• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.1
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• pp.56-62
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• 2009

Stable carbon isotope analysis was used to investigate the autotrophic carbon sources supporting fisheries in three coastal bay systems of the southern coast of Korea. Carbon isotope ratios (${\delta}^{13}C$) of 31 fish species were analysed and compared with those of a range of potential primary food sources [e.g., seagrass (Zostera marina), seagrass epiphytes, benthic microalgae, macroalgae, marine particulate organic matter (marine POM), marsh plant (Phragmites australis) and terrestrial POM]. ${\delta}^{13}C$ values (range, -16.2${\sim}$-8.3‰) of fishes from the coastal embayment systems were overlapped with those of seagrass (-8.3${\pm}$1.9‰), seagrass epiphytes (-12.4${\pm}$0.6‰), benthic microalgae (-15.4${\pm}$1.6‰) and macroalgae (-16.0${\pm}$1.8‰). In addition, fishes (-12.9${\pm}$1.5‰) from the study area had distinctly higher ${\delta}^{13}C$ values compared to those collected in offshore sites (-17.3${\pm}$0.8‰) of the southern sea of Korea and Nakdong River (-23.2${\pm}$1.6‰). This result indicates that carbon supporting fish communities of these coastal bay systems is mainly derived from the local benthic producers.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.29 no.2
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• pp.101-115
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• 2024

The ocean heatwave is emerging as a major issue due to global warming, posing a direct threat to marine ecosystems and humanity through decreased food resources and reduced carbon absorption capacity of the oceans. Consequently, the prediction of ocean heatwaves in the vicinity of the Korean Peninsula is becoming increasingly important for marine environmental monitoring and management. In this study, an LSTM model was developed to improve the underestimated prediction of ocean heatwaves caused by the coarse vertical grid system of the Korean Peninsula Ocean Prediction System. Based on the results of ocean heatwave predictions for the Korean Peninsula conducted in 2023, as well as those generated by the LSTM model, the performance of heatwave predictions in the East Sea, Yellow Sea, and South Sea areas surrounding the Korean Peninsula was evaluated. The LSTM model developed in this study significantly improved the prediction performance of sea surface temperatures during periods of temperature increase in all three regions. However, its effectiveness in improving prediction performance during periods of temperature decrease or before temperature rise initiation was limited. This demonstrates the potential of the LSTM model to address the underestimated prediction of ocean heatwaves caused by the coarse vertical grid system during periods of enhanced stratification. It is anticipated that the utility of data-driven artificial intelligence models will expand in the future to improve the prediction performance of dynamical models or even replace them.

• Geophysics and Geophysical Exploration
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• v.27 no.2
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• pp.91-107
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• 2024

Single-channel seismic exploration has proven effective in delineating subsurface geological structures using small-scale survey systems. The seismic data acquired through zero- or near-offset methods directly capture subsurface features along the vertical axis, facilitating the construction of corresponding seismic sections. However, substantial noise in single-channel seismic data hampers precise interpretation because of the low signal-to-noise ratio. This study introduces a novel approach that integrate noise reduction and signal enhancement via matrix rank optimization to address this issue. Unlike conventional rank-reduction methods, which retain selected singular values to mitigate random noise, our method optimizes the entire singular value spectrum, thus effectively tackling both random and erratic noises commonly found in environments with low signal-to-noise ratio. Additionally, to enhance the horizontal continuity of seismic events and mitigate signal loss during noise reduction, we introduced an adaptive weighting factor computed from the eigenimage of the seismic section. To access the robustness of the proposed method, we conducted numerical experiments using single-channel Sparker seismic data from the Chukchi Plateau in the Arctic Ocean. The results demonstrated that the seismic sections had significantly improved signal-to-noise ratios and minimal signal loss. These advancements hold promise for enhancing single-channel and high-resolution seismic surveys and aiding in the identification of marine development and submarine geological hazards in domestic coastal areas.

• Korean Chemical Engineering Research
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• v.54 no.1
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• pp.140-144
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• 2016

In this study, the physical factors for amylase production by Arthrobacter sp. were optimized using response surface methodology(RSM). Antarctic microorganism Arthrobacter sp. PAMC 27388 was obtained from the Polar and Alpine Microbial Collection(PAMC) at the Korea Polar Research Institute. This microorganism was confirmed for the excretion of amylase with Lugol's solution. The amylase activity was after flask culture was as low as 1.66 mU/L before optimization. The physical factors including the inoculum volume, the initial culture pH, and the medium volume were chosen to be optimized for the enhanced amylase production. The calculated results using RSM indicate that the optimal physical factors were 2.49 mL inoculum volume, 6.85 pH and 42.87 mL medium volume with a predicted amylase production of 2.84 mU/L. The experimentally obtained amylase activity was 2.50 mU/L, which was a 150% increase compared to the level before optimization.

