• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.5 no.1
• /
• pp.27-36
• /
• 2000

We investigated the phytoplankton community from June to September 1997 in the waters off Kohung, Korea where red tides dominated by harmful dinoflagellates had occurred from August to September or October since 1995. We took water samples five times from 5 depths at 6 or less stations in this study period. The most dominant harmful dinoflagellate during the red tide which had outbroken on August 24, 1997 was Gyrodinium impudicum, not Cochlodinium polykrikoides. On August 21 just before the harmful red tide occurred the abundance of G. impudicum at the inner bay station, 90cells $ml^{-1}$, was higher than that at the outer bay station. However, on August 27 just after the red tide had outbroken, the abundance of G. impudicum at the inner bay station did not increase, whereas that at the outer bay increased rapidly and reached to the maximum of 30,000 cells $ml^{-1}$. Instead, diatoms such as Skeleltonema costatum, Chaetoceros pseudocurvisetus, Pseudonitzschia pungens rapidly increased at the inner bay station where fresh water from lands has reached. The high abundance of diatoms might have inhibited the growth of red tide dinoflagellates at this station. The transport of already formed red tide patches from offshore areas, aggregation of scattered cells driven by physical forces, and/or competition between diatom and dinoflagellates might be responsible for this appearance of dense red tide patches at the outer bay station.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.14 no.4
• /
• pp.239-252
• /
• 1981

The East China Sea is an important region as nursery and spawning grounds for pelagic fishes such as jack mackerel, common mackerel etc. , and thus constitutes a major fishing area for purse-seine fishery. The environment surrounding in this region is under the influence of the Yellow Sea Cold Water, China Coastal Water and Kuroshio Current. The purpose of this study was to clarify the effects of oceanographic conditions and thermal fronts on the formation of the fishing grounds for the mackerels in the East China Sea. Through the analyses of fisheries statistics during 1968-1976 and temperature data, the following facts are found: 1) Approximately $70\%$ of the total mackerel(common) catches appeared to be come from the Tsushima Current region which includes Sakai coast of the Japan Sea, eastern Tsushima and Shirase Island, and Jeju Island of Korea. This area covers only about $8\%$ of the East China Sea. 2) Main fishing grounds for the jack mackerel are also centered around the area of southwestern Goto, Shirase and eastern Tsushima Island where the catches accounted for about $54\%$ of the total jack mackerel catches. 3) Fluctuations in annual catches are relatively small in the Tsushima Current region, compared to other regions such as Yellow Sea, southwestern coast of Kyushu and mid-western part of the East China Sea, where the fisheries yields varied considerably due to unstable fishing conditions. 4) It appears that the fishing grounds for the jack mackerel are mainly distributed along the warmer region ($15-20^{\circ}C$) of the thermal front, and those for the common mackerel are in somewhat colder region ($13-16^{\circ}C$) in the Tsushima Current.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.9 no.4
• /
• pp.203-215
• /
• 2006

Field observations on the spatio-temporal distribution of organic matter of the surface sediment were carried out at 15 stations in the central parts of the South Sea of Korea from April 2002 to January 2003. The range of water temperature and salinity in bottom waters, mud content and water content of surface sediment were $8.06{\sim}23.35^{\circ}C,\;29.20{\sim}34.51\;psu,\;71.2{\sim}99.9%$ and $38.7{\sim}68.9%$, respectively. Measured parameters on the surface sediments of ignition loss (IL), chemical oxygen demand (CODs), phaeopigment, particulate organic carbon (POC) and particulate organic nitrogen (PON) also ranged in $3.9{\sim}l2.5%,\;9.60{\sim}44.05\;mgO_2/g-dry,\;1.58{\sim}29.51\;{\mu}g/g-dry,\;3.12{\sim}13.01\;mgC/g-dry$ and $0.49{\sim}2.00\;mgN/g-dry$, respectively. The spatio-temporal distribution of organic matter demonstrated higher concentrations offshore than at lesions near the coastal line. Higher concentrations occurred in the summer and spring. The results indicated that the origin of organic matter in surface sediments in the central part of the South Sea was autochthonous rather than allocthonous because the organic matter had an average C/N ratio of 6.44 (${\pm}0.51$). However, the composition of autochthonous organic matter was mainly derived from detritus rather than living phytoplankton, which was Indicated by the results of the POC/phaeopigment ratio. A principal component analysis (PCA) indicated that 73.2% of the variability in the data was described by two factors: 1) an 'environmental factor concerning the accumulation of materials (57.3%)' and 2) 'origin of organic matter and the composition by primary production (15.9%)'. The sedimentary environment in the central part of the South Sea was divided into four regions from the factor score of the PCA by the concentrations of organic matter and the composition ratio of organic matters from phytoplankton in surface sediments.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.19 no.6
• /
• pp.563-574
• /
• 1986

