Authorship：Corresponding author  

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Language：English   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10872-023-00688-3

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Other Link： https://link.springer.com/article/10.1007/s10872-023-00688-3/fulltext.html

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Authorship：Lead author,　Corresponding author  

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10872-021-00616-3

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Other Link： https://link.springer.com/article/10.1007/s10872-021-00616-3/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020jc017141

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JC017141

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.csr.2021.104551

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Coastal Oceanography Research Committee, the Oceanographic Society of Japan  

DOI： 10.32142/engankaiyo.2021.2.24

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

The Japan Sea is a semi-closed sea with straits such as the Tsushima Strait (Korea Strait). The nutrient transport through the Tsushima Strait impacts on the ecosystem around the coast of Japan. We analyzed hydrographic data from the Tsushima Straits to reveal interannual variations in the volume transport, nutrient concentration, and nutrient transport. The nutrient transport in the strait has large interannual variations of +/- 50% of average transport. We developed a coupled ocean circulation and ecosystem model, in which the lateral boundary condition was applied based on our observation data, and investigated the biogeochemical responses in the Japan Sea to the variations in horizontal nutrient flux through the Tsushima Strait.We reproduced the lower trophic ecosystem in the Japan Sea and evaluated the contribution ratio of dissolved inorganic nitrogen supplied from the Tsushima Strait to the biogeochemical cycles in the Japan Sea. A primary production of more than 70% in the region of 300-400 km from the coast of Japan is determined by the nutrient inflow through the Tsushima Straits. We investigated the response of the lower trophic ecosystem in the Japan Sea associated with nutrient transport change (+/- 50%) through the Tsushima Strait. We found large impacts on primary production related to horizontal nutrient flux change in the central regions in the Japan Sea and near the East Korea Warm Current region. The increase of chlorophyll a in the central regions is caused by the transportation of nutrients through the sub-surface layer of the Tsushima Straits from 50 m to 100 m. Horizontally transported nutrients in the sub-surface layer are not utilized by phytoplankton during the summer because of stratification, but they are supplied in the surface layer in autumn and winter by vertical mixing. These processes also increase primary production in broader regions (132 degrees E, 37-41 degrees N). The case study on the increased time for nutrient transport showed that the nutrient flux change in summer had the highest impact on the lower ecosystem changes. The present study suggests that the interannual variations in the nutrient transport through the Tsushima Straits impact the productivity of autumn blooms in the broader regions of the Japan Sea.

DOI： 10.1016/j.ecss.2019.106386

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Publishing type：Research paper (conference, symposium, etc.)  

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Publishing type：Part of collection (book)  

© 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.

DOI： 10.1016/B978-0-12-813060-5.00004-3

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Authorship：Lead author   Language：English   Publishing type：Research paper (other academic)  

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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.

DOI： 10.1016/j.csr.2017.12.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

To identify water with an excess nitrate concentration to phosphate ratio and its potential source, the nutrient concentrations in the Tsushima Strait (TSS) were investigated over ten cruises in August and September 2007-2014, excluding 2010. On the basis of the Redfield ratio, water with an excess nitrate concentration of > 1 mu M (positive ExNOx water) was identified below the surface mixed layer during four cruises in 2011-2013. Positive ExNOx water was present mainly in less-saline (< 34) waters with a density of 22-25 sigma (theta) , and 25-75 m depth. However, in August 2012, positive ExNOx was detected in dense (25-25.5 sigma(theta) ) and deep (50-110 m depth) waters near the salinity maximum, although the salinity during this period was significantly lower than that in other years. The horizontal length of positive ExNOx water was > 100 km across the TSS during two cruises in August 2012 and September 2013, respectively. According to multi-regression analysis conducted on the silicate concentration, temperature, and salinity, the silicate concentration was increased in the less-saline subsurface water. The required amount of original freshwater was 10(8-9) m(3) day(-1) based on the excess nitrate concentration. This evidence indicates that the positive ExNOx water originated from large river waters such as the Changjiang. Thus, discharged water from the rivers of the East Asia is contributing to the increased N:P ratio in the Tsushima Warm Current, southern Japan Sea.

