• Ocean and Polar Research
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• v.33 no.1
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• pp.21-34
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• 2011

We determined potential meso-scale benthic-pelagic ecosystem coupling in the north equatorial Pacific by comparing surface chl-a concentration with sediment bacterial abundance and adenosine triphosphate (ATP) concentration (indication of active biomass). Water and sediment samples were latitudinally collected between 5 and $11^{\circ}N$ along $131.5^{\circ}W$. Physical water properties of this area are characterized with three major currents: North Equatorial Current (NEC), North Equatorial Count Current (NECC), and South Equatorial Current (SEC). The divergence and convergence of the surface water occur at the boundaries where these currents anti-flow. This low latitude area ($5{\sim}7^{\circ}N$) appears to show high pelagic productivity (mean phytoplankton biomass=$1266.0\;mgC\;m^{-2}$) due to the supplement of high nutrients from nutrient-enriched deep-water via vertical mixing. But the high latitude area ($9{\sim}11^{\circ}N$) with the strong stratification exhibits low surface productivity (mean phytoplankton biomass=$603.1\;mgC\;m^{-2}$). Bacterial cell number (BCN) and ATP appeared to be the highest at the superficial layer and reduced with depth of sediment. Latitudinally, sediment BCN from low latitude ($5{\sim}7^{\circ}N$) was $9.8{\times}10^8\;cells\;cm^{-2}$, which appeared to be 3-times higher than that from high latitude ($9{\sim}11^{\circ}N$; $2.9{\times}10^8\;cells\;cm^{-2}$). Furthermore, sedimentary ATP at the low latitude ($56.2\;ng\;cm^{-2}$) appeared to be much higher than that of the high latitude ($3.3\;ng\;cm^{-2}$). According to regression analysis of these data, more than 85% of the spatial variation of benthic microbial biomass was significantly explained by the phytoplankton biomass in surface water. Therefore, the results of this study suggest that benthic productivity in this area is strongly coupled with pelagic productivity.

• Journal of the Korea Society of Computer and Information
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• v.27 no.3
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• pp.1-12
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• 2022

In the event of a maritime distress accident, rapid search and rescue operations using rescue assets are very important to ensure the safety and life of drowning person's at sea. In this paper, we analyzed the surface layer current in the northwest sea area of Ulleungdo by applying machine learning such as multiple linear regression, decision tree, support vector machine, vector autoregression, and LSTM to the meteorological information collected from the maritime observation buoy. And we predicted the drowning person's route at sea based on the predicted current direction and speed information by constructing each prediction model. Comparing the various machine learning models applied in this paper through the performance evaluation measures of MAE and RMSE, the LSTM model is the best. In addition, LSTM model showed superior performance compared to the other models in the view of the difference distance between the actual and predicted movement point of drowning person.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.5
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• pp.393-400
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• 2011

The mass transport is very complicated at the area which has the macro tide and complex geometry such as Gyeonggi bay. Especially, the long period current has a strong influence on the estuarine ecosystem and the long-term distribution of substances. The long period current is caused by several external forcing, whose unique characteristic varies spatially and temporally. The variation characteristics of long period current is analysed and its generation mechanism is studied. The tidal nonlinear constituents such as overtide and compound tide are generated due to nonlinear interaction and it causes mean sea level setup. The tidal wave propagating up into estuary is transformed rapidly by decrease of cross-sectional area and depth. Therefore the mean sea level is getting rise toward upriver. The high and low tide level is similar between down-river(Incheon) and up-river(Ganghwa) during neap tide when the tidal deformation is decreased. The tidal phase difference between two tidal stations causes a periodic fluctuation of sea level difference. The low water level of Ganghwa station during spring tide does not descend under EL(-)2.5 m, but the low water level of Incheon fall down under EL(-)4.0 m. The variation of tidal range and its sea level are increased during spring tide. It is found that the long period current $M_{sf}$ is quite similar to that of sea level difference between the two tidal stations. It means that the sea surface inclination caused by the spatial difference of tidal deformation is important forcing for the generation of long period current.

