Tsushima Warm Current Research Articles

Late Quaternary terrestrial climatic variability recorded in deep-sea turbidites along the Toyama Deep-Sea Channel, central Japan Sea

Stratigraphic variations of coarse fraction, and frequency and thickness of turbidites in three cores collected along the Toyama Deep-Sea Channel (TDSC) in the central Japan Sea show consistent temporal trends with changes in terrestrial climatic records. These temporal changes in turbidite deposition may reflect climatic forcing in the sediment source areas for the last 70 ka. Comparison of temporal changes in turbidite deposition with paleoclimatic and paleoceanographic records in the central Japanese mainland and the Japan Sea revealed the following modes of climatic linkages; (1) During the stadials and interstadials of the last glacial period (70–22 ka) when the Tsushima Warm Current (TWC) periodically flowed into the Japan Sea, the Japanese mainland climate was cold and periodically wet, resulting in occasional glacial advances in adjacent mountains. Turbidite flux increased in the TDSC system during the major glacial advances because of the increased production of coarse debris by glacial processes and high transport potential due to high precipitation. (2) During the last glacial maximum (22–18 ka) when the Japan Sea was capped by cold, low-salinity surface water, the terrestrial climate was cold and dry due to low evaporation from the Japan Sea. As a result of low precipitation, less coarse debris was transported into deep basins, and so during this period, the turbidite flux along the TDSC was reduced. (3) During the last deglaciation (18–8 ka), precipitation in central Japan increased due to intensified summer monsoons. This resulted in destabilization of mountain slopes and increased transport of detritus to the lowlands and also to the TDSC system. (4) After the TWC flowed into the Japan Sea, the land climate became warm, wet, and stable. Enhanced vegetation and re-stabilized mountain slopes have reduced sediment input to the TDSC system since 8 ka.

Seasonal variation of the Korea Strait Bottom Cold Water and its relation to the bottom current

Analysis of high resolution hydrographic and current data revealed that the Korea Strait Bottom Cold Water (KSBCW) flowed into the Korea Strait from May to January and contained two temperature minimums, one in August/September and another in December/January. With the main current flows confined within 70 km of the Korean coast, maximum southwestward bottom currents corresponded with the temperature minimums. Time‐series of bottom current and temperature near the Korean coast clearly showed that the bottom temperature decreased as the bottom current strengthened. Seasonal variation of the KSBCW was linked to the combined effects of the barotropic and baroclinic current variations in the Korea Strait. The annual minimum bottom temperature of the KSBCW was associated with the maximum southwestward baroclinic component. The KSBCW had a secondary maximum southwestward bottom current and secondary minimum temperature in December/January when the Tsushima Warm Current (TWC), flowing into the East/Japan Sea (EJS), had the minimum volume transport.

Monthly variations of water masses in the East China Seas

A simple spiciness index parameter ( β) is proposed which accounts for the combined contribution of temperature ( T) and salinity ( S) to water density. Historical monitoring data in the East China Seas (ECSs) have been processed using a formula to determine the spatial and temporal distributions of β. Based on the values of β, three key boundaries between water masses were identified, including the diluted water boundary (DWB, β = - 2.7 ) along the coast, the equilibrium line (EL, β = 0 ) of water masses and the Kuroshio Margin (KM, β = 1.9 ) on the continental shelf. Two northward points (NP1 and NP2) of the warm water mass head, two southward points (SP1 and SP2) of the diluted water mass head along the equilibrium line and one northward point (NP3) along the boundary of the warm current water are used as indicators of the extent and variability of the current system, in view of its sensitivity to the annual variation of the intensity of the warm current and the cooler coastal current that are driven, respectively, by the Kuroshio and the Eastern Asian Winter Monsoon. It was found that the evolution of the water masses in the ECSs can be divided into three phases per year, as indicated by its monthly variations. In the winter phase from October through April, the distribution of water masses is strongly influenced by the coastal current under the East Asian Winter Monsoon. In the transitional phase from May to June, the warm current intensifies whereas the coastal current weakened. In the summer phase from July through September, the water mass system is unstable in the area. The results demonstrate that the Yellow Sea coastal current (YSCC) plays an important role in the evolution of the ECSs water masses. Specifically it causes the intensification of the Min-Zhe coastal current (MZCC) and the Yellow Sea warm current (YSWC) water, and blocks the northeastward dispersion of the Taiwan warm current (TWWC) water. The result shows that the water mass of the East China Seas can be divided into four types. The first is the diluted cold water mass containing the Bohai Sea, the Yellow Sea coastal current, the Min-Zhe coastal current and the Korea coastal current (KCC) water inside the diluted water boundary. Second is the warm and salty water mass containing the Kuroshio and the Taiwan Strait warm current (TWSWC) water beyond the Kuroshio margin. Third is the mixed coastal water containing the outspread part of the YSCC and the YSWC between the diluted water boundary and equilibrium line. Fourth is the mixed warm water containing the Taiwan warm current, the Tsushima Warm Current (TSWC) and the Yellow Sea warm current between the equilibrium line and Kuroshio margin.

