Japan/East Sea Research Articles

A consistent structure of phytoplankton communities across the warm–cold regions of the water mass on a meridional transect in the East/Japan Sea

Three cruises were undertaken along a meridional transect in the East/Japan Sea (EJS) in spring (May 2007), summer (July 2009), and fall (October 2012) to determine the geographic variations in phytoplankton biomass and community composition. This study revealed a gradient of surface temperature and a fluctuation of hydrographic conditions along the transect. Although a subpolar front (SPF) formed between the warm- and cold-water masses (37–40°N), no significant differences in phytoplankton biomass and community composition were detected between the southern and northern parts of the EJS. These results disprove our initial hypothesis that different water masses may contain differently structured phytoplankton communities. In the present study, isothermal layers (≤ 12°C) fluctuated over a depth of 50m in both warm- and cold-water masses, depending on the SPF. In contrast, the nitracline (i.e. 2.5μM nitrate isopleth) depth was recorded within a limited range of 20–40m in spring, 30–50m in summer, and 40–60m in fall. The chlorophyll a concentrations at the subsurface chlorophyll maxima (SCM) were significantly higher in spring and summer (356 ± 233 and 270 ± 182ngL–1, respectively) than in fall (117 ± 89ngL–1). The relative contributions of individual phytoplankton groups to the depth-integrated chlorophyll a concentration conformed to the composition of the phytoplankton community in the SCM layer, showing a dominance of diatoms (58 ± 19% in spring, 48 ± 11% in summer, and 30 ± 20% in fall). Canonical correspondence analysis revealed that the geographic structures of phytoplankton communities were strongly associated with the vertical structures of water temperature and nutrient concentration in the water column rather than with horizontal gradients of hydrographic conditions. Finally, our findings suggest that water column stability and light–nutrient availability in the euphotic zone play a key role in determining geographical consistency of the biomass and the community structure of phytoplankton in the EJS.

Comparison of biochemical compositions of phytoplankton during spring and fall seasons in the northern East/Japan Sea

The East/Japan Sea (EJS) where is surrounded by the Korean peninsula, the Japanese islands, and the Russian coast has been experiencing a large change in physicochemical properties. Based on biochemical composition analysis (carbohydrates, proteins, and lipids), the current qualitative status of phytoplankton was identified in the northern EJS from two different sampling seasons (fall and spring in 2012 and 2015, respectively). The average chlorophyll-a (chl-a) concentration integrated from the euphotic depths was significantly higher in 2015 (99.3 ± 69.2mgm−2) than 2012 (21.5 ± 6.7mgm−2). Large phytoplankton (> 2µm) were predominant in 2015 accounting for 64.5 ± 19.7% whereas small-size phytoplankton (0.7–2µm) were dominant (49.1 ± 17.5%) in 2012. The biochemical compositions of phytoplankton were predominated by lipids (42.6 ± 7.8%) in 2012 whereas carbohydrate composition largely contributed (53.2 ± 11.7%) to the total biochemical composition in 2015, which is mainly due to different nutrient availabilities and growth stages. Interestingly, the averaged FM concentrations and calorific values for phytoplankton based on the biochemical compositions had similar values between the two years, although the integrated chl-a concentrations were substantially different between 2012 and 2015. In terms of different cell sizes of phytoplankton, we found that small phytoplankton assimilate more FM and calorific energy per unit of chl-a concentration than total phytoplankton. Our results are meaningful for the understanding of future marine ecosystems where small phytoplankton will become dominant at a scenario of ongoing warmer oceans.

Strong linkages between surface and deep-water dissolved organic matter in the East/Japan Sea

Abstract. Vertical and horizontal distributions of total dissolved amino acids (TDAAs), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) were measured in the East/Japan Sea (EJS). The euphotic zone of this sea is N-limited, and the N : P ratio is ∼ 13 below 200 m depth. Elevated TDAA concentrations (137 ± 34 nM) and DOC-normalized yields (0.8 ± 0.2 % of DOC) were observed in deep waters ( ≥ 1000 m) of the EJS and compared with those in the deep North Pacific Ocean. Significantly high TDAA concentrations and yields were observed in a region of deep-water formation, indicating the convection of margin-derived bioavailable dissolved organic matter (DOM) to deep waters. Declining TDAA concentrations (36 ± 12 %) and yields (33 ± 13 %) were observed between 1000 and 3000 m throughout the EJS, indicating the utilization of bioavailable DOM in deep waters. Concentrations of the D-enantiomers of amino acids (Ala, Glx, Asx, and Ser) were relatively high in deep waters of the EJS, indicating substantial bacterial contributions to DOM from surface and upper mesopelagic waters. Climate warming during the past few decades in the EJS is weakening deep convection during the winter, and one consequence of this reduction in deep convection is a decline in the supply of bioavailable DOM from surface waters.