• Journal of the Korean earth science society
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• v.42 no.3
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• pp.247-263
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• 2021

Climate change has been accelerating in coastal waters recently; therefore, the importance of coastal environmental monitoring is also increasing. Chlorophyll-a concentration, an important marine variable, in the surface layer of the global ocean has been retrieved for decades through various ocean color satellites and utilized in various research fields. However, the commonly used chlorophyll-a concentration algorithm is only suitable for application in clear water and cannot be applied to turbid waters because significant errors are caused by differences in their distinct components and optical properties. In addition, designing a standard algorithm for coastal waters is difficult because of differences in various optical characteristics depending on the coastal area. To overcome this problem, various algorithms have been developed and used considering the components and the variations in the optical properties of coastal waters with high turbidity. Chlorophyll-a concentration retrieval algorithms can be categorized into empirical algorithms, semi-analytic algorithms, and machine learning algorithms. These algorithms mainly use the blue-green band ratio based on the reflective spectrum of sea water as the basic form. In constrast, algorithms developed for turbid water utilizes the green-red band ratio, the red-near-infrared band ratio, and the inherent optical properties to compensate for the effect of dissolved organisms and suspended sediments in coastal area. Reliable retrieval of satellite chlorophyll-a concentration from turbid waters is essential for monitoring the coastal environment and understanding changes in the marine ecosystem. Therefore, this study summarizes the pre-existing algorithms that have been utilized for monitoring turbid Case 2 water and presents the problems associated with the mornitoring and study of seas around the Korean Peninsula. We also summarize the prospective for future ocean color satellites, which can yield more accurate and diverse results regarding the ecological environment with the development of multi-spectral and hyperspectral sensors.

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.1177-1186
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• 2021

As the Arctic melt ponds play an important role in determining the interannual variation of the sea ice extent and changes in the Arctic environment, it is crucial to monitor the Arctic melt ponds with high accuracy. Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2), which is the NASA's latest altimeter satellite based on the green laser (532 nm), observes the global surface elevation. When compared to the CryoSat-2 altimetry satellite whose along-track resolution is 250 m, ICESat-2 is highly expected to provide much more detailed information about Arctic melt ponds thanks to its high along-track resolution of 70 cm. The basic products of ICESat-2 are the surface height and the number of reflected photons. To aggregate the neighboring information of a specific ICESat-2 photon, the segments of photons with 10 m length were used. The standard deviation of the height and the total number of photons were calculated for each segment. As the melt ponds have the smoother surface than the sea ice, the lower variation of the height over melt ponds can make the melt ponds distinguished from the sea ice. When the melt ponds were extracted, the number of photons per segment was used to classify the melt ponds covered with open-water and specular ice. As photons are much more absorbed in the water-covered melt pondsthan the melt ponds with the specular ice, the number of photons persegment can distinguish the water- and ice-covered ponds. As a result, the suggested melt pond detection method was able to classify the sea ice, water-covered melt ponds, and ice-covered melt ponds. A qualitative analysis was conducted using the Sentinel-2 optical imagery. The suggested method successfully classified the water- and ice-covered ponds which were difficult to distinguish with Sentinel-2 optical images. Lastly, the pros and cons of the melt pond detection using satellite altimetry and optical images were discussed.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.1
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• pp.73-94
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• 2023

We carried out the sensitive high resolution ion microprobe (SHRIMP) zircon U-Pb age dating and whole-rock geochemical analysis of granitoids and felsic porphyries in the Ssangyong Valley, Yongchu Valley, and Mungyeong Saejae geosites in the Mungyeong Geopark. The igneous rocks crop out in the western, northwestern and central parts of the Mungyeong city area, respectively, and intruded (meta)sedimentary successions of the Ogcheon Metamorphic Belt, Cambro-Ordovician Mungyeong Group and Jurrasic Daedong Group. The U-Pb isotopic compositions of zircon from two felsic porphyries and one granite samples in the Ssanyeong Valley yielded the Cretaceous intrusion ages of 93.9±3.3 Ma (tσ), 95.1±4.0 Ma (tσ) and 94.4±2.0 Ma (tσ), respectively. On the other hand, a felsic dike sample and a granite in the Yongchu Valley and a porphyritic granite in the Mungyeong Saejae had intrusion ages of 90.2±2.0 Ma (tσ), 91.0±3.0 Ma (tσ) and 88.6±1.5 Ma (tσ), respectively. Based on the average standard error calculated in combination with results of previous studies in this area (Lee et al., 2010; Yi et al., 2014; Aum et al., 2019), the geochronological results show that spatial variation in intrusion age of ~5 Myr between the Ssangyong (94.5±0.2 Ma) and Yongchu Valleys (89.7±0.4 Ma) is apparent. The geochemical compositions of major and trace elements in the samples showed an affinity of typical post-orogenic granite, indicating their petrogenesis during the late stage of Early Cretaceous magmatic activity possibly in association with subduction events of the Izanagi Plate.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.1
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• pp.48-55
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• 2009

