• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.1-11
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• 2020

This study investigated the mesozooplankton community and the related environmental factors in the Nakdong River Estuary in May and early October shortly after passage of the typhoon "DUJUAN" in 2015. The mesozooplankton community was dominated by barnacle nauplii, foraminiferans, and Noctiluca scintillans, and the environmental characteristics were characterized by freshwater inflow through the Nakdong River barrage, the intrusion of warm currents, and the effect of typhoon passage in October. In May, cladocerans, such as Evadne nordmanni and Podon polyphemoides, as indicator species of brackish water, prevailed throughout the study area. The surface salinity was lowest on the inner side of the barrier-islands and increased gradually to the outer side during the study. The average concentration of total suspended solids in October was higher than that in May, while the averaged concentration of nitrate and chlorophyll-a in May was higher than those in October. On the other hand, there was no temporal difference in the total averaged abundance of mesozooplankton. In contrast, the distributional pattern of the mesozooplankton community was associated with the salinity gradient in both seasons. These results suggest that the temporal difference of the mesozooplankton community depended on the extent of freshwater inflow by barrage opening, the intrusion intensity of warm currents, and typhoon passage in the Nakdong River estuary in 2015.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.1
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• pp.65-74
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• 2020

The purpose of this study was to investigate the physical characteristics of marine environment, and to predict the probability of the occurrence of hypoxia in the Dangdong bay. We predicted hypoxia using the logistic regression model analysis by observing the water temperature, salinity, and dissolved oxygen concentration. The analysis showed that the Brunt-Väisälä frequency which was shallow than the deep bay entrance, was higher inside the bay due to a lesser amount of fresh water inflow from the inner side of the bay, and density stratification was formed. The Richardson number, and Brunt-Väisälä frequency were very high occasionally from June to September; however, after September 2, the stratification had a tendency to decrease. Analysis of dissolved oxygen, water temperature, and salinity data observed in Dangdong bay showed that the dissolved oxygen concentration in the bottom layer was mostly affected by the temperature difference (dt) between the surface layer and bottom layer. Meanwhile, when the depth difference (dz) was set as a fixed variable, the probability of the occurrence of hypoxia varied with respect to the difference in water temperature. The depth difference (dz) was calculated to be 5 m, 10 m, 15 m, 20 m, and the difference in water temperature (dt) was found to be greater than 70 % at 8℃, 7℃, 5℃, and 3℃. This indicated that the larger the difference in depth in the bay, the smaller is the temperature difference required for the generation of hypoxia. In particular, the place in the bay, where the water depth dif erence was approximately 20 m, was found to generate hypoxia.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.21 no.6
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• pp.331-340
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• 1988

Using the oceanographic data during 196s~ 1983, the seasonal variation of the water type in the Tsushima Current is discussed by analyzing the thermosteric anomaly $(\delta_T)$. By investigating with the index of $33.8\%_{\circ}$ in salinity, it is shown that the low saline water inflowed through the Korea Strait affects the variations of water type in surface layer from summer to fall. On the sea surface, the value of $\delta_T$ is affected mainly by the sea surface temperature (SST). However, in summer, $\delta_T$ is temporarily influenced by the transitional characteristic of the surface salinity. It has the minimum value in winter when the SST is the highest and the sea surface salinity is the lowest. In fall, it decreases as the SST decreases. Specifically, the value of $\delta_T$ is 779 cl/t in August in the region of Korea Strait and 667 cl/t in September in the East Coast of Korea. These values are larger than that of the Kuroshio where is 622 cl/t in August. This phenomenon is due to the inflow of low saline water into these area during summer. In loom depth, the seasonal variation of the $\delta_T$ is not so significant as the surface and is mainly dependent on the annual temperature variation. In general, $\delta_T$ decreases as the Tsushima Current flows to the north.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.3
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• pp.157-170
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• 2002