Concentrations of trace metals in tissues of Chionoecetes crabs (Chionoecetes japonicus and Chionoecetes opilio) caught from the East/Japan Sea waters and potential risk assessment.

The concentrations of trace metals (As, Cd, Co, Cu, Fe, Hg, Pb, and Zn) were measured in muscle and hepatopancreas of two Chionoecetes crabs (Chionoecetes japonicus and C. opilio) caught from the East/Japan Sea (EJS) in order to assess the potential health risk by the consumption of deep sea crabs. The highest metal concentrations in muscle and hepatopancreas were As and Fe, respectively, while the lowest metal concentration in two tissues was Pb. The mean concentrations of Cd, Co, Cu, Fe, and Pb in Chionoecetes crabs were one or two orders of magnitude higher in hepatopancreas than in muscles. The mean concentrations of As, Cu, and Hg in muscle and hepatopancreas were relatively higher in C. japonicus than in C. opilio. The estimated daily intakes (EDI) of all metals in muscle were below 0.1% of the provisional tolerable daily intake (PTDI) adopted by the Joint FAO/WHO Expert Committee on Food Additives. Similarly, the target hazard quotient (THQ) of all trace metals in muscle was less than 1.0. These results imply that Chionoecetes crabs caught from EJS do not have an adverse impact on the Korean health. Based on the mean metal concentrations, PTDI, and THQ, the daily maximum permissible intakes of C. japonicus and C. opilio were estimated to be approximately 240 and 410g/day, respectively.

Long-term trend of satellite-observed significant wave height and impact on ecosystem in the East/Japan Sea

Significant wave height (SWH) data of nine satellite altimeters were validated with in-situ SWH measurements from buoy stations in the East/Japan Sea (EJS) and the Northwest Pacific Ocean. The spatial and temporal variability of extreme SWHs was investigated by defining the 90th, 95th, and 99th percentiles based on percentile analysis. The annual mean of extreme SWHs was dramatically increased by 3.45m in the EJS, which is significantly higher than the normal mean of about 1.44m. The spatial distributions of SWHs showed significantly higher values in the eastern region of the EJS than those in the western part. Characteristic seasonality was found from the time-series SWHs with high SWHs (>2.5m) in winter but low values (<1m) in summer. The trends of the normal and extreme (99th percentile) SWHs in the EJS had a positive value of 0.0056m year−1 and 0.0125m year−1, respectively. The long-term trend demonstrated that higher SWH values were more extreme with time during the past decades. The predominant spatial distinctions between the coastal regions in the marginal seas of the Northwest Pacific Ocean and open ocean regions were presented. In spring, both normal and extreme SWHs showed substantially increasing trends in the EJS. Finally, we first presented the impact of the long-term trend of extreme SWHs on the marine ecosystem through vertical mixing enhancement in the upper ocean of the EJS.

Physical boundaries of Intrathermocline Ulleung Eddies in the East/Japan Sea

A new eddy detection algorithm is developed based on the particle tracking experiment (PTE) to determine the spatial extent of the Intrathermocline Ulleung Eddies (IUE) in the East/Japan Sea (EJS). The new eddy detection method enables us to identify three regions of interests: the IUE, transitional regions between the IUE and mean currents, and mean current regions around IUE. The estimated spatial boundary of the IUE is expressed as least square fitted elliptic characteristics from February to September, 2015. Accordingly, we could obtain three main results after analyzing the IUE: (1) the center and the highest sea level height of the IUE are not co-located, suggesting that the IUE is sustained by potential vorticity through the relative vorticity in response to bathymetry changes; (2) the highest sea level is always anchored around Ulleung Island, which is associated with the relatively high Chlorophyll concentration (Chl) around the edge of the IUE; and (3) the shape of the IUE is strongly influenced by the current systems in the Ulleung Basin. Furthermore, the semi-major and semi-minor axes, and its ratios are determined as well as the mean areas and the highest sea surface height of the IUE to understand the spatio-temporal characteristics of the IUE and the dominant frequencies on it.

