fields suggest that the formation of wavy aggregations is closely related to the presence of internal waves. However, internal waves alone cannot induce patchy and layered aggregations, indicating that particular biological processes (e.g., swimming behavior) are also necessary for such aggregations to form.
  • Zhao Jun Liu, Hirohiko Nakamura, Xiao Hua Zhu, Ayako Nishina, Xinyu Guo, Menghong Dong
    Journal of Geophysical Research: Oceans 124 8 6030 - 6049 2019年08月 [査読有り]
     研究論文(学術雑誌) 
    ©2019. American Geophysical Union. All Rights Reserved. Transverse-vertical structure and temporal variability of the Kuroshio current across the Tokara Strait during 2003–2012 measured by a ferryboat acoustic Doppler current profiler with a 2-km horizontal resolution and a two-day interval are presented. The Kuroshio passing through the Tokara Strait exhibits a multicore velocity structure. Its seasonal volume transport variation is biannual for baroclinic components relative to 700 m, peaking in July and December–January. However, the barotropic transport component exhibits an annual cycle with a maximum in December. Empirical orthogonal function analysis of the cross-sectional velocity is performed. The first two empirical orthogonal function modes reveal the north-south shift of the Kuroshio current axis and the change in Kuroshio volume transport, respectively. Temporal variabilities of the leading two modes correspond to those of the Kuroshio Position Index and the sea level difference across the strait, respectively. The third empirical orthogonal function mode, with a relatively smaller horizontal scale, was examined in terms of turbulent mixing. The banded structure captured by this mode is likely induced by flow-topography interaction because islands in the Kuroshio route could cause horizontal and vertical flow separation. Additional analysis based on high-resolution reanalysis data suggested that (1) inertial instability, which is expected in the areas with negative Ertel's potential vorticity, arises to enhance vertical mixing around the islands in the Tokara Strait, and (2) when the Kuroshio directly impinges the islands, flow divergence in the lee of the islands drives upwelling and leads to uplift of isotherms.
  • Aobo Wang, Xinyu Guo, Jie Shi, Chongxin Luo, Huiwang Gao
    Science of the Total Environment 664 522 - 535 2019年05月 [査読有り]
     研究論文(学術雑誌) 
    © 2019 Elsevier B.V. A three-dimensional transport-ecosystem-POP coupled model is configured to simulate the seasonal variation and budget of decabromodiphenyl ether (BDE-209) in a semi-enclosed bay adjacent to the Yellow Sea. The model includes five types of BDE-209 (gaseous, dissolved, phytoplankton-bound, detritus-bound, and suspended particulate matter (SPM)-bound) and related physical and biogeochemical processes, such as advection and diffusion due to seawater motion, input from rivers, air-sea exchange, decomposition of dissolved BDE-209, uptake and depuration between dissolved and phytoplankton-bound BDE-209, mortality of phytoplankton-bound BDE-209, remineralization and sinking of detritus-bound BDE-209, and sinking of SPM-bound BDE-209. Model results show that the dissolved and particulate BDE-209 in the bay are higher in the nearshore area than in offshore area and are higher in summer than in other seasons; these results are consistent with field data. SPM-bound BDE-209 is dominant among the five types due to its large supplying from rivers. Dissolved BDE-209 concentrations are around 5-fold that of phytoplankton-bound BDE-209, which depends on uptake and depuration rate constants between dissolved and phytoplankton-bound BDE-209 and biomass of phytoplankton. Evaluation of mass balance indicates that the input from rivers is major source of BDE-209, while the exchange with the Yellow Sea is major sink. Sensitivity experiments demonstrate that the input of BDE-209 from rivers plays the most significant role in the seasonal variation of dissolved and particulate BDE-209 concentrations, and the change in water temperature is a secondary factor.
  • Miho Ishizu, Yasumasa Miyazawa, Tomohiko Tsunoda, Xinyu Guo
    Sustainability (Switzerland) 11 9 2019年05月 [査読有り]
     研究論文(学術雑誌) 
    © 2019 by the authors. We developed a biogeochemical and carbon model (JCOPE_EC) coupled with an operational ocean model for the North Western Pacific. JCOPE_EC represents ocean acidification indices on the background of the risks due to ocean acidification and our model experiences. It is an off-line tracer model driven by a high-resolution regional ocean general circulation model (JCOPE2M). The results showed that the model adequately reproduced the general patterns in the observed data, including the seasonal variability of chlorophyll-a, dissolved inorganic nitrogen/phosphorus, dissolved inorganic carbon, and total alkalinity. We provide an overview of this system and the results of the model validation based on the available observed data. Sensitivity analysis using fixed values for temperature, salinity, dissolved inorganic carbon and total alkalinity helped us identify which variables contributed most to seasonal variations in the ocean acidification indices, pH and Ωarg. The seasonal variation in the pHinsitu was governed mainly by balances of the change in temperature and dissolved inorganic carbon. The seasonal increase in Warg from winter to summer was governed mainly by dissolved inorganic carbon levels.
  • Junying Zhu, Xinyu Guo, Jie Shi, Huiwang Gao
    Marine Pollution Bulletin 141 91 - 103 2019年04月 [査読有り]
     研究論文(学術雑誌) 
    © 2019 Elsevier Ltd Riverine input is an important source of contaminants in the marine environments. Based on a hydrodynamic model, the dilution characteristics of riverine contaminants in the Seto Inland Sea and their controlling factors were studied. Results showed that contaminant concentration was high in summer and low in winter. Contaminant concentration decreased with the reduction of its half-life period, and the relationship between them followed power functions. Sensitivity experiments suggested that the horizontal current and vertical stratification associated with air-sea heat flux controlled the seasonal cycle of contaminant concentration in the water column; however, surface wind velocity was the dominant factor affecting the surface contaminant concentration. In addition, contaminant concentration in a sub-region was likely controlled by the variations in river discharges close to the sub-region. These results are helpful for predicting contaminant concentrations in the sea and are expected to contribute to assessing the potential ecological risks to aquatic organisms.
  • Rui Shi, Qinbo Cai, Lingyu Dong, Xinyu Guo, Dongxiao Wang
    Journal of Geophysical Research: Atmospheres 124 7 3702 - 3725 2019年04月 [査読有り]
     研究論文(学術雑誌) 
    ©2019. American Geophysical Union. All Rights Reserved. The modulation of coastal rainfall at Hainan by large-scale circulation and coastal upwelling is studied using observations and numerical modeling. Tropical Rainfall Measuring Mission data show that the monthly mean rainfall off southern Hainan was considerably higher in August 2010 than in August 2011. The main cause of this difference is an intensification of offshore rainfall from midnight to early morning. Compared with the multiyear (2000–2017) average field, reanalysis data show that there is an apparent increase in atmospheric humidity in August 2010. During this time, a moderate El Niño was decaying and a new La Niña event was developing, so a significant adjustment of the large-scale circulation was observed in the western Pacific. The resulting anomalous onshore wind depresses the development of upwelling, leading to a relatively warm sea surface temperature off the south coast of Hainan, which in turn enhances the land-sea thermal contrast and land breeze at night. Decreases in upwelling intensity and asymmetric intensification of nocturnal and daytime offshore rainfall are confirmed not only in the summer of 2010 but also in the summer of 2003. Numerical simulations using the Weather Research and Forecasting model verify that the enhanced land breeze ultimately leads to pronounced coastal rainfall off southern Hainan at night. The results indicate that localized surface convergence associated with the sea and land breezes may be more important than the atmospheric humidity and convective instability in modulating the diurnal cycle of rainfall for tropical islands.
  • Xinyan Mao, Xinyu Guo, Yucheng Wang, Katsumi Takayama
    Sustainability 11 8 2019年04月 [査読有り]
     研究論文(学術雑誌) 
    © 2019 by the authors. The snow crab (Chionoecetes opilio) sustains an important bottom trawling fishery in the Sea of Japan. Its response to global warming is attracting the attention of the public. Using a transport and survival model for crab larvae in the Sea of Japan, we examined the spatial-temporal variations of crab spawning and larval settlement in the past (mid-20th century), present (early 21st century), and future (mid- and late 21st century) under the low and high radiative forcing scenarios. It was found that the variations in spawning differed between the regions south of and north of 41.5° N, on both seasonal and long-term scales. Larval settlement in the Sea of Japan was projected to increase in the future, which is mainly attributed to a reduction in mortality due to the low water temperature. Moreover, the aggregating location of the settled megalopae will likely shift northward, with increasing settlement off Hokkaido Island. With additional sensitivity experiments, we confirmed that the change in water temperature has a stronger impact on larval settlement than that in the current field. The change in water temperature controlled both the amount and distribution of crab larval settlement, while a change in current field only affected the distribution to some extent.
  • Jie Gao, Xin Yan Mao, Xin Yu Guo
    Oceanologia et Limnologia Sinica 50 2 269 - 277 2019年03月 [査読有り]
     研究論文(学術雑誌) 
    © 2019, Science Press. All right reserved. Based on a hydrodynamic model (JCOPE-T model: Japan Coastal Ocean Predictability Experiment-Tides) in 3-km horizontal resolution, we studied the internal tides in the Tokara Strait, Japan. The strait features complex topography and stable stratification, in which significant isopycnal movement (up to 30 m) is generated. Internal tides in the strait could form up near the seamounts and islands where topography changes drastically. After an internal tide is generated, it would propagate outwards perpendicular to the isobaths in two directions: one goes northwestward and finally enters the shelf of the East China Sea; another moves southeastward and finally enters the Pacific Ocean. Therefore, the strait is abundant in tidal energy. The model data averaged over-14 diurnal tidal periods show that the barotropic energy propagated into the region is 13.92 GW of which 3.73 GW is converted into internal tidal energy. About 77.2% of the internal tidal energy is dissipated locally, while the remaining part transmits mainly through the northwestern and southeastern boundaries. Both the input of the barotropic tidal energy and the conversion rate (from barotropic tides to baroclinic tides) during spring tide roughly doubled those during neap tide. Even though, the main generation area and the propagation direction remain largely unchanged, namely, internal tides transmit mainly through the northwestern and southeastern boundaries. The dissipation rate of internal tidal energy is between 76%-79% in both neap and spring tides. Therefore, the spring-neap tidal cycle affects only the amount of internal tidal energy generated in the Tokara Strait but does not affect the generation area, the propagation direction, and the dissipation rate.
  • Haiyan Wang, Xinyu Guo, Zhe Liu
    Journal of Marine Systems 191 24 - 37 2019年03月 [査読有り]
     研究論文(学術雑誌) 
    © 2018 Elsevier B.V. The age of Yodo River water, the largest river flowing in the Seto Inland Sea (SIS), was calculated using the constituent-oriented age and residence time theory (CART) in order to understand the long-term material transport and environmental issues in this semi-enclosed sea. The Yodo River water was found to have a mean age of 152 days for the entire SIS. Inside the SIS, the age of Yodo River water shows spatial variation ranging from 97 days in Osaka Bay, 199 days in the Harima-Nada, and 450 days in other areas. The age of Yodo River water shows an apparent seasonal variation in the SIS. Tracing water from the Yodo River reveals two pathways for its movement around Osaka Bay: one brings ~5/8 river water directly into the Kii Channel through the Kitan Strait; the other brings ~3/8 river water into the Harima-Nada through the Akashi Strait that eventually enters the Kii Channel through the Naruto Strait. The mean age of Yodo River water is 128 days at the Kitan Strait, 125 days at the Akashi Strait, 203 days at the Naruto Strait, and 271 days at the Bisan Strait. The above estimation considers the return of old Yodo River water into Osaka Bay that does not change the spatial distribution of Yodo River water age inside Osaka Bay but increases the value of water age by ~80%. Without tidal forcing, the mean ages of Yodo River water in Osaka Bay and the Harima-Nada increase by 6% and 51%, respectively, and nearly all the Yodo River water flows directly into the Kii Channel through the Kitan Strait. Without considering baroclinic forcing, the mean ages of Yodo River water in Osaka Bay and the Harima-Nada increases by 52% and 51%, respectively, while the influence of local winds and the Yodo River discharge on the age of Yodo River water are negligible.
  • Yu Long, Xiao Hua Zhu, Xinyu Guo
    Geophysical Research Letters 46 3 1513 - 1520 2019年02月 [査読有り]
     研究論文(学術雑誌) 
    ©2019. American Geophysical Union. All Rights Reserved. The Oyashio, a subarctic western boundary current in the North Pacific, transports cool, fresh, and nutrient-rich water equatorward. The Oyashio nutrient stream was assessed using long-term mean hydrographic observation data. Its nitrate transport (about 350 kmol/s) is comparable to that of the Kuroshio but has a much shallower subsurface core at 250-m depth. In the layer ranging from 26.6 to 27.4 σ θ , the Oyashio nitrate transport to the mixed water region is about 110 kmol/s. This corresponds to the nitrate transport of the Oyashio to the North Pacific Intermediate Water in the mixed water region. Along with this process, the subarctic gyre nitrate export to the subtropic gyre reaches 24 kmol/s. This work first quantifies the Oyashio nutrient transport and its intrusion into the mixed water region and suggests its importance in local/basin-scale nutrient cycles.
  • Haejin Kim, Katsumi Takayama, Naoki Hirose, Akihiko Morimoto, Ryota Shibano, Masashi Ito, Tetsutaro Takikawa, Xinyu Guo, Yucheng Wang, Taishi Kubota, Naoki Yoshie, Katazakai Saki, Jing Zhang, Takafumi Yoshida
    Integrated Coastal Management in the Japanese Satoumi: Restoring Estuaries and Bays 85 - 129 2019年01月 [査読有り]
     論文集(書籍)内論文 
    © 2019 Elsevier Inc. All rights reserved. The Environment Research and Technology Development Fund of the Ministry of the Environment, Japan S-13 was started from FY2014, aiming to develop a coastal environmental management methodology for sustainable coastal areas. This project selected three target sea areas, namely, the coastal area of the Sanriku region, the Seto Inland Sea and the Japan Sea to verify the developed management methodology. Among the three areas, our group focused on the Japan Sea.
  • Yu Long, Xiao Hua Zhu, Xinyu Guo, Haocai Huang
    Journal of Geophysical Research: Oceans 123 11 7896 - 7913 2018年11月 [査読有り]
     研究論文(学術雑誌) 
    ©2018. American Geophysical Union. All Rights Reserved. The temporal variation of the Kuroshio nutrient stream south of Japan was examined using quarterly hydrographic data at section 137E from 2000 to 2013. During the seasonal cycle, nitrate flux and transport reach the maximum (minimum) in autumn (winter). The Kuroshio recirculation contributes about 60% to the mean eastward nitrate transport and the seasonal variations thereof. Empirical orthogonal function analysis showed two dominant modes in nitrate flux, nitrate concentration, and velocity at section 137E; these were associated with Kuroshio path meander and the Kuroshio Extension decadal oscillation. The Kuroshio large meander induced a significant increase in the eastward nitrate transport, from 609 to 1,723 kmol/s, at the section. Due to the modulation of the Kuroshio Extension decadal oscillation, both the eastward nitrate transport and the Kuroshio recirculation were stronger in an unstable state compared to when in a stable state. The variation in the eastward nitrate transport in these dynamic patterns can be attributed to the strength, location, and spatial expansion of the Kuroshio recirculation south of Japan. Nitrate transport from the south of Japan to the Kuroshio Extension was relatively stable at 400 kmol/s. There was a strong seasonal variation in the surface chlorophyll concentration over the subtropical gyre including Kuroshio recirculation region, whereas variations in the Kuroshio region was controlled by the Kuroshio path shift. The velocity-weighted nitrate concentration in the dense layer along the Kuroshio path increased throughout the year while that in the light layer decreased in spring and autumn and increased in summer and winter.
  • Rui Bao, Tessa S. van der Voort, Meixun Zhao, Xinyu Guo, Daniel B. Montluçon, Cameron McIntyre, Timothy I. Eglinton
    Global Biogeochemical Cycles 32 9 1420 - 1432 2018年09月 [査読有り]
     研究論文(学術雑誌) 
    ©2018. The Authors. Understanding the effects of hydrodynamic forcing on organic matter (OM) composition is important for assessment of organic carbon (OC) burial in marginal seas on regional and global scales. Here we examine the relationships between regional oceanographic conditions (bottom shear stress), and the physical characteristics (mineral surface area and grain size) and geochemical properties (OC content [OC%] and carbon isotope compositions [13C, 14C]) of a large suite of surface sediments from the Chinese marginal seas to assess the influence of hydrodynamic processes on the fate of OM on shallow continental shelves. Our results suggest that 14C content is primarily controlled by organo-mineral interactions and hydrodynamically driven resuspension processes, highlighted by (i) positive correlations between 14C content and OC% (and surface area) and (ii) negative correlations between 14C content and grain size (and bottom shear stress). Hydrodynamic processes influence 14C content due to both OC aging during lateral transport and accompanying selective degradation of OM associated with sediment (re) mobilization, these effects being superimposed on the original 14C characteristics of carbon source. Our observations support the hypotheses of Blair and Aller (2012, https://doi.org/10.1146/annurev-marine-120709-142717) and Leithold et al. (2016, https://doi.org/10.1016/j.earscirev.2015.10.011) that hydrodynamically driven sediment translocation results in greater OC 14C depletion in broad, shallow marginal seas common to passive margin settings than on active margins. On a global scale, this may influence the extent to which continental margins act as net carbon sources and sinks. Our findings thus suggest that hydrodynamic processes are important in shaping the nature, dynamics, and magnitude of OC export and burial in passive marginal seas.
  • Xiaojie Yu, Xinyu Guo
    Continental Shelf Research 165 26 - 36 2018年08月 [査読有り]
     研究論文(学術雑誌) 
    © 2018 Elsevier Ltd Bottom cold water (BCW) is widely reported to occur in many coastal areas in summer. Some BCW masses have an increase in temperature of only 1 °C from early spring to summer (e.g., North Sea, Yellow Sea), while the others have a 4–10 °C increase (e.g., Irish Sea, Seto Inland Sea). A model of heat transport with vertical diffusion alone gave good approximation of the temperature increase in the North Sea type BCW masses, while additional heat input from other processes was required to simulate the large temperature increases in Irish Sea type BCWs. BCWs in the Yellow Sea and the Seto Inland Sea are then taken as examples to compare heat transport into the two types of BCWs through three-dimensional numerical modeling. The small warming range of the BCW in the Yellow Sea results mainly from downward heat input by vertical diffusion. In contrast, the large temperature range of warming in the BCW in the Seto Inland Sea is a result of both advection of heat from the surrounding water and vertical diffusion. We therefore infer that advection of heat into the BCW is a necessary condition for the high temperature increase range in Irish Sea type BCWs. Moreover, advection of heat into one BCW in the Seto Inland Sea intensifies from April to July, which is induced by gradually intensified bottom currents. This example supports the importance of heat transport by advection for BCWs where the temporal change in advection of heat is capable of altering the temperature increase rate inside the BCW.
  • 島袋寛盛, 吉田吾郎, 加藤亜記, 郭新宇
    海洋と生物 40 3 233 - 242 2018年06月 研究論文(学術雑誌)
  • Li Zou, Xiao Yao, Hitomi Yamaguchi, Xinyu Guo, Huiwang Gao, Kai Wang, Mingyi Sun
    Journal of Ocean University of China 17 2 437 - 444 2018年04月 [査読有り]
     研究論文(学術雑誌) 
    © 2018, Science Press, Ocean University of China and Springer-Verlag GmbH Germany, part of Springer Nature. In order to examine the seasonal and spatial distributions of benthic animals in the intertidal mudflat of the southern Yellow River Delta, field investigations were carried out in 2007 and 2008 and multiple methods were applied. Results showed that, the biomass of macro benthos ranged at 0.75-1151.00 g wet m−2 and averaged at 156.31 g wet m−2, in which Mactra veneriformis accounted for 75.6%-93.4% of the total macro benthic biomass. More than 90% of macro benthos inhabited in the middle and low tide lines, and higher biomass occurred in early summer and lower in winter. Statistical analysis showed that: 1) M. veneriformis growth was primarily favored at higher temperature and lower salinity; 2) after long time interaction, benthic bivalve grazers led to patching distributions of Chlorophyll a (Chl a); 3) macro benthic biomass positively related with Chl a when the concentration of Chl a was low, but they were negatively related when Chl a concentration was high; and 4) furthermore, the biomass of benthic bivalves peaked in the sediment with median grain size about 0.55 mm, but decreased gradually in coarse or fine sediments. The secondary productivity ranged at 0.37-283.68 g m−2yr−1 and averaged at 47.88 g m−2 yr−1, in which 69.7% was contributed by M. veneriformis It was estimated that primary production was transformed to secondary production at a rate of 6.87% approximately, which implies that there is a local sustainability of high bivalve production.
  • Qiang Chu, Ying Liu, Jie Shi, Chao Zhang, Xiang Gong, Xiaohong Yao, Xinyu Guo, Huiwang Gao
    Journal of Geophysical Research: Biogeosciences 123 3 1101 - 1116 2018年03月 [査読有り]
     研究論文(学術雑誌) 
    ©2018. American Geophysical Union. All Rights Reserved. Dust deposition is an important nutrient source to the South China Sea (SCS), but few in situ experiments were conducted on phytoplankton response to the deposition. We conducted onboard incubation experiments at three stations near Luzon Strait in the SCS, with addition of multiple dissolved inorganic nutrients, Asian dust, and rainwater. From our results, nitrogen and phosphorus were both urgently needed for phytoplankton growth in the SCS, indicated by the evident Chl a response to the addition of nitrogen and phosphorus together. Almost no evident response was observed by adding phosphorus or iron alone to incubation waters, although a delayed response of Chl a in mass concentration was observed by adding nitrogen alone. The latter implied a possible utilization of dissolved organic phosphorus because of insufficient dissolved inorganic phosphorus in incubation waters. Under such nutrient condition, Asian dust showed an apparent promotion effect on phytoplankton growth by providing sufficient amounts of nitrogen but low phosphorus. Meanwhile, it was found that large sized (> 5 μm) phytoplankton community showed different responses to dust addition at different stations. At stations A3 and A6, Chaetoceros spp. became the dominant species during the bloom period, while at station WG2, Nitzschia spp. became dominant. In combination with different initial nutrients and Chl a levels at the three stations, the different phytoplankton community evolution implied the response difference to external inputs between oligotrophic (stations A3 and A6) and ultraoligotrophic (station WG2) conditions in the SCS.
  • Chao Zhang, Huiwang Gao, Xiaohong Yao, Zongbo Shi, Jinhui Shi, Yang Yu, Ling Meng, Xinyu Guo
    Biogeosciences 15 3 749 - 765 2018年02月 [査読有り]
     研究論文(学術雑誌) 
    © 2018 Author. In this study, five on-board microcosm experiments were performed in the subtropical gyre, the Kuroshio Extension region of the northwest Pacific Ocean (NWPO), and the Yellow Sea (YS) in order to investigate phytoplankton growth following the addition of artificially modified mineral dust (AM dust) and various nutrients (nitrogen (N), phosphorus (P), iron (Fe), NCP, and NCPCFe). The two experiments carried out with AM-dust addition in the subtropical gyre showed a maximum chlorophyll a (Chl a/concentration increase of 1.7- A nd 2.8-fold, while the cell abundance of large-sized phytoplankton (<5μm) showed a 1.8- A nd 3.9-fold increase, respectively, relative to the controls. However, in the Kuroshio Extension region and the YS, the increases in maximum Chl a and cell abundance of largesized phytoplankton following AM-dust addition were at most 1.3-fold and 1.7-fold larger than those in the controls, respectively. A net conversion efficiency index (NCEI) newly proposed in this study, size-fractionated Chl a, and the abundance of large-sized phytoplankton were analysed to determine which nutrients contribute to supporting phytoplankton growth. Our results demonstrate that a combination of nutrients, N.P or NCPCFe, is responsible for phytoplankton growth in the subtropical gyre following AM-dust addition. Single nutrient addition, i.e., N in the Kuroshio Extension region and P or N in the YS, controls the phytoplankton growth following AM-dust addition. In the AM-dust-addition experiments, in which the increased N.P or P was identified to determine phytoplankton growth, the dissolved inorganic P from AM dust (8.6 nmol L-1/was much lower than the theoretically estimated minimum P demand (∼20 nmol L-1/for phytoplankton growth. These observations suggest that additional supply augments the bioavailable P stock in incubated seawater with AM-dust addition, most likely due to an enhanced solubility of P from AM dust or the remineralization of the dissolved organic P.
  • Xiaojie Yu, Xinyu Guo, Akihiko Morimoto, Anukul Buranapratheprat
    Continental Shelf Research 153 16 - 29 2018年02月 [査読有り]
     研究論文(学術雑誌) 
    © 2017 Elsevier Ltd River plumes are a general phenomenon in coastal regions. Most previous studies focus on river plumes in middle and high latitudes with few studies examining those in low latitude regions. Here, we apply a numerical model to the Upper Gulf of Thailand (UGoT) to examine a river plume in low latitudes. Consistent with observational data, the modeled plume has seasonal variation dependent on monsoon conditions. During southwesterly monsoons, the plume extends northeastward to the head of the gulf; during northeasterly monsoons, it extends southwestward to the mouth of the gulf. To examine the effects of latitude, wind and river discharge on the river plume, we designed several numerical experiments. Using a middle latitude for the UGoT, the bulge close to the river mouth becomes smaller, the downstream current flows closer to the coast, and the salinity in the northern UGoT becomes lower. The reduction in the size of the bulge is consistent with the relationship between the offshore distance of a bulge and the Coriolis parameter. Momentum balance of the coastal current is maintained by advection, the Coriolis force, pressure gradient and internal stresses in both low and middle latitudes, with the Coriolis force and pressure gradient enlarged in the middle latitude. The larger pressure gradient in the middle latitude is induced by more offshore freshwater flowing with the coastal current, which induces lower salinity. The influence of wind on the river plume not only has the advection effects of changing the surface current direction and increasing the surface current speed, but also decreases the current speed due to enhanced vertical mixing. Changes in river discharge influence stratification in the UGoT but have little effect on the behavior of the river plume.
  • Junying Zhu, Jie Shi, Xinyu Guo, Huiwang Gao, Xiaohong Yao
    Continental Shelf Research 152 14 - 26 2018年01月 [査読有り]
     研究論文(学術雑誌) 
    © 2017 The Yellow Sea Cold Water Mass (YSCWM), which occurs during summer in the central Yellow Sea, plays an important role in the hydrodynamic field, nutrient cycle and biological species. Based on water temperature observations during the summer from 1978 to 1998 in the western Yellow Sea, five specific YSCWM years were identified, including two strong years (1984 and 1985), two weak years (1989 and 1995) and one normal year (1992). Using a three-dimensional hydrodynamic model, the YSCWM formation processes in these five years were simulated and compared with observations. In general, the YSCWM began forming in spring, matured in summer and gradually disappeared in autumn of every year. The 8 °C isotherm was used to indicate the YSCWM boundary. The modelled YSCWM areas in the two strong years were approximately two times larger than those in the two weak years. Based on the simulations in the weak year of 1995, ten numerical experiments were performed to quantify the key factors influencing the YSCWM intensity by changing the initial water condition in the previous autumn, air-sea heat flux, wind, evaporation, precipitation and sea level pressure to those in the strong year of 1984, respectively. The results showed that the air-sea heat flux was the dominant factor influencing the YSCWM intensity, which contributed about 80% of the differences of the YSCWM average water temperature at a depth of 50 m. In addition, the air-sea heat flux in the previous winter had a determining effect, contributing more than 50% of the differences between the strong and weak YSCWM years. Finally, a simple formula for predicting the YSCWM intensity was established by using the key influencing factors, i.e., the sea surface temperature before the cooling season and the air-sea heat flux during the cooling season from the previous December to the current February. With this formula, instead of a complicated numerical model, we were able to roughly predict the YSCWM intensity for the following summer by using the data available online in winter.
  • Yingying Hu, Xinyu Guo, Liang Zhao
    Journal of Oceanology and Limnology 36 1 62 - 76 2018年01月 [査読有り]
     研究論文(学術雑誌) 
    © 2018, Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature. Long-term datasets of water temperature, salinity, dissolved oxygen, phosphate and nitrate from 1973 to 2013 were used to study interannual variations of these parameters along a transect (section PN) across the Kuroshio and shelf area in the East China Sea. Water temperature and salinity at depths of 0–200 m showed a low-high-low-high pattern over the 40-year period. Water temperature and salinity at 500 m were relatively high from 1985 to 1990 and decreased continuously thereafter. Salinity at 800 m was lowest around 1993 and increased thereafter. Nutrients were highest between 1980 and 1985. After 1985, nutrients at 500 m were increasing. The range of variation in nutrients was large before 1985 and the magnitude increased with greater depths. Apparent oxygen utilization at 500 m depth was decreasing before 1990 and started to increase after 1992. Significant changes after 1990 at 500 m depth may be due to the upward trend of the upper boundary of Kuroshio intermediate water. Interannual variation of water temperature, salinity, dissolved oxygen, phosphate and nitrate along section PN has a significant correlation with the Pacific Decadal Oscillation index.
  • Yucheng Wang, Xinyu Guo, Liang Zhao
    Journal of Oceanology and Limnology 36 1 48 - 61 2018年01月 [査読有り]
     研究論文(学術雑誌) 
    © 2018, Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature. Using a three-dimensional coupled biophysical model, we simulated the responses of a lowtrophic ecosystem in the East China Sea (ECS) to long-term changes in nutrient load from the Changjiang (Yangtze) River over the period of 1960–2005. Two major factors affected changes in nutrient load: changes in river discharge and the concentration of nutrients in the river water. Increasing or decreasing Changjiang discharge induced different responses in the concentrations of nutrients, phytoplankton, and detritus in the ECS. Changes in dissolved inorganic nitrogen (DIN), silicate (SIL), phytoplankton, and detritus could be identified over a large area of the ECS shelf, but changes in dissolved inorganic phosphate (DIP) were limited to a small area close to the river mouth. The high DIN:DIP and SIL:DIP ratios in the river water were likely associated with the different responses in DIN, DIP, and SIL. As DIP is a candidate limiting nutrient, perturbations in DIP resulting from changes in the Changjiang discharge are quickly consumed through primary production. It is interesting that an increase in the Changjiang discharge did not always lead to an increase in phytoplankton levels in the ECS. Phytoplankton decreases could be found in some areas close to the river mouth. A likely cause of the reduction in phytoplankton was a change in the hydrodynamic field associated with the river plume, although the present model is not suitable for examining the possibility in detail. Increases in DIN and DIP concentrations in the river water primarily led to increases in DIN, DIP, phytoplankton, and detritus levels in the ECS, whereas decreases in the SIL concentration in river water led to lower SIL concentrations in the ECS, indicating that SIL is not a limiting nutrient for photosynthesis, based on our model results from 1960 to 2005. In both of the above-mentioned cases, the sediment accumulation rate of detritus exhibited a large spatial variation near the river mouth, suggesting that core sample data should be carefully interpreted.
  • Yang Yu, Huiwang Gao, Jie Shi, Xinyu Guo, Guangliang Liu
    Journal of Geophysical Research: Oceans 122 12 9870 - 9888 2017年12月 [査読有り]
     研究論文(学術雑誌) 
    © 2017. American Geophysical Union. All Rights Reserved. This study investigates the seasonal variation in temperature induced by diurnal forcing in the eastern shelf seas of China (ESSC) using a high-resolution Regional Ocean Modeling System model forced by the National Center for Environmental Prediction and the National Center for Atmospheric Research re-analysis data for surface fluxes with both 6 h and daily frequencies, respectively. The comparison between two experiments revealed a ±0:4ºC modification of the variation in seasonal temperature by diurnal forcing, which also increases the mixed-layer depth (MLD) in August by 26% and reduces the volume of the Yellow Sea Cold Water Mass (YSCWM) by 25%. Sensitivity experiments using different forcing variables indicated that diurnal wind can explain over 80% of the variability in seasonal temperature induced by diurnal forcing. Diurnal wind led to an increase in the net heat flux into the ocean by about 13 W/m2 in summer and a decrease by about 15 W/m2 in winter. Diurnal wind also generated an additional downward heat transport of 21 W/m2 over the ESSC that contributed to variability in the mean MLD and YSCWM in August. Experiments changing the temporal interval of wind forcing suggested that the increase in the forcing temporal interval gradually enhanced the reproduction of the variability in seasonal temperature generated by diurnal wind; a 6 h wind forcing can capture 70% of this type of variability given by 1 h wind forcing, while a 3 h or shorter wind forcing can capture 90%.
  • Zhen Li, Haiyan Wang, Xinyu Guo, Zhe Liu, Huiwang Gao, Guiling Zhang
    Journal of Ocean University of China 16 5 727 - 737 2017年10月 [査読有り]
     研究論文(学術雑誌) 
    © 2017, Science Press, Ocean University of China and Springer-Verlag GmbH Germany. Abrupt changes in freshwater inputs from large rivers usually imply regime shifts in coastal water environments. The influence of a water regulation event on the age of the Yellow River water in the Bohai was modeled using constituent-oriented age and residence time theory to better understand the change in the environmental function of the hydrodynamic field owing to human activities. The water ages in Laizhou Bay, the central basin, and the Bohai strait are sensitive to water regulation. The surface ages in those areas can decrease by about 300 days, particularly in July, and the age stratification is also strengthened. A water regulation event can result in declines in the water age in early July ahead of declines in the water age under climatological conditions (without the regulation event) by about 1 and 5 months in the central basin and Laizhou Bay, respectively. The change in the coastal circulation due to the water regulation event is the primary reason for the change in the Yellow River water age. The high Yellow River flow rate can enhance the density flow and, therefore, reduce the age of the Yellow River water. The subsequent impact of a single water regulation event can last about 1.0 to 4.0 years in different subregions.
  • Eisuke Tsutsumi, Takeshi Matsuno, Ren Chieh Lien, Hirohiko Nakamura, Tomoharu Senjyu, Xinyu Guo
    Journal of Geophysical Research: Oceans 122 9 7082 - 7094 2017年09月 [査読有り]
     研究論文(学術雑誌) 
    © 2017. American Geophysical Union. All Rights Reserved. Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ∼ O(10−3)–O(10−2) m2 s−1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10−1) m2 s−1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10−3) m2 s−1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.
  • Ze Nan Zhu, Xiao Hua Zhu, Xinyu Guo, Xiaopeng Fan, Chuanzheng Zhang
    Journal of Geophysical Research: Oceans 122 9 7013 - 7030 2017年09月 [査読有り]
     研究論文(学術雑誌) 
    © 2017. American Geophysical Union. All Rights Reserved. For the first time, we present the application of an unstructured triangular grid to the Finite-Volume Community Ocean Model using the ensemble Kalman filter scheme, to assimilate coastal acoustic tomography (CAT) data. The fine horizontal and vertical current field structures around the island inside the observation region were both reproduced well. The assimilated depth-averaged velocities had better agreement with the independent acoustic Doppler current profiler (ADCP) data than the velocities obtained by inversion and simulation. The root-mean-square difference (RMSD) between depth-averaged current velocities obtained by data assimilation and those obtained by ADCPs was 0.07 m s−1, which was less than the corresponding difference obtained by inversion and simulation (0.12 and 0.17 m s−1, respectively). The assimilated vertical layer velocities also exhibited better agreement with ADCP than the velocities obtained by simulation. RMSDs between assimilated and ADCP data in vertical layers ranged from 0.02 to 0.14 m s−1, while RMSDs between simulation and ADCP data ranged from 0.08 to 0.27 m s−1. These results indicate that assimilation had the highest accuracy. Sensitivity experiments involving the elimination of sound transmission lines showed that missing data had less impact on assimilation than on inversion. Sensitivity experiments involving the elimination of CAT stations showed that the assimilation with four CAT stations was the relatively economical and reasonable procedure in this experiment. These results indicate that, compared with inversion and simulation, data assimilation of CAT data with an unstructured triangular grid is more effective in reconstructing the current field.
  • Ze Nan Zhu, Xiao Hua Zhu, Xinyu Guo
    Continental Shelf Research 143 219 - 227 2017年07月 [査読有り]
     研究論文(学術雑誌) 
    © 2016 Depth-averaged current data, which were obtained by coastal acoustic tomography (CAT) July 12–13, 2009 in Zhitouyang Bay on the western side of the East China Sea, are used to estimate the semidiurnal tidal current (M2) as well as its first two overtide currents (M4 and M6). Spatial mean amplitude ratios M2:M4:M6 in the bay are 1.00:0.15:0.11. The shallow-water equations are used to analyze the generation mechanisms of M4 and M6. In the deep area, where water depths are larger than 60 m, M4 velocity amplitudes measured by CAT agree well with those predicted by the advection terms in the shallow water equations, indicating that M4 in the deep area is predominantly generated by the advection terms. M6 measured by CAT and M6 predicted by the nonlinear quadratic bottom friction terms agree well in the area where water depths are less than 20 m, indicating that friction mechanisms are predominant for generating M6 in the shallow area. In addition, dynamic analysis of the residual currents using the tidally averaged momentum equation shows that spatial mean values of the horizontal pressure gradient due to residual sea level and of the advection of residual currents together contribute about 75% of the spatial mean values of the advection by the tidal currents, indicating that residual currents in this bay are induced mainly by the nonlinear effects of tidal currents. This is the first ever nonlinear tidal current study by CAT.
  • Jie Shi, Yi Liu, Xinyan Mao, Xinyu Guo, Hao Wei, Huiwang Gao
    Continental Shelf Research 143 257 - 270 2017年07月 [査読有り]
     研究論文(学術雑誌) 
    © 2016 Elsevier Ltd The interannual variations of the start timing, magnitude and duration of the spring phytoplankton bloom (SPB) in the central southern Yellow Sea (SYS) were studied using the satellite-derived surface chlorophyll-a concentrations (Chl-a) from 2000 to 2014. The correlations between the characteristics of SPB and the generation rate of turbulent kinetic energy (TKERT) supplied from the atmosphere to the ocean were examined. The start timing of SPB was delayed in years with high TKERT supplied to the ocean before SPB. The TKERT during SPB had no relationship with the magnitude of SPB, but had positive correlation with the duration. A 1-D physical-biological model was used to examine the influencing mechanisms of the TKERT on the characteristics of SPB quantitatively. The wind speeds and related TKERT before the start of SPB were stronger in 2010 than in 2008. Comparison of the model results forced by winds in the two years suggested that the enhanced physical dilution of phytoplankton caused by the stronger TKERT in 2010 induced a later start timing of SPB. When increasing the winds during SPB period, more phytoplankton was taken downward from the surface layer by the enhanced vertical mixing. Meanwhile, more nutrients were pumped upward to the surface layer and supported more net growth of phytoplankton. These two contrary processes led to the independence of the magnitude of SPB on the TKERT during the SPB period. However, larger TKERT along with stronger wind resulted in a longer duration of SPB because of more nutrients supply by stronger vertical mixing.
  • Ruixiang Zhao, Xiao Hua Zhu, Xinyu Guo
    Continental Shelf Research 143 240 - 256 2017年07月 [査読有り]
     研究論文(学術雑誌) 
    © 2016 We deployed 5 pressure-recording inverted echo sounders (PIES) along a section in the northern South China Sea (NSCS), and estimated well the distributions of temperature, salinity and velocity across the section. Applying the empirical orthogonal function (EOF) method, we found that variability of the estimates is dominated by two modes: one named the seasonal mode affecting strongly on the hydrographic distribution with explained variability of temperature/salinity by 62.9/72.2%; the other named the eddy mode, corresponding to the arrival of mesoscale eddies, affecting strongly on the circulation pattern with explained variability of velocity by 63.2%. Temporal variation of the seasonal mode is highly correlated with the monsoon winds southeast of Vietnam, suggesting a nonlocal forcing mechanism. Case studies looking at the structures and evolutions of three captured eddies, whose impacts were well quantified by the eddy mode. The monsoon (eddies) significantly affects temperature, salinity and velocity shallower than 635 m (860 m), 160 m (150 m) and 1055 m (920 m), respectively. The monsoon (eddies) can induce maximum temperature, salinity and velocity anomalies up to −1.6 to 2.1 °C (−2.5 to 2.2 °C), −0.11 to 0.14 psu (−0.13 to 0.27 psu) and −0.31 to 0.46 m/s (−0.40 to 0.38 m/s), respectively. Mean volume transport (VT) across the section is 1.0 Sv (1 Sv=1×106 m3 s−1, positive to the northeast). Seasonal VT (with eddy impacts removed) is −4.6 Sv, 11.4 Sv, −5.1 Sv and −4.1 Sv for spring, summer, autumn and winter, respectively.
  • Narumi K. Tsugeki, Narumi K. Tsugeki, Michinobu Kuwae, Yukinori Tani, Xinyu Guo, Koji Omori, Hidetaka Takeoka
    Journal of Oceanography 73 3 309 - 320 2017年06月 [査読有り]
     研究論文(学術雑誌) 
    © 2016, The Oceanographic Society of Japan and Springer Japan. We examined fossil pigments in a 210 Pb-dated sediment core to document the temporal variations in phytoplankton biomass over the past 150 years in a semi-enclosed bay, Beppu Bay, in the western Seto Inland Sea, Japan. The flux of fossil pigments was used as an index of phytoplankton biomass, which we reconstructed after removing the effect of post-burial degradation on the concentrations of fossil pigments. The flux doubled from the 1960s to the early 1970s, decreased or remained stable in the early 1980s, and increased again from the late 1980s to the early 1990s. The first increase in phytoplankton biomass during the 1960s was likely caused by eutrophication due to an increase in terrestrial nutrient fluxes from watersheds. The decreasing phytoplankton biomass in the early 1980s was likely related to the establishment of a sewage treatment system that reduced the terrestrial nutrient fluxes to the sea. However, the terrestrial nutrient fluxes could not explain the second increase from the late 1980s to the early 1990s. Intensification of the influx of nutrients from the shelf slope to the sea was likely the cause of the second increase in phytoplankton biomass. This is supported by the inverse relationship between phytoplankton biomass and sea level at the shelf slope, the latter being an index of the intensity of the influx of oceanic nutrients from the shelf slope to the sea. The supply of oceanic nutrients may be therefore a critical factor in the determination of primary production in the western Seto Inland Sea.
  • Yasumasa Miyazawa, Sergey M. Varlamov, Toru Miyama, Xinyu Guo, Tsutomu Hihara, Keiji Kiyomatsu, Misako Kachi, Yukio Kurihara, Hiroshi Murakami
    Ocean Dynamics 67 6 713 - 728 2017年06月 [査読有り]
     研究論文(学術雑誌) 
    © 2017, The Author(s). A multi-scale three-dimensional variational (MS-3DVAR) scheme is developed to assimilate high-resolution Himawari-8 sea surface temperature (SST) data for the first time into an operational ocean nowcast/forecast system targeting the North Western Pacific, JCOPE2. MS-3DVAR improves representation of the Kuroshio path south of Japan, its associated sea level variations, and temperature/salinity profiles south of Japan, the Kuroshio/Oyashio mixed water region, and the Japan Sea as compared to those of the products by the traditional single-scale 3DVAR. Validation results demonstrate that MS-3DVAR well assimilates the sparsely distributed in situ temperature and salinity profiles data by spreading the information over the large scale and by representing the detailed information near the measurement points. MS-3DVAR succeeds to assimilate the Himawari-8 SST product without noisy features caused by the cloud effects. We also find that MS-3DVAR is more effective for estimating oceanic conditions in regions with smaller mesoscale variability including the mixed water region and Japan Sea than in south of Japan.
  • Jing Zhang, Xinyu Guo, Liang Zhao, Yasumasa Miyazawa, Qun Sun
    Journal of Physical Oceanography 47 5 1043 - 1060 2017年05月 [査読有り]
     研究論文(学術雑誌) 
    © 2017 American Meteorological Society. Onshore and offshore currents and the associated volume transport across three isobaths (50, 100, and 200 m) over the continental shelf of the East China Sea were examined using daily reanalysis data in 1993-2012. After being averaged along the isobaths, the velocities across 100 and 50 m are onshore in the bottom layer but offshore in the surface layer. In contrast, those across the 200-m isobath are onshore in the surface and bottom layers but without a clear direction in the midlayer, suggesting a three-layer structure. The surface offshore current across the 100-m isobath mainly arises from the Taiwan Strait Current, while the surface onshore current across the 200-m isobath mainly arises from the Kuroshio, both of which converge in the area between the 100- and 200-m isobaths and flow toward the Tsushima Strait. The control of bottom Ekman dynamics on the onshore bottom currents is important at the 100-m isobath, partly important at the 200-m isobath, and slightly important at the 50-m isobath. The seasonal variations of onshore and offshore currents in the surface layers across the three isobaths are likely caused by local winds, the Taiwan Strait Current, and the Changjiang discharge, while those in midlayer across the 200-m isobath demonstrate a strong geostrophic control and can be interpreted from a traditional viewpoint on the Kuroshio intrusion over the entire water column across the shelf slope. The close connection of bottom onshore currents across the three isobaths suggests that the bottom layer is an important pathway for water exchange of shelf water and the open sea.
  • Rui Shi, Ju Chen, Xinyu Guo, Lili Zeng, Jian Li, Qiang Xie, Xin Wang, Dongxiao Wang
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 122 7 3733 - 3753 2017年04月 [査読有り]
     研究論文(学術雑誌) 
    The response of the marine atmospheric boundary layer (MABL) structure to an oceanic front is analyzed using Global Positioning System (GPS) sounding data obtained during a survey in the northwestern South China Sea (NSCS) over a period of about 1week in April 2013. The Weather Research and Forecasting (WRF) model is used to further examine the thermodynamical mechanisms of the MABL's response to the front. The WRF model successfully simulates the change in the MABL structure across the front, which agrees well with the observations. The spatially high-pass-filtered fields of sea surface temperature (SST) and 10m neutral equivalent wind from the WRF model simulation show a tight, positive coupling between the SST and surface winds near the front. Meanwhile, the SST front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer. Analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient. It is found that the front in the NSCS is wide enough for slowly moving air parcels to be affected by the change in underlying SST. The different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the MABL, which dominates the change in the wind profile across the front.
  • 放射性物質の分散シミュレーションに影響を及ぼす沿海域海況変動過程とその再現性
    升本 順夫, 津旨 大輔, 郭 新宇, 内山 雄介, 宮澤 泰正
    沿岸海洋研究 54 2 151 - 157 2017年02月 [査読有り]
     研究論文(学術雑誌)
  • Rui Shi, Ju Chen, Xinyu Guo, Lili Zeng, Jian Li, Qiang Xie, Xin Wang, Dongxiao Wang
    Journal of Geophysical Research 122 7 3733 - 3753 2017年 [査読有り]
     研究論文(学術雑誌) 
    The response of the marine atmospheric boundary layer (MABL) structure to an oceanic front is analyzed using Global Positioning System (GPS) sounding data obtained during a survey in the northwestern South China Sea (NSCS) over a period of about 1 week in April 2013. The Weather Research and Forecasting (WRF) model is used to further examine the thermodynamical mechanisms of the MABL’s response to the front. The WRF model successfully simulates the change in the MABL structure across the front, which agrees well with the observations. The spatially high-pass-filtered fields of sea surface temperature (SST) and 10m neutral equivalent wind from the WRF model simulation show a tight, positive coupling between the SST and surface winds near the front. Meanwhile, the SST front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer. Analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient. It is found that the front in the NSCS is wide enough for slowly moving air parcels to be affected by the change in underlying SST. The different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the MABL, which dominates the change in the wind profile across the front.
  • Shanshan Pan, Jie Shi, Huiwang Gao, Xinyu Guo, Xiaohong Yao, Xiang Gong
    JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 122 1 212 - 229 2017年01月 [査読有り]
     研究論文(学術雑誌) 
    In this study, a one-dimensional physical-biogeochemical coupled model was established to investigate the responses of the upper ocean to Typhoon Damrey in the basin area of the South China Sea. The surface chlorophyll a concentration (Chl a) increased rapidly from 0.07 to 0.17mgm(-3) when the typhoon arrived and then gradually reached a peak of 0.61mgm(-3) after the typhoon's passage. The subsurface Chl a decreased from 0.34 to 0.17mgm(-3) as the typhoon arrived and then increased gradually to 0.71mgm(-3). Analyses of model results indicated that the initial rapid increase in the surface Chl a and the decrease in the subsurface Chl a were caused mainly by physical process (vertical mixing), whereas the subsequent gradual increases in the Chl a in both the surface and subsurface layers were due mainly to biogeochemical processes (net growth of phytoplankton). The gradual increase in the Chl a lasted for longer in the subsurface layer than in the surface layer. Typhoon Damrey yielded an integrated primary production (IPP) of 6.5x10(3)mg C m(-2) (similar to 14% of the annual IPP in this region).
  • Eisuke Tsutsumi, Xinyu Guo
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 121 7 4649 - 4669 2016年07月 [査読有り]
     研究論文(学術雑誌) 
    The climatology and linear trend of seasonal water temperature and heat budget in a semienclosed sea connected to the Kuroshio region (Seto Inland Sea: SIS) are investigated by constructing and analyzing a gridded data set of water temperature, salinity, and air-sea heat fluxes. In the SIS, winter-time water temperature and ocean heat content (OHC) showed a significant increasing trend while those in summer-time exhibited no significant change. By analyzing the heat budget between the tendency of ocean heat content OHC/t and air-sea net heat flux Q(net), the driving factor of the winter-time warming trend in the SIS was identified as autumn Q(net), while the unchanged summer-time OHC is mainly due to decreased spring-time oceanic heat transport to the SIS from the Kuroshio region. In addition, we showed that the decreased spring-time heat transport could have been induced by upwelling due to wind curl and wind speed in the shelf-slope region, heat transport by the Kuroshio south of Shikoku Island, and freshwater input to the SIS from rivers. The importance of both oceanic and atmospheric forcing mechanisms for explaining variation in the water temperature in coastal areas is demonstrated.
  • Etsuko Nakashima, Atsuhiko Isobe, Shin'ichiro Kako, Takaaki Itai, Shin Takahashi, Xinyu Guo
    MARINE POLLUTION BULLETIN 107 1 333 - 339 2016年06月 [査読有り]
     研究論文(学術雑誌) 
    The long-distance transport potential of toxic lead (Pb) by plastic marine debris was examined by pure water leaching experiments using plastic fishery floats containing high level of additive-Pb such as 5100 74.3 mg kg(-1). The leaching of Pb ended after sequential 480-h leaching experiments, and the total leaching amount is equivalent to approximately 0.1% of total Pb in a float. But it recovered when the float was scratched using sandpaper. We propose that a "low-Pb layer," in which Pb concentration is negligibly small, be generated on the float surface by the initial leaching process. Thickness of the layer is estimated at 2.5 +/- 1.2 mu m, much shallower than flaws on floats scratched by sandpaper and floats littering beaches. The result suggests that the low-Pb layer is broken by physical abrasion when floats are washed ashore, and that Pb inside the floats can thereafter leach into beaches. (C) 2016 Elsevier Ltd. All rights reserved.
  • Tangdong Qu, Tomoki Tozuka, Shinichiro Kida, Xinyu Guo, Yasumasa Miyazawa, Qinyu Liu
    World Scientific Series on Asia-Pacific Weather and Climate 7 151 - 186 2016年 [査読有り]
     研究論文(学術雑誌) 
    This article focuses on the physical and dynamical processes of the marginal seas of the Western Pacific. The nature of the circulation regimes and their interconnectivity are discussed in detail, with emphasis on individual basins. In addition to the Kuroshio and its variability in the North Pacific, the circulation regimes in the South China Sea and Indonesian Seas are presented for an overall view of the circulation system. These circulations play important roles in regional ocean dynamics and global climate variations such as the El Niño/Southern Oscillation.
  • Shinichiro Kida, Humio Mitsudera, Shigeru Aoki, Xinyu Guo, Shin-Ichi Ito, Fumiaki Kobashi, Nobumasa Komori, Atsushi Kubokawa, Toru Miyama, Ryosuke Morie, Hisashi Nakamura, Tomohiro Nakamura, Hideyuki Nakano, Hajime Nishigaki, Masami Nonaka, Hideharu Sasaki, Yoshi N. Sasaki, Toshio Suga, Shusaku Sugimoto, Bunmei Taguchi, Koutarou Takaya, Tomoki Tozuka, Hiroyuki Tsujino, Norihisa Usui
    Hot Spots in the Climate System: New Developments in the Extratropical Ocean-Atmosphere Interaction Research 1 - 30 2016年01月 [査読有り]
     論文集(書籍)内論文 
    This article reviews progress in our understanding of oceanic fronts around Japan and their roles in air–sea interaction. Fronts associated with the Kuroshio and its extension, fronts within the area of the Kuroshio-Oyashio confluence, and the subtropical fronts are described with particular emphasis on their structure, variability, and role in air–sea interaction. The discussion also extends to the fronts in the coastal and marginal seas, the Seto Inland Sea and Japan Sea. Studies on oceanic fronts have progressed significantly during the past decade, but many of these studies focus on processes at individual fronts and do not provide a comprehensive view. Hence, one of the goals of this article is to review the oceanic fronts around Japan by describing the processes based on common metrics. These metrics focus primarily on surface properties to obtain insights into air–sea interactions that occur along oceanic fronts. The basic characteristics derived for each front (i.e., metrics) are then presented as a table. We envision that many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.
  • Tomohiro Komorita, Xinyu Guo, Naoki Yoshie, Naoki Fujii, Hidetaka Takeoka
    CONTINENTAL SHELF RESEARCH 112 68 - 77 2016年01月 [査読有り]
     研究論文(学術雑誌) 
    Monthly field surveys conducted from April to November 2009 in a tidal front in the Seto Inland Sea, Japan provided a spatial and temporal dataset for investigating seasonal variations in nutrient supply and the formation of a chlorophyll a (Chl-a) maximum. The upward diffusive flux of nutrients is estimated from observational data but it accounted for less than 5% of the nutrients needed to support the primary production of phytoplankton in the front area of the stratification region when the density difference between the surface layer and bottom layer is greater than 0.5 kg m(-3). Instead of vertical diffusion, the lateral intrusion of water with high nutrient concentration from the mixed area represented the major nutrient supply in the front area. The depth of the lateral intrusion changed with the month: the surface layer in July became the middle layer in August. According to the calculation of numerical model, an anticlockwise circulation is intensified by removing river runoff (i.e., low precipitation) in this study area, and the change of lateral intrusion is likely caused by the change of anti-clockwise circulation along with the temporal variation in river runoff. Consequently, the Chl-a peak appeared in the vicinity of the surface front (up to 3 mu g L-1) in July, but was in the subsurface (up to 9 mu g L-1) in August. Diatom species were a relatively minor taxa of the phytoplankton community up to July, although a relatively high Si(OH)(4)-Si concentration (up to 20 mu mol L-1) was confirmed. In contrast, the subsurface Chl-a maximum (SCM) in August was mainly comprised of diatoms as evidenced by the reduction of both Si(OH)(4)-Si and SUN from the surface to subsurface layer (0-20 m depth). Therefore, the supply of both nutrients and the seed population necessary for the formation of the SCM results from the tidal frontal system and phytoplankton assemblages within the tidal front system should be varied on a monthly basis. (C) 2015 Elsevier Ltd. All rights reserved.
  • Xiaojie Yu, Xinyu Guo, Hidetaka Takeoka
    JOURNAL OF PHYSICAL OCEANOGRAPHY 46 1 159 - 177 2016年01月 [査読有り]
     研究論文(学術雑誌) 
    Summer hydrographic data from 1971 to 2000 demonstrate the presence of bottom cold water (BCW) and a bottom thermal front around the BCW in a semienclosed sea in the Seto Inland Sea of Japan. The horizontal gradient of water temperature across the bottom front was larger in neap tide than in spring tide, which is the opposite the pattern observed in the fortnightly variations in other areas (e.g., the Irish Sea). A numerical model for the Inland Sea reproduced the presence of BCW and a bottom front as well as the same fortnightly variation in the horizontal gradient of water temperature across the bottom front as in observational data. Being the same BCW as those in other areas, the presence of BCW in the Inland Sea is also caused by spatial variation in tidal mixing. The intensification of the bottom front in neap tide in the Inland Sea results from a combination of tidal mixing and horizontal advection of warm water to the BCW. The presence of a bottom residual current in the direction across the bottom front results in the horizontal advection of warm water to the BCW, and its fortnightly variation is responsible for the fortnightly variation of the bottom front in the Inland Sea. The presence of the BCW induces a surface cyclonic circulation in the direction approximately along the bottom front; the intensification and weakening of the bottom front with the spring-neap tidal cycle, combined with the fortnightly variation in the bottom boundary layer thickness, produce a slightly stronger surface cyclonic circulation in neap tide than in spring tide.
  • Xiao-Hua Zhu, Ruixiang Zhao, Xinyu Guo, Yu Long, Yun-Long Ma, Xiaopeng Fan
    JOURNAL OF OCEANOGRAPHY 71 6 663 - 673 2015年12月 [査読有り]
     研究論文(学術雑誌) 
    We deployed five pressure-recording inverted echo sounders (PIES) along a satellite altimeter track across the continental slope of the northern South China Sea (NSCS) from October 2012 to July 2014, and obtained a time series of volume transport (VTPIES) across the section from their records. Applying the empirical relationship between VTPIES and the satellite altimeter sea surface height anomaly difference across the section, we obtained a time series of volume transport (VTNSCS) over 22 years from 1992 to 2014. The VTNSCS shows a small mean value of -1.6 Sv (1 Sv = 10(6) m(3) s(-1)) (i.e., toward the southwest), but a significant seasonal reversal and mesoscale eddy induced fluctuations (-11.8 to 19.7 Sv). The monthly mean of VTNSCS over 22 years shows a maximum (3.6 Sv) in July and a minimum (-7.3 Sv) in December. This is the first long time series of volume transport for the NSCS based on in situ data.
  • Yasumasa Miyazawa, Xinyu Guo, Sergey M. Varlamov, Toru Miyama, Ken Yoda, Katsufumi Sato, Toshiyuki Kano, Keiji Sato
    SCIENTIFIC REPORTS 5 2015年12月 [査読有り]
     研究論文(学術雑誌) 
    At the present time, ocean current is being operationally monitored mainly by combined use of numerical ocean nowcast/forecast models and satellite remote sensing data. Improvement in the accuracy of the ocean current nowcast/forecast requires additional measurements with higher spatial and temporal resolution as expected from the current observation network. Here we show feasibility of assimilating high-resolution seabird and ship drift data into an operational ocean forecast system. Data assimilation of geostrophic current contained in the observed drift leads to refinement in the gyre mode events of the Tsugaru warm current in the north-eastern sea of Japan represented by the model. Fitting the observed drift to the model depends on ability of the drift representing geostrophic current compared to that representing directly wind driven components. A preferable horizontal scale of 50 km indicated for the seabird drift data assimilation implies their capability of capturing eddies with smaller horizontal scale than the minimum scale of 100 km resolved by the satellite altimetry. The present study actually demonstrates that transdisciplinary approaches combining bio-/ship- logging and numerical modeling could be effective for enhancement in monitoring the ocean current.
  • Xiao-Hua Zhu, Ze-Nan Zhu, Xinyu Guo, Yun-Long Ma, Xiaopeng Fan, Menghong Dong, Chuanzheng Zhang
    CONTINENTAL SHELF RESEARCH 108 65 - 75 2015年10月 [査読有り]
     研究論文(学術雑誌) 
    Quantifying the tidal current and volume transport through the Qiongzhou Strait (QS) is vital to understanding the circulation in the northern South China Sea. To measure the tidal current in the strait, a 15-day coastal acoustic tomography (CAT) experiment was carried out at four acoustic stations in March 2013. The horizontal distributions of the tidal currents were calculated by inverse analysis of CAT data. The diurnal tidal current constituents were found to dominate: the ratio of the amplitudes O-1, K-1, M-2, S-2, and MSF was 1.00:0.60:0.47;0.21:0.11. The residual currents were found to flow westward in the northern QS and turn southward in the southern Q. The residual current velocities were larger in the northern area than in the southern area, with a maximum westward velocity of 12.4 cm s(-1) the northern QS. Volume transport estimated using the CAT data varied between -0.710 Sv and 0.859 Sv, with residual current transport of -0.044 Sv, where negative values indicate westward. We conducted a dynamic analysis of the observations made during the study, which suggested that tidal rectification and sea level difference between the two entrances of the QS are important in maintaining the residual current through the strait. This is the first estimation, from synchronous measurements, of major tidal current constituents, residual currents, and volume transport in this strait. (C) 2015 Elsevier Ltd. All rights reserved.
  • Shinichiro Kida, Humio Mitsudera, Shigeru Aoki, Xinyu Guo, Shin-ichi Ito, Fumiaki Kobashi, Nobumasa Komori, Atsushi Kubokawa, Toru Miyama, Ryosuke Morie, Hisashi Nakamura, Tomohiro Nakamura, Hideyuki Nakano, Hajime Nishigaki, Masami Nonaka, Hideharu Sasaki, Yoshi N. Sasaki, Toshio Suga, Shusaku Sugimoto, Bunmei Taguchi, Koutarou Takaya, Tomoki Tozuka, Hiroyuki Tsujino, Norihisa Usui
    JOURNAL OF OCEANOGRAPHY 71 5 469 - 497 2015年10月 [査読有り]
     