To examine the structure and distribution of the Keum River plume produced by continuous river discharge we carried out three-dimensional numerical model experiments with or without Coriolis force and tide. When Coriolis force is included but tide is not the model plume forms the clockwise circulation north of southern channel in the developing stage. As the plume expansion progresses the center of circulation moves to the southwest, with fuming the discharging axis of low-salinity water to the southwest from the mouth of southern channel. These results are explained mainly in terms of barotropic geostrophy by surface slope maintained with accumulated low-salinity(buoyant) water in front of the estuary mouth due to of offshore strong salinity front. When the M$_2$ tide is included the model plume extends farther to the northwest, forming large tongue-like salinity distribution. The tidally averaged surface flows of the offshore plume are mainly in geostrophic balance. These changes in plume distribution are explained in terms of low-salinity water advection by tidal excursion and active tidal mixing; the former supplies low salinity water to the north off the estuary mouth and the later increases mean sea level along the plume and surface salinity in northern shallow coastal area. The main features of observed Keum River plume(Lee et al., 1999; Choi et al., 1999), which showed the northwestward deflection of the plume axis and northward deepening of the plume thickness from the estuary mouth region, are well reproduced by the model in which tide is included.

• Journal of Fisheries and Marine Sciences Education
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• v.23 no.3
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• pp.425-432
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• 2011

In order to understand the characteristics of the distribution and the nutrients of the Yellow Sea Bottom Cold Water during summer to fall, temperature, salinity and nutrients have been investigated in the fifteen stations in the Yellow Sea. In september, the Changjiang diluted water with more than $20^{\circ}C$ distributed in the surface and the Yellow Sea Bottom Cold Water distributed in the layer below 30m depth with less than $10^{\circ}C$. Specially, water mass with less than $5^{\circ}C$ in the layer below 50m depth expanded southward down to the north latitude of $35^{\circ}$ with expanding more to the coasts of China than to the coasts of Korea. The salinity of the cold water mass with $8^{\circ}C$ in the deep layer of more than 50m depth was relatively high as 33.5 psu and expanded northward forming fronts of temperature and salinity. The concentration of total inorganic nitrogen was two times higher in the cold water mass than in the surface water, which means that resolution and consumption were low due to cold temperature in the bottom layer. In conclusion, the cold water expanded southward down to the north latitude of $35^{\circ}$ by September and had high concentration of nutrients.

• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.4
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• pp.297-313
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• 2009

Long-term trends and distribution patterns of water quality were investigated in the Gunsan coastal areas of Yellow Sea, Korea from 1972 to 2006. Water samples were collected at 6 stations and physicochemical parameters were analyzed including water temperature, salinity, suspended solids(SS), chemical oxygen demand(COD), dissolved oxygen(DO) and nutrients. Spatial distribution patterns of temperature, DO and SS were not clear among stations but the seasonal variations were distinct except COD and SS. The trend analysis by principal component analysis(PCA) during 24 years revealed the significant variations in water quality in the study area. Spatial water qualities were clearly classified into 3 clusters by PCA; station cluster 1, 2~4, and 5~6. Annual water qualities were clearly classified into 4 surface water clusters and 5 bottom water clusters by PCA. By this multi-variate analysis. The annual trends were summarized as follows; Salinity, pH and DO tended to increase since late 1970's, COD to increase since 1987, and SS to decrease and nutrients to increase in Gunsan coastal waters due to the input of fresh water from land same as in Kyoungin coastal area, Asan coastal area and Choensoo bay.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.2
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• pp.296-301
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• 1998

The physical and chemical characteristics were examined in the southern sea of Korea including the Cheju Strait, and the entrance of the Korea Strait in the period of May 30 to June 8, 1995. The results are as follows. Firstly, the variation ranges of the temperature and salinity at the Cheju Stratit during 24 hours observation were larger in the surface layer than that in the deep layers. Secondly, daily variations of nutrients show that total inorganic nitrogen, phosphate phosphorous, and silicate silicon concentration are higher at night than at day. Thirdly, water temperature and salinity distributions show highest values at the entrance of Korea Strait, which is thought to be influenced directly by Tsushima Warm Current, while they show the lowest values in Cheju Strait. This means that the surface waters in Korea Strait are greatly influenced from the entrance of Korea Strait and bottom waters is greatly influenced from Cheju Strait. Fourthly, nutrients distribution shows highest values in Korea Strait but dissolved oxygen shows lowest values in the area. These seem to be caused by the oxygen consumption used in the inorganization of nutrients to decompose organisms and the liquidation of nutrients.