DOI： 10.1007/s10872-017-0430-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We investigated lateral profiles of Ra-228 (half-life; 5.75 years) activity and Ra-228/Ra-226 (1600 years) activity ratio using 241 surface water samples collected in/around the Sea of Japan and the East China Sea (ECS) during June October of 2009-2014. In the ECS, the Ra-228/Ra-226 ratio in the surface waters exhibited markedly wide variation ( < 0.05-3.5) in June, predominantly reflecting the mixing between the Ra-228-rich continental shelf water and the Ra-228-depleted Kuroshio Current water. In July, the surface waters of the central Sea of Japan (135-138 degrees E) became separated into three currents: the Offshore Branch of the Tsushima Warm Current (OBTWC) (Ra-228/Ra-226 =0.7-1.2) at 39-41 degrees N, the Coastal Branch of the TWC (CBTWC) (similar to 0.7) on the southern side, and sub-Arctic Current (similar to 0.7) on the northern side. From the central to northeastern Sea of Japan, the Ra-228/Ra-226 ratio at the surface (0.8-1.0) was within a range between that of the CBTWC and OBTWC. The fraction of continental shelf water in the CBTWC, OBTWC, and in their combined current was estimated to be 11-16%, similar to 8%, and 10-11%, respectively.

DOI： 10.1016/j.csr.2016.08.010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This study found an unusually large variation in the coastal sea level difference (SLD) in the southwestern Japan Sea from July to October 2013. The time and horizontal scales were about 4 months and 1000 km along the coast, respectively. During the exceptionally hot summer of 2013, strong monsoon winds blew through the Tsushima Straits into the southwestern Japan Sea, because the North Pacific High was located farther west than average. The southwesterly winds averaged 7 m s(-1) parallel to the coast in July 2013, resulting in Ekman transport toward the coast. The most noticeable SLD was measured between Omijima and Mishima, normal to the 250 km rectilinear coastal line. The velocity of the first branch of the Tsushima Warm Current increased to about 50 cm s(-1) between Omijima and Mishima from late July to early August. Although the SLD seemed to simultaneously increase and decrease along the Japanese coast with large time scale, the variation in coastal SLD propagated along the Japanese coast, reaching Niigata-nishi in the eastern Japan Sea. The propagation speed in the wide continental shelf of the southern Japan Sea was much higher than that in the narrow eastern shelf, which was consistent with the behavior of continental shelf waves.

DOI： 10.1016/j.csr.2016.06.004

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Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

J-GLOBAL

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Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

From summer to autumn, in the southwestern Japan Sea, the maximum subsurface nutrient (DIN: nitrate + nitrite) concentration and minimum dissolved oxygen (DO) concentration layers lie at depths of approximately 75-125 dbar. The subsurface nutrient-rich water originates from the East China Sea through the lower layer (50-100-dbar depths) of the Tsushima Straits. On a smaller scale, in the subsurface nutrient-rich layer, submesoscale structures (similar to 10 km) with high DO and chlorophyll-a (Chl-a) concentrations were observed below the surface euphotic zone and the minimum Chl-a layer in late October 2008. Considering that photosynthesis cannot occur in the minimum Chl-a layer, the submesoscale Chl-a maxima did not coincide with the normal maximum subsurface chlorophyll layer, where phytoplankton can mature, in the seasonal pycnocline in summer. The subsurface submesoscale water masses were zonally distributed from west to east downstream of the Tsushima Warm Current. In late November 2008, high DO and Chl-a water subducted from the surface density front to the subsurface layers along the isopycnal surface. In the large-scale frontal region of the Tsushima Warm Current, the subsurface isopycnals were convex upward both in October and November 2008, suggesting meso- and submesoscale upwellings.

DOI： 10.1007/s10872-015-0340-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Water column conditions in the Gulf of Thailand (GoT) were analyzed by considering four major factors including surface heat fluxes, freshwater inputs from river discharge and atmospheric fluxes, tidal and wind stirrings. The analytical results suggested that surface heat fluxes and tidal stirring are the most important factors to control water column conditions, followed by freshwater fluxes. Well-mixing was predicted to occur from November to February resulted from relatively large tidal stirring, surface heat loss and low freshwater input, but the climatological density data suggested stratification during this period because of local freshwater accumulation. The South China Sea (SCS) and the northeast wind played significant contributions to freshwater accumulation by generating surface water flow into the gulf during the northeast monsoon. On the other hand, the development of stable and strong stratification during the southwest monsoon was enhanced by SCS subsurface water intrusion and surface outflow induced by the southwest wind. Strong surface heat fluxes coincident with SCS intrusion in April and May make water stratification more complex. This phenomenon generates double thermocline and multi-stratified water in some GoT area. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2016.02.016