Possible source of advected water mass and residence times in the multi‐structured Sea of Japan using rare earth elements

The Sea of Japan is a small, fast‐acting model of global oceanic circulation. Observations from 1998 and 2001 are analyzed to clarify its circulation. New bottom water formed in early 2001 off Vladivostok was observed later that year near the southeastern edge of the Japan Basin, implying a velocity of 2.3–3.9 cm s−1. Tb–Yb patterns of rare earth elements distinguish two classes of water volume: inactive old/well‐mixed water and active relatively young water, frequently affected by the subduction of the surface water originating from Tsushima Warm Current (TWC). The proportion of TWC to old water and each residence time are: 50–75% and ∼15 years (200–400 m), and 35–80% and ∼38 years (600–1500 m). Using six strata, an improved estimate of the average residence time of Japan Sea Proper Water is >86 years; this includes the contributions from active and inactive strata.

Structure of the Tsushima warm current in the northeastern Japan Sea

By using Acoustic Doppler Current Profiler (ADCP) measurements with the four round-trips method to remove diurnal/semidiurnal tidal currents, the detailed current structure and volume transport of the Tsushima Warm Current (TWC) along the northwestern Japanese coast in the northeastern Japan Sea were examined in the period September–October 2000. The volume transport of the First Branch of the TWC (FBTWC) east of the Noto Peninsula was estimated as approximately 1.0 Sv (106 m3/s), and the FBTWC continued to flow along the Honshu Island to the south of the Oga Peninsula. To the north of the Oga Peninsula, the Second Branch of Tsushima Warm Current and the eastward current established by the subarctic front were recombined with the FBTWC and the total volume transport increased to 1.9 Sv. The water properties at each ADCP line strongly suggested that most of the upper portion of the TWC with high temperature and low salinity flowed out to the North Pacific as the Tsugaru Warm Current. In the north of the Tsugaru Strait, the volume transport of the northward current was observed to be as almost 1 Sv. However, the component of the TWC water was small (approximately 0.3 Sv).

Long-term changes in the fish community structure from the Tsushima warm current region of the Japan/East Sea with an emphasis on the impacts of fishing and climate regime shift over the last four decades

Japanese fisheries production in the Japan/East Sea between 1958 and 2003 increased to their peak (1.76 million tons) in the late 1980s and decreased abruptly with the collapse of Japanese sardine. Catch results for 58 fisheries and various environmental time-series data sets and community indices, including mean trophic level (MTL) and Simpson’s diversity index (DI), were used to investigate the impacts of fishing and climate changes on the structure of the fish community in the Tsushima warm current (TWC) region of the Japan/East Sea. The long-term trend in fisheries production was largely dependent on the Japanese sardine that, as a single species, contributed up to 60% of the total production in the Japanese waters of the Japan/East Sea during the late 1980s. Excluding Japanese sardine, production of the small pelagic species was higher during 1960s and 1990s but lower during 1970s and 1980s. This variation pattern generally corresponds with the trend in water temperature, warmer before early 1960s and after 1990s but colder during 1970s and 1980s. The warm-water, large predatory fishes and cold water demersal species show opposite responses to the water temperature in the TWC region, indicating the significant impact of oceanic conditions on fisheries production of the Japan/East Sea. Declines in demersal fishes and invertebrates during 1970s and 1980s suggested some impact of fishing. MTL and DI show a similar variation pattern: higher during 1960s and 1990s but lower during 1970s and 1980s. In particular, the sharp decline during the 1980s resulted from the abundant sardine catches, suggesting that dominant species have a large effect on the structure of the fish community in the Japan/East Sea. Principal component analysis for 58 time-series data sets of fisheries catches suggested that the fish community varied on inter-annual to inter-decadal scales; the abrupt changes that occurred in the mid-1970s and late 1980s seemed to correspond closely with the climatic regime shifts in the North Pacific. These results strongly suggest that the structure of the fish community in the Japan/East Sea was largely affected by climatic and oceanic regime shifts rather than by fishing. There is no evidence showing “fishing down food webs” in the Japan/East Sea. However, in addition to the impacts of abrupt shifts that occurred in the late 1980s, the large predatory and demersal fishes seem to be facing stronger fishing pressure with the collapse of the Japanese sardine.

