• Journal of the Korean earth science society
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• v.27 no.2
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• pp.198-208
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• 2006

To investigate the provenance of outer-shelf mud patch in the East China Sea, the geochemical compositions were analyzed and compared with those of Chinese rivers sediments. The mud sedimentary facies are distributed in the central region and sandy mud facies are also widely distributed around the study area. The major elements (Fe, Mg, K, Ti, and Mn) show strong positive correlation with Al, and trace elements also indicate the same characteristics; hence, clay minerals are likely to be the promising host for those elements. The high concentration of Fe, Ti, and Mn elements are found in the western middle part near the Changjiang estuary, indicating that it seems to result from the influence of the Changjiang River. Elemental ratios including Sc/Al, Ti/Nb, Th/Sc, Cr/Th, Nb/Co, and Th/U were thus used as provenance indicators to identify the sediment origins of the East China Sea. The discrimination diagrams clearly show that most of the sediment in the northern part are originated from the Huanghe River, while the muddy sediments in the western part near the Changjiang estuary might come from the Changjiang River, suggesting that the outer-shelf muddy sediments of East China Sea are originated from diverse sources.

• The Korean Journal of Quaternary Research
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• v.17 no.2
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• pp.33-38
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• 2003

This study is conducted to examine the data of climate or environmental change in the northeastern Asia during the last glacial maximum. A remarkable feature of the 18,000 BP biome reconstructions for China is the mid-latitude extention of steppe and desert biomes to the modem eastern coast. Terrestrial deposits of glacial maximum age from the northern part of Yellow Sea suggest that this region of the continental shelf was occupied by desert and steppe vegetation. And the shift from temperate forest to steppe and desert implies conditions very much drier than present in eastern Asia. Dry conditions might be explained by a strong winter monsoon and/or a weak summer monsoon. A very strong depression of winter temperatures at LGM. has in the center of continent has influenced in northeast Asia similarly. The vegetation of Hokkaido at LGM was subarctic thin forest distributed on the northern area of middle Honshu and cool and temperate mixed forest at southern area of middle Honshu in Japan. The vegetation landscape of mountain- and East coast region of Korea was composed of herbaceous plants with sparse arctic or subarctic trees. The climate of yellow sea surface and west region of Korea was much drier and temperate steppe landscape was extended broadly. It is supposed that a temperate desert appeared on the west coast area of Pyeongan-Do and Cheolla-Do of Korea. The reconstruction of year-round conditions much colder than today right across China, Korea and Japan is consistent with biome reconstruction at the LGM.

• Journal of the korean society of oceanography
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• v.39 no.2
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• pp.119-135
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• 2004

A three-dimensional numerical model using POM (the Princeton Ocean Model) is established in order to understand the dispersion processes of the Yangtze River water in the Yellow and East China Seas. The circulation experiments for the seas are conducted first, and then on the bases of the results the dispersion experiments for the river water are executed. For the experiments, we focus on the tide effects and wind effects on the processes. Four cases of systematic experiments are conducted. They comprise the followings: a reference case with no tide and no wind, of tide only, of wind only, and of both tide and wind. Throughout this study, monthly mean values are used for the Kuroshio Current input in the southern boundary of the model domain, for the transport through the Korea Strait, for the river discharge, for the sea surface wind, and for the heat exchange rate across the air-sea interface. From the experiments, we obtained the following results. The circulation of the seas in winter is dependent on the very strong monsoon wind as several previous studies reported. The wintertime dispersion of the Yangtze River water follows the circulation pattern flowing southward along the east coast of China due to the strong monsoon wind. Some observed salinity distributions support these calculation results. In summertime, generally, low-salinity water from the river tends to spread southward and eastward as a result of energetic vertical mixing processes due to the strong tidal current, and to spread more eastward due to the southerly wind. The tide effect for the circulation and dispersion of the river water near the river mouth is a dominant factor, but the southerly wind is still also a considerable factor. Due to both effects, two major flow directions appear near the river mouth. One of them is a northern branch flow in the northeast area of the river mouth moving eastward mainly due to the weakened southerly wind. The other is a southern branch flow directed toward the southeastern area off the river mouth mostly caused by tide and wind effects. In this case, however, the tide effect is more dominant than the wind effect. The distribution of the low salinity water follows the circulation pattern fairly well.

