• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.2
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• pp.259-266
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• 1998

A study on the biological and chemical characteristics in the middle last Sea of Korea was carried out at 31 stations in October $11\~18$, 1995 on board the R/V Tam-Yang. The chlorophyll a concentration, new and regenerated production, and the vertical diffusion of nitrate from the thermocline structure were investigated. From the vertical distribution of chlorophyll a, subsurface maxima were observed near the thermorline at most stations including the frontal zone, except at the southern stations where the maximum chloropyll a concentration occurred at the surface, The nanophytoplankton was the most dominant fraction comprising $83.5\%$ of total phytoplankton cell numbers, but netphytoplankton were common at the southern stations where the dominant species were Rhizosolenia sp. Nitrogenous new production and regenerated productions were measured using the stable isotope $^{15}N$ nitrate and ammonia uptake method. The vertically integrated nitrogen production varied between 8.470 and $72.945\;mg\;N\;m^{-2}\;d^{-1}$. The f-ratio, which is the traction of new production from primary production, waried between 0.03 and 0.72, indicating that $3\%$ to $72\%$ of primary production was supported by the input of nutrients from below the euphotic zone and the rest are supported by ammonia recycled within the euphotic layer. This range of f-ratio encompasses from extremely oligotrophic to eutrophic area characteristics. The differences in productivity and f-ratio among stations were related to frontal structure and the bottom topography. The values were high near the frontal zone and low outside of it, and the station near Ulleng Island showed the highest f-ratio. Vertical diffusion coefficients were calculated from both the water column stability (Kz-1) of King and Devol's equation (1979) and new nitrogen requirement (Kz-2). The values of Kz-2 ($0.11\~0.55\;cm^2/s$) were relatively low compared to the values reported previously.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.76-88
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• 2012

In order to investigate the distribution of water masses and spatio-temporal variation of nutrients in the coastal areas of Gangwon province of the Korean East Sea, a survey of the physico-chemical parameters (temperature and salinity) and nutrients ($NO_2$-N, $NO_3$-N, $NH_4$-N, $PO_4$-P, and $SiO_2$-Si) was carried out at 5 locations (Goseong, Sokcho, Yangyang, Gangneung, and Donghae) in February, May, August, and November 2009. The water masses included in the study area were divided into 4 groups; 1) Tsushima Surface Water (TSW), 2) Tsushima Middle Water (TMW), 3) North Korean Cold Water (NKCW), and 4) East Sea Proper Water (ESPW). The distribution of water masses was affected by the change of season. In February, surface water was derived from the TMW. The TSW was not observed in May, but only observed in August. In November, as the influence of the TSW weakened, that of the NKCW strengthened. Considering the vertical profiles of nutrients, the concentrations in all the seasons were very low within the surface water, but increased rapidly near the thermocline. Most of nutrient concentrations, except for dissolved silicate, remained constant below the depth of 200 m. However, the dissolved silicate concentration increased with depth, suggesting that silicate has a delayed regenerative pattern. The ESPW had the highest nutrient concentration, followed by the NKCW, TMW, and TSW. In February, May, and November, the N/P ratio in most of the water masses was similar to or larger than the Redfield ratio, indicating that nitrogenous nutrients did not act as a limiting factor for phytoplankton growth. However, in August, the N/P ratio in the TSW was less than the Redfield ratio, and the concentration of $NO_2$-N+$NO_3$-N was 0.86 ${\mu}m$, indicating that nitrogenous nutrients did act as a limiting factor for phytoplankton growth in the study area.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.2
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• pp.238-245
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• 1996