ENSO Teleconnection to the Isopycnal Depth Fluctuations of the East/Japan Sea Intermediate Water in the Ulleung Basin during 1968–2002

AbstractThis study first detects the decadal variability in the depths of the East/Japan Sea (EJS) Intermediate Water (ESIW) using in situ observations and relates it to strong El Niño–Southern Oscillations (ENSOs). Using multitaper cross-spectrum and cyclostationary empirical orthogonal function analysis, this study found significant coherences at the 99% confidence level and opposite phases between Niño-3 and the ESIW isopycnal depths in the Ulleung Basin (UB) at a period of 14.1 yr during 1968–2002. This suggests a teleconnection between strong ENSOs and the ESIW, the cause of which is explored. When a strong El Niño (EN) develops, the Pacific–North American pattern is intensified by the EN-related Rossby wave interfering constructively with the climatological stationary wave. The amplified wave propagates upward into the stratosphere and breaks, weakening the polar vortex. The EN-related geopotential height increases over the pole with poleward converging air and decreases over the Yakutsk Basin (YB), indicating a negative northern annular mode with the south-to-north gradient balancing the easterly anomaly that responds to vortex weakening. The converged air at the pole warms adiabatically and raises the height as it sinks. This height distribution, including the east-to-west gradient balancing the southward flow, induces the polar vortex split into two with the colder one in the YB where the EJS is closer than from the pole. The EN-related northwesterly wind directing toward the EJS is also strong. Thus, the coldest air with negative wind stress curls reaches the EJS quickly and forms more ESIW, which converges into the UB, causing the observed decadal isopycnal fluctuations.

An east‐west contrast of upper ocean heat content variation south of the subpolar front in the East/Japan Sea

AbstractLong‐term variability of nonseasonal ocean heat content (OHC) in the upper 500 m in the East/Japan Sea (EJS) exhibits a distinct east‐west contrast during the recent 30 years. The contrasting OHC variations are revisited and investigated more in detail by analyzing two observational data sets, the gridded data from 1976 to 2007 and in situ data from 1976 to 2011 in the southwestern EJS that covers the zone of western boundary current. The OHC variability shows in‐phase and predominant decadal variation in both east and west regions before 1995, but uncorrelated and predominant interannual variations after 1995. Heaving effects due to major branches of warm currents in the EJS, the East Korea Warm Current (EKWC) in the western part and other two branches in the eastern part, mainly contribute to the OHC variations. The heaving effect in the western EJS is shown to be associated with changes in winter wind‐stress curl field in the northern EJS. Weakening of the subpolar gyre due to weakening of positive wind‐stress curl in the Japan Basin related with wintertime Western Pacific teleconnection pattern and Siberian High appears to enhance the northward penetration of the EKWC resulting in an increase of OHC in the western EJS. The heaving effect in the eastern EJS is significantly correlated with the Siberian High, but the causative mechanism is inconclusive. This study also demonstrates the importance of using highly resolved data sets for areas affected by strong and narrow boundary currents in computing and understanding the OHC variability.

Distinct characteristics of the intermediate water observed off the east coast of Korea during two contrasting years

AbstractThe intermediate water known as “East Sea Intermediate Water” found south of the Subpolar Front (SF) is known to be formed in the northern East/Japan Sea (EJS), and its physical properties are determined by wintertime air‐sea interaction north of the SF. Hydrographic data collected off the Korean coast show significant decadal oscillations in spiciness (π) following isopycnals of intermediate layer, which are explained by the Arctic Oscillation (AO) and consequent cold‐air outbreaks. During positive AO phases, the cold‐air outbreak and water formation are more active and the intermediate water having the same π reaches higher density (higher π following the same isopycnals). At interannual time scale, however, the π variability is well beyond the relationship with the AO. Especially, significantly lower π (both fresher and colder) intermediate water was observed in spring of 2010 than 2001 under the same surface net‐heat flux peaks in the northern EJS in the two winters. Such contrasting characteristics of intermediate water between 2001 and 2010 are consistent with the HYCOM reanalysis results which indicate widespread extension of low‐ (high‐) π intermediate water in the southwestern EJS in 2010 (2001). A clear contrast in circulation pattern is suggested to derive the distinctly different characteristics of the intermediate water. Northward penetration of the East Korea Warm Current (EKWC) inhibited the southward extension of the intermediate water in 2001 off the east coast of Korea. On the other hand, the EKWC that poorly developed in 2010 allowed low‐π intermediate water to prevail in the southwestern EJS.