    This article reviews progress in our understanding of oceanic fronts around Japan and their roles in air-sea interaction. Fronts associated with the Kuroshio and its extension, fronts within the area of the Kuroshio-Oyashio confluence, and the subtropical fronts are described with particular emphasis on their structure, variability, and role in air-sea interaction. The discussion also extends to the fronts in the coastal and marginal seas, the Seto Inland Sea and Japan Sea. Studies on oceanic fronts have progressed significantly during the past decade, but many of these studies focus on processes at individual fronts and do not provide a comprehensive view. Hence, one of the goals of this article is to review the oceanic fronts around Japan by describing the processes based on common metrics. These metrics focus primarily on surface properties to obtain insights into air-sea interactions that occur along oceanic fronts. The basic characteristics derived for each front (i.e., metrics) are then presented as a table. We envision that many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.
  • Rui Shi, Xinyu Guo, Dongxiao Wang, Li Li Zeng, Ju Chen
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 119 30 - 39 2015年09月 [査読有り]
     研究論文(学術雑誌) 
    High-resolution reanalysis data of Sea Surface Temperature (SST) show pronounced seasonal variations in oceanic fronts in the coastal area of the Northern South China Sea (NSCS), which are accompanied by the seasonality of monsoons. The NSCS oceanic fronts cover a wider area of the coastal sea in winter than in summer as strong winter monsoons progress. Nonetheless, the average SST gradients of the frontal area in both seasons are comparable. The response of surface wind to SST perturbations attributed to oceanic fronts in the NSCS coastal area has also been investigated by the observation data of satellite borne scatterometers and the simulation data of the Weather Research and Forecasting (WRF) model. Both the satellite observations and the simulations of the WRF model show apparent positive linear SST-wind coupling for most months in 2008, indicating the local influence of coastal SST fronts on the sea surface wind in the NSCS. The SST-wind coupling coefficients in the NSCS coastal sea are larger than those observed at mid-latitude oceans but smaller than those observed near equatorial oceans. It is also found that the influence of topography on the sea surface wind could be more important than that of the SST front at the southern end of the Taiwan Strait in winter. The transition of the monsoon could also affect the SST-wind coupling in the NSCS. (C) 2013 Elsevier Ltd. All rights reserved.
  • Xiao Hua Wang, Yang-Ki Cho, Xinyu Guo, Chau-Ron Wu, Junliang Zhou
    ESTUARINE COASTAL AND SHELF SCIENCE 163 235 - 243 2015年09月 [査読有り]
     研究論文(学術雑誌) 
    Coastal environments are a key location for transport, commercial, residential and defence infrastructure, and have provided conditions suitable for economic growth. They also fulfil important cultural, recreational and aesthetic needs; have intrinsic ecosystem service values; and provide essential biogeochemical functions such as primary productivity, nutrient cycling and water filtration. The rapid expansion in economic development and anticipated growth of the population in the coastal zones along the Yellow and East China Sea basin has placed this region under intense multiple stresses. Here we aim to: 1) synthesize the new knowledge/science in coastal oceanography since 2010 within the context of the scientific literature published in English; 2) report on a citation analysis that assesses whether new research topics have emerged and integrated over time, indicate the location of modelling and field-based studies; and 3) suggest where the new research should develop for heavily impacted estuaries and coastal seas of East Asia. The conclusions of the synthesis include: 1) China has emerged as a dominant force in the region in producing scientific literature in coastal oceanography, although the area of publications has shifted from its traditional fields such as physical oceanography; 2) there has been an increasing number of publications with cross-disciplinary themes between physical oceanography and other fields of the biological, chemical, and geological disciplines, but vigorous and systematic funding mechanisms are still lacking to ensure the viability of large scale multi-disciplinary teams and projects in order to support trans-disciplinary research and newly emerging fields; 3) coastal oceanography is responding to new challenges, with many papers studying the impacts of human activities on marine environment and ecology, but so far very few studying management and conservation strategies or offering policy solutions. (c) 2015 Elsevier Ltd. All rights reserved.
  • Yu-Lin Chang, Yasumasa Miyazawa, Xinyu Guo
    JOURNAL OF PHYSICAL OCEANOGRAPHY 45 6 1651 - 1666 2015年06月 [査読有り]
     研究論文(学術雑誌) 
    This study shows that mesoscale eddies can alter the Taiwan Strait Current. The 20-yr data-assimilated Japan Coastal Ocean Predictability Experiment 2 (JCOPE2) reanalysis data are analyzed, and the results are confirmed with idealized experiments. The leading wind-forced seasonal cycle is excluded to focus on the effect of the eddy. The warm eddy southwest of Taiwan is shown to generate a northward flow, whereas the cold eddy produces a southward current. The effect of the eddy penetrates onto the shelf through the joint effect of baroclinicity and relief (JEBAR). The cross-isobath fluxes lead to shelfward convergence and divergence, setting up the modulation of the sea level slope. The resulting along-strait current anomaly eventually affects a wide area of the Taiwan Strait. The stronger eddy leads to larger modification of the cross-shelf flows and sea level slope, producing a greater transport anomaly. The composite Sea-Viewing Wide Field-of-View Sensor chlorophyll-a (Chl-a) serves as an indicator to show the change in Chl-a concentration in the strait in response to the eddy-induced current. During the warm eddy period, the current carries the southern water of lower concentration northward, reducing Chl-a concentration in the strait. In contrast, Chl-a is enhanced because the cold eddy-induced southward current carries the northern water of higher concentration southward into the strait.
  • Yu-Lin Chang, Yasumasa Miyazawa, Xinyu Guo
    PROGRESS IN OCEANOGRAPHY 135 64 - 76 2015年06月 [査読有り]
     