Satellite detection of harmful algal bloom occurrences in Korean waters

Cochlodinium polykrikoides ( p) is a planktonic dinoflagellate known to produce red tides responsible for massive fish kills and thereby serious economic loss in Korean coastal waters, particularly during summer and fall seasons. The present study involved analyzing chlorophyll- a (Chl- a) from SeaWiFS ocean color imagery collected over the period 1998–2002 to understand the spatial and temporal aspects of C. polykrikoides blooms that occurred in the enclosed and semi-enclosed bays of the Korean Southeast Sea. NOAA-AVHRR data were used to derive Sea Surface Temperature (SST) to elucidate physical factors affecting the spatial distribution and abundance of C. polykrikoides blooms. The time series of SeaWiFS-derived Chl- a gave an impression that recent red tide events with higher concentrations appeared to span more than 8 weeks during summer and fall seasons and were widespread in most of the Korean Southeast Sea coastal bays and neighboring oceanic waters. Coupled eutrophication and certain oceanic processes were thought to give rise to the formation of massive C. polykrikoides blooms with cell abundances ranging from 1000 to 30,000 cells ml −1, causing heavy mortalities of aquaculture fish and other marine organisms in these areas. Our analysis indicated that Chl- a estimates from SeaWiFS ocean color imagery appeared to be useful in demarcating the locality, spatial extent and distribution of these blooms, but unique identification of C. polykrikoides from non-bloom and sediment dominated waters remains unsuccessful with this data alone. Thus, the classical spectral enhancement and classification techniques such as Forward Principal Component Analysis (FPCA) and Minimum Spectral Distance (MSD) to uniquely identify and better understand C. polykrikoides blooms characteristics from other optical water types were attempted on both low spatial resolution SeaWiFS ocean color imagery and high spatial resolution Landsat-7 ETM+ imagery. Application of these techniques could capture intricate and striking patterns of C. polykrikoides blooms from surrounding non-bloom and sediment dominated waters, providing improved capability of detecting, predicting and monitoring C. polykrikoides bloom in such optically complex waters. The result obtained from MSD classification showed that retrieval of C. polykrikoides bloom from the mixed phase of this bloom with turbid waters was not feasible with the SeaWiFS ocean color imagery, but feasible with Landsat-7 ETM+ imagery that provided more accurate and comparable spatial C. polykrikoides patterns consistent with in situ observations. The dense phase of the bloom estimated from these imageries occupied an area of more than 25 km 2 around the coastal bays and the mixed phase extended over several hundreds kilometers towards the Southeast Sea offshore due to exchange of water masses caused by coastal and oceanic processes. Sea surface temperature analyzed from AVHRR infrared data captured the northeastward flow of Tsushima Warm Current (TWC) waters that provided favorable environmental conditions for the rapid growth and subsequent southward initiation of C. polykrikoides blooms in hydrodynamically active regions in the Korean Southeast Sea offshore.