Role of wind and thermal forcing in the formation of the water circulation variability in the Japan/East Sea Central Basin in 1958–2006

Based on the numerical experiment on simulation of the Japan/East Sea (JES) water circulation response to the atmospheric forcing for 1958–2006, the analysis is made of its long-term variability in the JES Central Basin (CB). It was found that during the climatic year, the circulation remains cyclonic, strengthening in spring and weakening in autumn. The analysis of mean relative vorticity (MRV) at intermediate depths in the JES CB showed one that the spectrum of its interannual variability is formed mainly by oscillations of periods ∼2, ∼4 and ∼5 years, and in the decadal range with ∼10 and ∼14 years. Along the depth, the spectral composition of MRV variability does not change, but there is a noticeable weakening of decadal variability amplitude, which does not occur with the 4- and 5-year oscillations. Using SVD-analysis, the connection is established between MRV variability, wind stress curl (WSC), as well as sensible heat flux. The strong connection between MRV and WSC is revealed in the range of 4–5 years, and in the decadal range (period is 10 years) the significant connection is with both WSC and air-sea temperature as a result of winter cooling and following deep convection.

Extraordinary slow degradation of dissolved organic carbon (DOC) in a cold marginal sea.

Dissolved organic carbon (DOC) is the largest organic carbon reservoir in the ocean, and the amount of carbon in this reservoir rivals that in atmospheric CO2. In general, DOC introduced into the deep ocean undergoes a significant degradation over a centennial time scale (i.e., ~50 μM to ~34 μM in the North Atlantic and Mediterranean Sea). However, we here show that high concentrations of DOC (58 ± 4 μM) are maintained almost constantly over 100 years in the entire deep East/Japan Sea (EJS). The degradation rate in this sea is estimated to be 0.04 μmol C kg−1 yr−1, which is 2–3 times lower than that in the North Atlantic and Mediterranean Sea. Since the source of DOC in the deep EJS is found to be of marine origin on the basis of δ13C-DOC signatures, this slow degradation rate seems to be due to low temperature (<1 oC) in the entire deep water column. This observational result suggests that the storage capacity of DOC in the world ocean is very sensitive to global warming and slowdown of global deep-water overturning.

Comparative simulation study of effects of eddy-topography interaction in the East/Japan Sea deep circulation

In this study the structure and seasonal variations of deep mean circulation in the East/Japan Sea (EJS) were numerically simulated using a mid-resolution ocean general circulation model with two different parameterizations for the eddy-topography interaction (ETI). The strong deep mean circulations observed in the EJS are well reproduced when using the ETI parameterizations. The seasonal variability in the EJS deep layer is shown by using ETI parameterization based on the potential vorticity approach, while it is not shown in the statistical dynamical parameterization. The driving mechanism of the strong deep mean currents in the EJS are discussed by investigating the effects of model grids and parameterizations. The deep mean circulation is more closely related to the baroclinic process and potential vorticity than it is to the wind driven circulation.

Understanding interannual variability in the distribution of, and transport processes affecting, the early life stages of Todarodes pacificus using behavioral-hydrodynamic modeling approaches

To understand interannual variability in the distribution of the early life stages of Todarodes pacificus summer spawning population, and to identify the key transport processes influencing this variability, we used a coupled bio-physical model that combines an individual-based model (IBM) incorporating ontogenetic vertical migration for paralarval behavior and temperature-dependent survival process with a ROMS oceanographic model. Using the distribution of paralarvae observed in the northern East China Sea (ECS) during several field cruises as an end point, the spawning ground for the summer-spawning population was estimated to extend from southeast Jeju Island to the central ECS near 29°N by running the model backwards in time. Running the model forward, interannual variability in the distribution of paralarvae predicted by the model was consistent with that observed in several field surveys; surviving individuals in the northern ECS were substantially more abundant in late July 2006 than in 2007, in agreement with observed paralarval distributions. The total number of surviving individuals at 60days after release based on the simulation throughout summer spawning period (June–August) was 20,329 for 2006, compared with 13,816 for 2007. The surviving individuals were mainly distributed in the East/Japan Sea (EJS), corresponding to a pathway following the nearshore branch of the Tsushima Warm Current flowing along the Japanese coast during both years. In contrast, the abundance of surviving individuals was extremely low in 2007 compared to 2006 on the Pacific side of Japan. Interannual variability in transport and survival processes made a substantial impact on not only the abundance of surviving paralarvae, but also on the flux of paralarvae to adjacent waters. Our simulation results for between-year variation in paralarval abundance coincide with recruitment (year n+1) variability of T. pacificus in the field. The agreement between the simulation and field data indicates our model may be useful for predicting the recruitment of T. pacificus.