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We compiled a long-term record of monthly mean sea surface currents in the Japan Sea from satellite altimetry and satellite-tracked drifter data. The record covers the entire Japan Sea for the period from May 1995 through January 2009. Using these data, we examined the path of the Tsushima Warm Current in the southwestern part of the Japan Sea. The mean sea surface current field revealed a "triple-branch" pattern. The first branch through the eastern channel of the Tsushima Strait flows along the coast ofJapan with a mean current velocity of 20 cm s(-1). The second branch flows along the continental shelf edge at around the 200-m isobath with a mean current velocity of 12 cm s(-1). The third branch flows along the east coast of the Korean peninsula with a mean current velocity of 25 cm s(-1). We investigated seasonal variation in the path of each branch. The first branch flowing along the Japanese coast throughout the year is highly stable. The second branch is stable throughout the year except in November. The third branch flowing along the east coast of Korea is highly stable until 38 degrees N. Downstream of the third branch around 38 degrees N, the current bifurcates into northeastward and southeastward currents. The northeastward current exhibits stable flow from June to February except in January. This current joins an eastward current originating around 39 degrees N, 128.5 degrees E. The southeastward current flows stably in June, September, and December. There were two current paths east of 131 degrees E over the continental shelf off the San'in coast of Japan. The nearshore current flows along the Japanese coast with a mean current velocity of 23 cm s(-1), and the offshore current flows around the continental shelf area with a mean current velocity of 19 cm s(-1). These two currents are highly stable throughout the year. A current flows to the west of Oki Island to around 38.5 degrees N and is highly stable in all months except March to July. These results provide a schematic view of the paths of the Tsushima Warm Current in the southwestern part of the Japan Sea. (c) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pocean.2013.10.007

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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DOI： 10.1007/s10811-013-0152y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An analysis of a surface flow field in the East China Sea (ECS) obtained by combining satellite altimeter and drifter data provides comprehensive information of its mean field and annual variation. The Taiwan Warm Current, the onshore Kuroshio intrusion, the Kuroshio, the northeastward Kuroshio branch, the northward current west of Kyushu, the Cheju Warm Current, and the Tsushima Warm Current are regarded as persistent currents. Annual variation is a dominant signal in the ECS and is a major component of the seasonal variation. The contribution of the annual variation to the seasonal variation is estimated as 50% over the ECS, and exceeds 70% for the Kuroshio northeast of Taiwan, the Taiwan Warm Current, the Taiwan Strait Warm Current, the onshore Kuroshio intrusion, the northeastward Kuroshio branch, the northward current west of Kyushu, and the Tsushima Warm Current. The annual variation is characterized by propagation of vorticity anomalies from northeast of the Taiwan Strait and in the Tsushima Strait. The vorticity anomaly from northeast of the Taiwan Strait propagates downstream in the northeastward Kuroshio branch along isobaths of about 100 m on the shelf edge. In contrast, the vorticity anomaly in the Tsushima Strait propagates upstream of the Tsushima Warm Current along isobaths of 100-200 m. The propagation of the vorticity anomalies causes the annual variation with a phase difference in the northeastward Kuroshio branch and the northward current west of Kyushu, and the behavior of the vorticity anomalies can be well explained as a first approximation by a dispersion relation of a quasigeostrophic topographic Rossby wave propagating in a mean flow. Generation of the vorticity anomalies from northeast of the Taiwan Strait and in the Tsushima Strait appears to be closely related to the annual variation of the Kuroshio's current speed northeast of Taiwan and of volume transport through the Tsushima Strait, respectively. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pocean.2013.01.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREA OCEAN RESEARCH DEVELOPMENT INST  

Japanese and Taiwanese institutes have collaborated to obtain ocean radar data with significantly increased coverage in the upstream Kuroshio region. An international joint survey was conducted in June 2012, in which intensive in situ observations were performed within the radar coverage. Details of the joint survey are presented in this paper with brief descriptions of preliminary results on the surface and subsurface currents near and within the Kuroshio.