The structure of gonads, gametogenesis and reproductive cycle of the jackknife clams, Solen strictus and Solen gordonis were investigated mainly by histological observation. The first species used were monthly sampled at the coastal area of Dadaepo, Pusan, Korea and Naechodo, Kunsan, Korea for one year from February 1982 to January 1983. The second species were monthly sampled at the sand beach of Dadaepo, Pusan, Korea, from February 1982 to January 1983. Sexualities of Solen strictus and Solen gordonis are dioecious, and these species are oviparous. The gonads are irregularly arranged from the subregion of mid-intestinal gland in visceral cavity to reticular connective tissue of foot. The ovary was composed of a number of small ovarian sacs and the testis was composed of several testicular lobuli which from the tubular structure. Early multiplicating oogonium was about $10{\mu}m$ in diamater. Nucleus and nucleolus, at that time, were distinct in appearance. Each of the early growing oocytes made an egg-stalk, connected to the germinal epithelium of the ovarian sac. A great number of undifferentiated mesenchymal tissue and eosinophilic granular cells are abundantly distributed in the ovarian sacs in the early development stages. With the further development of gonad, these tissue and cells gradually disappeared. Then the undifferentiated mesenchymal tissue and eosinophilic granular cells function as nutritive cells in the formation and development of the early stage germ cells. Mature oocytes were free in the lumen of ovarian sacs and gradually become round or oval. Ripe oocyte was about 80 to $90{\mu}m$ in diameter. With the further development of testis, each of the testicular lobuli formed stratified layers composed of spermatogonia, spermatocytes, spermatids and spermatozoa in groups on the germinal epithelium. After spawning, the gonad gradually degenerated, and disorganized completely. Then new differentiated tissues were rearranged next year. The annual reproductive cycle of those species could be classified into five stages; multiplicative, growing, mature, spent, degenerative and resting stage. It seems that the spawning season is closely related to the water temperature, and the spawning of Solen strictus occurs from June to July at above $20^{\circ}C$ in water temperature. The peak spawning season appeared in June at Dadaepo and in July at Kunsan, The spawning of Solen gordonis occurs from May to June with the peak spawning season in June. Percentages of the first maturity in female of Solen strictus ranging from 5.1-6.0 cm and 7.1-8.0 cm in shell length were $50\%$ and $100\%$, respectively.

• Korean Journal of Remote Sensing
• /
• v.26 no.2
• /
• pp.251-262
• /
• 2010

In order to provide quantitative control of the standard products of Geostationary Ocean Color Imager (GOCI), on-board radiometric correction, atmospheric correction, and bio-optical algorithm are obtained continuously by comprehensive and consistent calibration and validation procedures. The calibration/validation for radiometric, atmospheric, and bio-optical data of GOCI uses temperature, salinity, ocean optics, fluorescence, and turbidity data sets from buoy and platform systems, and periodic oceanic environmental data. For calibration and validation of GOCI, we compared radiometric data between in-situ measurement and HyperSAS data installed in the Ieodo ocean research station, and between HyperSAS and SeaWiFS radiance. HyperSAS data were slightly different in in-situ radiance and irradiance, but they did not have spectral shift in absorption bands. Although all radiance bands measured between HyperSAS and SeaWiFS had an average 25% error, the 11% absolute error was relatively lower when atmospheric correction bands were omitted. This error is related to the SeaWiFS standard atmospheric correction process. We have to consider and improve this error rate for calibration and validation of GOCI. A reference target site around Dokdo Island was used for studying calibration and validation of GOCI. In-situ ocean- and bio-optical data were collected during August and October, 2009. Reflectance spectra around Dokdo Island showed optical characteristic of Case-1 Water. Absorption spectra of chlorophyll, suspended matter, and dissolved organic matter also showed their spectral characteristics. MODIS Aqua-derived chlorophyll-a concentration was well correlated with in-situ fluorometer value, which installed in Dokdo buoy. As we strive to solv the problems of radiometric, atmospheric, and bio-optical correction, it is important to be able to progress and improve the future quality of calibration and validation of GOCI.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.6
• /
• pp.882-889
• /
• 2022