Spatial and temporal aspects of phytoplankton blooms in complex ecosystems off the korean coast from satellite ocean color observations

Complex physical, chemical and biological interactions off the Korean coast created several striking patterns in the phytoplankton blooms, which became conspicuous during the measurements of ocean color from space. This study concentrated on analyzing the spatial and temporal aspects of phytoplankton chlorophyll variability in these areas using an integrated dataset from a Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Advanced Very High Resolution (AVHRR) sensor, and Conductivity Temperature Depth (CTD) sensor. The results showed that chlorophyll concentrations were elevated in coastal and open ocean regions, with strong summer and fall blooms, which appeared to spread out in most of the enclosed bays and neighboring waters due to certain oceanographic processes. The chlorophyll concentration was observed to range between 3 and 54 mg m-3 inside Jin-hae Bay and adjacent coastal bays and 0.5 and 8 mg m-3 in the southeast sea offshore waters, this gradual decrease towards oceanic waters suggested physical transports of phytoplankton blooms from the shallow shelves to slope waters through the influence of the Tsushima Warm Current (TWC) along the Tsushima Strait. Horizontal distribution of potential temperature (θ) and salinity (S) of water off the southeastern coast exhibited cold and low saline surface water (θ 12°C; S>34.4) at 75dBar, corroborating TWC intrusion along the Tsushima Strait. An eastward branch of this current was called the East Korean Warm Current (EKWC), tracked with the help of CTD data and satellite-derived sea surface temperature, which often influenced the dynamics of mesoscale anticyclonic eddy fields off the Korean east coast during the summer season. The process of such mesoscale anticyclonic eddy features might have produced interior upwelling that could have shoaled and steepened the nutricline, enhancing phytoplankton population by advection or diffusion of nutrients in the vicinity of Ulleungdo in the East Sea.

Late Pleistocene–Holocene paleoenvironmental changes inferred from the diatom record of the Ulleung Basin, East Sea (Sea of Japan)

The diatom floral record from two piston cores (00GHP-01 and 00GHP-07) taken from the southwestern margin of the Ulleung Basin, East Sea (Sea of Japan) reveals a series of well-defined changes in glacio-eustatic sea level and paleoceanographic conditions during the late Pleistocene–Holocene. Six assemblage zones and two barren zones in 00GHP-01 and four assemblage zones in 00GHP-07 are erected respectively on the basis of frequency of variations in, and occurrences of, biostratigraphically significant diatom species. All assemblage zones have been strongly influenced by the Tsushima Warm Current (TWC). The TWC has an important affect on controlling the distribution and composition of diatom flora, which in turn, reveal the history of the TWC in this area. The distribution pattern of diatoms in the diatom assemblages reveals sea surface temperature and salinity affected by the sediments type and terrigenous material input. Diatom temperature (Td) values show that the site of 00GHP-01 in the Ulleung Basin has been influenced by a relatively enhanced TWC twice during the deposition of lowermost and uppermost intervals. A relatively weak TWC was recorded in the middle interval since the latest Pleistocene. The diatom assemblages of 00GHP-07 represent an apparently continuous Late Quaternary record, spanning the Last Glacial Maximum, Bølling-Allerød, Younger Dyras and Holocene. High abundance of a low-salinity, coastal water diatom Paralia sulcata may reflect the influx of the East China Sea water through the Korean Strait to the East Sea (Sea of Japan). During the Last Glacial Maximum, the sea level was low enough that selected basin with shallow sills along the margin of the East Sea (Sea of Japan) became isolated from the Pacific Ocean. Salinity also decreased due to increased freshwater input from rivers draining the surrounding lands. The density-stratified water column may have prevented vertical mixing and resulted in anoxic bottom-water conditions.

Nonseasonal sea level variations in the Japan/East Sea from satellite altimeter data

A merged TOPEX/POSEIDON and ERS‐1/2 altimeter data set is used to estimate nonseasonal variations of sea surface height (SSH) in the Japan/East Sea (JES) from October 1992 through February 2002. The altimeter data have a good correlation (0.95) with tide gauge data in the western JES. The nonseasonal variability of the SSH is higher in the southern warm region than in the northern cold region. The root‐mean square value of the nonseasonal SSH is 5–10 cm in the southern area, whereas it is about 4 cm in the northern area. Empirical orthogonal function analysis of the nonseasonal SSH shows the first mode to be related to intraseasonal oscillations over the entire JES and the second mode to interannual path variations of the Tsushima Warm Current (TWC). The path change of the TWC is responsible for the high variability of SSH in the southern region.

