Abstracts The present study was conducted to investigate the oceanic characteristics of the northern waters of East China Sea and the East Sea through identification of long-term variation patterns of oceanic environment factors, for the objective of gaining understanding of oceanic environment char...
Abstracts The present study was conducted to investigate the oceanic characteristics of the northern waters of East China Sea and the East Sea through identification of long-term variation patterns of oceanic environment factors, for the objective of gaining understanding of oceanic environment characteristics of the northern waters of East China Sea and the East Sea, which closely influence the oceanic environments of waters nearby South Korea. The study methodology included the use of oceanographic data (water temperature, salinity, dissolved oxygen, nutrients, and chlorophyll-a) on the East Sea and northern waters of East China Sea from the Korea Oceanographic Data Center(KODC), collected by season for 20 years between 1995 and 2014. Moreover, for the study on the distribution of nutrients, chlorophyll-a, and dissolved trace metal (Cu, Ni, Cd, Pb)in the surface layer of the East Sea an oceanic survey focused on Ulleung Basin and Japan Basin was conducted in the summer of 2009. The main water masses that affected the northern waters of East China Seaduring the study period were classified as Changjiang diluted water, (CDW), Tsushima warm current (TWC), Yellow Sea bottom cold water (YSBCW), and Kuroshio source water (KSW). The forces of CDW and TWC that forms on the surface and sub-surface layers had weakened for 20 years and the force of KSW that forms on the intermediate layer showed a distinctively decreasing trend. However, YSBCW showed a trend of expanding its force. Phosphate and silicate exhibited a decreasing tendency and phosphate showed a pattern of being depleted on the surface layer after 2009. It is determined that one of the reasons for this is the concentration of nutrients introduced through CDW and TWC being too low. The concentration of chlorophyll-a exhibited an increasing tendency during the study period, the reasons for which are determined to be the influences of increase in water temperature, supply of nutrients via YSCW, and increases in light transmission from decrease in suspended solid due to the construction of the Three Gorges Dam. The main water masses of the East Sea were classified as Tsushima surface water (TSW), Tsushima middle water (TMW), North Korean cold water (NKCW), and bottom layer of East Sea proper water (ESPW). The strengths of water masses showed an increasing trend in TSW and NKCW, while TMW and ESPW showed a decreasing trend. Due to the influences of TSW, which forms primarily at depth of 6m, and NKCW, which forms at depth of about 125m, the water temperatures at the surface and 100m water layers resulted in increase of 0.56 ℃during 20 years. As such, it is believed that if the strength of TSW and NKCW continue to increase, then the water temperatures near the surface and 100m water layers of the East Sea will continue to increase. Moreover, the water temperature and salinity of ESPW exhibited significant increases, while the concentration of dissolved oxygen was shown be decreasing. The reason for this is determined to be the decrease of inflow of surface water that settles from the surface layer to the bottom layer. The distribution of nutrients, chlorophyll-a, and dissolved trace metals in the East Sea appeared divided by cold versus warm region. In the cold region, the distribution of nutrients, chlorophyll-a, and dissolved trace metals was determined by inflow of bottom layer water at a low depth point due to greater influence from seabed topography than land. In the warm region, the concentrations of Pb and Cd were shown to have been influenced by TWC, while the concentration of Cu was shown to be high due to inflow from the atmosphere to the surface layer. In conclusion, it is determined that nutrients, chlorophyll-a, and dissolved trace metals in the northern waters of East China Sea are influenced by the expansion of YSCW, while salinity is decreased due to decrease in the strength of KSW. Moreover, increase in nitrogen and decrease in phosphorus causes abnormal increase in the N/P ratio to create a species shift from traditional diatiom-centric phytoplankton community to small-sized dinoflagellates. This increase in dinoflagellates can lead to microbial food web and is believed to have the potential to reduce the productivity of fishery. The surface water in the East Sea is experiencing increase in water temperature and decrease in salinity. The water temperature and salinity of ESPW, which makes up 90% of the East Sea, are increasing, while the concentration of dissolved oxygen is decreasing. In other words, this indicates reduction in the inflow of surface water that settles to the bottom layer, which is determined to lead to future weakening or complete end to thermohaline circulation in the East Sea. Moreover, due to decrease in dissolved oxygen that is supplied from the surface layer to the bottom layer, it is believed that the East Sea will undergo changes in its oceanic ecosystem.