    In this study, 20 years of model reanalysis data are analyzed to study the effects of the subtropical countercurrent (STCC) eddies on the upstream Kuroshio, from east of Luzon to east of Taiwan. The effects are assessed from individual events to interannual time scales. The wind-driven Kuroshio is modified by the STCC eddies, with high spatiotemporal variations. The mass balance in the composite eddy events indicates that the strengthening and weakening of the Kuroshio transport are locally caused by the mass convergence and divergence produced by the eddies. The same analogy applies to the interannual time scale. In the eddy-rich years, the upstream Kuroshio is generally stronger because of wind forcing, yet the strengthening is nonuniform because of modification by the eddies. The larger number of warm eddies to the east of Taiwan and Luzon Island further strengthen the jet, whereas the larger number of cold eddies to the east of the Luzon Strait weaken the Kuroshio in the Luzon Strait. Drifter trajectories show larger Luzon Strait intrusion during the occurrence of cold eddies. The local weakening of the Kuroshio by cold eddies leads to a weaker potential vorticity jump, producing favorable conditions for the intrusion of a water mass into the South China Sea. (C) 2015 Elsevier Ltd. All rights reserved.
  • Sergey M. Varlamov, Xinyu Guo, Toru Miyama, Kaoru Ichikawa, Takuji Waseda, Yasumasa Miyazawa
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 5 3681 - 3710 2015年05月 [査読有り]
     研究論文(学術雑誌) 
    We analyze a concurrent simulation result of the ocean circulation and tidal currents using a data-assimilative ocean general circulation model covering the Western North Pacific with horizontal resolution of 1/36 degrees to investigate possible interactions between them. Four sites of active M-2 internal tide variability in open ocean (hot spots), such as Tokara Strait, Izu Ridge, Luzon Strait, and Ogasawara Ridge, are detected from both the satellite observation and the simulation. Energy cycle analysis of the simulated M-2 baroclinic tide indicates two types of the hot spots: dissipation (Tokara Strait and Izu Ridge) and radiation (Luzon Strait and Ogasawara Ridge) dominant sites. Energy conversion from barotropic to baroclinic M-2 tides at the hot spots is modulated considerably by the lower-frequency changes in the density field. Modulation at the two spots (Tokara Strait and Izu Ridge) is affected by the Kuroshio path variation together with the seasonal variation of the shallow thermocline. At the other two sites, influence from changes in the relatively deep stratification through the Kuroshio intrusion into South China Sea (Luzon Strat) and mesoscale eddy activity (Ogasawara Ridge) is dominant in the modulation.
  • 宮澤泰正, 美山透, GUO Xinyu, VARLAMOV Sergey M
    沿岸海洋研究 52 2 131 - 137 2015年02月 [査読有り]
  • Wang Haiyan, Guo Xinyu, Liu Zhe, Gao Huiwang
    JOURNAL OF OCEAN UNIVERSITY OF CHINA 14 1 47 - 58 2015年02月 [査読有り]
     研究論文(学術雑誌) 
    CART (Constituent-oriented age and residence time theory) and PTM (Particle-tracking method) are two widely used numerical methods to calculate water age. These two methods are essentially equivalent in theory but their results may be different in practice. The difference of the two methods was evaluated by applying them to calculate water age in an idealized one-dimensional domain. The model results by the two methods are consistent with each other in the case with either spatially uniform flow field or spatially uniform diffusion coefficient. If we allow the spatial variation in horizontal diffusion, a term called pseudo displacement arising from the spatial variation of diffusion coefficient likely plays an important role for the PTM to obtain accurate water age. In particular, if the water particle is released at a place where the diffusion is not the weakest, the water age calculated by the PTM without pseudo displacement is much larger than that by the CART. This suggests that the pseudo displacement cannot be neglected in the PTM to calculate water age in a realistic ocean. As an example, we present its potential importance in the Bohai Sea where the diffusion coefficient varies spatially and greatly.
  • Yasumasa Miyazawa, Nobuyoshi Yamashita, Sachi Taniyasu, Eriko Yamazaki, Xinyu Guo, Sergey M. Varlamov, Toru Miyama
    JOURNAL OF OCEANOGRAPHY 70 6 535 - 547 2014年12月 [査読有り]
     研究論文(学術雑誌) 
    The Great East Japan Earthquake on 11 March 2011, followed by the tsunami and fire, resulted in serious environmental problems in and around Japan. A huge amount of material was discharged into the ocean after the tremendous flood damage of the tsunami. A monitoring survey of the perfluoroalkyl substances (PFAs) found evidence showing an abrupt increase in the PFA concentration in the ocean east of Japan in 2011 after the earthquake. To confirm the anomalous input of two typical PFAs, perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), from the Japanese coast into the ocean, associated with the earthquake, we conducted a series of chemical tracer simulations using an eddy-resolving ocean reanalysis product: JCOPE2. The simulation model involves processes representing the emission of PFAs from the land triggered by the tsunami flood, advection of the polluted waters, and decay of the concentration by the background oceanic turbulence. Comparison of the PFOA simulation results with the observation confirms a spike-like input of PFOA into the Western North Pacific after the earthquake. Advection and diffusion by the Kuroshio Extension and the mesoscale eddies play a key role in the dilution of the concentration. Optimization of unknown simulation parameters leads to an estimation of the total amount of the anomalous PFOA emission. In contrast, the PFOS simulations are not able to explain the observed distribution, suggesting possible differences in the oceanic transport processes between PFOS and PFOA.
  • Xiao-Hua Zhu, Yun-Long Ma, Xinyu Guo, Xiaopeng Fan, Yu Long, Yaochu Yuan, Ji-Liang Xuan, Daji Huang
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 119 11 8039 - 8060 2014年11月 [査読有り]
     研究論文(学術雑誌) 
    In spring 2013, 33 repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K-1, O-1, M-2, S-2, and MSf). The ratio of the amplitudes of O-1, K-1, M-2, S-2, and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.02.1 cm s(-1); the associated volume transport through the section is -0.0650.046 Sv (Sv=10(6) x m(3) s(-1)), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.
  • Endro Soeyanto, Xinyu Guo, Jun Ono, Yasumasa Miyazawa
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 119 6 3595 - 3616 2014年06月 [査読有り]
     研究論文(学術雑誌) 
    Results of a data-assimilative ocean model (JCOPE2) from 1993 to 2012 were used to examine the correlation between the Pacific Decadal Oscillation (PDO) index and interannual variations of the Kuroshio transport in the East China Sea (ECS) and the influences of mesoscale eddies on this correlation. In a period from 1993 to 2002, the Kuroshio transport estimated from the JCOPE2 reanalysis has a positive correlation with the PDO index. This well-known correlation became weak or even disappeared when the analysis period was extended from 1993-2002 to 1993-2012. This occurs because the variation range of the PDO index became small during enhanced mesoscale eddy activity southeast of Taiwan in years after 2002. The eddies caused a larger variation in the Kuroshio transport in the years after 2002 than before 2002, and therefore, changed the correlation between the PDO index and Kuroshio transport in the ECS. The influence of mesoscale eddies on the Kuroshio transport has strong regional dependence: the Kuroshio transport from the area east of Taiwan to the midway along the shelf break in the East China Sea depends mainly on eddies arriving from southeast of Taiwan, while transport from the midway along the shelf break to the Tokara Strait depends mainly on the eddies arriving from northeast of Okinawa Island. The combination of PDO-related signals and eddy-related signals determines the interannual variations of the Kuroshio transport in the ECS and sufficient attention must be paid to the spatial dependence of the Kuroshio transport in the ECS on eddies.
  • Zhongya Cai, Zhe Liu, Xinyu Guo, Huiwang Gao, Qiang Wang
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 119 3 2017 - 2033 2014年03月 [査読有り]
     研究論文(学術雑誌) 
    Using synchronous observational water temperature and salinity data collected simultaneously by 21 ships in summer and a three-dimensional robust diagnostic model, we calculated the density-driven current in Jiaozhou Bay (JZB), a semienclosed bay in the Yellow Sea. Special attention was paid to the influences of intratidal variations in temperature and salinity on the density-driven current. The density-driven current in JZB has a maximum speed of similar to 0.1 m s(-1) and is stronger than the tide-induced residual current in some places. The density-driven current is characterized by the intrusion of high-density (low-density) water in deep (shallow) areas. The results of the diagnostic model depend heavily on the observational data. For example, the density-driven current calculated from nonsynchronous data obtained by one ship at the same 21 stations is not consistent with that calculated from synchronous data because the nonsynchronous data correspond to different tidal phases at different stations. The intratidal variations of the density field result in a false spatial variation of density in the nonsynchronous data, which induces a false density-driven current that is of the same order as that calculated from the synchronous data. In contrast, the tidally averaged water temperature and salinity, which were used to remove intratidal variations from the synchronous data, diagnosed a density-driven current consistent with that from synchronous data. We, therefore, conclude that it is not necessary to explicitly resolve the intratidal variations in density in the calculation of density-driven current, but it is necessary to remove intratidal variations in the density field before the calculation.
  • Endro Soeyanto, Xinyu Guo, Jun Ono, Yasumasa Miyazawa
    Journal of Geophysical Research: Oceans 119 6 3595 - 3616 2014年 [査読有り]
     研究論文(学術雑誌) 
    Results of a data-assimilative ocean model (JCOPE2) from 1993 to 2012 were used to examine the correlation between the Pacific Decadal Oscillation (PDO) index and interannual variations of the Kuroshio transport in the East China Sea (ECS) and the influences of mesoscale eddies on this correlation. In a period from 1993 to 2002, the Kuroshio transport estimated from the JCOPE2 reanalysis has a positive correlation with the PDO index. This well-known correlation became weak or even disappeared when the analysis period was extended from 1993-2002 to 1993-2012. This occurs because the variation range of the PDO index became small during enhanced mesoscale eddy activity southeast of Taiwan in years after 2002. The eddies caused a larger variation in the Kuroshio transport in the years after 2002 than before 2002, and therefore, changed the correlation between the PDO index and Kuroshio transport in the ECS. The influence of mesoscale eddies on the Kuroshio transport has strong regional dependence: the Kuroshio transport from the area east of Taiwan to the midway along the shelf break in the East China Sea depends mainly on eddies arriving from southeast of Taiwan, while transport from the midway along the shelf break to the Tokara Strait depends mainly on the eddies arriving from northeast of Okinawa Island. The combination of PDO-related signals and eddy-related signals determines the interannual variations of the Kuroshio transport in the ECS and sufficient attention must be paid to the spatial dependence of the Kuroshio transport in the ECS on eddies. 2003 © 2014. American Geophysical Union. All Rights Reserved.
  • Zhongya Cai, Zhe Liu, Xinyu Guo, Huiwang Gao, Qiang Wang
    Journal of Geophysical Research: Oceans 119 3 2017 - 2033 2014年 [査読有り]
     研究論文(学術雑誌) 
    Using synchronous observational water temperature and salinity data collected simultaneously by 21 ships in summer and a three-dimensional robust diagnostic model, we calculated the density-driven current in Jiaozhou Bay (JZB), a semienclosed bay in the Yellow Sea. Special attention was paid to the influences of intratidal variations in temperature and salinity on the density-driven current. The density-driven current in JZB has a maximum speed of ∼0.1 m s-1 and is stronger than the tide-induced residual current in some places. The density-driven current is characterized by the intrusion of high-density (low-density) water in deep (shallow) areas. The results of the diagnostic model depend heavily on the observational data. For example, the density-driven current calculated from nonsynchronous data obtained by one ship at the same 21 stations is not consistent with that calculated from synchronous data because the nonsynchronous data correspond to different tidal phases at different stations. The intratidal variations of the density field result in a false spatial variation of density in the nonsynchronous data, which induces a false density-driven current that is of the same order as that calculated from the synchronous data. In contrast, the tidally averaged water temperature and salinity, which were used to remove intratidal variations from the synchronous data, diagnosed a density-driven current consistent with that from synchronous data. We, therefore, conclude that it is not necessary to explicitly resolve the intratidal variations in density in the calculation of density-driven current, but it is necessary to remove intratidal variations in the density field before the calculation. © 2014. American Geophysical Union. All Rights Reserved.
  • Yu Long, Xiao-Hua Zhu, Xinyu Guo
    CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING, PTS 1-4 838-841 2361 - + 2014年 [査読有り]
     研究論文(国際会議プロシーディングス) 
    To confirm Spatial variations of Kuroshio nutrient transport from the East China Sea to South of Japan, we apply an inverse method to hydrographic data from sections across the Kuroshio path from the East China Sea (Sections PN and TK) to south of Japan (Sections ASUKA and 137E) to get absolute geostrophic velocity, then the nutrient flux (velocity times concentration) and nutrient transport (integration of flux over a section) were calculated. In addition, Section OK east of the Ryukyu Islands was also examined. The nitrate flux during winter of 2009 shows a subsurface maximum core with a value of 11, 15, 7, 19, and 10 mol m(-2)s(-1) at Sections PN, TK, OK, ASUKA and 137E, respectively. The depth of subsurface maximum core is about 280, 470, 800, 200, and 470 m at Sections PN, TK, OK, ASUKA and 137E, respectively. The eastward nitrate transport is 248.6, 213.3, 97.7, 804.3, 879.0 k mol s(-1) at Sections PN, TK, OK, ASUKA and 137E respectively. Comparisons between nitrate transport through Section ASUKA and the sum of transports through Sections TK and OK and nitrate transport of Section 137E, suggest that the Kuroshio recirculation south of Shikoku can significantly intensify the eastward nitrate transport by the Kuroshio and therefore plays an important role in the nitrate transport in the Kuroshio region.
  • Yasumasa Miyazawa, Hiroshi Murakami, Toru Miyama, Sergey M Varlamov, Xinyu Guo, Takuji Waseda, Sourav Sil
    Remote Sensing 5 6 3123 - 3139 2013年06月 [査読有り]
     研究論文(学術雑誌) 
    We develop an assimilation method of high horizontal resolution sea surface temperature data, provided from the Moderate Resolution Imaging Spectroradiometer (MODIS-SST) sensors boarded on the Aqua and Terra satellites operated by National Aeronautics and Space Administration (NASA), focusing on the reproducibility of the Kuroshio front variations south of Japan in February 2010. Major concerns associated with the development are (1) negative temperature bias due to the cloud effects, and (2) the representation of error covariance for detection of highly variable phenomena. We treat them by utilizing an advanced data assimilation method allowing use of spatiotemporally varying error covariance: the Local Ensemble Transformation Kalman Filter (LETKF). It is found that the quality control, by comparing the model forecast variable with the MODIS-SST data, is useful to remove the negative temperature bias and results in the mean negative bias within -0.4 °C. The additional assimilation of MODIS-SST enhances spatial variability of analysis SST over 50 km to 25 km scales. The ensemble spread variance is effectively utilized for excluding the erroneous temperature data from the assimilation process. © 2013 by the authors.
  • X. Y. Guo, X. H. Zhu, Y. Long, D. J. Huang
    Biogeosciences 10 10 6403 - 6417 2013年 [査読有り]
     研究論文(学術雑誌) 
    Based on absolute geostrophic velocity, which was calculated using repeated hydrographic data of 39 cruises from 2000 to 2009 and nitrate concentrations measured in the same areas from 1964 to 2009, we obtained the temporally averaged nitrate flux (the product of velocity and nitrate concentration) and nitrate transport (integration of flux over one section) of four sections across the Kuroshio from the East China Sea (sections PN and TK) to an area south of Japan (sections ASUKA and 137E). In addition, we examined section OK east of the Ryukyu Islands in order to understand how the Ryukyu Current contributes to the transport of nutrients by the Kuroshio south of Japan. The mean nitrate flux shows a subsurface maximum core with values of 9.6, 10.6, 11.2, 10.5, and 5.7 mol m-2 s-1 at sections PN, TK, ASUKA, 137E, and OK, respectively. The depth of the subsurface maximum core changes among these five sections and is approximately 400, 500, 500, 400, and 800 m at sections PN, TK, ASUKA, 137E, and OK, respectively. The mean downstream nitrate transport is 204.8, 165.8, 879.3, 1230.4, and 338.6 kmol s-1 at sections PN, TK, ASUKA, 137E, and OK, respectively. The transport of nutrients in these sections suggests the presence of the Kuroshio nutrient stream from its upstream to downstream regions. The deep current structure of the Ryukyu Current (section OK) contributes to the same order of nitrate transport as does the Kuroshio from the East China Sea (section TK) to the area south of Japan however, the former only has one-fifth the volume transport of the latter. A budget calculation suggests that the downstream increase of transported nitrate along the Kuroshio is mainly caused by the recirculation of nitrate into the Kuroshio. This conclusion, however, depends on water depth. In the upper layers (< 26.5& sigma & theta ), the downstream change of nitrate concentration along the Kuroshio and that from the recirculation of nitrate has a significant contribution to the downstream increase of nitrate transport along the Kuroshio. In the deep layers (> 26.5& sigma & theta ), the change in nitrate concentration is small and the Kuroshio recirculation dominates the downstream increase of nitrate transport. © 2013 Author(s) .
  • Zhe Liu, Haiyan Wang, Xinyu Guo, Qiang Wang, Huiwang Gao
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 117 2012年11月 [査読有り]
     研究論文(学術雑誌) 
    To quantitatively understand the transport timescales of dissolved material discharged from large rivers into a semienclosed sea, the age of Yellow River water in the Bohai Sea was calculated with the constituent-oriented age and residence time theory (CART) and particle-tracking method. Yellow River water has a mean age of 3.0 years for the entire Bohai Sea. The spatial variation of the water age is significant: 1.2 years near the Yellow River estuary but 3.9 years in the Liaodong Bay. However, the temporal variation in water age is insignificant. The water particles released at the river mouth need only several days to reach the estuary area. The great water age (1.2 years) near the Yellow River estuary is caused by the presence of old water particles that initially left this area but returned to this area again. Without the reentry of Yellow River water from the Yellow Sea to the Bohai Sea, the mean age of Yellow River water in the entire Bohai Sea decreases to 1.2 years. Calculations without tidal forcing give a reduction in water age by more than 50%, suggesting that tidal forcing plays the most dominant role in controlling the age of Yellow River water in the Bohai Sea. Calculations without winds give an increase in water age by 20-30%, suggesting that wind forcing is secondary factor to the age of Yellow River water. Changes in discharge of the Yellow River and in thermal stratification have limited influence on the age of Yellow River water.
  • Jun Ono, Daisuke Takahashi, Xinyu Guo, Shin Takahashi, Hidetaka Takeoka
    CHEMOSPHERE 89 4 389 - 397 2012年10月 [査読有り]
     研究論文(学術雑誌) 
    A three-dimensional/high-resolution transport model for persistent organic pollutants (POPs) has been developed for the East China Sea (ECS). The POPs model has four compartments (gaseous, dissolved, phytoplankton-bound, and detritus-bound phases) and includes processes for diffusive air-water exchange, phytoplankton uptake/depuration to POPs, decomposition of dissolved phase, vertical sinking of phytoplankton, detritus production by phytoplankton mortality, and vertical sinking and decomposition of detritus. The POPs model is coupled with an ocean circulation model that can reproduce the seasonal variation in physical variables to represent the advection and diffusion of POPs. We applied the POPs model to the polychlorinated biphenyl congener 153 (PCB 153) from the atmosphere and examined the behavior of PCB 153 in the ocean. The model showed a remarkable seasonal variability of PCB 153. Concentrations in the dissolved and particulate phases are high in winter (January-March) and low in summer (July-September). In coastal regions, where chlorophyll a concentration is high, horizontal and vertical distributions in the dissolved and particulate PCB 153 concentrations are strongly affected by phytoplankton uptake. The sensitivity experiments on the dynamics of PCB 153 suggested that a change of Henry's law constant associated with water temperature is the major factor controlling the seasonal variability of PCB 153. The model-based yearly mass balance of PCB 153 in the ECS indicated that most of the atmospheric input (35.5 kg year(-1)) is removed by the horizontal advection outside the ECS (19.0 kg year(-1)) and accumulates to the sea bottom by vertical sinking (15.7 kg year(-1)). For comparison with PCB 153, we also conducted simulations for PCB 52, 101, and 180. The seasonal variations are similar to that of PCB 153. The mass balance of PCB 52 that has short half-life time and less hydrophobic property shows the different results compared with PCB 101, 153, and 180. (C) 2012 Elsevier Ltd. All rights reserved.
  • Atsuhiko Isobe, Shin'ichiro Kako, Xinyu Guo, Hidetaka Takeoka
    OCEAN DYNAMICS 62 4 633 - 644 2012年04月 [査読有り]
     研究論文(学術雑誌) 
    The finite volume coastal ocean model downscaling ocean reanalysis and forecast data provided by the Japan Coastal Ocean Predictability Experiment (JCOPE2) are used to forecast sudden Kuroshio water intrusion events (kyucho) induced by frontal waves amplified south of the Bungo Channel in 2010. Two-month hindcast computations give initial conditions of the following 3-month forecasts computations which consist of ten ensemble members. The temperature time series computed by these ten members are averaged to compare with that actually observed in the Bungo Channel, where sudden temperature rises related to kyucho events are remarkable in February, August, and September. Overall, the intense kyucho events actually observed in these months are predicted successfully. However, intense kyucho events are forecasted frequently during the period of May through June even though intense kyucho events are absent during this period in the actual ocean. It is suggested that the present downscaling forecast model requires reliable lateral boundary conditions provided by JCOPE2 data to which numerous Argo data are assimilated to enhance the accuracy. In addition, it seems likely that the model accuracy is reduced by small eddies moving along the shelf break.
  • Yasumasa Miyazawa, Toru Miyama, Sergey M. Varlamov, Xinyu Guo, Takuji Waseda
    OCEAN DYNAMICS 62 4 645 - 659 2012年04月 [査読有り]
     研究論文(学術雑誌) 
    We investigated the feasibility of the ensemble Kalman filter (EnKF) to reproduce oceanic conditions south of Japan. We have adopted the local ensemble transformation Kalman filter algorithm based on 20 members' ensemble simulations of the parallelized Princeton Ocean Model (the Stony Brook Parallel Ocean Model) with horizontal resolution of 1/36A degrees. By assimilating satellite sea surface height anomaly, satellite sea surface temperature, and in situ temperature and salinity profiles, we reproduced the Kuroshio variation south of Japan for the period from 8 to 28 February 2010. EnKF successfully reproduced the Kuroshio path positions and the water mass property of the Kuroshio waters as observed. It also detected the variation of the steep thermohaline front in the Kii Channel due to the intrusion of the Kuroshio water based on the observation, suggesting efficiency of EnKF for detection of open and coastal seas interactions with highly complicated spatiotemporal variability.
  • Zhe Liu, Haiyan Wang, Xinyu Guo, Qiang Wang, Huiwang Gao
    Journal of Geophysical Research: Oceans 117 11 2012年 [査読有り]
     研究論文(学術雑誌) 
    To quantitatively understand the transport timescales of dissolved material discharged from large rivers into a semienclosed sea, the age of Yellow River water in the Bohai Sea was calculated with the constituent-oriented age and residence time theory (CART) and particle-tracking method. Yellow River water has a mean age of 3.0 years for the entire Bohai Sea. The spatial variation of the water age is significant: 1.2 years near the Yellow River estuary but 3.9 years in the Liaodong Bay. However, the temporal variation in water age is insignificant. The water particles released at the river mouth need only several days to reach the estuary area. The great water age (1.2 years) near the Yellow River estuary is caused by the presence of old water particles that initially left this area but returned to this area again. Without the reentry of Yellow River water from the Yellow Sea to the Bohai Sea, the mean age of Yellow River water in the entire Bohai Sea decreases to 1.2 years. Calculations without tidal forcing give a reduction in water age by more than 50%, suggesting that tidal forcing plays the most dominant role in controlling the age of Yellow River water in the Bohai Sea. Calculations without winds give an increase in water age by 20-30%, suggesting that wind forcing is secondary factor to the age of Yellow River water. Changes in discharge of the Yellow River and in thermal stratification have limited influence on the age of Yellow River water. © 2012 American Geophysical Union. All Rights Reserved.
  • Xinyu Guo, Xiao-Hua Zhu, Qing-Song Wu, Daji Huang
    Journal of Geophysical Research: Oceans 117 1 2012年 [査読有り]
     研究論文(学術雑誌) 
    Using in situ data from 88 cruises from 1987 to 2009 in the East China Sea, downstream nutrient flux (the product of velocity and nutrient concentration) and nutrient transport (integration of flux over a section) by Kuroshio were examined. The presence of a maximum nutrient flux core in the middle layer was confirmed. Seasonal variation in the nutrient flux was not significant and was much smaller than interannual variations. The change in the Kuroshio speed and current structure were major causes for interannual variations in the nutrient flux. The downstream nitrate transport by the Kuroshio in the East China Sea had a mean value of 170.8 kmol s-1 and a standard deviation of 41.6 kmol s-1. The mean seasonal nitrate transport ranged between about 161 and 177 kmol s-1 and the absolute interannual variation from about 100 to 280 kmol s-1. The phosphate flux and phosphate transport can be approximately estimated by the ratio (13.64) of nitrate concentration to phosphate concentration. The nitrate concentration in the middle and bottom layers across the Kuroshio in the East China Sea was found to increase significantly over the 23 year period, and especially after 2004 but not at ratios with oxygen that suggest increased remineralization of organic matter. The nutrient transport, however, did not increase significantly because increases in the surface layer were offset by decreases in the middle and bottom layers caused by reduction in velocity in the density ranges of 26.0 to 27.2 below the Kuroshio. Copyright 2012 by the American Geophysical Union.
  • Saito M, Onodera S, Guo X, Onishi K, Shimizu Y, Yoshikawa M, Jin G, Tokumasu M, Takeoka H
    Interdisciplinary Studies on Environmental Chemistry 6 339 - 344 2012年 [査読有り]
     研究論文(国際会議プロシーディングス)
  • Yudi Adityawarman, Arata Kaneko, Naokazu Taniguchi, Hidemi Mutsuda, Katsuaki Komai, Xinyu Guo, Noriaki Gohda
    Acoustical Science and Technology 33 1 45 - 51 2012年 [査読有り]
     研究論文(学術雑誌) 
    The tidal current in the Kurushima Strait of the Seto Inland Sea, Japan was successfully measured during July-August 2009 (36 days) among the three acoustic stations (KR4, KR5 and KR6), located on both sides of the strait. The travel time differences for the two sound transmission lines KR4-KR5 and KR4-KR6 are converted into the range-averaged currents along the transmission lines. The hourly mean of the range-averaged currents varied in the range from -31:1 to 53.8 cm/s for the KR4-KR5 and in the range from -45:4 to 48.7 cm/s for the KR4-KR6 with the error bars of 5.0 cm/s and 6.6 cm/s, respectively. The hourly mean along-line currents are further transformed into the geophysical coordinates with the variation range from -99:1 to 91.6 cm/s and the mean current of -6:6 cm/s for the eastward component V E, and that of (-54:2-31.5) cm/s and the mean current of -7:6 cm/s for the northward component V N. The cross-line volume transport varied in the range of (-17:928 to +17.569) × 10 4 m 3/s, resulting in the mean westward transport of 0:727 × 10 4 m3/s. This mean transport reaches a significant level over the error bar of 0:474 × 10 4 m 3/s. © 2012 The Acoustical Society of Japan.
  • Xinyu Guo, Xiao-Hua Zhu, Qing-Song Wu, Daji Huang
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 117 2012年01月 [査読有り]
     研究論文(学術雑誌) 
    Using in situ data from 88 cruises from 1987 to 2009 in the East China Sea, downstream nutrient flux (the product of velocity and nutrient concentration) and nutrient transport (integration of flux over a section) by Kuroshio were examined. The presence of a maximum nutrient flux core in the middle layer was confirmed. Seasonal variation in the nutrient flux was not significant and was much smaller than interannual variations. The change in the Kuroshio speed and current structure were major causes for interannual variations in the nutrient flux. The downstream nitrate transport by the Kuroshio in the East China Sea had a mean value of 170.8 kmol s(-1) and a standard deviation of 41.6 kmol s(-1). The mean seasonal nitrate transport ranged between about 161 and 177 kmol s(-1) and the absolute interannual variation from about 100 to 280 kmol s(-1). The phosphate flux and phosphate transport can be approximately estimated by the ratio (13.64) of nitrate concentration to phosphate concentration. The nitrate concentration in the middle and bottom layers across the Kuroshio in the East China Sea was found to increase significantly over the 23 year period, and especially after 2004 but not at ratios with oxygen that suggest increased remineralization of organic matter. The nutrient transport, however, did not increase significantly because increases in the surface layer were offset by decreases in the middle and bottom layers caused by reduction in velocity in the density ranges of 26.0 to 27.2 sigma(theta) below the Kuroshio.
  • Jianyu Hu, Jiayi Pan, Xinyu Guo, Quanan Zheng
    JOURNAL OF OCEANOGRAPHY 67 6 675 - 676 2011年12月 [査読有り]
  • Jianyu Hu, Jiayi Pan, Xinyu Guo, Quanan Zheng
    JOURNAL OF OCEANOGRAPHY 67 4 359 - 363 2011年08月 [査読有り]
  • Yudi Adityawarman, Arata Kaneko, Koji Nakano, Naokazu Taniguchi, Katsuaki Komai, Xinyu Guo, Noriaki Gohda
    JOURNAL OF OCEANOGRAPHY 67 2 173 - 182 2011年04月 [査読有り]
     研究論文(学術雑誌) 
    A 30 km-range reciprocal sound transmission experiment was carried out on the line connecting Honshu and Shikoku (the first and fourth biggest main Japanese islands, respectively) in the central part (Aki-nada) of the Seto Inland Sea, Japan, during March-May 2010 to measure the mean current and temperature variations over the sea. The range-averaged current along the sound transmission line was estimated to have a mean and standard deviation of (3.8-4.4) +/- A (1.7-1.8) cm/s after converting the travel time difference data into currents, including a fortnightly tidal variation in the range of +/- 30 cm/s. The positive mean current implies slow water movement from the west to east through Aki-nada. The range-averaged speed of sound was estimated by converting from the mean travel time or one-way travel time into the speed of sound, and further converted into temperature for fixed values of salinity and depth, according to the standard speed of sound formula. Besides the precise measurement (to an accuracy of 0.01A degrees C) of semidiurnal and diurnal tidal variations and seasonal warming, the temperature data showed periodic variations with periods of 7.0 and 21.1 days that had never been observed in Aki-nada before. This study suggests that reciprocal sound transmission is a powerful technique for the long-term accurate measurement of mean current and temperature variations in coastal and inland seas.
  • Yucheng Wang, Zhe Liu, Huiwang Gao, Lian Ju, Xinyu Guo
    CONTINENTAL SHELF RESEARCH 31 6 685 - 694 2011年04月 [査読有り]
     研究論文(学術雑誌) 
    To investigate how salinity changes with abrupt increases and decreases in river discharge, three surveys were conducted along six sections around the Yellow River mouth before, during and after a water regulation event during which the river discharge was increased from similar to 200 to > 3000 m(3) s(-1) for the first 3 days, was maintained at > 3000 m(3) s(-1) for the next 9 days and was decreased to <1000 m(3) s(-1) for the final 4 days. The mean salinity in the Yellow River estuary area during the event varied similar to 1.21, which is much larger than its seasonal variation (similar to 0.50) and interannual variation (similar to 0.05). Before the event, a small plume was observed near the river mouth. During the event, the plume extended over 24 km offshore in the surface layer in the direction of river water outflow. After the event, the plume diminished in size but remained larger than before the event. The downstream propagation of the plume (as in a Kelvin wave sense) was apparent in the bottom layer during the second survey and in both the surface and bottom layers during the third survey. The plume sizes predicted by the formulas from theoretical studies are larger than those we observed, indicating that factors neglected by theoretical studies such as the temporal variation in river discharge and vertical mixing in the sea could be very important for plume evolution. In addition to the horizontal variation of the plume, we also observed the penetration of freshwater from the surface layer into the bottom layer. A comparison of two vertical processes, wind mixing and tidal mixing, suggests that the impact of wind mixing may be comparable with that of tidal mixing in the area close to the river mouth and may be dominant over offshore areas. The change in Kelvin number indicates an alteration of plume dynamics due to the abrupt change in river discharge during the water regulation event. (C) 2011 Elsevier Ltd. All rights reserved.
  • Process study on numerical simulation for persistent organic pollutants in the East China Sea.
    Ono, J, Takahashi, D, Guo, X, Takahashi, S, Takeoka, H
    Interdisciplinary Studies on Environmental Chemistry, Vol. 5, Modeling and Analysis of Marine Environmental Problems 197 - 204 2011年03月 [査読有り]
     研究論文(国際会議プロシーディングス)
  • Rui Shi, Xinyu Guo, Hidetaka Takeoka
    BOUNDARY-LAYER METEOROLOGY 138 2 299 - 319 2011年02月 [査読有り]
     研究論文(学術雑誌) 
    A regional numerical model of the atmosphere was applied to an inland sea, the Seto Inland Sea in Japan, to study the influence of sea-surface temperature (SST) variations, accompanied by a tidal front, on the coastal winds in summer when tidal fronts fully develop. After confirmation of the model performance, two sensitivity simulations, which used spatially uniform SST with the highest and lowest values over the study area, were performed. The control and sensitivity simulations show that the mean wind speeds were apparently reduced by the low SST and the SST gradient accompanying the tidal front. The comparison of the terms in the momentum equations in control and sensitivity simulations indicates that the change of the perturbation pressure gradient force with the SST gradient is the most important factor in the modification of near-surface winds with SST variations. When the air flows across a tidal front, the air cools over the low SST area and warms over the high SST area. Consequently, the surface perturbation pressure increases over the low SST area and decreases over the high SST area. This adjustment in surface perturbation pressure produces an additional pressure gradient force with direction from the low SST area to the high SST area that decelerates the surface wind in the area upwind of the tidal front and accelerates the surface wind downwind of the tidal front.
  • Ecosystem and nutrient dynamics in the Seto Inland Sea
    Yoshie, N, X.Guo, N.Fujii, T.Komorita
    Interdisciplinary Studies on Environmental Chemistry, Modeling and Analysis of Marine Environmental Problems 5 39 - 49 2011年 [査読有り]
  • L. Zhao, X. Guo
    OCEAN SCIENCE 7 1 27 - 43 2011年 [査読有り]
     研究論文(学術雑誌) 
    A three dimensional coupled biophysical model was used to examine the supply of oceanic nutrients to the shelf of the East China Sea (ECS) and its role in primary production over the shelf. The model consisted of two parts: the hydrodynamic module was based on a nested model with a horizontal resolution of 1/18 degree, whereas the biological module was a lower trophic level ecosystem model including two types of phytoplankton, three elements of nutrients, and biogenic organic material. The model results suggested that seasonal variations occurred in the distribution of nutrients and chlorophyll a over the shelf of the ECS. After comparison with available observed nutrients and chlorophyll a data, the model results were used to calculate volume and nutrients fluxes across the shelf break. The annual mean total fluxes were 1.53 Sv for volume, 9.4 kmol s(-1) for DIN, 0.7 kmol s(-1) for DIP, and 18.2 kmol s(-1) for silicate. Two areas, northeast of Taiwan and southwest of Kyushu, were found to be major source regions of oceanic nutrients to the shelf. Although the onshore fluxes of nutrients and volume both had apparent seasonal variations, the seasonal variation of the onshore nutrient flux did not exactly follow that of the onshore volume flux. Additional calculations in which the concentration of nutrients in Kuroshio water was artificially increased suggested that the oceanic nutrients were distributed in the bottom layer from the shelf break to the region offshore of the Changjiang estuary from spring to summer and appeared in the surface layer from autumn to winter. The calculations also implied that the supply of oceanic nutrients to the shelf can change the consumption of pre-existing nutrients from rivers. The response of primary production over the shelf to the oceanic nutrients was confirmed not only in the surface layer (mainly at the outer shelf and shelf break in winter and in the region offshore of the Changjiang estuary in summer) but also in the subsurface layer over the shelf from spring to autumn.
  • Su Mei Liu, Xinyu Guo, Qi Chen, Jing Zhang, Yan Feng Bi, Xin Luo, Jian Bing Li
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 115 2010年11月 [査読有り]
     研究論文(学術雑誌) 
    As the first attempt to estimate the nutrient transport across the winter thermohaline frontal zone on the northern shelf of the South China Sea, the nutrient dynamics around the front and the effects of cross-frontal water exchange on nutrient transport were investigated using wintertime field observations. Both water temperature and salinity increased from coastal to oceanic waters, showing the presence of a thermohaline front. The concentrations of dissolved inorganic nutrients decreased oceanward, especially across the thermohaline front, while those of dissolved organic nutrients (i.e., dissolved organic nitrogen (DON) and dissolved organic phosphorus) showed patchy distributions. Ammonium was the major constituent of dissolved inorganic nitrogen, and DON was the main component of total dissolved nitrogen. Molar ratios of PO(4)(3-)/total dissolved phosphorus decreased from coastal to oceanic waters, indicating that PO(4)(3-) was rapidly removed and/or consumed from the water column and that organic matter degradation increased offshore, replenishing PO(4)(3-). Molar ratios of NO(3)(-)/(NH(4)(+) + DON) were 0.01-0.6, indicating dominance of regenerated nitrogen. Surface water convergence and bottom water divergence were identified in the across-shore velocity field, and the calculated across-shore nutrient fluxes suggest that the presence of the winter thermohaline front promotes the offshore transport of nutrients from coastal waters. The transport path begins with convergence of surface coastal waters toward the front, followed by the sinking in the frontal region and the oceanward movement through the bottom layer of the front offshore side. With an assumption of 500 km as the length of thermohaline front on the northern shelf of the South China Sea, the calculated offshore fluxes of nutrients across the entire front are larger than those from the Zhujiang (Pearl River) and the Changjiang (Yangtze River).
  • Xiao Yao, Hitomi Yamaguchi, Li Zou, Li Zou, Hui Wang Gao, Hui Wang Gao, Xin Yu Guo
    Chinese Journal of Ecology 29 1762 - 1769 2010年09月 [査読有り]
     