DOI： 10.1007/s12601-013-0011-4

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Language：English  

DOI： 10.5270/esa.sp-710.altimetry2012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The seasonal variation of counterclockwise eddies downstream of the Tsushima Islands in the Tsushima Straits was investigated from 2004 to 2008 using long-term acoustic Doppler current profiler (ADCP) data. Eddy activity was high from summer to autumn (July-November). The eddies were formed in short-term intervals of 5-8 days, almost corresponding to the formation cycle of Karman vortices. The eddy activity varied on a longer time period (about 13 days). The mean kinetic energy (MKE) converted to eddy kinetic energy (EKE) at current shears between the eastern and western channels of the Tsushima Straits. The counterclockwise eddies that formed downstream of the Tsushima Islands were intensified and maintained by energy conversion from MKE to EKE at the northern shear of the current core in the eastern channel. The countercurrent east of the Tsushima Islands from summer to autumn was intensified by energy conversion from EKE to MKE. (c) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pocean.2012.04.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We conducted hydrographic observations 23 times across the eastern channel of the Tsushima/Korea Straits (ECTKS) to estimate material transports from 2005 to 2008. Freshwater and nutrient transports through the ECTKS became high from summer to autumn, with quite large interannual variations. Freshwater and dissolved inorganic nitrogen (DIN) transport in 2007 was much lower than in other years. The interannual variation in freshwater transport seemed to show almost the same pattern as that of the volume transport of the Tsushima Warm Current and Changjiang discharge. However, we could not explain the interannual variation in freshwater transport quantitatively. The DIN transport in August 2007 was approximately one third of that in 2005 due to the much lower DIN concentration in the bottom layer of the ECTKS in 2007 than in 2005. The difference of DIN concentration between the years was caused by different water mass intrusions into the ECTKS. Water mass analysis and alkalinity data revealed that the water mass in 2005 came from the Yellow Sea or the shelf of the East China Sea, while that in 2007 came from the Kuroshio region. Examination of long-term water temperature data indicated that the origin of ECTKS water masses has changed many times in the past. We suggest that variations of the Changjiang discharge and wind field over the Yellow and East China seas might relate to the change of water mass in the ECTKS. (c) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pocean.2012.04.011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Short-term flow and water temperature fluctuations in Sagami Bay were examined using mooring and hydrographic data observed during the non-large-meander path (NLM) of the Kuroshio. In the surface layer (<150 m), the flow fluctuation is predominant and is excited by the sudden strong eastward flow with speeds greater than 20 cm s(-1) in the central part of the bay. This flow is a part of an intrusion of Kuroshio water via the Oshima West Channel into the bay and/or a cyclonic circulation in the northern part of the bay. The cyclonic circulation, which is approximately balanced under the geostrophic flow relationship, is mainly generated or enhanced by the intrusion, which is accompanied by eastward propagation of the small meander of the Kuroshio south of Japan during the transition from the nearshore non-large-meander path (nNLM) to the offshore non-large-meander path (oNLM), regardless of season. The water temperature fluctuation in the subsurface layer (similar to 150 m) is caused by upwelling of cold deeper water and is closely related to the eastward flow fluctuations in the surface layer in the central part of the bay. Our analysis leads us the conclusion that the upwelling occurs as the response of the subsurface density field to the surface flow field under the Earth's rotation. Additionally, the intrusion of Kuroshio water via the Oshima West Channel tends to cause, not only cyclonic circulation and upwelling in the northern part of the bay, but also the Kyucho, which is the coastal density current under the Earth's rotation, in the bay's coastal area during the non-large-meander path (NLM). (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pocean.2012.04.012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A simple effective method of inverse estimation provided by model Green's functions is examined to calibrate tides in a regional circulation model for the East Asian marginal seas. The Green's function optimization derived by perturbing the model parameters significantly improves the estimate relative to observation as compared with baseline integration. Among the optimized model parameters, the largest effects on cost function reduction come first from the harmonic constant of M-2 along the open boundaries with the optimized values of 89.7 +/- A 0.8% for amplitude, and second from the bottom friction with the optimized value of (3.06 +/- A 0.08) x 10(-3).

DOI： 10.1007/s10872-011-0097-1

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Publishing type：Research paper (scientific journal)   Publisher：The Oceanographic Society of Japan  

DOI： 10.5928/kaiyou.20.3-4_59

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Horizontal, vertical and temporal distribution of a cyclonic (counterclockwise) eddy, where biological productivity is high, downstream of the Tsushima Islands in the eastern channel of the Tsushima Straits in November 2007 was revealed using conductivity-temperature-depth and acoustic Doppler current profiler data. The eddy had a horizontal scale of approximately 40-60 km, and the accompanying baroclinic current was more than 15 cm s(-1) at the edge of the eddy. The island-induced cyclonic eddy moved east-northeastward at about 10 km day(-1) (similar to 10 cm s(-1)) along the Tsushima Warm Current and was intensified by the barotropic instability in the current shear. The cyclonic eddy with high surface chlorophyll a concentrations intensified in the vicinity of the Tsushima Islands and was advected by the Tsushima Warm Current towards the southwestern Japan Sea.