• Journal of the Korean earth science society
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• v.29 no.6
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• pp.454-465
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• 2008

Benthic foraminiferal assemblage and AMS radiocarbon dating of core sediments from the northern shelf of the East China Sea were analyzed in order to understand the paleoenvironment and sedimentary environmental changes around the Korean marginal seas since the last glacial maximum (LGM). The core sediments, containing continuous records of the last 16,000 years, reveal a series of well-defined vertical changes in number of species (S), P/T ratio and species diversity (H) as well as foraminiferal assemblage. Such down-core variations display a sharp change at a core depth of approximately 240 cm, which corresponds to ca. 10,000 year B.P. The sediments of the lower part of the core (240${\sim}$560 cm, Zone I), including the well-developed tide-influenced sedimentary structures, are characterized by high abundances of Ammonia beccarii and Elphidium clavatum (s.l.) and low values in number of species, P/T ratio and diversity. These tide-influenced signatures and foraminiferal assemblage characters suggest that the sediments of Zone I were deposited in a coastal environment (water depths of 20${\sim}$30 m) such as tidal estuary with an influence of the paleo-rivers (e.g., old-Huanghe and Yangtze rivers) during the early phase of the sea-level rise (ca. 16,000 to 10,000 years) since the LGM. In contrast, the upper core sediments (0${\sim}$240 cm, Zone II) are characterized by abundant Eilohedra nipponica and Bolivina robusta with a minor contribution of A. ketienziensis angulata and B. marginata. and high values in number of species, P/T ratio and diversity. Based on relative abundance of these assemblage, Zone II can be divided into two subzones (IIa and IIb). Zone IIa is interpreted to be deposited under the inner-to-middle shelf environment during the marine transgression in the early Holocene (after ca. 9,000 yr B.P.) when sea level rapidly increased. The sediments of zone IIb most likely deposited after 6,000 yr B.P. under the outer shelf environment (80${\sim}$100 m water depth), which is similar to modem depositional environments. The muddy sediments of zone IIb were probably transported from the old-Huanghe and Yangtze Rivers during the late Holocene. We suggest that the present-day oceanographic conditions over the Yellow and the East China Seas have been established after ca. 7,000${\sim}$6,000 yr B.P. when the Kuroshio Current began to influence this area.

• Economic and Environmental Geology
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• v.39 no.1 s.176
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• pp.39-51
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• 2006

Rare earth elements(REEs) in transgressive shelf core sediments were analysed to identify constraints of REE distribution patterns and sediment provenances in the northern East China Sea(ECS). Sediments of Chinese and Korean rivers, such as Huanghe and Yangtz rivers, Keum and Yeongsan rivers that supply sediments to the northern ECS, were also analysed to figure out their typical REE distribution patterns. The distribution patterns of Chinese and Korean river sediments, which are normalized with upper continental crust (UCC) REE values, appear to be enriched in middle rare earth elements (MREEs) in Chinese river sediments, whereas in light rare earth elements (LREEs) in Korean river sediments. We assign the MREE-enriched convex-type distribution pattern in Chinese river sediments as 'C-type', and the LREE-enriched linearly decreasing pattern in Korean river sediments as 'D-type'. A major constraint of the REE concentration in northern ECS core sediments is interpreted to be LREE-enriched monazite $((Ce,\;La)PO_4)$ that is ubiquitous in and around the study area. Meanwhile, the distribution pattern of northern ECS sediments appears to be between the C-type and the D-type. We suggest that the nothern ECS sediments are the mixture of China and Korea riverine sediments that have been accumulated in paleo-river mouth, paleo-coast, and present-day shelf environment as well.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.5
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• pp.399-405
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• 1992

Using $MnO_2-coated$ fiber extraction and gamma counting techniques, we measured the distributions of $^{226}Ra$\;and\;^{228}Ra$ in the surface waters at 14 stations of East Sea of Korea in September, 1988. The concentrations of $^{226}Ra$\;and\;^{228}Ra$ in the surface waters ranged $70-110\;dpm/10^3l$ and 102=232 $dpm/10^3l$, respectively. In general, the concentrations of Ra isotopes were shown higher in the coastal and southern stations than those in the outer and northern stations in our observed area. Also, the concentrations of Ra isotopes in the study area were significantly higher than values in the other area of the East Sea and Kuroshio surface water, but much lower than the concentrations in the surface water of Yellow Sea reported previously. There was an inverse relationship between the $^{226}Ra/^{228}Ra$ ratio and salinity in the surface waters of Kuroshio, Yellow Sea and East Sea of Korea. This indicates that the continental shelf waters such as Yellow Sea and East China Sea are main source of Ra isotopes in surface waters of the East Sea of Korea.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.3
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• pp.133-142
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• 2009

In order to understand the present environmental condition and future impingement of Changjiang(Yangtze River) outflow upon the adjacent seas after the scheduled completion of the Sanxia (Three Gorges) Dam in 2009, we tried to estimate the mixing ratios among surface waters of three end-members: Changjiang Water (CW), Kuroshio Water (KW), and East China Sea Water (ECSW) using $^{228}Ra/^{226}Ra$ activity ratio and salinity as tracers. Water samples were collected from 32 stations in November 2005 (R/V Tamgu 3), from 20 stations in July 2006 (R/V Ocean 2000) and from 17 stations in August 2006 (R/V Ieodo) in the northern part of the East China Sea. Radium isotopes in ~300 liters of surface seawater were extracted onboard by filtering through manganese impregnated acrylic fibers and following coprecipitation as $Ba(Ra)SO_4$. Activities of radium isotopes were determined by a high purity germanium detector. Results show that the fraction of CW was in the range of 1-23% in the study area, while KW was in the range of 0-30 % and ECSW 58-100 %. The eastward plume of Changjiang outflow, commonly observed in satellite images during summer and also displayed by the eastward-decreasing CW fraction in this study, could be attributed to Ekman transport caused by the SE monsoon prevailing in this region during summer. Results of this study showed that in the drought season, there was a little or no fraction of CW in the study area. Concentration of dissolved inorganic nitrogen (DIN) showed strong positive relationship with the fraction of CW, suggesting Changjiang as the major source of nitrogen. The mixing curve of DIN indicates the removal of nitrate by biological uptake during the mixing of CW with ambient seawater in the study area.