    In September 2007 and in April and July 2008, sediment samples were collected from the southern intertidal area of Yellow River Delta to study the distribution pattern of benthic chlorophyll-a (Chl-a) content and its relations to sediment grain size. In study area, the Chl-a content increased from the north to the south. In the spring, the Chl-a content ranged from 0. 623-8. 734 μg · -1 g with an average of 2. 542 μg · g -1 and increased from high tide zone to low tide zone; while in summer and autumn, the Chl-a content ranged from 0. 307-5. 195 μg · g -1 (averaging 1. 832.g · g -1 ) and 0. 426-4.749 μg · g -1 (averaging 1. 591 μg -1 · g -1 ), respectively, and decreased from high tide zone to low tide zone. The sediments were unanimously composed of silt, with the median size ranging from 0. 025-0. 081 mm (averaging 0. 045 mm) and increased from high tide zone to low tide zone. The distribution pattern of benthic Chl-a was primarily affected by the grain size of sediment, and had significant correlation with the content of fine particles. There was a negative relationship between benthic Chl-a content and elevation height, suggesting that soft, flat, and stable sediment could benefit the growth and reproduction of benthic micro-algae.
  • 兼田 淳史, 小泉 喜嗣, 高橋 大介, 福森 香代子, 郭 新宇, 武岡 英隆
    水産海洋研究 74 3 167 - 175 水産海洋学会 2010年08月 [査読有り]
  • Zhu Xiao-Hua, Huang DaJi, Guo XinYu
    SCIENCE CHINA-EARTH SCIENCES 53 4 603 - 609 2010年04月 [査読有り]
     研究論文(学術雑誌) 
    Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports (VTs) of the Ryukyu Current in the region east of the northern Ryukyu Islands. The inverse calculation results show that the Ryukyu Current is dominated by a subsurface velocity core with maximum velocities from 15.1 to 80.0 cm/s, whose positions vary between 110 and 600 dbar and 27.2A degrees-28.2A degrees N along the transect. The mean velocity exhibits a subsurface velocity core with a maximum value of 24.6 cm/s at 326 dbar depth, a VT of 14.0 Sv (1 Sv a parts per thousand 10(6) m(3)/s), a vertical dimension of 800 m, and a horizontal dimension of 60 km. The seasonal mean velocities show that the Ryukyu Current is stronger in autumn than in other seasons. It is suggested that this seasonal variation is coincident with the intensification of the anticyclonic eddy south of Shikoku, Japan.
  • 郭 新宇, Varlamov Sergey M, 宮澤 泰正
    沿岸海洋研究 47 2 113 - 123 日本海洋学会 2010年02月 [査読有り]
     