DOI： 10.1007/s12237-011-9395-5

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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.

DOI： 10.1016/j.csr.2009.07.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The enhancement of primary productivity (PPenh) in the southern East China Sea (ECS) following 16 typhoon passages was investigated using ocean color data and a primary productivity model. PPenh tended to be higher when typhoons traversed slowly with trajectories that allowed strong southerly winds to prevail over Yonaguni Island. Such long-lasting southerly winds were believed to push the Kuroshio current axis shelfward, enhancing the upwelling of nutrients, hence promoting new productivity (NP). The importance of long-lasting southerly winds as a proxy for physical perturbations underlying PPenh was expressed by an empirical equation by which 88% of PPenh variation could be explained. Applying this equation, we assessed that typhoon passages accounted for a minimum of 0.6-11.8% of the ECS summer-fall NP, suggesting that typhoon passage over the southern ECS is an important phenomenon supporting NP in the ECS. Citation: Siswanto, E., A. Morimoto, and S. Kojima (2009), Enhancement of phytoplankton primary productivity in the southern East China Sea following episodic typhoon passage, Geophys. Res. Lett., 36, L11603, doi: 10.1029/2009GL037883.

DOI： 10.1029/2009GL037883

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Using long-term sea surface temperature (SST) and acoustic Doppler current profiler (ADCP) data, we examined variations in the current axis of the Tsushima Warm Current (TWC) off the San'in coast of Japan, near the entrance to the Japan Sea. There were large horizontal temperature gradients along the shelf edge in the southwestern Japan Sea from October to May, suggesting that the second branch of the TWC appears not only in spring and autumn but also in winter. From the ADCP data analysis, we found that currents with speeds of approximately 20 cm s(-1) and greater appeared around the shelf edge off San'in coast in all seasons. The SST and ADCP data analyses suggested that the second branch of the TWC exists around the shelf edge off the San'in coast throughout the year. This finding differed from those of previous studies. A relatively strong current (speed greater than 15 cm s(-1)) appeared on the shore side in all seasons, except at line W in winter. This current might be the first branch of the TWC. The first branch seemed to occur around in 100 m isobaths, but shifted northward and southward because the bottom topography around lines W and M was relatively flat and the shelf was broad. The first branch was very obscure, and it was difficult to define the two branches of the TWC off the San'in coast from the seasonally averaged vectors. However, snapshots of current distribution derived from the ADCP data clearly showed these branches. Hence, both the first and second branches might occur throughout the year off the San'in coast. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2009.03.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

We investigated the movement of the Kuroshio axis on the northeast shelf of Taiwan associated with the passage of typhoons, using sea surface current data observed by the ocean radar system on Yonaguni and Ishigaki islands. First, we examined daily Kuroshio axis variation on the northeast shelf of Taiwan during typhoon events. The ocean radar data showed that the Kuroshio axis moved onto the shelf after passages of typhoons. The Kuroshio moved onto the shelf and stayed there after the passage of Typhoon Hai-Tang; while the Kuroshio maintained this pattern, southerly wind blew continuously for 4 days. The mean current speed northeast of Taiwan after the typhoon's passage increased by 18 cm s(-1). In addition, the sea level difference between two satellite altimetry tracks east of Taiwan increased by 14.4 cm. These results suggest that coastal upwelling east of Taiwan caused by the southerly wind generated an east-west sea level difference that, in turn, generated a northward geostrophic current. This current could have enhanced the Kuroshio east of Taiwan, and pushed it onto the shelf. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ecss.2009.02.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD  

The relationship between island-induced cyclonic eddies and chlorophyll a (chl-a) was investigated using field data and satellite images in the eastern channel of the Tsushima Straits. The maximum chl-a concentration around the leeward eddy of the Tsushima islands was two or three times greater than that of outside the eddy. Two different mechanisms of chl-a enhancement associated with island-induced cyclonic eddies were found in the post-bloom periods. In summer, when nutrients were depleted in the surface layer, eddy pumping increased the nutrient supply in the euphotic zone, resulting in enhanced chl-a around the shallow thermocline near the eddy core. In late autumn, when the mixed layer deepened over the euphotic zone, the mixed layer depth became shallow due to the doming effect of the cyclonic eddy, therefore, the improved irradiance condition led to an increase in the chl-a concentration in the surface mixed layer. Nighttime satellite visible images showed a number of fishing vessels in the lee region of the Tsushima Islands, implying that the enhanced phytoplankton biomass may have resulted in good feeding conditions for fishes and squids in the Tsushima Straits. (c) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ecss.2008.11.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait and are horizontally transported through the ECTS. Nutrient transports are high in July-August and October and low in April and November. Increased nutrient transports in July-August and October are due to the appearance of a cold saline water mass in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current region.