Lithogenic flux in the Japan Sea measured with sediment traps

Spatial and temporal variations of particulate flux were observed by sediment trap experiments at three locations in the Japan Sea (western Japan Basin, eastern Japan Basin and Yamato Basin) during the period 1999–2002. Annual mean mass flux at 1 km depth was 455 mg/m 2/day in the western Japan Basin, 252 mg/m 2/day in the eastern Japan Basin and 147 mg/m 2/day in the Yamato Basin. In the Japan Sea, the regional differences in mass flux were much larger than the change of mass flux at different depths in each area. At 1 km depth in the Japan Sea, more than 60% of settling particles consisted of lithogenic aluminosilicates and biogenic opal. In order to determine indicators of the origin of aluminosilicates, concentrations of 28 elements in surface sediment at six areas of the Japan Sea were compared. Regional differences in concentration were seen in manganese (Mn), cobalt (Co) and rare earth elements (REEs). The La/Yb and Mn/Al ratios were used as indicators of the origin of aluminosilicates and the “freshness” of particles, respectively. These indicators suggested three sources of lithogenic material for the Japan Sea, (1) atmospheric input of “fresh” Asian loess (i.e. Kosa), (2) lateral transport of “old” Asian loess from the East China Sea by the Tsushima Warm Current (TWC), and (3) lateral transport from the Island arc of the Sakhalin and the Japan Islands. In the western Japan Basin, particles originating from the Asian Continent were observed during winter and spring, and it comprised 84% of annual lithogenic fluxes at 1 km depth in the western Japan Basin. These particles are considered to have been supplied directly to the surface of the Japan Sea by the input of KOSA, because these particles showed the signature of “fresh” particles. On the other hand, “old” Asian loess were found in the Yamato Basin, suggesting that the TWC transported Asian loess from the East China Sea to the southern margin of the Japan Sea. A sporadic current in the southern Japan Sea is considered to play a role in bringing loess particles to the interior of the Yamato Basin. In the eastern Japan Basin, it was calculated that 87% of annual lithogenic flux originated from the Island-arc. These particles likely were transported laterally from the Japanese Islands through the water column.

Nd concentration and isotopic composition distributions in surface waters of Northwest Pacific Ocean and its adjacent seas

Nd isotopic composition and concentration distributions were determined in surface waters of the Northwest Pacific Ocean and its adjacent seas, i.e., the Okhotsk and Japan Seas. The Okhotsk and Japan Seas samples showed higher Nd concentrations (19∼31 pmol/kg) than the Northwest Pacific Ocean samples, suggesting a large amount of Nd input from the land areas surrounding the Okhotsk and Japan Seas. Although the Nd isotopic composition data were limited for those regions, each oceanic area showed a distinctive value. The lone sample from the Okhotsk Sea had radiogenic Nd (eNd = −3.6) that was comparable to samples from the Pacific Ocean, indicating a large amount of radiogenic Nd supply from the Kuril Islands. On the other hand, the Japan Sea samples had the most highly unradiogenic Nd (eNd = −8.9∼−7.2). The southernmost sample had the most negative value, due to the influence of the Tsushima Warm Current (TWC) having a low eNd value. The latitudinal distributions of Nd isotopic composition and concentration in the surface waters of the Northwest Pacific Ocean showed marked variations. Nd concentration was low at low latitudes (3∼8 pmol/kg) and was increased with increasing latitude (16∼20 pmol/kg). On the other hand, Nd isotopic composition showed a mid-latitude minimum (eNd = ∼−6) and high eNd values at low and high latitudes (eNd = −2∼−1). The distribution of the eNd values seemed to be controlled by three currents: Kuroshio Extension, Oyashio Current and North Equatorial Current (NEC). The Kuroshio Extension, which showed a low eNd value, seemed to play an important role in transporting continentally derived Nd to the central Pacific. The Oyashio Current and NEC are supplied with large amounts of radiogenic Nd from the Kuril and Aleutian Islands, and the Hawaiian Islands, respectively. Based on the Nd isotopic composition and concentration distributions, we calculated the radiogenic Nd flux to the Pacific Ocean surface waters and estimated the Nd residence time. Our calculation suggested that the radiogenic Nd flux required to account for the Nd isotopic composition is higher than 70% of the unradiogenic Nd flux including Nd remobilization from coastal and shelf sediments and atmospheric input. It was also revealed that a large Nd remobilization flux is necessary to attain a global Nd residence time of ∼400 y as estimated in previous studies.