    入れ子手法とは,粗いメッシュを有するモデル領域内部に,細かいメッシュでサブモデルを構築することである.我々は,この手法を利用して,太平洋モデル内に日本近海黒潮モデルを,瀬戸内海全域モデル内に内海奥部の潮汐モデルを,日本近海モデル内に日本南岸黒潮・潮汐結合モデルを構築してきた.細かいメッシュを使用することにより,平滑化による地形への影響が少なくなり,モデル地形が実地形に近づくようになる.この効果は特に陸棚縁や海釜のような水深が急変する場所で顕著である.地形以外に,水温や塩分場の水平勾配もメッシュサイズの変化に敏感であり,特に黒潮近傍の水温勾配が高解像度であるほど強くなる.その結果,黒潮の鉛直シアが大きくなり,より傾圧的になる.黒潮モデルに潮汐を導入することにより,沿岸域での潮汐混合効果以外にも,薩南諸島や小笠原諸島のような地形変化に富んだ沖合海域で,内部潮汐の発生とそれによる密度場の変化が見られた.また,潮汐を考慮しない黒潮モデルと比較すると,潮汐を取り込んだ黒潮モデルでは,トカラ海峡東部の黒潮離岸,豊後水道沖の黒潮接岸,そして四国沖から小笠原諸島までの黒潮の離岸が見られた.このような黒潮流軸変化に応答して,黒潮本流から沿岸域までの密度場や流動場も変化する.
  • Su Mei Liu, Xinyu Guo, Qi Chen, Jing Zhang, Yan Feng Bi, Xin Luo, Jian Bing Li
    Journal of Geophysical Research: Oceans 115 11 2010年 [査読有り]
     研究論文(学術雑誌) 
    As the first attempt to estimate the nutrient transport across the winter thermohaline frontal zone on the northern shelf of the South China Sea, the nutrient dynamics around the front and the effects of cross-frontal water exchange on nutrient transport were investigated using wintertime field observations. Both water temperature and salinity increased from coastal to oceanic waters, showing the presence of a thermohaline front. The concentrations of dissolved inorganic nutrients decreased oceanward, especially across the thermohaline front, while those of dissolved organic nutrients (i.e., dissolved organic nitrogen (DON) and dissolved organic phosphorus) showed patchy distributions. Ammonium was the major constituent of dissolved inorganic nitrogen, and DON was the main component of total dissolved nitrogen. Molar ratios of PO43-/total dissolved phosphorus decreased from coastal to oceanic waters, indicating that PO43- was rapidly removed and/or consumed from the water column and that organic matter degradation increased offshore, replenishing PO43-. Molar ratios of NO3-/(NH4+ + DON) were 0.01-0.6, indicating dominance of regenerated nitrogen. Surface water convergence and bottom water divergence were identified in the across-shore velocity field, and the calculated across-shore nutrient fluxes suggest that the presence of the winter thermohaline front promotes the offshore transport of nutrients from coastal waters. The transport path begins with convergence of surface coastal waters toward the front, followed by the sinking in the frontal region and the oceanward movement through the bottom layer of the front offshore side. With an assumption of 500 km as the length of thermohaline front on the northern shelf of the South China Sea, the calculated offshore fluxes of nutrients across the entire front are larger than those from the Zhujiang (Pearl River) and the Changjiang (Yangtze River). © 2010 by the American Geophysical Union.
  • Atsuhiko Isobe, Xinyu Guo, Hidetaka Takeoka
    Journal of Geophysical Research: Oceans 115 4 2010年 [査読有り]
     研究論文(学術雑誌) 
    Prerequisite(s) for ocean circulation models capable of hindcasting "kyucho" occurrence (a sudden coastal temperature rise induced by Kuroshio frontal waves) in the Bungo Channel, Japan, is investigated using long-term observed temperature and sea level time series, archived hydrographic data, and reanalysis data provided by the Japanese Coastal Ocean Predictability Experiment (JCOPE) group. Anticyclonic mesoscale eddies impinging on the Kuroshio front south of the Bungo Channel enhance the frontal sharpness, frontal wave growth, and activity of kyucho phenomena. A kyucho hindcast is carried out to examine the reliability of a numerical model including realistic anticyclonic eddies propagating south of Japan. The Finite Volume Coastal Ocean Model (FVCOM) for which boundary conditions are given by daily JCOPE2 reanalysis data is adopted in the present study. This numerical model does a reasonable job of hindcasting kyucho occurrence in 2003. It is therefore considered that forecasts of kyucho occurrence up to 2 or 3 months ahead are possible by using the FVCOM in conjunction with JCOPE2 forecast data. Copyright 2010 by the American Geophysical Union.
  • Atsuhiko Isobe, Xinyu Guo, Hidetaka Takeoka
    Journal of Geophysical Research: Oceans 115 2010年01月 [査読有り]
     
