• Proceedings of the KSRS Conference
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• v.1
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• pp.174-179
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• 2006

Information on the distribution characteristics of tuna resources in Kiribati EEZ waters in three zones (Zone 1: west Gilbert region, Zone 2: central Phoenix region, and Zone 3: east Line region) as well as their relationship with the ocean environment is critical for sustainable managing the migratory tuna resource and fishing practices in this region. Therefore, this study is designed to investigate the spatial and temporal distribution and concentration of bigeye (BET) and yellowfin tuna (YFT) in Kiribati EEZ waters in relation to sea surface temperature (SST) and thermocline depth so as to better understand the tuna resources management basis in Kiribati waters. The geographic and temporal distribution and concentration were first displayed. Paired t-test was utilized to compare the distribution between the two tuna species based on Catch per Unit Effort (CPUE) derived from the Korean longliners during 1996 to 2004, and also among the three zones of Kiribati EEZ waters. Environmental conditions of the three zones were then compared and correlated with the CPUE of YFT and BET. In addition, the effect of ENSO phenomena on the environmental conditions and the distribution of YFT and BET within the three zones were also examined. The BET was relatively higher in the Zone 3 whereas YFT predominate in the Zone 1 and the Zone 2 due to oceanographic differences among the three zones and the ecological habitats of the two tuna species. It was suggested that El Ni?o/Southern Oscillation (ENSO) phenomena altered the oceanographic conditions of the three zones that in turn change the distribution of the two tuna species. During El Ni?o, the warm phase of ENSO, resulted in having more BET in all the three zones and the opposite observed during La Ni?a (cold phase) replacing by having relatively higher catch rate for YFT, particularly in the Zone 2. Although the results of the study are from short periods (1996 to 2004) in considering oceanographic anomality, these environmental variations should be considered into sustainable fisheries management of tuna fisheries in Kiribati EEZ waters.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.1
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• pp.45-52
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• 1998

The transport of suspended matter was interpreted in the coastal zone off Taean Peninsula during the summer (June) in 1996. Coastal waters were homogenous in water temperature and salinity, whereas offshore waters were characterzed by the strong thermocline. Mixing between coastal and offshore waters are negligeable, largely lessened, due to the existence of strong tidal front between the two water masses. In the offshore area, less saline coastal waters from the Kyunggi Bay are considered to be transported southward along the mid-depth layer of thermocline. Concentration of suspended matters was higher than 5 mg/l in the northern coastal area near the Kyunggi Bay, but generally less than 2 mg/l in the offshore area. Less saline waters along the mid-depth layer in the offshore area sustain maximum turbidities throughout the water column. Therefore suspended matters supplied from the coastal area of Kyunggi Bay are considered to be transported southward by the advective movement of less saline coastal waters. Mean particle size of the suspended matters shows 2~9 ${\mu}m$. Coarse grains (mean size larger than 7 ${\mu}m$) are predominant in the less saline coastal waters extending to the offshore mid-depth waters. Such size distributions of suspended matters together with the characteristics of water masses are considered to be an indicator for the southward movement of suspended matters derived from Kyunggi Bay.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.379-387
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• 2012

In order to see the oceanographic conditions, the observations of aquaculture farm of ascidian in Youngdeuk, the east coast of Korea were conducted through 6 times-23 February, 6 April, 8 June, 19 August, 6 October and 20 December-in 2010. Surveys were conducted in 20 stations bimonthly using SBE 19 CTD instrument. The mixed layer depth (MLD) was deep in winter and shallow in summer. The cold water below $5^{\circ}C$ in temperature was occupied below thermocline through all season. The temperature was high in the southeastern area. The salinity was increased from the coast to the open sea. The halocline was distinct at 20 m depth in August and at 40 m depth in October. The lowest value of salinity was appeared at the depth of 10 m in October. In addition the value of precipitation minus evaporation denoted negative in October. These low saline water seemed to inflow to the coast from the open sea. Therefore the low saline water moved to the east coast of Korea. The EKWC may play an important role to convey the low saline water. It may affect the aquaculture farm along the coast as the mass mortality of ascidian. It needs to clarify the role and pathway of EKWC to transfer the low saline water along the east coast of Korea.

• 한국해양학회지
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• v.15 no.1
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• pp.17-33
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• 1980