DOI： 10.1007/s10872-009-0006-z

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Language：English   Publishing type：Research paper (scientific journal)  

The magnitude and geographical distribution of the error in the Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO) altimetry data associated with tidal correction around Asian marginal seas has been revealed. The errors were evaluated by harmonic analysis of the AVISO corrected sea surface heights data (CorSSH). Errors of more than 15 cm of tidal correction were recognized in the western and northern parts of the Yellow Sea, Celebes Sea, Kuril Islands, and the northwestern part of the Okhotsk Sea. It was found that the CorSSH and sea level anomaly (SLA) data downloaded from the AVISO are not available for direct use in those marginal seas. To reduce the tidal correction error, the harmonic constants calculated from the latest tide model and regional tide model were applied as the tidal correction of the Altimetry data. The tidal errors in the Yellow Sea and the northwestern part of the Okhotsk Sea were reduced by approximately 20 cm and 10 cm, respectively. Root mean square differences between the harmonic constants derived from tide models and those derived from altimetry data were calculated. The root mean square differences were large in the Yellow and the Okhotsk Seas. Root sum squares for four principal tidal constituents in the Yellow and East China Seas and Okhotsk Sea were 7.72 cm and 8.36 cm, respectively. © 2009 Springer Science+Business Media B.V.

DOI： 10.1007/s10872-009-0041-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Two different cold waters were found under the surface mixed layer in Tsushima Straits and the southwestern Japan Sea in autumn 2004. One is cold saline water with a low concentration of dissolved oxygen, and the other is cold less saline water with a high concentration of dissolved oxygen. The older saline water originates from the bottom of the East China Sea, strongly influenced by the Kuroshio water with high salinity. The bottom density in the eastern channel of the Tsushima Straits is coincident with that of the East China Sea in autumn, corresponding to the season when the cold saline water was frequently found in the Tsushima Straits. The newer less saline water originates from the front of Tsushima Warm Current between the Tsushima Warm Current water and the surface cold water in the Japan Sea. This water is formed by subduction above the isopycnal surface from the front of the Tsushima Warm Current.

DOI： 10.1007/s10872-008-0049-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We elucidated ocean physical and biogeochemical responses to slow-moving Typhoon Meari using a new method combining Argo float and satellite observations. Meari-driven upwelling brought colder, nutrient-rich deep water to the surface layer, causing sea surface cooling (3-6 degrees C) and threefold enhancement of primary production (PP). Maximum surface cooling (and hence nutrient injection) and peak PP enhancement lagged Meari's passage by 1 and 3 days, respectively, implying that remarkable PP enhancement was attributed to new production (NP). This NP accounted for approximately 3.8% of annual carbon export in the East China Sea (ECS) outer shelf, suggesting that typhoon-driven upwelling is important for biogeochemical processes in the ECS. Given the wide coverage of Argo float and satellite data, our new approach may prompt comparative studies in other basins and advance the understanding of the role of tropical cyclones in the global ocean biogeochemical cycle.

DOI： 10.1029/2008GL035040

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Other Link： http://agriknowledge.affrc.go.jp/RN/2010780549

Language：Japanese  

Tidal current constituents along the track of the ferryboat Camellia in Tsushima Straits were previously estimated by ADCP measurements of ferry-based monitoring. Shipboard ADCP measurements using training vessels were carried out along the ferry track. The tidal currents are removed from the ADCP data. Comparisons of the current velocity normal to the section with the results of Camellia ADCP measurement show positive correlations where the root mean squares are 7-9cm s^<-1>. The difference between these results depends not only on the accuracies of the ADCP but also on current variations within a short time scale, especially in the east of the Tsushima Islands with a southwestward countercurrent. The difference between volume transports through the eastern channel estimated by the ferryboat Camellia and the training vessels on the same day is about 0.2Sv (Sv≡10^6m^3 s^<-1>).