Use of nighttime visible images to detect Japanese common squid Todarodes pacificus fishing areas and potential migration routes in the Sea of Japan

This study used Defense Meteorological Satellite Program (DMSP)/Operational Line- scan System (OLS) satellite images to classify and analyze the spatial and temporal variability of nighttime fishing vessel lights in the Sea of Japan. OLS images can detect the powerful lights used to attract squid. We examined DMSP/OLS nighttime visible images from 1994 to 1999. Fishing areas of the Japanese common squid Todarodes pacificus were defined as the bright areas created by 2-level slicing methods on DMSP/OLS images. T. pacificus fishing areas were mainly found along the east coast of Korea, between Cheju and Tsushima Islands, around the Yamato Rise, along the coast of Honshu, and in northern areas of the Sea of Japan. Using image classification and separability analy- sis, we divided the Sea of Japan into 7 areas based on different temporal variability in squid fishing area characteristics. The classification takes the potential northern and southern squid migration pat- terns into account. One of the potential northern migration patterns formed along Honshu Island to the north; another appeared along the east coast of Korea, northward through Yamato Rise. Southern migration patterns were almost the reverse of northern migration patterns. These 7 classified areas also correspond to the oceanographic characteristics of the Sea of Japan, i.e. a polar front at latitude 40°N, the inflow of the Tsushima Warm Current (TWC), and warm eddies. The use of remotely- sensed data demonstrated in this study offers a powerful and innovative way in which to determine the migration and ecology of the Japanese common squid.

夏季石狩湾海域における流動・水温変動特性

Field observation of currents and water temperature was carried out at the sites of water depth of 700m and 40m of the Ishikari bay in the summer season. At the site of water depth of 700m, the change of flow and the water temprature at the cycle of 15-20 days according to change of Tsushima warm current is dominant.The vertical distribution of the Tsushima warm current was clarified.The change of flow at the cycle of 16 hours exists. At the site of water depth of 40m, flow is mainly driven by the wind, and the change of flow at the cycle of about four days is dominant. The compensation flow by the land breeze is shown in the decrease in the water temperature. This shows upwelling of the deep water. The changes of flow and water temperatureat the cycle of 16-24 hours are exist.

Effect of the Environmental Conditions on the Structure and Distribution of Pacific Saury in the Tsushima Warm Current Region

To provide evidence that the changes in oceanic environmental conditions are useful indices for predicting stock structure and distribution of the Pacific saury (Cololabis saira), the body length compositions and catch per unit fishing effort were examined in relation to the sea surface temperature(SST) anomalies in the Tsushima Warm Current(TWC) region. The size of the fish became larger(smaller) than the average in the same size category during the season of higher SST(lower SST) as opposed to the normal SST. The year-to-year changes in body size caused by the changes in the environmental conditions led the stock to be homogeneous during the period of high stock level from the late 1950s to early 1970s and in the 1990s. The changes in body size manifested by higher(lower) occurrence rates of larger (smaller) sized groups in relation to temperature anomalies suggest that the changes in the environmental conditions affect the distribution and the structure of the stock in the TWC region. Therefore, if the SST anomaly derived from satellite data is large enough in the early spring months(Mar. or Apr.), it is possible to predict whether or not sea temperature will be favorable for large sized groups of saury at normal or slightly earlier time of commencement of the fishery in spring(Apr.∼June).

동해에서 쓰시마난류의 변동과 관련한 극전선의 공간적 변화

Variation of the polar front in the East Sea is studied using temperature and dissolved oxygen data obtained from Japan Meteorological Agency from 1972 to 1999. Variation of the polar front in the East Sea has a close relation to the variation of the Tsushima Warm Current (TWC). When the TWC spreads widely in the East Sea, polar front moves northward. The spatial variation of the polar front is greater in the southwestern area of the East Sea and the northern area of Tsugaru Strait where the variation of the TWC's distribution area is greater than those in others of the East Sea. Hence, in the southeastern area of the East Sea, that is, between near Noto peninsula and Tsugaru Strait, the spatial variation of the polar front is not so wide as in the southwestern area because the flow of TWC is stable.