Long-term comparison of satellite and in-situ sea surface temperatures around the Korean Peninsula

Satellite remotely sensed sea surface temperature (SST) was compared with in-situ SST in the seas around the Korean Peninsula from 1984 to 2013. A matchup dataset between satellite and in-situ SSTs was used. The root mean square error (RMSE) between satellite and in-situ SSTs was approximately 1°C in the offshore area and 2~3°C in the coastal area. The satellite SST exhibits a cold bias of 1°C or less in the offshore area and a warm bias of 1~3°C in the coastal area. The satellite SSTs generally agree with the in-situ data in the East/Japan Sea (EJS) better than in the South Sea and the Yellow Sea (YS). The RMSE between the two SSTs in the South Sea (SS) is 1~2°C. In-situ and satellite SST analyses respectively indicate a warming trend of 0.024°C/year and 0.011°C/year for the study period in the seas around the Korean Peninsula. The difference in the long-term trends from the two data sources is mainly due to the difference in the YS. The satellite SST showed a warm bias of 0.5~1.0°C in the early 1980’s and a cold bias of 0.5°C in the early 2010’s, which should be carefully considered in studying long-term trends with satellite SST data.

Estimating Denitrification Rates in the East/Japan Sea Using Extended Optimum Multi-Parameter Analysis

Denitrification rates in the East/Japan Sea (EJS) were examined with extended Optimum Multi-Parameter (eOMP) analysis. The potential denitrification locations expected from the eOMP analysis occurred only in the Ulleung Basin (UB) and near the Tatar Strait (TtS) of the Eastern Japan Basin (EJB). Estimated denitrification rates were ~0.3-3 and ~4-11 μmol N m^(-2) d^(-1) in the UB and in the EJB, respectively. These rates agree with previous published results. The EJS's rates were lower than reported for other marginal seas. However, considering the rapid EJS response to climate change, we predict that denitrification may be enhanced in the near future.

NOAA/AVHRR sea surface temperature accuracy in the East/Japan Sea

Sea surface temperature (SST) retrieved from Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration (NOAA) polar orbiting environmental satellites were validated in the East/Japan Sea (EJS) using surface drifter measurements as ground truths from 2005 to 2010. Overall, the root-mean-square (rms) errors of multichannel SSTs (MCSSTs) and non-linear SSTs (NLSSTs) using global SST coefficients were approximately 0.85°C and 0.80°C, respectively. An analysis of the SST errors (satellite – drifter) revealed a dependence on the amount of atmospheric moisture. In addition, satellite-derived SSTs tended to be related to wind speeds, particularly during the night. The SST errors also demonstrated diurnal variations with relatively higher rms from 0.80°C to 1.00°C during the night than the day, with a small rms of about 0.50°C. Bias also exhibited reasonable diurnal differences, showing small biases during the daytime. Although a satellite zenith angle has been considered in the global SST coefficients, its effect on the SST errors still remained in case of the EJS. Given the diverse use of SST data, the continuous validation and understanding of the characteristic errors of satellite SSTs should be conducted based on extensive in-situ temperature measurements in the global ocean as well as local seas.

Summer primary productivity and phytoplankton community composition driven by different hydrographic structures in the East/Japan Sea and the Western Subarctic Pacific

AbstractThe East/Japan Sea (EJS) is a highly productive marginal sea in the northwest Pacific, consisting of three basins (Ulleung Basin: UB, Yamato Basin: YB, and Japan Basin: JB). To find causes of the reportedly high primary productivity in summer in the EJS, especially in the UB, we measured primary productivity, phytoplankton composition, and other environmental variables. The water column was strongly stratified in the EJS compared with the Western Subarctic Pacific (WSP). Integrated primary productivity was two times higher in the EJS (612 mg C m−2 d−1) than in the WSP (291 mg C m−2 d−1). The vertical distributions of physicochemical and biological factors confirmed that production in the subsurface chlorophyll maximum layer in the study regions was an important factor regulating primary productivity within the water column. While picoplankton (&lt;2.7 µm) dominated in the WSP, JB, and YB, micro/nanoplankton (≥2.7 µm) dominated in the UB. Contribution by picoplankton to total biomass and primary productivity in the UB was significantly lower than in the other regions. CHEMTAX analysis using marker pigments showed that diverse phytoplankton groups inhabited the study regions. Cluster and canonical correspondence analyses showed high correlation between the spatial variation in phytoplankton assemblages with the water mass properties mainly represented by water temperature and nitrate concentration. Overall, our results suggest that the hydrographic structure of water column in the study region is an important controlling factor of the biomass and productivity of phytoplankton as well as their diversity in size and taxonomic groups.