The materials were obtained in the eastern Gulf of Alaska and the south- eastern Bering Sea during the cruise of the research vessel, Ohdae San, from July to October 1978. A total of 76 samples were taken by NORPAC net from a depth of 200 meters or less in coastal areas. 1. The surface water temperature in the coastal waters, varing from 9 to 10$^{\circ}C$, was lower than that in offshore waters which varied from 10 to 12.9$^{\circ}C$ in the eastern Gulf of Alaska. Thermocline was formed in the 30∼50 meter layer. Salinity of the coastal waters of Kenai Peninsula and Kodiak was 30 which was slightly lower than that of offshore. 2. The water temperature of the surface layer down to 30 meters varied from 7 to 10$^{\circ}C$ and from 1 to 9$^{\circ}C$ in the layer below 30 meters in the south-eastern Bering Sea. Meandering thermal front spread from the Alaska Peninsula to St. Matthew Island by way of St. Paul, and a thermocline was found at the 30∼50 meter layer Salinity ranged from 31.0 to 33.0 and that of northern and coastal waters was little lower than that of offshore. 3. Zooplankton biomass fluctuated from 0.1 to 23.6cc/10㎥ in the eastern Gulf of Alaska and 2.0 to 26.1cc/10㎥ in the south-eastern Bering Sea. Plankton was rich in the following areas, the inshore Kodiak waters, the northern Bering Sea, the Coastal waters and waters adjacent to Alutian islands however, poor in the central Bering Sea. In general, the south-eastern Bering Sea has a higher concentration of plankton volume than the eastern Gulf of Alaska. 4. Twenty three species representing 17 genera of copepods were identified from the samples. These were mostly composed of the cold water species, such as Pseudocalanus minutus, Acartia longiremis, Metridia lucens and Eucalanus bungii var. bungii. 5. The cold oceanic species were composed of Calanus cristatus, C.plumchrus, Metridia lucens, Eucalanus bungii var. bungii and Scolecithricella minor. The cold neritic species were Centropages abdominalis, Pseudocalanus minutus, Acartia longiremis, Eurytemora herdmanii, Pontella pulvinata, P. longipedata and Tortanus discaudatus. On the other hand, the warm oceanic species were Calanus tenuicornis and Oithona plumifera. The cosmopolitan species were Calanus finmarchicus and Oithona similis. 6. It was suggested that the cold oceanic species, Eucalanus bungii var. bungii and Metridia lucens in the south-eastern Bering Sea can be recommended as a valuable indicator species for finding the fishing grounds of demersal fish such as pollock and yellowfin sole in this area.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.1
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• pp.20-25
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• 1990

During the summer of 1989, the authors carried out the hydroacoustic surverys to investigate the vertical distribution of volume backscattering strength in the East China Sea and simultaneously the biological sampling of the scattering layers by bottom trawling. The echoes from the scattering layers was continuously measured by using a 50 kHz echo sounder during the day and night. A data acquisition system was used to record digitally the envelope of the echoes and the echo integration technique was used to determine the scattering strength proportional to biomass density in each layer. The vertical profiles of volume backscattering strength also were compared with the one of water temperature. The results obtained can be summarized as follows: 1. The vertical profiles of mean volume backscattering strength at day and night suggested that during the night the biggest fish concentrations appeared in the mixed layer above the thermocline and during the day near the bottom. In another profiles where the thermocline was not well developed, peaks in scattering appeared at midwater depths and near the bottom. 2. The maximum values of mean volume backscattering strengths varied from -49.3 dB to -48.0 dB on different regions and at different times of the day and night. 3. Trawl data indicated that the organisms consisting of the scattering layer near the bottom were squid and various species of demersal fishes.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.8 no.6
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• pp.1-12
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• 2005

Treatment level and pond reactions of a pond system were examined from May to October 2002. The system was constructed in July 2000 for purifying water of Sinyang stream that flows into Koheung Estuarine Lake located in the southern part of the Korean Peninsula. The system was composed of a primary and a secondary pond in series and established on the rice field near the lake. Water pumped from the stream was funneled into the primary pond, whose effluent was discharged into the secondary pond by gravity flow. Effluent from the secondary pond was funneled into wetlands. About 130 $m^3$/day of water was pumped into the primary pond and detention time of the primary and secondary pond was about 2 days. DO from the surface to the 1.0 m depth of the primary and secondary pond was in the rage of 5.2 to 11.0 mg/L and 4.3 to 0.7 mg/L, respectively. DO at the bottom layer of the primary pond was 0 mg/L and that of the secondary pond ranged 3.0~4.7 mg/L. The primary pond functioned as a facultative pond and the secondary as an aerobic one. The temperature difference between the surface and bottom layers of the ponds in August was about $2.5^{\circ}C$ and that in May and October was about $1.0^{\circ}C$. Thermocline was observed in the primary pond during the high ambient temperature of August. The sludge depth of the primary pond in May, August, and October was 2.4, 1.9, and 2.2 cm, respectively. That of the secondary pond was 1.2, 1.0, and 1.1 cm, respectively. SS, $BOD_5$, T-N, and T-P concentrations in influent averaged 16.64, 6.71, 6.21, and 0.23 mg/L and those in effluent from the primary pond averaged 11.48, 4.97, 4.81, and 0.17 mg/L, respectively. The removal rates of the primary pond for SS, $BOD_5$, T-N and T-P were 31%, 26%, 22%, and 24%, respectively. Average concentrations of SS, $BOD_5$, T-N, and T-P in effluent from the secondary pond were 9.81, 4.07, 4.03, and 0.14 mg/L, respectively and the abatement rates of the secondary pond for SS, $BOD_5$, T-N and T-P were 20%, 12%, 13%, and 15%, respectively. SS, $BOD_5$, T-N and T-P concentrations in effluent from the primary pond were significantly low(p=0.001) when compared with those from the secondary one.