• Ocean and Polar Research
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• v.23 no.2
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• pp.77-95
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• 2001

Temperature, salinity, nutrients, chlorophyll-a, and primary production were measured within the upper 200 m water column in the area around the South Shetland Islands in January, 2000. Surface temperature was relatively high in the Drake Passage north of the South Shetland Islands and low in the northeastern area of the Antarctic Peninsula. In contrast, surface salinity was low in the Drake Passage and increased toward the Antarctic Peninsula, reaching the maximum value in the northeastern area of the Antarctic Peninsula. Surface nutrients were low in the Drake Passage and high in the area near the South Shetland Islands. Surface chlorophyll-a was also low in the Drake Passage and near the Antarctic Peninsula and high in the area of the northern King George Island. The study area could be classified as four geographical zones based on the characteristic shape of the T/S diagrams;the Drake Passage, the Bransfield Strait, the mixed zone, and the Weddell Sea. Each geographical zone showed apparently different physical, chemical, and biological characteristics. Phytoplankton biomass was relatively low in the Drake Passage and the Weddell Sea and high in the Bransfield Strait and the mixed zone. The low phytoplankton biomass in the Weddell Sea could be explained by the low water temperature and deep surface mixing down to 200 m. The high grazing pressure and low availability of iron could be responsible for the low phytoplankton biomass in the Drake Passage.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.1
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• pp.59-65
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• 2007

Rapid variation of coastal ecosystem in the East Sea of Korea, such as fishery resource variation and subtropical chang of bentic flora, accordong to the global warming are actually noticed. In this study we try to identify the characterics of water mass existing in this coastal area and to consider the variation of their physical and chemical properties using data of temperature, salinity and dissolved oxygen obtained by National Fisheries Research & Development Institute from 1960 to 2005. The temperature of all water mass rise during last 45 years; the rise of North Korea Cold Water temperature (about $2.33^{\circ}C$) is 1.5 times higher than that of Tsushima warm water (about $1.6^{\circ}C$), and the temperature rise of Tsushima Surface Water, directly affected by climate chang is $2.57^{\circ}C$, higher than the atmospheric temperature rise during same period, indicating that subtropical change makes progress more rapidly in the coastal marine ecosystem than in the land ecosystem. Otherwise, the salinity in the surface water decrease $0.29\%_{\circ}$ during last 45 years due to the rising trend of rainfall with atmospheric temperature. The dissolved oxygen concentration in the all water mass make a decreasing trend. Specially for the North Korea Cold Water, the dissolved oxygen concentration diminish 0.021 mg/l per year and the decrease in the East Sea Proper Water indicate a change of inner water circulation system.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.3
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• pp.117-123
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• 2006

The water quality before and after a typhoon was investigated as a part of a study on the increase of organic matter and on the fundamental measures to counter chemical oxygen demand (COD) in the eutrophic Soho coastal seawaters of Gamak Bay. The dissolved oxygen (DO) saturations were <54% when water column was stratified. The DO saturation was similar at surface and in the bottom layer after a typhoon $(78\sim88%)$, and a very high DO saturation (234%) was observed in the surface water after mass phytoplankton growth. The highest values of $NH_4-N,\;NO_3-N,\;PO_4-P$, and $SiO_2-Si$ were 18.22, 38.90, 1.58, and $52.10{\mu}M$, respectively, when freshwater entered after heavy rainfall events. In addition, high concentrations of $NH_4-N,\;PO_4-P$, and $SiO_2-Si$ were detected with low DO saturations in bottom water (>5m). A maximum chlorophyll (Chl.) concentration of $311.0{\mu}gl^{-1}$ was observed after typhoon, when a high-density Scrippsiella trochoidea red tide occurred with cell density of 42,000 cells $ml^{-1}$. The algal growth potential (AGP) was high after the typhoon. Nitrogen was always a limiting nutrient for phytoplankton growth. The highest COD level was $10.55mgl^{-1}$, and the main reason of the variation in COD was likely to be phytoplankton growth $(r^2=0.612,\;p=0.000)$. Organic matter, which entered the water column when the typhoon stirred the sediments, seems to have little effects on COD increase.