• 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.

• 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.

• Proceedings of the KSRS Conference
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• v.2
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• pp.934-937
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• 2006

In the northeastern South China Sea (SCS), fast westward moving (about 2.9 m/s) non-linear internal waves (NLIWs) are emanated nearly daily from the Luzon Strait. Their propagation speed is faster than NLIWs previously observed in the deep water of world oceans, their amplitude of 140 m or more is the largest free propagating NLIWs so far observed in the deep ocean. These NLIWs energized the top 1500 m of the water column, heaving it up and down in 20 min. Their associated energy density and energy flux are the largest observed to date. During 2005 and 2006 experiment, they were found west of the HengChun Ridge (HCR) that links Luzon and Taiwan Islands. This coincides with founding in satellite images, no NLIW front was found east of HCR. But, the turbulent environment east of HCR may prohibit surface signature of NLIWs that were emanated from sills between Batan Islands. The relative contribution of the two ridges on NLIW in Luzon Strait is still under study.

• Journal of Climate Change Research
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• v.1 no.2
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• pp.133-145
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• 2010

This study examined the characteristics of tropical cyclone(TC) activity over the western North Pacific(WNP) in 2009. Twenty-two TCs formed in 2009, which is slightly below normal(1979~2009 average: 25.8) and most of these occurred during the months of July to October. Most TCs in 2009 was formed over the northern Philippines and the eastern part of the WNP and they moved towards the South China Sea and the east of Japan, resulting in less TC affecting the East China Sea and Korea. The TC activity in 2009 is modulated by the large-scale circulations induced by the El $Ni{\tilde{n}}o$ and vigorous convection activity over the WNP. As the general characteristics of El $Ni{\tilde{n}}o$ year, the difference in sea surface temperature between the central Pacific and the eastern Pacific causes an anomalous westerly winds, expanding the WNP monsoon trough farther eastward. Accordingly, TC formation has relatively increased in the east part of the WNP. Active convection activities over the subtropical western Pacific excite a Rossby wave propagating from the South China Sea to mid-latitudes, resulting in an anomalous easterly steering flow in the South China, anomalous northwesterly over the East China Sea and Korea, and anomalous southwesterly over the east of Japan. Summing up, the TCs cannot enter the East China Sea and Korean region and instead they move towards the South China Sea or south-east of Japan. There were no effects of TCs in Korea in 2009. It is anticipated that this study which analyzed unusual TC activity and large-scale circulations in 2009 would help the predictability of TC effects to increase according to climate change in the East Asia.

• The Korean Journal of Quaternary Research
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• v.23 no.1
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• pp.25-37
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• 2009

Geochemical composition and clay minerals of surface and core sediments around off the Jeju Island were analyzed for identification of sediment origins. The clay mineral distribution is mainly controlled by the sediment source and the dominant circulation pattern. Smectite is highly concentrated (>8%) in the northwest near the South Yellow Sea and in the outer-shelf mud patch. It seems to be due to the high supply of smectite transported from China where fine-grained sediments are discharged from modern and ancient Huanghe River. The relatively high abundance of kaolinite are found in northeastern nearshore area and the southwest near Changjiang estuary. It seems to be supplied from Changjiang River and the southwestern Korea rivers. The sediment accumulation rates measured by $^{210}Pb$ geochronrom mowere 0.20 to 0.54cm/mr or 0.15 to $0.42g/cm^2{\cdot}mr^{-1}$ AOJI, with decreasing rates from the west part to the east part, resulting in the supply of fine-grained suspended sediments from the Changjiang and Huanghe Rivers system. The discrimination diagrams clearly show that the sediments around Jeju Island in the northern East China Sea are ultimately sourced from Chinese rivers, especially from the Huanghe River, whereas the sediment in the northeast part might come from Korean rivers and the Jeju Island.

• Korean Journal of Environmental Biology
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• v.41 no.1
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• pp.89-100
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• 2023

We investigated the spatial distribution of heterotrophic bacteria associated with different water masses in the northern East China Sea(ECS) in summer. The surface water masses were divided into the Changjiang Diluted Water (CDW) and high salinity water (HSW). In the CDW region, the concentrations of dissolved inorganic nitrogen (DIN) and chlorophyll-a (Chl-a), and micro Chl-a contribution were high; and bacterial abundance (BA) and ciliate abundance (CA) were also high. In the HSW region with relatively low DIN concentrations, Chl-a concentration and micro Chl-a contribution were low, but pico Chl-a contribution was increased compared to those in the CDW region. BA did not show any significant difference from the CDW region, but CA was decreased. BA showed a positive correlation with Chl-a concentration in the CDW region; however, it did not show a significant correlation with Chl-a concentration in the HSW region. The ratio of bacterial carbon biomass/phytoplankton carbon biomass was exponentially increased with a decrease in the Chl-a concentration. Compared to the past (1990-2000s), the surface phosphate concentrations and the size of dominant phytoplankton have recently decreased in the ECS. Considering this trend of nutrient decrease and miniaturization of the phytoplankton, our results indicate that changes in the strength of the oligotrophic water mass could alter the function of the microbial food web.