In this study, to understand the factors influencing the flow change the Tsushima Warm Current (TWC), the correlation between the volume transport the TWC, El Niño Southern Oscillation (ENSO), and Pacific Decadal Oscillation (PDO) was analyzed. A calculation of the monthly volume transport of TWC for 25 years (1993-2018) revealed that the seasonal fluctuation cycle was the largest in summer and smallest in winter. Power spectrum analysis to determine the periodicity of the TWC volume transport, Oceanic Niño Undex (ONI), and PDO indicated that the TWC volume transport peaked at a one year cycle, but ONI and PDO showed no clear cycle. Further, to understand the correlation between the TWC transport volume and ONI and PDO, the coherence estimation method was used for analysis. The coherence of ONI and PDO had a high mutual contribution in long-period fluctuations of three years or more but had low mutual contribution in short-period fluctuations within one year. However, the coherence value between the two factors of the TWC volume transport and PDO was 0.7 in the 0.8-1.2 year cycle, which had a high mutual contribution. Meanwhile, the TWC volume transport and PDO have an inverse correlation between period I (1993-2002) and period III (2010-2018). When the TWC maximum transport volume (2.2 Sv or more) was high, the PDO index showed a negative value below -1.0, and the PDO index showed a positive value when the TWC maximum transport volume was (below 2.2 Sv). Therefore, using long-term PDO index data, changes in the TWC transport volume and water temperature in the East Sea coastal area could be predicted.

• The Journal of Engineering Geology
• /
• v.31 no.4
• /
• pp.603-620
• /
• 2021

A land nodal seismic system was employed to acquire seismic reflection data using stand-alone cable-free receivers in a land-river area. Acquiring reliable data using this technology is very cost effective, as it avoids topographic problems in the deployment and collection of receivers. The land nodal airgun system deployed on the mouth of the Hyungsan River (in Pohang, Gyeongsangbuk Province) used airgun sources in the river and receivers on the riverbank, with subparallel source and receiver lines, approximately 120 m-spaced. Seismic data collected on the riverbank are characterized by a low signal-to-noise (S/N) and inconsistent reflection events. Most of the events are represented by hyperbola in the field records, including direct waves, guided waves, air waves, and Scholte surface waves, in contrast to the straight lines in the data collected conventionally where source and receiver lines are coincident. The processing strategy included enhancing the signal behind the low-frequency large-amplitude noise with a cascaded application of bandpass and f-k filters for the attenuation of air waves. Static time delays caused by the cross-offset distance between sources and receivers are corrected, with a focus on mapping the shallow reflections obscured by guided wave and air wave noise. A new time-distance equation and curve for direct and air waves are suggested for the correction of the static time delay caused by the cross-offset between source and receiver. Investigation of the minimum cross-offset gathers shows well-aligned shallow reflections around 200 ms after time-shift correction. This time-delay static correction based on the direct wave is found essential to improving the data from parallel source and receiver lines. Data acquisition and processing strategies developed in this study for land nodal airgun seismic systems will be readily applicable to seismic data from land-sea areas when high-resolution signal data becomes available in the future for investigation of shallow gas reservoirs, faults, and engineering designs for the development of coastal areas.