Seasonal variations of microalgal biomass and community composition in both the sediment and the seawater were investigated by HPLC pigment analysis in an estuarine muddy sandflat of Gwangyang Bay from January to November 2002. Based on the photosynthetic pigments, fucoxanthin, diadinoxanthin, and diatoxanthin were the most dominant pigments all the year round, indicating that diatoms were the predominant algal groups of both the sediment and the seawater in Gwangyang Bay. The other algal pigments except the diatom-marker pigments showed relatively low concentrations. Microphytobenthic chlorophyll ${\alpha}$ concentrations in the upper layer (0.5 cm) of sediments ranged from 3.44 (March at the middle site of the tidal flat) to 169 (July at the upper site) mg $m^{-2}$, with the annual mean concentrations of $68.4{\pm}45.5,\;21.3{\pm}14.3,\;22.9{\pm}15.6mg\;m^{-2}$ at the upper, middle, and lower tidal sites, respectively. Depth-integrated chlorophyll ${\alpha}$ concentrations in the overlying water column ranged from 1.66 (November) to 11.7 (July) mg $m^{-2}$, with an annual mean of $6.96{\pm}3.04mg\;m^{-2}$. Microphytobenthic biomasses were about 3${\sim}$10 times higher than depth-integrated phytoplankton biomass in the overlying water column. The physical characteristics of this shallow estuarine tidal flat, similarity in taxonomic composition of the phytoplankton and microphytobenthos, and similar seasonal patterns in their biomasses suggest that resuspended microphytobenthos are an important component of phytoplankton biomass in Gwangyang Bay. Therefore, considering the importance of microphytobenthos as possible food source for the estuarine benthic and pelagic consumers, a consistent monitoring work on the behavior of microphytobenthos is needed in the tidal flat ecosystems.

• Journal of Environmental Impact Assessment
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• v.28 no.2
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• pp.169-182
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• 2019

This study assessed biological water quality using epilithic diatoms in the Yeong river, Naeseong stream and Wi stream in the upper region of the Nakdong river from May to October 2016. Epilithic diatoms were not mobile, so they could reflect long-term water quality. The sampled epilithic diatoms were identified a total 158 taxa which were composed to 2 orders, 3 suborders, 8 families, 34 genera, 143 species and 15 varieties. Dominant species were Achnanthes convergens and Achnanthes minutissima at Yeong river, Nitzschia inconspicua at Naeseong stream, and Achnanthes minutissima, Cocconeis placentula var. lineata and Navicula minima at Wi stream. As a result of the CCA, Electrical conductivity, total nitrogen and total phosphorus were important factors determining the diatom species composition in the upper region of the Nakdong river. The correlation between diatom indices (DAIpo & TDI) measured to be high in the correlation coefficient (0.87) from the result of correlation analysis. In the result of the assessment of biological water quality using DAIpo and TDI, Yeong river was rated as class A at most sites. Naeseong stream was rated as class C to D at all sites except for N1 which was rated as Class A. Wi stream was rated as class B to C for DAIpo of W1, and TDI was rated as class D. The assessment of biological water quality at this site showed inferior TDI result compared to that of DAIpo. DAIpo and TDI of W2 were rated as class A to D, and the water quality has changed a lot. W3 and W4 were mostly rated as class B and C respectively.

• Maritime Security
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• v.1 no.1
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• pp.311-343
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• 2020

Because of the global warming, the Arctic Ocean is expected to be ice-free by the year 2035. When the Arctic Ocean will be opened, a number of national interests will become more salient as experiencing a shortened sailing distance and decreasing navigation expense, possibility of natural resources transport by sea from Arctic Circle, and indirect-profit making by building a herb port in Asia. To secure the national interests and support the free activities of people in this region, R.O.K government is trying to make advanced policies. In order to carry out the naval tasks in the Arctic Ocean, using the operational characteristics(mobility, flexibility, sustainability, presence of capabilities, projection) is necessary. To this end, ROK Navy should analyze the operational environment (O.E.) by its capability(weakness and strength), opportunity, and threat. R.O.K. Navy should make an effort over the following issues to implement the tasks in the Arctic Ocean: first, Navy needs to map out her own plan (Roadmap) under the direction of government policies and makes crews participate in the education·training programs in home and abroad for future polar experts. Third, to develop the forces and materials for the tasks in cold, far operations area, Navy should use domestic well-experienced shipbuilding skills and techniques of the fourth industrial revolution. Next, improving the combined operations capabilities and military trust with other countries in the Arctic region to cover the large area with lack of forces' number and to resolve the ports of call issues. Lastly, preparation in advance to execute a variety of missions against military and non-traditional threats such as epidemics, HA/DR, SOLAS, in the future operation area is required.