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10578164

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INTER-RESEARCH  

A 'Kyucho' (an intrusion of warm surface water) occurs in the Bungo Channel, located in southwestern Japan. The abundances of Prochlorococcus and Synechococcus during a Kyucho, together with physical and chemical environmental factors, were investigated from the Kuroshio region to the Seto Inland Sea, via Bungo Channel, from 26 November to 5 December 2003. With the occurrence of the Kyucho, oceanic water intruded from the Kuroshio region into the middle of the Bungo Channel. The abundance of Prochlorococcus was the highest in the Kuroshio region and the southern part of the Bungo Channel (&gt; 25 x 10(3) cells ml(-1)), low in the northern part of the Bungo Channel (&lt; 1 x 10(3) cells ml(-1)), and below detection levels in the Seto Inland Sea. A relatively high abundance of Synechococcus cells (&gt; 15 x 10(3) cells ml(-1)) was detected in the Kuroshio region and in the southern part of the Bungo Channel, but the abundance (&lt; 6 x 10(3) cells ml(-1)) was low in other regions. In the Kuroshio region and the southern part of the Bungo Channel, high-phycourobilin (PUB)-type cells were dominant (&gt; 90%); at this location, most of the available light in the deeper layer (&gt; 25 m depth) was in the 450 to 500 nm range, corresponding to the peak absorbance of PUB. In contrast, the abundance of low-PUB-type cells accounted for &gt; 75% of the total in the northern part of the Bungo Channel and in the Seto Inland Sea, where most of the available light in the deeper layer (&gt; 10 m depth) was in the 480 to 560 nm range, including the peak absorbance of both PUB and phycoerythrobilin (PEB). These results indicate that Synechococcus cells of high-PUB type, which have a higher Ex 495:545 (&gt; 1.5; ratio of orange fluorescence intensity excited at 495 nm to that at 545 nm), as well as Prochlorococcus cells were advected to the Bungo Channel by the Kyucho. The co-occurrence of the 2 pigment types of Synechococcus in coastal waters is highly affected by a physical process, such as the Kyucho.

DOI： 10.3354/ame046191

Web of Science

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The altimetry data sets of satellite TOPEX/Poseidon and ERS-2 in the Asian marginal seas, the South China, the East China, the Yellow, the Japan/East and Okhotsk Seas, are produced applying the original tidal correction. In order to obtain a mean sea surface current field in the East China and the Japan/East Seas, the mean sea surface current is evaluated using ARGOS buoy trajectories data and altimetry data. From the mean sea surface current field, it is found that the northward current from the Kuroshio region to the Tsushima/Korea Strait exists throughout the year. The mean current field represents the detailed current feature in the Japan/East Sea such as the current path of Tsushima Warm Current.

DOI： 10.1109/IGARSS.2005.1525969

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：水産大学校  

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Other Link： http://ypir.lib.yamaguchi-u.ac.jp/fu/metadata/415

Language：English   Publishing type：Research paper (scientific journal)  

Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.

DOI： 10.1023/A:1011149401735

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

Temporal and spatial variations of sea surface circulation in the South China Sea were revealed with use of altimetric data provided by TOPEX/POSEIDON from December 1992 to October 1997. The estimated distribution of sea surface dynamic heights from altimetric data coincide well with the results of observation by Soong et al. (1995) and Chu et al. (1998). The RMS variability of sea surface dynamic height, which is obtained after tidal correction based on Yanagi et al. (1997), is high in the central part of the South China Sea, the Gulf of Tongking, the Sunda Shelf and the Gulf of Thailand. The high RMS variability in the Gulf of Tongking, the Sunda Shelf and the Gulf of Thailand is due to set up and set down of sea water by the East Asian monsoon, which is northeasterly during winter and southwesterly during summer. Also, the high RMS variability in the central part of the South China Sea is due to the variations of basin-wide circulation. The circulations are dominant in the central part of the South China Sea during summer and winter, an anticyclonic circulation during summer and a cyclonic circulation during winter. It is suggested that these circulations are controlled by the East Asian monsoon. Hence, there is an interannual variability of the basin-wide circulation associated with the variation of the East Asian monsoon.