• Journal of the Korean earth science society
• /
• v.43 no.1
• /
• pp.91-109
• /
• 2022

The ocean is a significant sink for atmospheric anthropogenic CO₂, absorbing one-third of the total CO₂ emitted by human activities. In return, oceans have experienced significant declines in seawater pH and the aragonite saturation state also called ocean acidification. This study evaluates the distribution of aragonite saturation state, an indicator to assess the potential threat from ocean acidification, by combining newly obtained data from the west coast of South Korea with previous datasets covering the Yellow Sea, East Sea, northern South China Sea, and southeast coast of South Korea. In general, offshore waters absorb atmospheric CO₂; however, most of the collected water samples show aragonite oversaturation. On the southeast coast, the aragonite saturation state was significantly affected by river discharge and associated variables, such as freshwater input with nutrients, seasonal stratification, biological carbon fixation, and bacterial remineralization. In summer, hypoxia and mixing with relatively acidic freshwater made the Jinhae and Gwangyang Bays undersaturated with respect to aragonite, possibly threatening marine organisms with CaCO₃ shells. However, widespread aragonite undersaturation was not observed on the west coast, which receives considerable river water discharge. In addition, occasional upwelling events may have worsened the ocean acidification in the southwestern part of the East Sea. These results highlight the importance of investigating site-specific ocean acidification processes in coastal waters. Along with the above-mentioned seasonal factors, the dissolution of atmospheric CO₂ and the deposition of atmospheric acidic substances will continue to reduce the aragonite saturation state in Korean waters. To protect marine ecosystems and resources, an ocean acidification monitoring program should be established for Korean waters.

• Korean Journal of Environmental Biology
• /
• v.40 no.2
• /
• pp.125-137
• /
• 2022

To assess the characteristics of meiofaunal community fluctuations related to environmental factors, seasonal surveys were conducted in the subtidal zone of Hallyeohaesang National Park. The average depth of the study area was about 20 m, and the average water temperature at the bottom was low in winter(11.33℃) and high in summer(17.95℃). The sedimentary particles mainly comprised silt and clay at most stations. The abundance of meiofauna ranged from 81.7 to 1,296.5 Inds. 10 cm^-2, and the average abundance was 589.3 Inds. 10 cm^-2. The average abundance of meiofauna in each season was the lowest at 416.5 Inds. 10cm^-2 in winter and the highest at 704.5Inds.10 cm^-2 in spring. The dominant taxa were nematodes (about 92%) and harpacticoids (about 5%). In the cluster analysis of meiofaunal communities, they were divided into four significant groups. The largest group mainly contained spring and summer samples, and contained stations with a high nematode density of over 500 Inds. 10 cm^-2 and harpacticoids below 50 Inds. 10 cm^-2 with a high composition ratio of nematodes. In the cluster analysis, no regional division was found between the stations, and it was thought to be divided by the seasons with high abundance according to seasonal variation and the composition ratio of nematodes and harpacticoids. In the Spearman rank correlation analysis, the density of total meiofauna and the most dominant taxa, nematodes, was not significantly related to environmental factors. However, the density of harpacticoids had a significant positive correlation with water depth and a negative correlation with sediment particle size.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.7
• /
• pp.902-909
• /
• 2023

This study evaluated the performance test of a small-sized LTE-Maritime(LTE-M) transceiver that was developed and promoted to expand the use of intelligent maritime traf ic information services led by the Ministry of Oceans and Fisheries with the aim of supporting the prevention of maritime accidents. Accoriding to statistics, approximately 30% of all marine accidents in Korean water occur with ships weighing less than 3 tons. Therefore, the blind spots of maritime safety must be supplemented through the development of small-sized transceivers. The small transceiver may be used in fishing boats that are active near coastal waters and in water leisure equipment near the coastline. Therefore, verifying whether sufficient performance and stable communication quality are provided is necessary, considering the environment of their real usage. In this study, we reviewed the communication quality goals of the LTE-M network and the performance requirements of small-sized transceivers suggested by the Ministry of Oceans and Fisheries, and proposed a test plan to appropriately evaluate the performance of small-sized transceivers. The validity of the proposed test method was verified for six real-sea areas with a high frequency of marine accidents. Consequently, the downlink and uplink transmission speeds of the small-sized LTE-M transceiver showed performances of 9 Mbps or more and 3 Mbps or more, respectively. In addition, using the coverage analysis system, coverage of more than 95% and 100% were confirmed in the intensive management zone (0-30 km) and interesting zone (30-50 km), respectively. The performance evaluation method and test results proposed in this paper are expected to be used as reference materials for verifying the performance of transceivers, contributing to the spread of government-promoted e-navigation services and small-sized transceivers.