Analysis of Yellow Sea circulation

Some features of the circulation in the Yellow Sea (hereafter referred to as YS) in the cold season (mid-November through mid-April) are analyzed emphatically by using the observations of several large-scale surveys in recent years together with historical data. Compared with the previous studies, a wealth of observed data have firstly been used in this study to further discuss the origin and path of the Yellow Sea Warm Current (YSWC). The analyses show that the YSWC is not a direct branch of the Tsushima Warm Current (TSWC), but derives from the mixed water region formed by TSWC water and the continental shelf water of the East China Sea (ECS). The path of the YSWC has certain seasonal and interannual variations. Then, the basic features of the Cheju Warm Current (CWC) discovered in recent years and its relation to the YSWC are expounded. The studies indicate that the CWC and the YSWC come basically from the same origin, and the main path of CWC is located roughly in water depths of greater than 80 m northwest of Chejudo. At last, the distribution features of the Korea Coastal Current (KCC) are delineated according to the new observations. The results show that the KCC moves toward south along the 40–50 m isobaths west of the Korean Peninsula, and its velocity increases from north to south.

동해의 쓰시마난류 분포역에서 음속의 변동

This study is to analyze the influence of the Tsushima Warm Current (TWC) on the variation of sound speed in the southern part of the East Sea. Sound speed is calculated by method of Chen and Millero (1977:, based on the CTD data measured in June of 1996. Sound speed in the central part of the TWC is about more fast than that in the other regions without the TWC. Sound speed minimum layer (SML) in the TWC region exists between loom and 341 m, while it exists between 260m and 290m in the non-TWC region. SML distributes along the path of TWC over continental shelf in the coastal waters of Japan.