DOI： 10.1023/A:1011159818531

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Language：English   Publishing type：Research paper (scientific journal)  

Satellite altimetric data have been very useful in the study of variation in the eddy field of the ocean. In order to investigate the variation in the eddy field, we have to remove tidal signals from altimetric data. However, global tidal models do not have sufficient accuracy in marginal seas such as the Japan Sea. In this study, we carried out harmonic analysis of temporal fluctuations of sea surface height data in the Japan Sea measured by TOPEX/POSEIDON. We could eliminate the tidal signals from altimetric data of TOPEX/POSEIDON and also from ERS-2 altimetric data with use of the harmonic constants derived from TOPEX/POSEIDON and tide gauge data along the coast. We draw co-tidal and co-range charts in the Japan Sea using the result of the harmonic analysis of TOPEX/POSEIDON altimetric data and tide gauge data along the coast. The results obtained turn out to be very useful for the tidal correction of altimetric data from satellite in the Japan Sea.

DOI： 10.1023/A:1011158423557

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

The Japan Sea is one of the eddy-rich areas in the world. Many researchers have described the variability of the eddy field and its structure in the Tsushima Warm Current region. On the other hand, since there are few data covering the northern part of the Japan Sea, we are not able to understand the detailed variability of the eddy field there. The variation of the eddy field in the Japan Sea is investigated using the temporal fluctuations of sea surface height measured by altimetric data from TOPEX/POSEIDON and ERS-2. Tidal signals are eliminated from the altimetric data on the basis of the results of Morimoto et al. (2000). Distributions of sea surface dynamic height are produced by using the optimal interpolation method every month. The distributions warm and cold eddies that we obtained coincide well with the observed isotherms at 100 m depth measured by the Japan Sea National Fisheries Research Institute and the sea surface temperature measured by satellite. There are areas with high RMS variability of temporal fluctuations of sea surface dynamic height in the Yamato Basin, the Ulleung Basin, east of North Korea, the eastern part of the Yamato Rise, the Tsushima Strait and west of Hokkaido. The characteristics of eddy propagation in the high RMS variability regions are examined using a lag correlation analysis. Seasonal variations in the number of warm and cold eddies are also examined.

DOI： 10.1023/A:1011184523983

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Oceanographic Society of Japan  

Previous studies showed that the sand waves in the Bungo Channel develop in the area whose water depth is 7Om through l00m. In this study, we calculated tides, tidal currents and the residual flow in autumn 1995 by means of a three-dimensional numerical model. We examined the relationship between the amplitude of tidal currents and the existence of sauad waves, and also between the direction of sand wave migration and that of residual flow. It is found that the distribution of sand waves coincides with the area where the amplitude of tidal currents at the spring tide is between 50cm/s and 70cm/s. The direction of sand wave migration approximately coincides with the direction of residual flow. Sand transport in the Bungo Channel is mainly controlled by the tide-induced residual flow. It is supposed that sands provided from the Hayasui Strait and the northern part of Kamadozaki are transported to the shelf slope region in the southern part of the Bungo Channel.

DOI： 10.5928/kaiyou.8.119

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

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J-GLOBAL

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Language：Japanese   Publisher：日本海洋学会沿岸海洋研究部会  

Japan Sea is a semi-enclosed international sea area. The East China Sea is located in the upstream area of the Japan Sea, and various substances, sea water, and heat are transported through the Tsushima Strait. In recent years, the Japan Sea has faced environmental changes. The sea surface temperature in the Japan Sea has increased with global warming. The rapid economic growth in the Northwest Pacific area influences the environment in the Japan Sea and surrounding sea areas. In order to propose an effective coastal environmental management method for Japanese coastal areas of the Japan Sea, the impacts and its influences of global warming and environmental changes in the East China Sea on the environment and ecosystem in the Japan Sea were studied using ecosystem numerical models. Our study clarified that the Japanese coastal area of the Japan Sea is strongly influenced by the East China Sea, and it is necessary to have a large-scale perspective for its management. Then, we proposed a three-layer management for the Japan Sea. The outputs of the project and the idea of the three-layer management are introduced in this paper.

DOI： 10.32142/engankaiyo.56.1_31

CiNii Books

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J-GLOBAL

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)  

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J-GLOBAL

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J-GLOBAL

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

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Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

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J-GLOBAL

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Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)  

DOI： 10.15017/1526196

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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Language：Japanese  

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Other Link： http://id.nii.ac.jp/1141/00047032/

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理工学研究科（博士後期課程2006〜）

Faculty of Science / Specialized Subjects

Graduate School of Science and Engineering(Master Course)

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

Faculty of Science / Specialized Subjects

理工学研究科（博士後期課程2006〜）

理工学研究科（博士後期課程2006〜）

General Education / Liberal Arts Section