• 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.

• Korean Journal of Environmental Biology
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• v.37 no.1
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• pp.93-108
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• 2019

To investigate the temporal-spatial distribution of picophytoplankton in relation to different water masses in the northern East China Sea (ECS), picophytoplankton abundance were investigated using flow cytometry with environmental factors in 2016-2017. The results from the analysis of flow cytometer data showed that Synechococcus appeared across all seasons, exhibiting its minimum abundance in winter and maximum abundance in summer. Furthermore, high abundance was detected in the surface mixed layer during spring and summer when vertical stratification occurs; in particular, Synechococcus exhibited maximum abundance in thermocline layer, indicating a close correlation to water temperature and thermocline formation. In addition, the abundance of Synechococcus indicated a decrease in the western seas in 2017 compared to 2016 under the strong influence of the Changjiang Diluted Water (CDW). This was determined by the significant influence of the CDW on the abundance of Synechococcus during summer in the northern waters of the ECS. In contrast, Prochlorococcus did not appear during winter and spring, and its distribution was limited during summer and autumn in the eastern seas under the influence of the Kuroshio current. The largest range of Prochlorococcus distribution was confirmed during autumn without the influence of the CDW. Thus, the distribution pattern of each picophytoplankton genus was found to be changing in accordance to the extension and reduction of sea current in different seasons and periods of time. This is anticipated to be a useful biological marker in understanding the distribution of sea currents and their influence in the northern waters of the ECS.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.1
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• pp.15-26
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• 2008

The NEMURO model is aimed to efficiently understand the interaction among factors of lower trophic level of a marine ecosystem, using data on solar radiation and sea water temperature. In this study, we analyzed the seasonal pattern of nutrients and planktons, and estimated productivity and biomass of planktons from 2002 to 2005. Nutrients($NO_3$, $NH_4$, and $Si(OH)_4$) which were used by phytoplankton showed a high concentration before the bloom of phytoplankton. Nutrients (DON, PON, and Opal) which were a byproduct of phytoplankton showed a high concentration in the same period as the bloom of phytoplankton. Both phytoplankton and zooplankton had two peaks in March and August. Estimated phytoplankton biomass from the NEMURO model showed a similar pattern with observed chlorophyll a concentrations. Biomasses of phytoplankton were bigger than those of zooplankton. Annual mean biomasses of small and large phytoplankton were estimated at 30.961 and $14.070\;{\mu}g\;l^{-1}$ respectively. Annual mean biomass of predatory zooplankton was greater than those of small and large zooplankton.

• The Korean Journal of Malacology
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• v.30 no.3
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• pp.281-293
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• 2014

The biogeography and diversity patterns of the marine bivalve molluscan fauna of the East Sea coast of South Korea are analyzed. The total species richness of the continental Korean bivalve fauna, excluding insular regions (Dok-do and Ullung-do), is 304, and from north to south the species richness of bivalves increases showing a clear gradient: Gangwon, 143 species ${\rightarrow}$ Gyeongbuk, 131 ${\rightarrow}$ Gyeongnam, 183. A zonal-geographical analysis of the entire fauna shows that the great majority are warm-water mollusks, constituting 77% (subtropical, 37%, tropical-subtropical, 30%, subtropical-boreal, 10%), The number of boreal (low-boreal, widely distributed boreal and circumboreal) species is lower, 19%, whereas boreal-arctic mollusks have only 4%. This demonstrates that the bivalve molluscan fauna of the eastern coast of Korea is subtropical, and has more affinities to the fauna of the East China Sea than to the northern East Sea. Separate analysis by provinces shows the increasing role of warm-water mollusks from north to south. While tropical-subtropical and subtropical species constitute 47% (68 species) in Gangwon, their dominance increases to 71% (93 species) in Gyeongbuk, and to 80% (148 species) in Gyeongnam. The Gyeongnam bivalve fauna is the most diverse in species composition and has the largest number of "endemics" (species known only from this province), 46%. The Gangwon fauna also contains many "endemics", up to 40%, while Gyeongbuk is an intermediate zone with low "endemicity", only at one-fifth of the regional fauna, and has the most species in common among the three provinces.