    Prerequisite(s) for ocean circulation models capable of hindcasting "kyucho" occurrence (a sudden coastal temperature rise induced by Kuroshio frontal waves) in the Bungo Channel, Japan, is investigated using long-term observed temperature and sea level time series, archived hydrographic data, and reanalysis data provided by the Japanese Coastal Ocean Predictability Experiment (JCOPE) group. Anticyclonic mesoscale eddies impinging on the Kuroshio front south of the Bungo Channel enhance the frontal sharpness, frontal wave growth, and activity of kyucho phenomena. A kyucho hindcast is carried out to examine the reliability of a numerical model including realistic anticyclonic eddies propagating south of Japan. The Finite Volume Coastal Ocean Model (FVCOM) for which boundary conditions are given by daily JCOPE2 reanalysis data is adopted in the present study. This numerical model does a reasonable job of hindcasting kyucho occurrence in 2003. It is therefore considered that forecasts of kyucho occurrence up to 2 or 3 months ahead are possible by using the FVCOM in conjunction with JCOPE2 forecast data. Copyright 2010 by the American Geophysical Union.
  • Pil-Hun Chang, Xinyu Guo, Hidetaka Takeoka
    JOURNAL OF OCEANOGRAPHY 65 6 721 - 736 2009年12月 [査読有り]
     研究論文(学術雑誌) 
    The seasonal variation of water circulation in the Seto Inland Sea is investigated using a high resolution, three-dimensional numerical ocean model. The model results are assessed by comparison with long-term mean surface current and hydrographic data. The simulated model results are consistent with observations, showing a distinct summer and winter circulation patterns. In summer the sea water is highly stratified in basin regions, while it is well mixed near the straits due to strong tidal mixing there. During this period, a cold dome is formed in several basins, setting up stable cyclonic eddies. The cyclonic circulation associated with the cold dome develops from May and disappears in autumn when the surface cooling starts. The experiment without freshwater input shows that a basin-scale estuarine circulation coexists with cyclonic eddy in summer. The former becomes dominant in autumn circulation after the cold dome disappears. In winter the water is vertically well mixed, and the winter winds play a significant role in the circulation. The northwesterly winds induce upwind (downwind) currents over the deep (shallow) water, forming a "double-gyre pattern" in the Suo-Nada, two cyclonic eddies in Hiuchi-Nada, and anticyclonic circulation in Harima-Nada in vertically averaged current fields.
  • Yasumasa Miyazawa, Ruochao Zhang, Xinyu Guo, Hitoshi Tamura, Daisuke Ambe, Joon-Soo Lee, Akira Okuno, Hiroshi Yoshinari, Takashi Setou, Kosei Komatsu
    JOURNAL OF OCEANOGRAPHY 65 6 737 - 756 2009年12月 [査読有り]
     研究論文(学術雑誌) 
    This paper describes a reanalysis of the variability of water mass properties and currents in the western North Pacific using an ocean forecast system, Japan Coastal Ocean Predictability Experiment 2 (JCOPE2), to provide the basic description and information about the quality for data users. We have created the reanalysis data with high horizontal resolution of 1/12 degrees to describe the oceanic variability associated with the Kuroshio-Kuroshio Extension, the Ovashio, and the mesoscale eddies from 1993 to 2007. The products made by an eddy-resolving ocean model combined with the three-dimensional variational data assimilation well reproduced the mean water mass property in the western North Pacific and the interannual variations of the Kuroshio-Kuroshio Extension and the Oyashio coastal branch. From the reanalysis data, we found that both the mean kinetic energy of the Kuroshio Extension axis at the first meandering crest and southward intrusion of the Ovashio coastal branch were closely related with the horizontal distribution of both the Oyashio Water and North Pacific Intermediate Water within the appropriate interannual time scale. The reanalysis data also indicated that the north-south migration of the Kuroshio Extension associated with its regime transitions affected the decadal modulation of the Subtropical Mode Water formation in the recirculation gyre of the Kuroshio Extension.
  • Arnoldo Valle-Levinson, Xinyu Guo
    JOURNAL OF MARINE RESEARCH 67 5 619 - 635 2009年09月 [査読有り]
     研究論文(学術雑誌) 
    Underway profiles of current velocity were combined with stationary profiles of temperature and salinity around a vertically mixed scour pit of the Seto Inland Sea throughout a semidiurnal tidal cycle. This was clone with the purpose of determining (a) whether flood flow is asymmetric relative to ebb over a pit with weakly stratified conditions. and (b) whether there is a dynamic transition from frictionally dominated tidal flow to advectively dominated tidal flow over the pit. These questions arose from previous studies elsewhere under stratified water columns, in contrast to the unstratified conditions at the study site. Observations showed an acceleration of the flood tidal flow over the pit and a deceleration during ebb. The flow acceleration over the pit during flood and deceleration during ebb was attributed to asymmetric patterns of flow convergence/divergence. In turn, these divergence patterns were influenced by the direction and strength of the baroclinic pressure gradient force, which was 10 to 30% of the advective term, despite the relatively weak horizontal gradients of order 10(-5) kg/m(4). The non-negligible influence of the baroclinic pressure gradient was possible from the relatively large depths that exceeded 100 m at the deepest part of the pit, compared to the surrounding depths of 30 m. From depth-averaged dynamical terms derived for flood and ebb phases of the tidal cycle, it was found that the advective terms became more important than frictional terms over the deep parts of the pit. Advection became more prominent than friction where the bottom slope exceeded the value of the bottom drag coefficient (similar to 0.003). Otherwise, frictional effects dominated outside the pit.
  • Daisuke Takahashi, Xinyu Guo, Akihiko Morimoto, Shoichiro Kojima
    CONTINENTAL SHELF RESEARCH 29 15 1896 - 1907 2009年08月 [査読有り]
     研究論文(学術雑誌) 
    An analysis of surface current data obtained from 2002 to 2005 using long-range high-frequency radar provides the first evidence for the presence of biweekly (11-14 day) periodic variations of the Kuroshio axis northeast of Taiwan. This analysis clarifies the spatio temporal characteristics of these variations and reveals that cyclonic/anticyclonic eddies propagating along the shelf slope from the vicinity of the deep channel east of Taiwan induce these variations northeast of Taiwan. The behavior of the cyclonic/anticyclonic eddies on the shelf slope is well explained by 2nd-mode interior shelf waves advected by the Kuroshio's mean flow. Remote effects from the vicinity of the deep channel east of Taiwan, or from outside the East China Sea, are believed to play an important role in the generation of these biweekly periodic variations of the Kuroshio axis northeast of Taiwan. Moreover, on the shelf slope, these variations cause an on shore current across the shelf slope, suggesting topographically controlled upwelling. Therefore, the biweekly periodic variations of the Kuroshio axis northeast of Taiwan might contribute not only to the on shore transport of Kuroshio surface water but also to transport nutrient-rich Kuroshio subsurface water on to the shelf in the East China Sea. (C) 2009 Elsevier Ltd. All rights reserved.
  • Lin Shaoying, Zou Tao, Gao Huiwang, Guo Xinyu
    ACTA OCEANOLOGICA SINICA 28 5 66 - 75 2009年 [査読有り]
     研究論文(学術雑誌) 
    The planar photosynthetically available radiation (PAR), turbidity and concentration of chlorophyll a (chl a), were measured at 26 stations in the Huanghai (Yellow) Sea during a cruise of China SOLAS from 19 to 27 March 2005. Due to low chl a (<0.35 mg.m(-3)) in upper layers (above 5 in), suspended particulate matter became the major factor that influenced the turbidity in early spring. The calculated vertical diffuse attenuation coefficient of PAR, K-PAR, varied with water depths with a maximum value in the upper 5 m layer. The mean K-PAR in survey area was 0.277 +/- 0.07 m(-1) that is considerably higher than most of the other case 2 waters. Within the survey area, K-PAR also showed distinct regional characteristics, corresponding to the distribution of turbidity. Based on measurements, the relationship between K-PAR and turbidity as well as chl a was established. It was suggested that suspended particulate matter plays an important role in light attenuation in the Huanghai (Yellow) Sea in spring.
  • Yasumasa Miyazawa, Takashi Kagimoto, Xinyu Guo, Hirofumi Sakuma
    Journal of Geophysical Research: Oceans 113 10 2008年10月 [査読有り]
     研究論文(学術雑誌) 
    The recent formation of the Kuroshio large meander southeast of the Kii Peninsula during the period from May to July 2004 has been simulated successfully in an eddy-resolving ocean forecast system (Japanese Coastal Ocean Predictability Experiment). The formation process was examined from the viewpoint of eddy-Kuroshio interactions using sensitivity experiments that had various initial conditions for eddies in March and May 2004. We confirmed that the large meander does not occur when the trigger meander southeast of the Kyushu Island has small amplitude and that the cyclonic eddy on the offshore side of the Kuroshio contributes to the large meander formation. Our results show that the large amplitude of the trigger meander southeast of Kyushu Island in April 2004 was caused by downstream advection of anticyclonic eddies along the Kuroshio in the East China Sea from east of Taiwan. The results suggest that the successive westward propagation of strong anticyclonic eddies in the subtropical frontal region from 2003 to 2004 was the origin of the formation of the Kuroshio large meander south of Japan in summer 2004. Copyright 2008 by the American Geophysical Union.
  • Yasumasa Miyazawa, Takashi Kagimoto, Xinyu Guo, Hirofumi Sakuma
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 C10 2008年10月 [査読有り]
     研究論文(学術雑誌) 
    The recent formation of the Kuroshio large meander southeast of the Kii Peninsula during the period from May to July 2004 has been simulated successfully in an eddy-resolving ocean forecast system (Japanese Coastal Ocean Predictability Experiment). The formation process was examined from the viewpoint of eddy-Kuroshio interactions using sensitivity experiments that had various initial conditions for eddies in March and May 2004. We confirmed that the large meander does not occur when the trigger meander southeast of the Kyushu Island has small amplitude and that the cyclonic eddy on the offshore side of the Kuroshio contributes to the large meander formation. Our results show that the large amplitude of the trigger meander southeast of Kyushu Island in April 2004 was caused by downstream advection of anticyclonic eddies along the Kuroshio in the East China Sea from east of Taiwan. The results suggest that the successive westward propagation of strong anticyclonic eddies in the subtropical frontal region from 2003 to 2004 was the origin of the formation of the Kuroshio large meander south of Japan in summer 2004.
  • Xinyu Guo, Arnoldo Valle-Levinson
    CONTINENTAL SHELF RESEARCH 28 17 2450 - 2471 2008年10月 [査読有り]
     研究論文(学術雑誌) 
    The response of the density-driven circulation in the Chesapeake Bay to wind forcing was studied with numerical experiments. A model of the bay with realistic bathymetry was first applied to produce the density-driven flow under average river discharge and tidal forcing. Subsequently, four spatially uniform wind fields (northeasterly, northwesterly, southwesterly, and southeasterly) were imposed to examine the resulting cross-estuary structure of salinity and flow fields. In general, northeasterly and northwesterly winds intensified the density-driven circulation in the upper and middle reaches of the bay, whereas southeasterly and southwesterly winds weakened it. The response was different in the lower bay, where downwind flow from the upper and middle reaches of the bay competed with onshore/offshore coastal flows. Wind remote effects were dominant, over local effects, on volume transports through the bay entrance. However, local effects were more influential in establishing the sea-level slopes that drove subtidal flows and salinity fields in most of the bay. The effect of vertical stratification on wind-induced flows was also investigated by switching it off. The absence of stratification allowed development of Ekman layers that reached depths of the same order as the water depth. Consequently, bathymetric effects became influential on the homogeneous flow structure causing the wind-induced flow inside the bay to show a marked transverse structure: downwind over the shallow areas and upwind in the channels. In the presence of stratification, Ekman layers became shallower and the wind-induced currents showed weaker transverse structure than those that developed in the absence of stratification. In essence, the wind-driven flows were horizontally sheared under weak stratification and vertically sheared under stratified conditions. (C) 2008 Elsevier Ltd. All rights reserved.
  • Qiang Wang, Xinyu Guo, Hidetaka Takeoka
    Journal of Geophysical Research: Oceans 113 8 2008年08月 [査読有り]
     研究論文(学術雑誌) 
    We investigated the behavior of the Yellow River plume in the Bohai Sea through a year and its controlling mechanisms using a numerical model driven by monthly averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal behavior of the Yellow River plume. In summer, the Yellow River plume extends northeastward into the central Bohai Sea in autumn, it turns southward and flows into Laizhou Bay along the coast in winter, most of the diluted water is found around southeastern corner of Laizhou Bay and in spring, a low-salinity area appears in southwest Laizhou Bay. With the same model, several well-designed numerical experiments were performed to investigate the effect on the behavior of the Yellow River plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal currents promote the offshore spread of diluted water, while the tide-induced residual currents prevent the plume from extending further downstream (in the direction of Kelvin wave propagation). Wind stresses lead to pronounced changes in the path and shape of the plume. In autumn and winter, northwesterly or northerly winds drive the buoyant water into Laizhou Bay along the coast. In summer, the combination of southeasterly winds and thermal stratification drives the plume extend northeastward into the central Bohai Sea. By changing only the magnitude of wind stress or river discharge in the experiments, we examined the sensitivity of summertime plume to the magnitude of wind stress and river discharge. Copyright 2008 by the American Geophysical Union.
  • Qiang Wang, Xinyu Guo, Hidetaka Takeoka
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 C8 2008年08月 [査読有り]
     研究論文(学術雑誌) 
    [1] We investigated the behavior of the Yellow River plume in the Bohai Sea through a year and its controlling mechanisms using a numerical model driven by monthly averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal behavior of the Yellow River plume. In summer, the Yellow River plume extends northeastward into the central Bohai Sea; in autumn, it turns southward and flows into Laizhou Bay along the coast; in winter, most of the diluted water is found around southeastern corner of Laizhou Bay; and in spring, a low-salinity area appears in southwest Laizhou Bay. With the same model, several well-designed numerical experiments were performed to investigate the effect on the behavior of the Yellow River plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal currents promote the offshore spread of diluted water, while the tide-induced residual currents prevent the plume from extending further downstream (in the direction of Kelvin wave propagation). Wind stresses lead to pronounced changes in the path and shape of the plume. In autumn and winter, northwesterly or northerly winds drive the buoyant water into Laizhou Bay along the coast. In summer, the combination of southeasterly winds and thermal stratification drives the plume extend northeastward into the central Bohai Sea. By changing only the magnitude of wind stress or river discharge in the experiments, we examined the sensitivity of summertime plume to the magnitude of wind stress and river discharge.
  • Takashi Kagimoto, Yasumasa Miyazawa, Xinyu Guo, Hideyuki Kawajiri
    HIGH RESOLUTION NUMERICAL MODELLING OF THE ATMOSPHERE AND OCEAN 209 - 239 2008年 [査読有り]
     研究論文(国際会議プロシーディングス) 
    We have developed a forecast system for the Kuroshio large meander with a high horizontal resolution (approximately 10 km). Using the system, we succeeded in predicting the path transitions of the Kuroshio from the nearshore nonlarge meander path to the offshore nonlarge meander path in 2003, and from the nearshore nonlarge meander path to the typical large meander path in 2004 as well as the occurrence of its triggering small meander south of Kyushu Island. We have also been developing a higher resolution forecast model for coastal oceans and bays south of Japan, where physical and biological states of the ocean are much affected by the path variation of the Kuroshio. This model, although the development is still under way, represents tides and tidal currents in two bays south of Japan in a realistic way.
  • 郭 新宇, Arnoldo Valle-Levinson
    沿岸海洋研究 44 2 117 - 127 日本海洋学会 2007年02月 [査読有り]
     