Vertical profiles of $^{210}Po\;and\;^{210}Pb$ were measured for the upper 100 m of water column at six stations in the middle region of the Korean East Sea during March 1993. The distribution patterns of these radionuclides with the water mass and controlling factors on their distributions were also discussed. $^{210}Pb$ activities were generally high at surface water and gradually decrease with depth. Vertical profiles of $^{210}Po$ were relatively homogeneous except for at station E3, where chlorophyll-a concentration was the highest and $^{210}Po$ activity in the upper 30 m was lower than below 50 m. The $^{210}Po$ activities relative to its parent $^{210}Pb$ at all stations were deficient at the upper 30 m, but were excess or nearly equilibrated values below 50 m. The magnitude of $^{210}Po$ deficiency was relatively high at station E3 and E6, where strong thermocline occured. However, $^{210}Pb$ activities showed strong excess in the upper 100 m of all stations, compared with its parent $^{226}Ra$. The residence time of $^{210}Po$ ranged from 1.0 to 7.8 years, and was relatively short at station E3 and E6. The data obtained at the upper 50 m water column during $1992\~1994$, also showed that removal rate constant of $^{210}Po$ and inventories of chlorophyll-a was negatively related. This indicates that the primary production plays an important role in controlling the distributions of $^{210}Po$ at the upper water column of the Korean last Sea in spring. While, inventories of excess $^{210}Pb$ was generally decreasing with increasing density difference between 50 m and 100 m, suggesting that $^{210}Pb$ concentrations in the upper water column were controlled by stability of water column.

• Korean Journal of Environmental Biology
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• v.31 no.1
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• pp.19-36
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• 2013

Physiochemical characters of sea waters during summer flood- and winter dry-seasons and their spatial variations were investigated along the coastal area off the eastern South Sea, Korea. Using the hierarchical clustering method, in this study, we present comprehensive analyses of coastal waters masses and their seasonal variations. The results revealed that the coastal water of the study area was classified into six water masses (A to F). During summer season, the surface water was mainly occupied by the coastal pseudo-estuarine water (water mass B) with low salinity and high nutrients and the river-dominated coastal water (water mass C) with low nutrients, respectively. The bottom water was dominated by cold water (water mass D) with very low temperature, high salinity and high nutrients, compared to masses of surface water. Notably, the water mass B, with high concentrations of nutrients (silicate and nitrogen) and low salinity, which is strongly controlled by the water quality of river freshwater, seems to play an important role in controlling the water quality and further regulating physical processes on ecosystem in the eastern coastal area of South Sea. The water mass D (bottom cold water) coupled with a strong thermocline, which exists in near-bottom layer along the western margin of Korea Strait, has a low temperature, pH and DO, but abundant nutrients. This water mass disappears in winter owing to strong vertical mixing, and subsequently may act as a pool for nutrients during winter dry-season. On the other hand, vertically well-mixed water column during the winter season was typically occupied by the Tsushima (water mass E) and the coastal water (water mass F) with a development of coastal front formed in a transition zone between them. These winter water masses were characterized by low nutrient concentration and balance in N/P ratio, compared with summer season with high nutrient concentrations and strong N-limitation. Accordingly, the analysis of water masses will help one to better chemical and biological processes in coastal area. In most of the study area, characteristically, the growth of phytoplankton community is limited by nitrogen, which is clearly different with coastal environment of West Sea of Korea, with a relative lack of phosphorus. It showed the western and the southern coasts in Korea are substantially different from each other in environmental and ecological characteristics.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.4
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• pp.503-526
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• 1996

A synoptic survery of chemical characteristics in the last Sea of Korea was carried out at the 11 stations near Ullungdo in November, 1994 on board R/V Tam-Yang. On the basis of the vortical distribution patterns of temperature, salinity and dissolved oxygen, water masses in the study area are divided into five groups; 1) Tsushima Surface Water (TSW), 2) Tsushima Middle Water (TMW), 3) East Sea Intermediate Water (ESIW), 4) last Sea Proper Water (ESPW), 5) Mixed Water (MW). In the vertical profiles of nutrients, the concentrations were very low in the surface layer and increased rapidly near the thermocline. There was a slight decrease in the ESIW and the concentrations were constant with the depth below 300m except dissolved silicate which still increased with depth. Relatively high value of Si/P ratio (25.2) in ESPW, whick is the oldest water mass, suggests that Si is regenerating more slowly compared to other nutrients. The relatively high value of N/P ratio (18.6) in the surface layer might be related to high vertical eddy diffusivity $(K_z)$ of $1.19\;cm^{2}/sec$ and high nitrate upward flux of $103.7\;{\mu}g-at/m^{2}/hr$, compared to the values reported in other areas. Apparent Oxygen Utilization (AOU) was very low in the surface layer and increased in the TMW, but there was a slight decrease in the ESIW. The highest value of AOU occurred in the ESPW. The slpoe of P/AOU was 0.50. The study on the relationship between water masses and nutrient distribution patterns is important in understanding the regeneration processes of nutrients in the polar region of the last Sea.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.2
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• pp.60-67
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• 2002