Semi-annual cycle of sea-surface temperature in the East/Japan Sea and cooling process

Semi-annual cycles of the sea-surface temperature (SST) in the East/Japan Sea (EJS) and their forcings were examined by analysing National Oceanic and Atmospheric Administration/Advanced Very-High-Resolution Radiometer data, scatterometer wind vectors, and heat flux data. The semi-annual cycle contributed to the total variance of the SST by 8% and amounted to 25% of the amplitudes of the annual SST cycle, particularly in the Tatarskiy Strait and along the continental shelf off Russia. The lowest phase, corresponding to the minimum SST, occurred during early November and 6 months earlier in May or June depending on the position. The forcings of the semi-annual cycle were not semi-annual but substantially annual with a lag of 6 months, which gave rise to SST cooling in spring and autumn. Our analyses illustrated that SST cooling in autumn was caused by direct, local atmospheric wind forcings, whereas the cooling with large amplitudes of the semi-annual cycle in spring was caused by the non-local, remotely forced cold water advection of the Liman Current associated with sea-ice melting in the Tatarskiy Strait. The phase lag of 1–2 months between the complete melting of the sea ice in the Tatarskiy Strait and the surface cooling along the Russian continental shelf was related to the advection of cold water from sea ice in the form of the Liman Cold Current. The semi-annual cycle also resulted from asymmetry of the time series of the SST due to a long cold winter and a short warm summer. To understand how SST curves are distorted and asymmetric, we suggested two mathematical parameters of kurtosis and skewness. In addition, we suggest that the ratio of the semi-annual amplitude to the annual amplitude of SST harmonics can be used as a typical indicator of the asymmetry in year-to-year SST variations.

Summer behavior of the Changjiang diluted water to the East/Japan Sea: A modeling study in 2003

The summer behavior of Changjiang diluted water (CDW) toward the East/Japan Sea (EJS) is investigated by using a numerical ocean model. The present study focuses on the summer 2003, in which significant low salinity water is observed in the southwestern EJS in spite of similar amount of Changjiang discharge to the normal year. This paper mainly compares two experimental results for the summer 2003 (Exp. Y2003) and the normal year (Exp. NML). The simulated CDW in summer 2003 reveals remarkable changes in the pathway toward the Tsushima/Korea (T/K) Strait. The northeastward CDW behavior to the Jeju Strait, a major pathway in the normal year, is significantly reduced, while an intense southeastward extension to the along-shelf current (i.e., Taiwan–Tsushima Warm Current System) is dominant, similar to the field observation in July 2003. It is suggested that the Ekman dynamics plays an active role in remarkable changes of the CDW behavior. Namely, the reduction of northeastward behavior is associated with the dominance of strong northerly wind anomaly where the fresher bulge develops. On the other hand, the strengthened southwesterly wind over the southern region off the river mouth reinforces the extension to the along-shelf current. In consequence, the CDW below 28.0psu joins the along-shelf current in the central East China Sea, and a passage of significant low salinity water is resulted at the T/K Strait in August 2003 due to the advection by along-shelf current. The additional experiment also exhibits that the strength of along-shelf current has an impact on the passage of CDW via the T/K Strait.

Westward intensification in marginal seas

An idealized model was used to examine why the strong western boundary current (WBC) is observed in the South China Sea (SCS) but not in the Gulf of Mexico (GOM) and Japan/East Sea (JES). Results suggested that the stronger WBC in the SCS is mainly attributed to the direct contribution of the inflow and the strong monsoon. Although the Gulf Stream transports a large amount of water into the GOM, the passage in the southeast corner guides the inflow out of the gulf and inhibits the inflow from intensifying the WBC. Meanwhile, the wind stress in the GOM is weakest among the three marginal seas. The meridional ocean ridge and the particular layout of the continental slope of JES prevent the whole basin from participating in the westward intensification. Besides, the throughflow has adverse effects on the formulation of WBC in JES. The variation of Coriolis parameter with latitude leads to the westward intensification in marginal seas. However, a strong WBC cannot be observed in the absence of reasonable collocation of wind, inflow, and topography.