    本研究は河口循環流が卓越する代表的な内湾の一つ,Chesapeake湾の実地形にPrinceton Ocean Modelを適用させ,潮汐と河川流量で基本場の河口循環流を再現した上に,代表的な風場を加えて,流動場,塩分場,そして乱流場の変動を調べた.風による塩分場の変動については湾内の成層構造と湾外の低塩分水の広がり面積に主な影響が現れる.湾内では風による成層構造の破壊あるいは弱化,湾外では風による低塩分水の接岸あるいは離岸が見られた.風による流動場の変動は湾内と湾外ともに顕著に現れた.しかし,これらの変動は河口循環流と吹送流の線形的な足し合わせでは十分に説明できない.その理由は,風による密度場の変動に伴う密度流の変動と,風による乱流場の変動に伴う流動構造の変動にあると考えられる.風による乱流場の変動は渦動粘性係数の増大に顕著に現れた.
  • Xinyu Guo, Arnoldo Valle-Levinson
    CONTINENTAL SHELF RESEARCH 27 1 20 - 42 2007年01月 [査読有り]
     研究論文(学術雑誌) 
    The response of the Chesapeake Bay to river discharge under the influence and absence of tide is simulated with a numerical model. Four numerical experiments are examined: (1) response to river discharge only; (2) response to river discharge plus an ambient coastal current along the shelf outside the bay; (3) response to river discharge and tidal forcing; and (4) response to river discharge, tidal forcing, and ambient coastal current. The general salinity distribution in the four cases is similar to observations inside the bay. Observed features, such as low salinity in the western side of the bay, are consistent in model results. Also, a typical estuarine circulation with seaward current in the upper layer and landward current in the lower layer is obtained in the four cases. The two cases without tide produce stronger subtidal currents than the cases with tide owing to greater frictional effects in the cases with tide. Differences in salinity distributions among the four cases appear mostly outside the bay in terms of the outflow plume structure. The two cases without tide produce an upstream (as in a Kelvin wave sense) or northward branch of the outflow plume, while the cases with tide produce an expected downstream or southward plume. Increased friction in the cases with tide changes the vertical structure of outflow at the entrance to the bay and induces large horizontal variations in the exchange flow. Consequently, the outflow from the bay is more influenced by the bottom than in the cases without tide. Therefore, a tendency for a bottom-advected plume appears in the cases with tide, rather than a surface-advected plume, which develops in the cases without tide. Further analysis shows that the tidal current favors a salt balance between the horizontal and vertical advection of salinity around the plume and hinders the upstream expansion of the plume outside the bay. (c) 2006 Elsevier Ltd. All rights reserved.
  • Xinyu Guo, Yasumasa Miyazawa, Toshio Yamagata
    JOURNAL OF PHYSICAL OCEANOGRAPHY 36 12 2205 - 2231 2006年12月 [査読有り]
     研究論文(学術雑誌) 
    A 1/18 degrees nested ocean model is used to determine locations, volume transports, and temporal variations of Kuroshio onshore fluxes across the shelf break of the East China Sea (ECS). The Kuroshio onshore flux shows strong seasonality: maximum similar to 3 Sv; 1 Sv equivalent to 10(6) m(3) s(-1)) in autumn and minimum (<0.5 Sv) in summer. Another short-term (similar to 17 days) variation due to Kuroshio meanders introduces large fluctuations in the onshore fluxes but its seasonal average almost vanishes. The Kuroshio onshore fluxes have two major sources, Kuroshio intrusion northeast of Taiwan and Kuroshio separation southwest of Kyushu; the former provides larger onshore flux than the latter. Therefore, in addition to the waters from the Taiwan Strait and the Kuroshio separation region southwest of Kyushu, the water due to the Kuroshio intrusion northeast of Taiwan is also a major source of the Tsushima Warm Current. A vorticity equation is used to separate the contribution of surface Ekman transport to the Kuroshio onshore fluxes in the ECS from that relating to density fields. For the total Kuroshio onshore flux across the entire shelf break, its seasonal variation is primarily controlled by the Ekman transport while the change in density field is secondary. For the Kuroshio onshore flux at a fixed location along the shelf break, its seasonal variation is primarily related to the change in density field and the Ekman transport is secondary. Furthermore, the role of the Taiwan Strait water and the Kuroshio water across the shelf break on material transport in the ECS is examined with passive tracer experiments. In summer, about half of the tracer in the Tsushima Strait originates in the Taiwan Strait, while the other half comes from the Kuroshio. From summer to winter, the ratio changes dramatically; the contribution from the Taiwan Strait decreases to 20% and that from the Kuroshio increases up to 80%. The tracer originating in the Kuroshio water dominates the bottom layer of the continental shelf in the ECS throughout the year.
  • Y Miyazawa, S Yamane, XY Guo, T Yamagata
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 110 C10 1 - 14 2005年10月 [査読有り]
     研究論文(学術雑誌) 
    Focusing on predictability of the Kuroshio meandering, we have done an ensemble forecast experiment; the application of the method to the problem addressed seems to be the first comprehensive attempt in the community of physical oceanography. By assimilating sea surface height anomaly into an ocean general circulation model in the preceding 40-day period, the observed Kuroshio meandering manifested south of Japan in November 1999 was successfully predicted 2 months before the event. The experiment yields a forecasting skill of the Kuroshio meander position for 60 days in the sense that the RMS error does not exceed the magnitude of the model climatic variation and those obtained from the non-assimilated simulation and persistence. In addition to a single trajectory forecast experiment, ensemble forecasts were conducted using 10 perturbed initial states generated by the breeding method. The predicted states realized as the ensemble members of the 80-day forecast are classified into two categories: large and non-large meander. It is found that the intensity of an anticyclonic eddy in the initial state seems to play a key role in selecting one of the two states.
  • 二村 彰, 武岡 英隆, 郭 新宇
    海の研究 14 3 429 - 440 日本海洋学会 2005年05月 [査読有り]
     
    燧灘全域, 来島海峡および備讃瀬戸西部において, 2002年5月末から8月中旬まで4回にわたりCTD観測を実施した。観測データを2層1ボックスモデルで解析することにより, 燧灘成層域上下層の海水交換に対する移流と水平・鉛直混合の寄与を明らかにするとともに, 各層の熱収支を定量的に評価した。その結果, 海水交換に対しての寄与は上下層ともに鉛直混合よりも水平混合が数倍大きく, さらに, 下層では水平混合が移流よりも大きいことが判明した。また熱収支からは, 成層域下層の加熱に対する鉛直混合の寄与は23%〜41%に過ぎず, 59%〜77%を水平混合と移流による加熱が占めていることも明らかになった。この結果は, 熱バイパス(Takeoka, 2002)が燧灘成層域下層の加熱に重要な役割を果たしていることを実証するものである。
  • Xinyu Guo, Akira Futamura, Hidetaka Takeoka
    Journal of Geophysical Research C: Oceans 109 12 1 - 23 2004年12月 [査読有り]
     研究論文(学術雑誌) 
    On the basis of the Princeton Ocean Model, a robust diagnostic model is developed to calculate the residual currents in the Hiuchi-Nada, a semi-enclosed bay of the Seto Inland Sea. The input water temperature and salinity data are from six hydrographic surveys in 2002, and the model results in the summer show a clockwise eddy in the western part of the bay and an anticlockwise eddy in the eastern part. The magnitude of two eddies is ∼10 cm/s. The modeled flow pattern is consistent with early observations derived from moored arrays. The two eddies are persistent throughout the summer because winds are usually weak and cannot influence their existence. The tide-induced residual currents are appreciable only in the close vicinity of the Kurushima Strait and Bisan Strait, the two straits connecting the bay to the other bays, and have little affect on the two eddies that are inside the bay. Thus the two density-driven eddies in the Hiuchi-Nada are the basic pattern of circulation in the summer. Using the calculated residual currents, we examined the intrusion route of waters from the Kurushima Strait and Bisan Strait with passive tracer experiments. The results show that the water in the Kurushima Strait intrudes into the bay mainly through the middle and bottom layers while the water in the Bisan Strait intrudes mainly through the surface layer. Furthermore, the tracer cannot reach the center of the anticlockwise eddy in the eastern part of the bay. This indicates that the eddy prevents water exchange between its center and outer edges and provides favorable conditions for the formation of oxygen-deficient waters in the central part of the eddy. Copyright 2004 by the American Geophysical Union.
  • Y Miyazawa, XY Guo, T Yamagata
    JOURNAL OF PHYSICAL OCEANOGRAPHY 34 10 2203 - 2222 2004年10月 [査読有り]
     研究論文(学術雑誌) 
    A high-resolution ocean general circulation model is developed to simulate connections between the Kuroshio path variations and mesoscale eddy activities as realistically as possible. The climatological mean of the modeled Kuroshio takes a nearshore nonlarge meander path. It is found that the model is capable of simulating two types of nonlarge meander state and a possible version of the large meander state. The offshore nonlarge meander is generated through interaction between the Kuroshio and an anticyclonic eddy. The large meander occurs just after significant intensification of the anticyclonic Kuroshio recirculation; successive intrusion of anticyclonic eddies from the upstream region is responsible for this process. Those anticyclonic eddies are advected by the Kuroshio from the region northeast of Luzon Island and increase the upstream Kuroshio volume transport on an interannual time scale. The cyclonic eddies propagating from the Kuroshio Extension region, on the other hand, weaken the Kuroshio meander after the merger. The Kuroshio path variations south of Japan thus seem to be closely related to eddy activities in the subtropical gyre system.
  • Hisashi Hukuda, Xinyu Guo
    Journal of Oceanography 60 5 893 - 904 2004年 [査読有り]
     研究論文(学術雑誌) 
    A two-way nested model has been constructed and applied to the idealized ocean where a uniform mean flow impinges on the isolated Gaussian-shaped seamount and produces two eddies (cold and warm) in the depths. The performance of the nested model has been evaluated subjectively and objectively. Both subjective and objective analyses confirm the traditional view that the nested model can well capture the performance of isolated eddies. Objective analysis, however, reveals some quantitatively important features of a two-way nested model. One is penetration of improved features into the coarse domain and another is the deterioration of mean flow field inside the nested area, neither of which is clear from subjective analysis. With successful application of two-way nested model to the seamount problem, we expect that such a nested model will also be applicable to other oceanic phenomena, particularly to some coastal problems whose time scale is short and where the topographic effects are dominant. Copyright © The Oceanographic Society of Japan.
  • Difference of nutrients budgets in the Bohai Sea between 1982 and 1992 related to the decrease of the Yellow River Discharge
    the Korean Society of OceanographyJournal of the Korean Society of Oceanography 39 1 14 - 19 2004年 [査読有り]
  • XY Guo, H Hukuda, Y Miyazawa, T Yamagata
    JOURNAL OF PHYSICAL OCEANOGRAPHY 33 1 146 - 169 2003年01月 [査読有り]
     研究論文(学術雑誌) 
    A triply nested ocean general circulation model was used to examine how the model horizontal resolution influences the Kuroshio in the East China Sea (ECS) and the sea level variability. As the model resolution increases from 1/2degrees to 1/18degrees the path, current intensity, and vertical structure of the model Kuroshio and the variability of sea level become closer to observations. In general, the higher-resolution model improves the baroclinic as well as barotropic component of the Kuroshio and thus reproduces more realistic density and current fields. This improvement, in addition to better representation of topography, results in better reproduction of the interaction between baroclinicity and bottom topography, that is, JEBAR (joint effect of baroclinicity and bottom relief) in a high-resolution model. Modeling the Kuroshio in the ECS provides an ideal example of such improvement. In particular, the Kuroshio veering phenomenon at (30degreesN, 129degreesE) southwest of Kyushu is discussed, together with the seasonal meridional migration of the path. It is shown that JEBAR and advection of the geostrophic potential vorticity are two major contributions to the vorticity balance in this area. The summer intensification of JEBAR resulting from the intensified stratification yields a strong offshore volume transport across the shelf break, thereby leading to the southward shift of the veering latitude. In winter, the weakened JEBAR, combined with the increased wind stress curl, decreases the offshore volume transport in a considerable amount, explaining the northward shift of the veering latitude. The present reproduction of seasonal migration of the Kuroshio axis at 129degreesE is in good agreement with observation.
  • 福田 久, 郭 新宇, 山形 俊男
    海の研究 11 5 513 - 527 日本海洋学会 2002年09月 [査読有り]
     
    黒潮の沿岸よりの流れが紀伊半島に当たることで発生する振り分け潮について,水平解像度1/18度の高解像海洋循環モデルを使って研究した。1997年のモデル再現実験データを観測結果と比較して,以下の結果を得た。紀南海域の平均的な水位分布は,振り分け潮による沿岸の低気圧性渦に伴うものであるが,モデルの年平均値は,この水位の平均描像を再現できない。しかし,個々のイベントについては平均描像と酷似した水位分布を再現できる。これは,モデルでは振り分け潮の発生頻度は10%ほどであるが,観測では70%の高頻度を示すためである。さらに流速場の時間変化図から,紀伊水道沖を高,低気圧渦が通過することによって励起される黒潮流軸の変動が振り分け潮の発生の引き金となることが分かった。振り分け潮は一連の高,低気圧性擾乱の通過による急激なトルクの作用によって紀伊半島に向かう黒潮の入射角が増加した後に発生すると考えられる。
  • SB Kraines, A Suzuki, T Yanagi, M Isobe, XY Guo, H Komiyama
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 104 C7 15635 - 15653 1999年07月 [査読有り]
     研究論文(学術雑誌) 
    Current measurements and conductivity-temperature-depth surveys of the lagoon and ocean at Majuro Atoll, the Republic of the Marshall Islands, were made from January 10 to 24, 1997. A vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements py Fourier transform. A three-dimensional, robust diagnostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles. We used the diagnostic model to examine the effects of wind stress, radiation stress, density gradients, and tidal stress on the exchange of water between the lagoon and the ocean. Wind effectively mixes the lagoon water in approximately 2 weeks. Tidal flushing appears to be restricted to a small area near the main channels connecting the lagoon to the ocean. Cross-reef-flat currents induced by radiation stress and flowing to the deep channels in the center of the northern boundary form the dominant mechanism for exchange between the lagoon and the open ocean, causing water to exchange completely with the ocean in about 15 days. Computer-generated particles tracked through the lagoon showed that radiation stress is also the main forcing mechanism for particle export from the lagoon. However, the coupling of tidal exchange through the Calalin Channel and wind-stress-induced mixing in the lagoon could also provide a significant export mechanism, particularly for particles originating uniformly inside the lagoon.
  • XY Guo, T Yanagi
    CONTINENTAL SHELF RESEARCH 18 6 677 - 693 1998年05月 [査読有り]
     研究論文(学術雑誌) 
    Observed zooplankton data show that the number of outer bay species of zooplankton appearing in the central part of Tokyo Bay have increased in recent years. Because these zooplankton cannot reproduce in the inner bay, they must be brought into the bay by the advective transport of the sea water from the adjacent open ocean (Nomura,1993 P. D. Thesis, Tokyo university of Fisheries). The increase of fresh water discharge is proposed as a mechanism for changing the residual current that is thought to bring the outer bay species of zooplankton into Tokyo Bay (Nomura,1996, Bulletinon Coastal Oceanography 34, 25-35). To clarify the variation of the residual current due to the increase of fresh water discharge quantitatively, a three-dimensional prognostic numerical model is developed. To verify of the prognostic numerical model, the observed temperature, salinity and residual current during the summer of 1979 are reproduced firstly. The calculated result confirms the existence of two eddies that have been reproduced by a diagnostic numerical model (Guo and Yanagi, 1996, Journal of Oceanography 52, 597-616). The first one is the anticlockwise circulation in the head region of the bay and the second one the clockwise circulation in the central part of the bay. Apart from these two eddies, the strong gravitational circulation at the mouth of the bay, which flows out of the bay in the upper layer and into the bay in the lower layer, is also reproduced. Next, the river discharge is increased to the level of the summer of 1989 and the calculation is carried out again. The difference between these two calculated results is considered as the variation induced by the increase of fresh water discharge. The calculated result shows that the increase of river water influences the residual current in the head region of the bay greatly. At the mouth of the bay, the gravitational circulation is strengthened by up to 0.5 cm/s. This variation of residual current is expected to bring more outer bay species of zooplankton into the inner bay from the adjacent open ocean. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • Xinyu Guo, Tetsuo Yanagi
    Journal of Oceanography 54 6 651 - 668 1998年 [査読有り]
     研究論文(学術雑誌) 
    A three-dimensional tidal current model is developed and applied to the East China Sea (ECS), the Yellow Sea and the Bohai Sea. The model well reproduces the major four tides, namely M2, S2, K1 and O1 tides, and their currents. The horizontal distributions of the major four tidal currents are the same as those calculated by the horizontal two-dimensional models. With its high resolutions in the horizontal (12.5 km) and the vertical (20 layers), the model is used to investigate the vertical distributions of tidal current. Four vertical eddy viscosity models are used in the numerical experiments. As the tidal current becomes strong, its vertical shear becomes large and its vertical profile becomes sensitive to the vertical eddy viscosity. As a conclusion, the HU (a) model (Davies et al., 1997), which relates the vertical eddy viscosity to the water depth and depth mean velocity, gives the closest results to the observed data. The reproduction of the amphidromic point of M2 tide in Liaodong Bay is discussed and it is concluded that it depends on the bottom friction stress. The model reproduces a unique vertical profile of tidal current in the Yellow Sea, which is also found in the observed data. The reason for the reproduction of such a unique profile in the model is investigated.
  • The role of the Taiwan strait in an ecological medel in the East china sea(共著)
    Acta Oceanographica Taiwanica 37 2 139 - 164 1998年 [査読有り]
  • Tetsuo Yanagi, Xinyu Guo, Toshiro Saino, Takashi Ishimaru, Sinichiro Noriki
    Journal of Oceanography 53 403 - 409 1997年08月 [査読有り]
     
    The detailed structure of the thermohaline front at the mouth of Ise Bay during winter has been investigated by intensive field observation. The transport of suspended matter from Ise Bay to the Pacific Ocean through the thermohaline front has also been investigated using the data from a time-series sediment trap, a current meter and a nephelometer moored at the bay mouth station. The mixed coastal and offshore water at the surface of the thermohaline front sinks to a depth of about 200 m in the offshore area.
  • GUO X, YANAGI T
    Journal of Oceanography 52 5 597 - 616 1996年 [査読有り]
     研究論文(学術雑誌) 
    The residual currents in Tokyo Bay during four seasons are calculated diagnostically from the observed water temperature, salinity and wind data collected by Unoki et al. (1980). The calculated residual currents, verified by the observed ones, show an obvious seasonal variable character. During spring, a clear anticlockwise circulation develops in the head region of the bay and a strong southwestward current flows in the upper layer along the eastern coast from the central part to the mouth of the bay. During summer, the anticlockwise circulation in the head region is maintained but the southwestward current along the eastern coast becomes weak. During autumn, the preceding anticlockwise circulation disappears but a clockwise circulation develops in the central part of the bay. During winter, the calculated residual current is similar to that during autumn. As a conclusion, the seasonal variation of residual current in Tokyo Bay can be attributed to the variation of the strength of two eddies. The first one is the anticlockwise circulation in the head region of the bay, which develops in spring and summer and disappears in autumn and winter. The second one is the clockwise circulation in the central part of the bay, which develops in autumn and winter, decreases in spring and nearly disappears in summer.
  • Wind-driven current in Tokyo Bay, Japan during winter(共著)
    La mer 33 2 89 - 101 1995年 [査読有り]
  • Three dimensional structure of tidal currents in Tokyo Bay(共著)
    La mer 32 3 173 - 185 1994年 [査読有り]

書籍

  • Interdisciplinary Studies on Environmental Chemistry, Vol. 5, Modeling and Analysis of Marine Environmental Problems
    TERRAPUB 2011年
  • High Resolution Numerical Modeling of the Atmosphere and Ocean
    Springer 2008年
  • Detailed flow structure around a thermohaline front at the mouth of Ise Bay. Japan(共著)
    AGUphysics of Estuaries and coastal seas American Geophysical Union 1996年

MISC

共同研究・競争的資金等の研究課題

  • 太平洋から沿岸への栄養塩供給システム;豊後水道の底入り潮の理解
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2020年04月 -2024年03月 
    代表者 : 森本 昭彦, 郭 新宇
  • 温暖化~成層強化による東シナ海外部陸棚域の低栄養化・貧酸素化と生態系への影響評価
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 張 勁, 郭 新宇, 遠藤 貴洋
  • 超高解像度観測と数値モデルを組み合わせた沿岸域における栄養塩動態の解明
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2017年04月 -2021年03月 
    代表者 : 吉江 直樹, 郭 新宇
     
    潮汐フロント域における超高解像度観測:伊予灘佐田岬周辺の潮汐フロント域において、海洋表層の成層強度が異なる初夏と盛夏の大潮・小潮時に現場観測を実施した。今年度は、潮汐フロントの詳細な3次元分布を捉えるために、昨年度までの中央観測ラインに加えて、南北2本の観測ラインを追加した。約1.5~5.0km間隔で高応答性センサー(硝酸計、浅海用乱流計、多項目センサー群[水温、塩分、濁度、PAR、DO、Chl.a濃度]、船底超音波多層流向流速計)を用いて観測した。また、センサーの校正のために、随時海水を採取して持ち帰り実験室にてChl.a濃度および硝酸塩濃度を高精度に分析した。さらに、低次生態系の群集構造把握のために、海水をサイズ分画濾過し植物のサイズ組成を分析した。 瀬戸内海における超高解像度数値モデルの開発:本研究の数値モデルは、物理モデルと生態系モデルから構成されるが、今年度は、複雑な低次栄養段階生態系と栄養塩動態を再現できる生態系モデルの改良を実施し、西部瀬戸内海の代表的な4つの灘において現実的な栄養塩と植物・動物プランクトンの季節変化を再現した。 佐田岬における高頻度時系列観測の実施:三崎漁協と共同で佐田岬に時系列モニタリングステーションを設け、水温・塩分・Chl.a濃度・濁度を20分間隔で、栄養塩濃度を1日間隔で観測した。また、約1月半毎に現地に赴き、センサー類の保守作業を実施した。また、三崎漁協の西濱らにより毎日採水・濾過処理・冷凍保存された栄養塩分析用海水サンプルを、実験室にて栄養塩自動分析機を用いて高精度に分析した。 ひまわり8号による高頻度時系列データの解析:静止軌道衛星ひまわり8号による1時間毎の海表面水温データを用いて、水平的な水温勾配の分布から潮汐フロントの水平分布を抽出すると共に、それらの短時間での水平的な移動について解析した。
  • 万年スケールでみた黒潮の流路変遷と黒潮分枝流の形成メカニズム
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2017年04月 -2021年03月 
    代表者 : 郭 新宇, 佐川 拓也, 加 三千宣, 森本 昭彦, 久保田 好美
     