Abstracts The present study was conducted to investigate the oceanic characteristics of the northern waters of East China Sea and the East Sea through identification of long-term variation patterns of oceanic environment factors, for the objective of gaining understanding of oceanic environment characteristics of the northern waters of East China Sea and the East Sea, which closely influence the oceanic environments of waters nearby South Korea. The study methodology included the use of oceanographic data (water temperature, salinity, dissolved oxygen, nutrients, and chlorophyll-a) on the East Sea and northern waters of East China Sea from the Korea Oceanographic Data Center(KODC), collected by season for 20 years between 1995 and 2014. Moreover, for the study on the distribution of nutrients, chlorophyll-a, and dissolved trace metal (Cu, Ni, Cd, Pb)in the surface layer of the East Sea an oceanic survey focused on Ulleung Basin and Japan Basin was conducted in the summer of 2009. The main water masses that affected the northern waters of East China Seaduring the study period were classified as Changjiang diluted water, (CDW), Tsushima warm current (TWC), Yellow Sea bottom cold water (YSBCW), and Kuroshio source water (KSW). The forces of CDW and TWC that forms on the surface and sub-surface layers had weakened for 20 years and the force of KSW that forms on the intermediate layer showed a distinctively decreasing trend. However, YSBCW showed a trend of expanding its force. Phosphate and silicate exhibited a decreasing tendency and phosphate showed a pattern of being depleted on the surface layer after 2009. It is determined that one of the reasons for this is the concentration of nutrients introduced through CDW and TWC being too low. The concentration of chlorophyll-a exhibited an increasing tendency during the study period, the reasons for which are determined to be the influences of increase in water temperature, supply of nutrients via YSCW, and increases in light transmission from decrease in suspended solid due to the construction of the Three Gorges Dam. The main water masses of the East Sea were classified as Tsushima surface water (TSW), Tsushima middle water (TMW), North Korean cold water (NKCW), and bottom layer of East Sea proper water (ESPW). The strengths of water masses showed an increasing trend in TSW and NKCW, while TMW and ESPW showed a decreasing trend. Due to the influences of TSW, which forms primarily at depth of 6m, and NKCW, which forms at depth of about 125m, the water temperatures at the surface and 100m water layers resulted in increase of 0.56 ℃during 20 years. As such, it is believed that if the strength of TSW and NKCW continue to increase, then the water temperatures near the surface and 100m water layers of the East Sea will continue to increase. Moreover, the water temperature and salinity of ESPW exhibited significant increases, while the concentration of dissolved oxygen was shown be decreasing. The reason for this is determined to be the decrease of inflow of surface water that settles from the surface layer to the bottom layer. The distribution of nutrients, chlorophyll-a, and dissolved trace metals in the East Sea appeared divided by cold versus warm region. In the cold region, the distribution of nutrients, chlorophyll-a, and dissolved trace metals was determined by inflow of bottom layer water at a low depth point due to greater influence from seabed topography than land. In the warm region, the concentrations of Pb and Cd were shown to have been influenced by TWC, while the concentration of Cu was shown to be high due to inflow from the atmosphere to the surface layer. In conclusion, it is determined that nutrients, chlorophyll-a, and dissolved trace metals in the northern waters of East China Sea are influenced by the expansion of YSCW, while salinity is decreased due to decrease in the strength of KSW. Moreover, increase in nitrogen and decrease in phosphorus causes abnormal increase in the N/P ratio to create a species shift from traditional diatiom-centric phytoplankton community to small-sized dinoflagellates. This increase in dinoflagellates can lead to microbial food web and is believed to have the potential to reduce the productivity of fishery. The surface water in the East Sea is experiencing increase in water temperature and decrease in salinity. The water temperature and salinity of ESPW, which makes up 90% of the East Sea, are increasing, while the concentration of dissolved oxygen is decreasing. In other words, this indicates reduction in the inflow of surface water that settles to the bottom layer, which is determined to lead to future weakening or complete end to thermohaline circulation in the East Sea. Moreover, due to decrease in dissolved oxygen that is supplied from the surface layer to the bottom layer, it is believed that the East Sea will undergo changes in its oceanic ecosystem.
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