• Korean Journal of Ichthyology
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• v.32 no.3
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• pp.148-159
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• 2020

This study investigated the seasonal and inter-annual changes in vertical distribution and size spectrum of walleye pollock, Gadus chalcogrammus inhabiting middle eastern coast of Korea (hear after pollock). Pollock was distributed between 50 m and 600 m depth range, and body size (total length) ranged from 16.6 cm to 81.5 cm. The trends of population body size were increased in autumn and winter and decreased in spring and summer. Vertical distribution of pollock showned depth-dependent patterns with distributing smaller individuals mainly in the upper layer (shallower depth), while larger fish in deeper habitats. Those patterns in vertical distribution of pollock population is probably due to be the results of energy-saving strategy, metabolic effects, and changes in prey selections according to pollock growth, derived from spatial and temporal changes in oceanic condition in habitat grounds. When water temperature in upper layer were increased and that of below thermocline depth became decreased in 2017, the ratio of smaller (<35 cm) and larger (≥35 cm) individuals was biased toward larger fishes, extending their distribution into shallow depth, and consequently main fishing ground was formed in far from coastal area. In addition, the ratio of smaller individual distributing between 100~300 m was increased with decreasing temperature gradient between below thermocline and bottom layer. Changes in spatial and temporal distributions of pollock population likely be related with vertical and horizontal changes in oceanic conditions and, consequently food supplies.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.1
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• pp.24-37
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• 2001

Physical and chemical properties of the northest Equatorial Pacific between 5° and 12° N along 131.5 °W wore investigated in association with changes in water column structures during the summer seasons of 1998 and 1999. Climatic disturbances such as El Nino and La Nina, should have affected this area during the study Period. In 1998, a thermocline where temperature rapidly decrease with depth, was formed at 90～110 m water depth. Nutrient depicting areas, specially for nitrate+nitrite and phosphate, or oligotrophic regions were extended down to approximately 100 m depth, which coincided with the surface mixed layer depth. However, in 1999, a very fluctuating thermocline was observed with latitudes. As a result of changes in the water column structures, nutrient concentrations also showed fluctuation parallel to the changes in other physical parameters. In the photic zone, depth integrated nitrogen and phosphorus values were 34 gN/m², 7 gP/m² in 1998 and 130 gN/m², 18 gP/m² in 1999, respectively. The results indicated that nitrogen (96 gN/m²) and phosphorus (11 gP/m²) are supported by up-welling and down-welling phenomena with convergence and divergence in the study area.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.708-720
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• 2021

As hypoxia adversely affects the marine environment in northwestern Gamak Bay every summer, the present study determined its comprehensive occurrence mechanisms using the Multiple Regression Analysis (MRA) and suggested management directions based on the primary MRA factors. The first hypoxia occurred by thermocline related to weather conditions, with organic matter deposited inside the bay on 26^th June, 2017. Additionally, on 12^th July, halocline was also developed by increased rainfall, and the hypoxia was most expanded horizontally and vertically. The primary factors were the stratification and deposited organic matter. In contrast, the hypoxia correlated to phytoplankton growth and deposited organic matter on 8^th August was diminished with remarkably less precipitation. However, the stable halocline was caused by massive precipitation, and the reproduced phytoplankton re-generated the expanded hypoxia on 16^th August despite a short sampling interval. Subsequently, the hypoxia influenced by the deposited organic matter spread shallowly along the seafloor on 13^th September as the extinction period. These results suggest that stratification alleviation technologies, and the improvement and removal of the organic matter deposited on the surface sediment are necessary.

• The Journal of the Acoustical Society of Korea
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• v.18 no.3E
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• pp.9-20
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• 1999

To investigate the characteristics of internal waves (IWs) and their effects on acoustic wave propagation, a series of sea experiment were performed in the east coast of Donghae city, Korea in 1997 and 1998 where the water depth varies between 130 and 140 m. Thermistor strings were deployed to measure water temperatures simultaneously at 9 depths. CW source signals with the frequencies of 250,670 and 1000 Hz were received by an array of 15 hydrophones. Through the Wavelet transform analysis, the IWs are characterized as having typical periods of 2-17 min and duration of 1-2 hours. The IWs exist in a group of periods rather than in one period. Underwater acoustic signals also show obvious energy peaks in the periods of less than 12 min. Consistency in the periods of the two physical processes implies that acoustic waves react to the IWs through some mechanisms like mode interference and travel time fluctuation. Based on the thermistor string data, mode arriving structures are analyzed. As thermocline depth varies with time, it may cause travel time difference as much as 4-10 ms between mode 1 and 2 over 10 km range. This travel time difference causes interference among modes and thus fluctuation from range-independent stratified ocean structure. In real situations, however, there exist additional spatial variation of IWs. Model simulations with all modes and simple IWs show clear responses of acoustic signals to the IWs, i.e., fluctuations of amplitude and phase.