    古気候モデルの不確実性を確認するため、昨年度に使った古気候モデル(IPSL-CM5)以外に、PMIP3からさらに4つのモデル(MIROC、CNRM-CERFACS、NASA-GISS、MRI)の結果を用いて、LGM時の風場と熱フラックスを比較した。黒潮流域を含む中高緯度では4つのモデルともに海洋から大気へ熱を放出している。そのうち、東シナ海付近ではCNRM-CERFACSが、日本南岸付近ではNASA-GISSが一番多く熱を失っている。一方、赤道域では、MIROCとMRIが熱を吸収しているが、CNRM-CERFACSとNASA-GISSは熱を失っている。その違いは雲量、海表水温と風場に由来している。また、黒潮の離岸緯度に関わる風応力の渦度がゼロになる緯度について、4つの古気候モデルは違いがほとんど見られなかった。 4つの古気候モデルから得られた外力(風応力と熱フラックス)を昨年開発した1/4度の海洋循環モデルに与える前に、古気候モデルのバイアスを修正する必要がある。そのために、古気候モデルのそれぞれの0kaの結果とNCEPの再解析データの差を利用して、それぞれの古気候モデルのLGM時の結果を修正した。修正済みの外力を利用して海洋循環モデルを40年間駆動して得られた黒潮は現在と似た流路を示し、基本的に台湾東部、沖縄の西側と九州南部を流れている。この結果は昨年の計算結果と矛盾していない。 これ以外に、LGM時の日本海の表層塩分の低下過程についても日本海の淡水収支を表すボックスモデルを用いて、対馬暖流の流量変動と淡水供給の影響を調べた。3万5千年前からLGMまでの期間中に、対馬暖流の流量が徐々に減少すると仮定した場合は、日本海の表層塩分がLGMまでの最後の1~2千年に急激に低下した可能性をボックスモデルが示唆した。この点について今後三次元の海洋循環モデルで検証する予定である。
  • 海洋混合学の創設:物質循環・気候・生態系をつなぐ統合的理解の推進
    日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2015年06月 -2020年03月 
    代表者 : 安田 一郎, 増田 周平, 西岡 純, 郭 新宇, 原田 尚美, 伊藤 進一, 日比谷 紀之, 羽角 博康
     
    鉛直混合の実態の解明を通じて、北太平洋において、どこでどのような鉛直混合が働き、栄養塩を含む中深層水が湧昇し、親潮や黒潮に影響を与え、気候を変え、生物生産の維持と長周期変動につながるのか、混合過程を軸として統合的に解明し、新しい学術領域「海洋混合学」を構築するために、総括班を組織する。本新学術領域の目的を達成するために、作業部会を設置し、計画研究・公募研究間や分野間、観測とモデリング等手法間の有機的連携を図った。本領域の基盤をなす、現場観測航海を実現し多くの成果が得られるよう、共有の乱流観測機器を導入・整備等を行う研究支援チーム等を通じて、班や研究分野を超えた協力体制を作り、多数の観測航海を成功させた。国際活動支援班を通じた研究者の招聘・派遣等、国内・海外研究機関との交流を図った。全体会議・国際会議・国内学会でのシンポジウム及び若手会を企画・運営し、次世代の研究者・若手の育成を図った。 H30年度は、4月に公募班・計画研究班・総括班合同会議及びWG合同シンポを開催し、H30-31公募研究一覧、8月にはH29年度成果報告書を出版した。WG活動として、レビュー6論文を「海の研究」に出版、関係会議8回開催、随時とりまとめ会議を開いた。10月には若手会主催のサマースクールを熱海で開催した。ニュースレター7・8号を発行し、HPに公募班の研究計画を掲載、順次ニュース・業績を更新した。ロシア船、台湾船、インドネシア白鳳丸航海を成功させ、研究航海計31航海を実施した。研究支援チームは20航海での観測機器の整備・管理した。国際活動15件を実施。学会・国際会議で23件のセッション・シンポジウムを開催した。第2回OMIX国際シンポジウム及び海洋学会でのOMIXシンポ実施。H31年3月全体会議・総括班会議(18.6年及びロシア船航海関係ナイトセッション含む)を定山渓にて合宿形式で開催した。
  • 黒潮とその源流域における混合過程・栄養塩輸送と生態系の基礎構造の解明
    日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2015年06月 -2020年03月 
    代表者 : 郭 新宇, 松野 健, 遠藤 貴洋, 張 勁, 市川 香, 中村 啓彦, 千手 智晴, 堤 英輔
     
    黒潮とその源流域をフィールドとして、大洋の縁辺域(西岸境界流域)における混合を定量的に評価し、境界混合がエネルギー消散と物質輸送に果たす役割、ならびに生態系への寄与を明らかにすることを目的として、物理および生物・化学的観測に基づいた分野連携的研究を実施している。 本年度は、2015年から続けてきたトカラ海峡の観測を6月と11月に2回実施したとともに、内部孤立波を期待する東シナ海陸棚縁辺部付近での観測、強い乱流現象を期待する台湾東沖のI-Lan Ridge周辺での観測を実施した。かごしま丸によるトカラ海峡の観測では、定点観測において、乱流,水質,植物・動物プランクトン組成の鉛直プロファイルの観測、トカラ海峡から室戸沖までの航走観測において、水質,乱流の微細空間構造の計測、そして船上での実験において、栄養塩を添加して動植物プランクトンの増殖を調べる培養実験を行った。長崎丸による東シナ海陸棚縁辺部付近での観測では、係留観測と、陸棚斜面の等深線に直交する測線における水温・塩分・水質構造の繰り返し観測を行った。国立台湾大学の研究船Ocean Researcher Ⅰによる台湾東沖の観測では、係留観測と黒潮に沿う測線と黒潮を横切る測線における乱流観測を行った。一方、前年度に行ったルソン海峡観測で取得したデータを用いて潮流によって励起した内部波の特性を解析した。また、黒潮・海山間相互作用に関する3次元数値実験において、理想化した海山と黒潮および現実の地形と黒潮を別々にモデルに導入し、乱流に関連するプロセスを解析した。また、台湾東沖における強い乱流が栄養塩と植物プランクトンの分布に与える影響を理解するためにOFESをベースにした数値生態系モデルの結果を解析した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2014年04月 -2018年03月 
    代表者 : 郭 新宇, 小松 幸生, 笹井 義一, 宮澤 泰正
     
    低次生態系モデルの出力を用いて、黒潮本流域を挟む両側面における栄養塩の水平輸送量および有光層の底面における栄養塩の鉛直輸送量の年平均値を求めた。計算結果から、1)日本南岸の黒潮内側域から黒潮本流域への栄養塩の水平輸送量が比較的大きいこと、2)混合水域から黒潮続流域に、さらに黒潮続流域から亜熱帯域に水平方向の硝酸塩輸送量を有すること、3)ルソン海峡付近と黒潮続流域では大きな鉛直方向の栄養塩輸送量があることが分かった。
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 松野 健, 張 勁, 武田 重信, 石坂 丞二, 梅澤 有, 吉川 裕, 郭 新宇, 千手 智晴, 遠藤 貴洋, 李 根淙
     
    東シナ海陸棚域における有光層での基礎生産に関して、栄養塩の窒素・リン酸比(N/P) と乱流混合による栄養塩輸送との関連から、鉛直混合による栄養塩の下層からの供給がしばしば亜表層クロロフィル極大層を形成していることが確かめられ、底層境界層では、乱流強度と懸濁物の濃度に明瞭な関係がある一方、堆積物からの再懸濁物に含まれる有機物の分解は栄養塩の供給にはあまり寄与していないことが見いだされた。また、生態系モデルからは、黒潮からの栄養塩が陸棚域の基礎生産に大きく寄与していることが明らかになった。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 森本 昭彦, 郭 新宇, 三野 義尚, 兼田 淳史
     
    本研究では、北部タイランド湾の底層で起こる貧酸素化の現状とその季節変化を明らかにすることを目的に船舶による現場観測を実施した。その結果、貧酸素化は6月~11月に湾北部で起こり、貧酸素水塊の分布は季節とともに湾東部から西部へと分布域が変化することが明らかになった。さらに、物理モデルと物理-低次生態系モデルを開発し、河川流量の変化に伴う湾内の流動場の変化とそのメカニズムの解明、および河川流量変化に伴う貧酸素化の変化を調べた。流動場は河川流量が変化しても大きく変わらないが、貧酸素化は河川流量の増加により悪化することが示された。
  • 日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 郭 新宇, 武岡 英隆, 吉江 直樹, 藤井 直紀
     
    宇和海に生息するミズクラゲについて、湾全体での現存量及びミズクラゲ集群内のクラゲ個体の空間分布、遊泳行動を、高台に設置された定点カメラによる空撮、水中カメラと計量魚群探知機を用いた船舶観測から調査した。海面で見られた帯状や塊状のミズクラゲパッチには、水中では中空の構造をしているものがあることを発見した。また、湾全体の現存量を知る方法として、計量魚群探知機により得られた音響データをクラゲ個体数密度に換算する手法が有効であることを立証した。今後、アメリカ西海岸でも同様に報告されているミズクラゲ集群の中空構造の形成メカニズムを解明することが期待される。
  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2010年04月 -2015年03月 
    代表者 : 磯辺 篤彦, 郭 新宇, 中村 啓彦, 広瀬 直毅, 石坂 丞二, 木田 新一郎, 加古 真一郎, 中村 知裕, 万田 敦昌
     
    日本南岸における黒潮流路変動が、南岸低気圧の経路に揺らぎを与えることを発見した。冬季東シナ海における浅海部の海面冷却は、これに連動した海面気圧と風系の変化を通して、負のフィードバック機構を持つことを示した。瀬戸内海での海面水温分布によって海陸風が変調すること、大潮・小潮周期の海面水温変化に応じて、海上風も変動することを発見した。以上、縁辺海や沿岸規模の海洋過程は大気過程に影響を与え、場合によって相互作用が成立することを示した。また、植物プランクトンの春季ブルームが海面水温を変化させ、これが低気圧の発達に影響を及ぼすといった、大気ー海洋ー生態系の結合過程を提案した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2010年 -2012年 
    代表者 : 森本 昭彦, 滝川 哲太郎, 郭 新宇
     
    本研究では、対馬暖流による東シナ海から日本海への物質輸送の現状把握と、 東シナ海・日本海の表層流の時間変化特性を現場観測と人工衛星海面高度計データにより行った。東シナ海から日本海への物質輸送量の経年変化は大きく、その変化は東シナ海上での流動場の変化が大きく関係していることが明らかになった。また、衛星高度計データ解析により東シナ海、日本海南西部の表層流の変動特性を明らかにし、さらに、東シナ海・黄海の衛星高度計データの精度向上のための潮汐同化モデルの開発に成功した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2010年 -2012年 
    代表者 : 張 勁, 日下部 実, 石橋 純一郎, 石坂 丞二, 郭 新宇
     
    沿岸性海底熱水活動(SWH)は,その周辺海域に酸性化と鉄供給をもたらし,生物基礎生産の観点からは相反する効果が予想される。本研究では,最近,台湾北東沿岸域で見いだされた SWH 域を,生物基礎生産への影響の検証に絶好の実験フィールドとしてSWH が環境に及ぼす影響を評価することを目的とした。熱水や熱水噴出口周辺海水の地球化学特性により,高温(80-110°C)かつ強酸性(pH, 2.1-3.5)の SWH はマントル起源の火山ガス噴出に伴い,1km 四方の海洋表層水に影響を及ぼしている;また,通常海水に比べ,有光層にSWH から高濃度の Si と P,特に Mn と Fe が供給され,同緯度海域に比べ数十~数百倍高いクロロフィル分布をもたらすことを明らかにした。SWH は天然の「海洋酸性化」と「栄養塩・微量元素供給」として,複合的に周辺海域の一次生産に大きく寄与していることが自然界において初めて発見された。また,薩摩硫黄島など日本周辺比較海域や台湾東沖における広域海洋観測により,SWH に伴う物質供給と周辺環境への影響について実態解明が進んだ。
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2009年 -2012年 
    代表者 : 磯辺 篤彦, 郭 新宇, 吉江 直樹, 加 三千宣, 武岡 英隆, 二村 彰, 斉藤 光代, 張 光玄, 木村 詞明, 守屋 和佳
     
    JCOPE2 などの海洋同化プロダクトを外洋側の境界条件とし、また、ASCAT 衛星風データを強制力とすることで急潮の再現がある程度可能なこと、また、同化プロダクトを初期条件にした予報モデルの結果を境界に与え、また予報風を強制力とすることで、急潮予報が可能であることを示した。予報を参照して実施した豊後水道における集中観測によって、急潮に伴う沿岸生態系の急激な変遷や流況変動を検出した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2009年 -2012年 
    代表者 : 郭 新宇, 武岡 英隆, 吉江 直樹, 木村 詞明, 小野 純, 齋藤 光代, 小森田 智大, 宮澤 泰正
     
    東シナ海と瀬戸内海をモデル海域として、数値生態系モデルを構築し、モデル実験より両海域での陸起源栄養塩と外洋起源栄養塩の輸送・循環過程を解明するとともに、年間基礎生産量に対する陸起源栄養塩と外洋起源栄養塩の寄与率を算出した。また、両海域が面している黒潮域における栄養塩輸送の空間構造と時間変化および黒潮中層水の栄養塩濃度の時間変化を観測データから明らかにした。さらに、モデル実験より、陸域と黒潮域での栄養塩濃度の変化に対する沿岸域での栄養塩濃度と基礎生産量の応答を検討した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2007年 -2009年 
    代表者 : 張 勁, 成田 尚史, 郭 新宇, 中川 書子, 角皆 潤
     
    本研究は,沿岸海底湧水(SGD)の淡水・熱フラックスに着目し,海洋大循環の1/10モデルである日本海をフィールドとして,高緯度海域における海水沈み込みへのSGDの影響解明を目的とした。降水のほとんどがSGDとして流出する利尻島及びその周辺海域,またオホーツク海に隣接するサロマ湖・能取湖を調査した結果,SGDが栄養塩など化学物質のみならず,淡水や熱輸送の重要なルートとして,海洋の成層構造/海洋循環に影響を及ぼしている実証が得られた。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2006年 -2008年 
    代表者 : 杉本 隆成, 澤本 彰三, 福井 篤, 岡田 喜裕, 萩原 直樹, 仁木 将人, 郭 新宇, 金子 新, 田所 和明, 郭 新宇, 金子 新
     
    駿河湾の急潮およびサクラエビの再生産環境に注目した流況と生態系の観測網を構築した。駿河湾を東西に横断するフェリーに搭載した音響ドップラー式流速鉛直プロ ファイラーADCPと、湾口および湾奥部における係留型の流速計による連続観測と、調 査船による水質およびプランクトンの隔週反復観測を中核としている。これらによって、後述するような成果が着々と得られつつある
  • ルソン海峡における黒潮の進入過程とそのフィリピン沿岸環境への影響評価
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2005年 -2007年 
    代表者 : 郭 新宇, BALOTRO R. S., BALOTRO Roland Sayo, BALOTRO R.S.
     
    本年度では、フィリピン沿岸海域に設置されていた水温計の回収とデータ解析が主要の研究内容である。水温計は6箇所(Basoc、Ivana、Pagudpud、Palaui、Palanan、Calaguas)で設置されていたが、5箇所(Basoc、Ivana、Pagudpud、Palaui、Calaguas)での水温計を回収できた。回収された水温計から計16本の水温データの時系列が得られた。これらの時系列からフィリピン沿岸での水温変動特性を把握し、さらに日本沿岸での水温計測データとの比較することにより、黒潮内側域での水温変動の相違性を明らかにしたい。 一方、数値モデル(JCOPE)結果の解析も進んでいる。解析結果によると、ルソン海峡での黒潮進入は3つの分枝があり、その形成は島の存在に関連すると考えられる。また、従来では、ルソン海峡での海水交換は鉛直方向のサンドイッチ型の流動構造によるものと認識されている。しかしながら、数値モデルは鉛直方向より水平方向のサンドイッチ型の流動構造を示しており、ルソン海峡での海水交換を考え直す必要を示している。また、ルソン海峡での黒潮進入は2004年が2003年と2005年と違う挙動を持ち、明らかな経年変動を持っている。この経年変動は局地的な効果よらず太平洋海盆スケールで起きる変動と密接に関連することも分かっている。以上の結果は5月に広島大学で行ったPAMS/JECSS(太平洋アジア縁辺海/日本海東シナ海研究)国際研究集会で発表し、国内外の研究者から関心を寄せてきた。
  • 三峡ダムと長江分水プロジェクトが東シナ海の海洋環境に及ぼす影響に関する研究
    日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2005年 -2006年 
    代表者 : 郭 新宇
     
    初年度に潮汐と河川流量を導入して、モデルの改良を図り、長江と黄河から淡水供給による形成された河川プルームの季節変動を再現できた。このモデルを利用して、さらに経年変動を調べることが昨年度の主要目標である。 過去50年間、長江の流量は大きく変動していなかったが、黄河の流量は50年代から徐々に減り、最近になって、50年代の2〜3割まで減少している。したがって、長江より黄河の流量激減に対する海洋の応答を明らかにする必要がある。そのため、1950年〜2000年の黄河流量を10年毎に平均して、季節変動を有する5つの気候値を用いて、モデル応答実験を行った。応答実験では、黄河河川流量以外の要素が変わらないと仮定した。 応答実験の結果から、特に渤海海峡を通した渤海と黄海の海水交換量の変動を注目して、解析を行った。黄河流量の減少に伴い、渤海海峡での交換流量も減少していることが確認できた。さらに、渤海海峡での交換流量の減少は黄河流量の減少との間に大きな時間差があることも分かった。黄河流量の減少は主に夏季に起こったが、渤海海峡での交換流量の減少は翌年の春に生じる。その理由は黄河プルームの挙動にある。黄河プルームは夏季には渤海海峡に到達せず、南東風により渤海中央部に到達することがモデル結果と観測データから分かっている。秋季になると、北西風により、黄河プルームが渤海南部に戻り、冬季と翌年の春季に渤海海峡から黄海に流出する。冬季の渤海海峡の流動構造は風により支配されているため、海峡での交換流量に経年変動はあまり見られなかったが、春季の渤海海峡の流動構造は密度流に支配されているため、経年変動が顕著になっている。そのため、渤海海峡での交換流量は春季の応答(減少)が最も大きくなっている。ただし、渤海海峡の流動構造は密度流以外の成分もあるため、河川流量の7割減に対して、渤海海峡での交換流量の減少は最大で2割しかなかった。
  • 三峡ダムと長江分水プロジェクトが東シナ海の海洋環境に及ぼす影響に関する研究
    科学研究費補助金
    研究期間 : 2005年 -2005年
  • 瀬戸内海における通過流の可能性に関する研究
    日本学術振興会:科学研究費助成事業 萌芽研究
    研究期間 : 2003年 -2003年 
    代表者 : 郭 新宇
  • 瀬戸内海海況予測モデル
  • ネスティングモデルによる黒潮のシミュレーション

委員歴

  • 2016年04月 - 現在   日本海洋学会   評議員
  • 2010年 - 現在   日本海洋学会   沿岸海洋研究部会 沿岸事業部メンバー
  • 2005年 - 2006年   日本海洋学会   学会誌「海の研究」編集委員

愛媛大学教員活動実績

教育活動(B)

担当授業科目(B01)

  • 2019, 前期, 学部, 沿岸海洋学
  • 2019, 前期, 学部, 地球科学野外研究
  • 2019, 前期, 修士, 大気海洋学特論
  • 2019, 前期, 修士, 地球科学高等実験Ⅰ
  • 2019, 前期, 修士, 地球科学高等実験Ⅴ
  • 2019, 前期, 修士, 地球科学フィールド高等実習Ⅰ
  • 2019, 前期, 修士, 地球科学フィールド高等実習Ⅲ
  • 2019, 前期, 修士, 地球科学プレゼンテーション特別実習Ⅰ
  • 2019, 前期, 修士, 地球科学プレゼンテーション特別実習Ⅲ
  • 2019, 前期, 修士, 地球科学ゼミナールⅢ
  • 2019, 前期, 修士, 地球科学プレゼンテーション特別実習Ⅱ
  • 2019, 前期, 修士, 地球科学フィールド高等実習Ⅱ
  • 2019, 前期, 修士, 地球科学高等実験Ⅲ
  • 2019, 前期, 博士, 環境動態学特論
  • 2019, 前期, 学部, 沿岸海洋学
  • 2019, 前期, 学部, コース英語I
  • 2019, 前期, 学部, 地球科学野外研究


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