• Journal of the Korean institute of surface engineering
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• v.49 no.5
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• pp.423-430
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• 2016

In this study, we investigated the corrosion damage characteristics of steel for offshore wind turbine tower substructure using an accelerated electrochemical test. The galvanostatic corrosion test method was employed with a conventional 3 electrode cell in natural sea water, and the steel specimen was served as a working electrode to induce corrosion in an accelerated manner. Surface and cross-sectional image of the damaged area were obtained by optical microscope and scanning electron microscope. The weight of the specimens was measured to determine the gravimetric change before and after corrosion test. The result revealed that the steel tended to suffer uniform corrosion rather than localized corrosion due to active dissolution reaction under the constant current regime. With increasing galvanostatic current density, the damage depth and surface roughness of surface was increased, showing approximately 25 times difference in damage depth between the lowest current density ($1mA/cm^2$) and the highest current density ($200mA/cm^2$). The gravimetric observation showed that the weight loss was proportionally increased with increment of current density that has 75 times different according by experimental conditions. Consequently, uniform corrosion of the steel specimen was conveniently induced by the electrochemically accelerated corrosion technique, and it was possible to control the extent of the corrosion damage by varying the current density.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.21 no.1
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• pp.1-10
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• 1988

The vertical temperature profiles of the Yellow Sea in summer are investigated by means of the nine air temperature (AT) patterns which are classified with the AT of winter and summer. The sea surface temperature (SST) is high when the AT of summer is high, and vice versa. The gradient of thermocline in the offshore region is higher than that in the coastal region and is not always favorable with the AT patterns. The relation between sea bottom temperature (SBT) and the AT of winter is favorable when the SBT is averaged in the coastal and offshore stations. In addition, the SST of coastal stations is higher than that of offshore stations because of the strong mixing by the tidal current in the coastal region. The correlation between the AT and the SST of August is favorable (r=0.44-0.69), while the correlation between the AT of February and the SBT of August is not favorable except the stations, A2 (r=0.57) and B2 (r=0.61).

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2000.05a
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• pp.181-182
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• 2000

Due to the instability of the EKWC, the oceanic conditions in the East Sea are affected by the fluctuations of the moving paths of the TWC, polar fronts, and warm eddies. In particular, warm eddies play an important role in spreading the surface water of the East Sea from its southern coastal region to its interior region (Isoda, 1994). However, the fluctuation characteristics of the meandering TWC and the warm eddies in the East Sea are not yet known due to the instability of the TWC. Hideaki(1999) showed that the moving paths and features of the TWC in the coastal regions of Japan were not constant. (omitted)

• 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.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.10a
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• pp.123-123
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• 2011

• Journal of Environmental Science International
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• v.14 no.11
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• pp.1063-1069
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• 2005

In order to investigate the distribution of suspended particulate matter of the surface water in the South Sea of Korea in early winter, the cruise results during 2 to 8 December 2004 were analyzed in relation to the hydrography. The front was formed along the line connecting between Tsushima and Cheju Islands, which divided the water into two water masses; the coastal water with for temperature and for salinity, and the Tsushima Warm Current Water with high temperature and high salinity. In the coastal water the suspended particulte matter was 5.0-6.5 mg/l, while in the oceanic water suspended particulate matter was 4.5-5.0 mg/l. The coastal water showed higher mixing effects, compared to the oceanic area where vertical stratification was clearly formed. These indicate that the distribution of suspended particulate matter was affected by the stratification or mixing of the water column. Also it is suggested that the mixing effects of sea surface cooling and rind play an important role on the distribution of suspended particulate matter in the South Sea of Korea in winter time.

• Ocean and Polar Research
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• v.31 no.1
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• pp.11-29
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• 2009

Variability of sea surface temperature (SST) in the Japan/East Sea (JES) was studied using complex empirical orthogonal function (CEOF) analysis. Two daily data sets were analyzed: (1) New Generation 0.05o-gridded SST from Tohoku University, Japan (July 2002-July 2006), and (2) 0.25o-gridded SST from the Japan Meteorological Agency (October 1993-November 2006). Linkages with wind stress curl were revealed using 6-h 1o-gridded surface zonal and meridional winds from ancillary data of the Sea- WiFS Project, a special National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) product (1998-2005). SST anomalies (SSTA) were obtained by removing the seasonal signal, estimated as the leading mode of the CEOF decomposition of the original SST. Leading CEOF modes of residual SSTA obtained from both data sets were consistent with each other and were characterized by annual, semiannual, and quasi-biennial time scales estimated with 95% statistical significance. The Semiannual Mode lagged 2 months behind the increased occurrence of the anticyclonic (AC) wind stress curl over the JES. Links to dynamic processes were investigated by numerical simulations using an oceanic model. The suggested dynamic forcings of SSTA are the inflow of subtropical water into the JES through the Korea Strait, divergence in the surface layer induced by Ekman suction, meridional shifts of the Subarctic Front in the western JES, AC eddy formation, and wind-driven strengthening/weakening of large-scale currents. Events of west-east SSTA movement were identified in July-September. The SSTA moved from the northeastern JES towards the continental coast along the path of the westward branch of the Tsushima Current at a speed consistent with the advective scale.