To determine whether nitrogen (N) uptake by phytoplankton below the euphotic zone in the Yellow Sea is considerable, we measured the uptake rates of nitrate and ammonium using $^{15}N$-labeled stable isotope $K^{15}NO_{3}$ and $^{15}NH_{4}Cl$, in May and November 1997 at total 10 stations. Depth-integrated uptake rates of nitrate and ammonium over the euphotic zone during this study ranged from 1.8 to 15.3 mg N $m^{-2}$ $d^{-1}$ and from 5.0 to 132.2 mg N $m^{-2}$ $d^{-1}$, respectively, and ammonium uptake predominated at 9 of 10 stations (1.9-19.4 fold). Depth-integrated uptake rates of nitrate and ammonium over the whole water column ranged from 2.9 to 22.0 mg N $m^{-2}$ $d^{-1}$ and from 15.7 to 175.5 mg N $m^{-2}$ $d^{-1}$, respectively. The significant proportion of whole water column N uptake was attributed to uptake by phytoplankton below the euphotic zone, ranging from 13.0 to 86.2% for nitrate and from 13.8 to 67.8% for ammonium, indicating that phytoplankton N uptake below the euphotic zone is at times considerable in the study area. The results suggest that when phytoplankton below the euphotic zone in the Yellow Sea are again entrained into the euphotic zone by a certain physical forcing such as turbulent mixing and the vertical movement of thermocline, these episodic events may significantly affect the material fluxes within the euphotic zone. Furthermore, the results suggest that a portion of regenerated production estimated from $^{15}N$-ammonium uptake should be included in new production estimates, which otherwise could be underestimated in the Yellow Sea.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.1
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• pp.8-18
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• 2003

In order to investigate the oceanic condition of fishing ground in the adjacent sea of Naro Island, the oceanographic observation were carried out by the training vessel of Yosu National University on winter, spring, summer, and autumn in 2000. Main features in the observation are as follows; 1) the ranges of temperature, salinity, and chlorophyll-a were from 4.$3\circ_C$ to 10.$1\circ_C$, from 33.1 psu to 34.9 psu, and from 0.1 $ug$/$\Omega$ to 26.2 $ug$/$\Omega$ in winter, from 8.$1\circ_C$ to 13.$7\circ_C$, from 33.1 psu to 34.3 psu, and from 0.1 $ug$/$\Omega$ to 24.4 $ug$/$\Omega$ in spring, from 14.$5\circ_C$ to 24.$2\circ_C$, from 30.5 psu to 34.1 psu, and from 0.1 $ug$/$\Omega$ to 30.0 $ug$/$\Omega$ in summer, and from 14.$8\circ_C$ to 18.$6\circ_C$, from 30.1 psu to 34.0 psu, and from 0.1 $ug$/$\Omega$ to 19.1 $ug$/$\Omega$ in autumn, respectively, 2) the temperature in the coastal region was higher than that in the open ocean while salinity was lower, and the convection was identified between the surface and the bottom during in winter and autumn, and the thermocline were made between surface and 20m layer with vertical gradients of 4.$0\circ_C$/7m in summer, 3) the chlorophyll-a in the this region was varied in each season, being highly distributed in spring, on bottom and coastal region, and 4) an evidence of sea water intrusion toward Sori Island was observed, and of inner water intrusion from Yeoja Bay was observed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.1
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• pp.19-26
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• 2003

In order to investigate the seasonal variation of watermass in the adjacent sea of Naro Island, oceanographic observation on the fishing grounds were carried out by the training vessel of Yosu National University on winter, spring, summer, and autumn in 2000. The results obtained are summarized as follows ; 1) the watermass in the fishing ground were divided into the coastal water (30.0∼31.4psu), mixing water (31.5∼32.9psu) and the offshore water (33.0∼35.0psu) according to the distribution of salinity from T-S diagram plotted all salinity data observed on winter, spring, summer, and autumn in 2000. 2) the ranges of temperature and salinity were from 4.$3\circ_C$ to 10.1$^{\circ}C$ and from 33.1psu to 34.9psu in winter, from 8.$1\circ_C$ to 13.$7\circ_C$ and from 33.1psu to 34.3psu in spring, from 14.5$^{\circ}C$ to 24.$2\circ_C$ and from 30.5psu to 34.1psu in summer, and from 14.$5\circ_C$ to 18.$6\circ_C$ and from 30.1psu to 34.0psu in autumn, respectively. 3) the distribution of watermass in the fishing ground varied largely each seasons, but a general tendency on the distribution was obtained. That is, in winter and spring the offshore water was distributed most widely and in summer the coastal and mixing water occupied the fishing ground but in autumn the mixing water prevailed. 4) variation of temperature and salinity were appeared between the surface and 20m layer in the sea aduacent to Naro Island. Therefore, in the summer the thermocline were made between surface and 20m layer with vertical gradients of 4.$0\circ_C$/7m.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.143-156
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• 2015