• Economic and Environmental Geology
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• v.38 no.6 s.175
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• pp.633-642
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• 2005

We present the sedimentary sequence and distribution pattern of the late Holocene muddy deposits in the northern East China Sea shelf using the high-resolution 'Chirp' profiles. The seismic sedimentary sequence overlying acoustic basement (basal reflector-B) can be divided into two depositional units (Unit 1 and 2) bounded by erosional bounding surface (mid reflector-M). The lower Unit 1 above basal reflector-H is characterized by the acoustically parallel to subparallel reflections and channel-fill facies. The upper Unit 2, up to 7 m in thickness, shows seismically semi-transparent seismic facies and lenticular body form. On the base of sequence stratigraphic concept, these two sediment units have developed during transgression and highstand period, respectively, since the last sea-level lowstand. The transgressive systems tract (Unit 1) lie directly on the sequence boundary (reflector B) that have farmed during the last glacial maximum. The transgressive systems tract in this study consists mostly of complex of delta, fluvial, and tidal deposits within the incised valley estuary system. The maximum flooding surface (reflector M) corresponding to the top surface of transgressive systems tract is obviously characterized by erosional depression. The highstand systems tract (Unit 2) above maximum flooding surface is made up of the mud patch filled with the erosional depression. The high-stand mud deposits showing a circle shape just like a typhoon symbol locates about 140 km off the south of Cheju Island with water depth of $60\~90m$. Coverage area and total sediment volume of the mud deposits are about $3,200km^2$ and $10.7\times10^9\;m^3$, respectively. The origin of the mud patch is interpreted as a result of accumulating suspended sediments derived from the paleo-Yellow and/or Yangtze Rivers. The circular distribution pattern of the mud patch appears to be largely controlled by the presence of cyclonic eddy in the northern East China Sea.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.5
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• pp.331-341
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• 2005

Distribution of anchovy (Engraulis japonica) eggs and larvae was studied in the southwestern sea of Korea in July and November, 2001. Anchovy eggs were found mainly in the oceanic fronts of the northern sea area which were formed in the offshore area of Chuja Is. Bogil Is. and Chungsan Is. from west to east. Anchovy eggs were also found in the surrounding sea of Cheju Is. in the southern sea front area. The waters were highly heterogeneous and the water masses were bordered based on temperature $(10.8-26.4^{\circ}C)$ and salinity (28.9-33.7 psu). The anchovy eggs were mostly found outside of the China Coastal Water, where salinity was below 31 psu. The anchovy eggs were not found in November. Abundance of the anchovy larvae were higher in July than November. Temperature ranged from $10.8^{\circ}C\;to\;25.9^{\circ}C\;and\;15.9^{\circ}C\;to\;20.5^{\circ}C$, and salinity ranged from 28.9psu to 34.1psu and 33.2psu to 34.1psu in July and November, respectively. Non-swimmable larvae were found throughout the whole area of the southwestern sea of Korea. The area beyond the oceanic front had anchovy eggs dispersed from the spawning grounds to offshore. Dispersion pattern showed that the eggs were transported from the spawning grounds with a process of advection and diffusion based on the flow pattern which were caused by winds. Distribution pattern of the anchovy eggs and larvae may be used for the prediction of oceanic currents in each area.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.3
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• pp.306-316
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• 2003

We conducted a time-series analysis of temperature and salinity of sea water around Jeju Island, Korea. Monthly mean temperature and salinity was influenced by precipitation and weather conditions on Jeju as well as by oceanographic conditions of the open sea such as the Tsushima Warm Current and sea water in coastal areas. Salinity of Jeju coastal waters was the highest in April, and it was always over 34.00 psu with tiny fluctuation between December and June. Due to the effects of the Tsushima Warm Current, Jeju coastal waters maintained high salinity and stability. Low salinity and its large fluctuations during summer were closely associated with the China Coastal Water and precipitation in Jeju. The place of the lowest water temperature was the northeast coasts of Jeju (Gimneong, Hado, Jongdalri). In winter, as warmer water of the Tsushima Warm Current appeared in western area of Jeju dwindled flowing along the northern coasts of Jeju area and becoming cool, the lowest water temperature often appeared locally in Gimnyeong and its vicinitly in summer. The Tsushima Warm Current flows into the east entrance of Jeju Strait, but its influence is weak because of geometry and strong vertical mixing due to fast tidal currents.