하계 한국 남해의 해황 변동과 멸치 초기 생활기 분포특성

한국 남해의 대마난류 변동에 따른 멸치 초기 생활기 분포와 해황과의 관계를 7월과 8월 (하계) 한국 남해 연안 및 대마난류 횡단 관측을 통해 조사하였다. 그 결과를 요약하면 다음과 같다. 1) 7월 말<TEX>$\~$</TEX>8월 초 한국 남해의 표층은 수온 <TEX>$20\~23^{\circ}C$</TEX> 이하, 염분 33.0 이상의 남해 연안수와 수온 <TEX>$21\~25^{\circ}$</TEX>, 염분 32.0<TEX>$\~$</TEX>32.5의 중간수 (대마난류계수) 그리고 수온 <TEX>$26^{\circ}$</TEX> 이상, 염분 31.5 이하의 대마난류수가 분포하였다. 해역별로 연안수는 거문도와 소리도 주변,욕지도<TEX>$\~$</TEX>거제도 남서연안에 분포하고 대마난류수는 제주도 북동 일부해역과 외해역에 분포했다. 대마난류계수는 연안수와 대마난류수사이에 존재하고 거문도<TEX>$\~$</TEX>소리도, 소리도<TEX>$\~$</TEX>욕지도에서 warm streamer 형태로 연안 유입되었다. 수온, 염분의 수평경도가 큰 해역은 청산도<TEX>$\~$</TEX>거문도, 거제도 남서해역 주변이었다. 2) 위성자료에 나타난 표면 수온 수평경도가 가장 큰 해역은 청산도와 거제도 남서 해역 주변이었다. 표면 수온의 일 변화에서 거문도<TEX>$\~$</TEX>소리도, 소리도<TEX>$\~$</TEX>욕지도 해역에서 난수 유입이 일어났다. 표층류는 고흥반도 남쪽<TEX>$\~$</TEX>소리도가 북서 방향, 소리도<TEX>$\~$</TEX>욕지도는 북동-북서 방향으로 수송되어 수온, 염분 분포에 나타난 표층 warm streamer의 연안 유입 형태와 일치하였다. 연안수나 외해의 대마난류수는 북동<TEX>$\~$</TEX>동으로 수송되었다 (Fig. 13) .3) 클로로필 (기초생산력)은 연안수역이 2.0<TEX>$\mu$</TEX>g/h 이상으로 높고 외해는 0.5<TEX>$\mu$</TEX>g/h 이하로 낮았다. 클로로필 농도 분포는 수온, 염분 분포와 거의 유사하였다. 농도가 가장 큰 해역은 수온, 염분의 수평경도가 가장 큰 거제도 남서해역으로 8.0<TEX>$\mu$</TEX>g/h이었다. 4) 멸치 난과 자 <TEX>$\cdot$</TEX> 치어는 연안수와 대마난류계수간 전선이 형성되는 거문도와 욕지도, 거제도 남서해역 주변에 많이 분포하였다. 이들 해역은 하계 기초 생산력이 타 해역에 비해 크고 남쪽에서 반 시계 방향으로 연안을 향해 유입하는 warm streamer가 존재하는 해역이었다. In the southern sea of Korea and the areas of Tsushima warm currents the relationship between the distributions of eggs and larvae of anchovy (Engraulis japonica) and oceanic conditions was examined on July and August 1997, The south Korean coastal waters, the water temperature of below <TEX>$20\~23^{\circ}$</TEX> and the salinity of above 33.0 (PSU), the mixed waters between the south Korean coastal waters and the Tsushima warm currents, <TEX>$21\~25^{\circ}$</TEX> and <TEX>$32.0\~32.5$</TEX> and the Tsushima warm currents, above <TEX>$26^{\circ}$</TEX> and below 31.5 were distributed at the surface layer. The Tsushima warm currents were distributed at the northeast of Jeju Is. and off the southern sea of Korea. As an appearance of warm streamer, the mixed waters were intruded into the coastal areas of Komun Is.<TEX>$\~$</TEX>Sori Is. and Sori Is.<TEX>$\~$</TEX>Yokji Is.. Approximate paths of surface water by the drift card experiments were similar with the intrusions of the warm water identified from the water temperature and salinity distributions. The distributions of chlorophyll concentration were consistent with the distributions of water temperature and salinity, Anchovy eggs and larvae were mostly distributed at Komun Is., Yokji Is, and the southwest of Koie Is. where chlorophyll concentrations were high and cyclonic circulations by the warm water intrusions (warm streamers) were formed.

Distribution of leptocephali in the Kuroshio Current and East China Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 235:279-288 (2002) - doi:10.3354/meps235279 Distribution of leptocephali in the Kuroshio Current and East China Sea Michael J. Miller1,*, Tsuguo Otake2, Gen Minagawa1, Tadashi Inagaki1, Katsumi Tsukamoto1 1Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan 2Faculty of Bioresources, Mie University, Kamihama, Tsu 514-8507, Japan *E-mail: miller@ori.u-tokyo.ac.jp ABSTRACT: A first-of-its-kind sampling survey using a large midwater plankton net appropriate for collecting leptocephali was carried out in transects across the shelf break at the edge of the Kuroshio Current and East China Sea and in the western North Pacific Ocean south of the Ryukyu Islands during late November and early December. Leptocephali of at least 45 species of 10 families of anguilliform eels were collected. Catch rates and the species richness of leptocephali were higher in the Kuroshio region than in the western Pacific Ocean. The most abundant leptocephali in the region were of the eel families Congridae, Synaphobranchidae, Ophichthidae and Muraenidae. Several taxa of congrid eels, including Gnathophis nystromi nystromi and Ariosoma spp., were spawning along the edge of the Kuroshio Current, as were muraenids, ophichthids, nettastomatids and Dysomma anguillare (Synaphobranchidae). The 2 most abundant species, G. nystromi nystromi and D. anguillare, appeared to be spawning near the edge of the shelf break in the central Kuroshio region, but the spawning of Ariosoma spp. and several other species was centered farther south to the northeast of Taiwan. This is the first discovery of the spawning of eels along a shelf break adjacent to a major western boundary current, and spawning in this region would result in their leptocephali having the potential for being transported to a wide range of areas by the Kuroshio and Tsushima Warm Currents. KEY WORDS: Leptocephali · Eels · Spawning area · Kuroshio Current · East China Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 235. Online publication date: June 19, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.