In order to understand the dynamic characteristics of water column environments in the Western Pacific seamount area (approximately $150.2^{\circ}E$, $20^{\circ}N$), we investigated the water mass and the behavior of water column parameters such as dissolved oxygen, inorganic nutrients (N, P), and chlorophyll-a. Physico-chemical properties of water column were obtained by CTD system at the nine stations which were selected along the east-west and south-north direction around the seamount (OSM14-2) in October 2014. From the temperature-salinity diagram, the main water masses were separated into North Pacific Tropical Water and Thermocline Water in the surface layer, North Pacific Intermediate Water in the intermediate layer, and North Pacific Deep Water in the bottom layer, respectively. Oxygen minimum zone (OMZ, mean $O_2$ $73.26{\mu}M$), known as dysoxic condition ($O_2<90{\mu}M$), was distributed in the depth range of 700~1,200 m throughout the study area. Inorganic nutrients typified by nitrite + nitrate and phosphate showed the lowest concentration in the surface mixed layer and then gradually increased downward with representing the maximum concentration in the OMZ, with lower N:P ratio (13.7), indicating that the nitrogen is regarded as limiting factor for primary production. Vertical distribution of water column parameters along the east-west and south-north station line around the seamount showed the effect of bottom water inflowing at around 500 m deep in the western and southern region, and concentrations of water column parameters in the bottom layer (below 2,500 m deep) of the western and southern region were differently distributed comparing to those of the other side regions (eastern and northern). The value of Excess N calculated from Redfield ratio (N:P=16:1) represented the negative value throughout the study area, which indicated the nitrogen sink dominant environments, and relative higher value of Excess N observed in the bottom layer of western and southern region. These observations suggest that the topographic features of a seamount influence the circulation of bottom current and its effects play a significant role in determining the behavior of water column environmental parameters.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.3
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• pp.155-166
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• 2007

We carried out a study on the marine environment, such as water temperature, salinity, density and chlorophyll ${\alpha}$, and the distribution of phytoplankton community, such as species composition, dominant species and standing crops in the Southwestern Sea of Korea during early summer 2005. According to the analysis of a T-S diagram, three characteristics of water masses were identified. We classified them into Korean and Chinese coastal water, the cold water and the oceanic water. The first was characterized by high temperature and low salinity in the surface layer influenced by river run offs from China and Korea, the second by low temperature and salinity in bottom layer originated from the bottom cold water of the Yellow Sea, and the third by high temperature and high salinity influenced by Tsushima warm currents. The internal discontinuous layer among them was formed at the intermediate depth (about $10{\sim}20\;m$ layer). And the thermal front appeared in the central parts between Tsushima warm currents and Korean and Chinese coastal waters in the Southwestern Sea of Korea. Chlorophyll ${\alpha}$ concentration was high values in the Korean coastal waters and sub-surface layers. But It was low concentration in the Tsushima warm currents regions. The $Chl-{\alpha}$ maximum layers appeared in the sub-surface layer below thermocline. The phytoplankton community in the surface and stratified layers was composed of a total of 40 species belonging to 26 genera. Dominant species were 2 diatoms, Paralia sulcata, Skeletonema costatum and a dinoflagellate, Scripsiella trochoidea. Standing crops of phytoplankton in the surface layer were very low with cell density ranging from 5 to $3.8\;{\times}\;10^3\;cells/L$. Diatoms were controlled by the expanded low salinity coastal waters of the low salinity with high concentrations of nutrients. Otherwise phytoflagellates were dominant in the high temperature regions where the Tsushima warm currents approches the Southwestern Sea of Korea in early summer.