• Korean Journal of Remote Sensing
• /
• v.37 no.5_1
• /
• pp.975-987
• /
• 2021

Potential habitat mapping of Meretrix lyrata which is found in large parts of South East Asian tidal flat was carried out to find out causes of collective death. Frequency Ratio (FR) method, one of geospatialstatistical method, was employed with some benthic environmental factors; Digital elevation model (DEM) made from Landsat imagery, slope, tidal channel distance, tidal channel density, sedimentary facesfrom WorldView-02 image. Field survey was carried out to measure elevation of each station and to collect surface sediment and benthos samples. Potential habitat maps of the all clams and the juvenile clams were made and accuracy of each map showed a good performance, 76.82 % and 69.51 %. Both adult and juvenile clams prefer sand dominant tidal flat. But suitable elevation of adult clams is ranged from -0.2 to 0.2 m, and that of juvenile clams is ranged from 0 to 0.3 m. Tidal channel didn't affect the habitat of juvenile clams, but it affected the adult clams. In the furtherstudy, comparison with case of Korean tidal flat will be carried out to improve a performance of the potential habitat map. Change in the benthic echo-system caused by climate change will be predictable through potential habitat mapping of macro benthos.

• Journal of the Korean earth science society
• /
• v.40 no.2
• /
• pp.149-162
• /
• 2019

In the macro-tide open coast of the Korean western coast, typhoon effects were investigated in terms of variations on topography, surface sediment, and sedimentary environment, which appeared before and after the typhoon Kompasu of 2010. The Kompasu of small size and strong intensity landed on the southwestern coast of the Korean Peninsula and passed across the inland between September 1st and 2nd in 2010. Topography and surface sediments before and after the typhoon were measured and sampled along the survey line of 22 sites in the Gochang Donghori intertidal flat. The intertidal area was divided into high tidal zone, middle tidal zone, and lower tidal zone on the basis of mean high water level, mean sea level, and mean low water level. Topographic variation before and after the typhoon represented deposition of average 0.03 m in high tidal zone, erosion of average -0.15 m in middle tidal zone, and erosion of average -0.39 m in lower tidal zone, respectively. Surface sediments of the intertidal flat consisted mainly of fine to medium sands, and the ratio of fine sand was the largest both before and after the typhoon. Surface sediments after the typhoon became finer in mean grain size showing well sorting rather than those before the typhoon.

• Journal of the Korean GEO-environmental Society
• /
• v.20 no.2
• /
• pp.69-79
• /
• 2019

The coastal area forms various sedimentary layers according to the environmental conditions such as the topography and geological features of the upper region of the river, ocean currents, and river mouth. Therefore, identifying the characteristics of the marine clay deposited in the coastal area plays a key role in the investigation of the formation of soft ground. In general, alluvial grounds are formed by a variety of factors such as changes in topography and natural environment, they have very diverse qualities depending on the deposited region or sedimentation conditions. The most important thing for the construction of social infrastructures in soft ground areas is economical and efficient treatment of soft ground. In this study, the author collected data from diverse laboratory and field tests on five areas in western and southern offshore with relatively high reliability, and then statistically analyzed them, thereby presenting standard constants for construction design. Correlation between design parameters such as over consolidation ratio, preconsolidation pressure was analyzed using linear and non-linear regression analyses. Also, proposed distribution characteristics of design parameters in consideration of each region's uncertainty through statistical analyses such as normality verification, outlier removal.

• Geophysics and Geophysical Exploration
• /
• v.22 no.2
• /
• pp.62-71
• /
• 2019

We conducted DC resistivity and MT survey to obtain the resistivity structure of the central Myanmar basin. We tried to analyze the underground structure through the resistivity variation of Myanmar by performing representative geophysical survey methods because researches on the electrical resistivity structure are insufficient in Myanmar. The electrical resistivity is expected to be low considering the marine sedimentary rocks composed of shale and sandstone in this area. The DC resistivity and MT survey were carried out using SmartRho of Geolux Co., Ltd. and MTU-5A of Phoenix geophysics Ltd., respectively, to visualize the electrical resistivity structure of study area. DC resistivity and MT survey showed an electrical resistivity less than dozens of ohm-m within the depth of 100 m. In particular, MT survey data were almost similar to TM and TE modes in the frequency range above 1 Hz. The two-dimensional inversion of MT data showed a subsurface structure with low resistivity below 150 ohm-m divided into east-west direction. We confirmed that the inversions of DC resisitivity and MT data along an overlapped survey line represented similar results. In the future, considering the high electrical conductivity, it would be effective to perform DC resistivity and MT survey simultaneously to study the electrical resistivity structure of the central Myanmar basin.

• Journal of The Geomorphological Association of Korea
• /
• v.18 no.4
• /
• pp.235-246
• /
• 2011

Sea level fluctuations during the Holocene reconstructed by the results of age dating, microfossils researches and sedimentary facies from coastal alluvial plains contain the valuable informations on climatic changes. The sea level during 'maximum phase of transgression' during 6,000~5,000 yr BP was slightly higher than the present by approximately 0.8~1.0 m and the summer temperature conditions seemed to be higher than those of the present by 2~3℃ in the Central Europe when the period of 'Climatic Optimum' might be dominant. The sea level in Korean Peninsula was assumed by 0.8~1.0 m higher at that time compared to the present and climate seemed to be warmer. At 2,000~1,800 yr BP in Korean Peninsula, the sea level reached the higher stand than the present by approximately 1.1~1.3 m and the climatic conditions might be warm similar to the period of 'Climatic Optimum'. Although the temperature in the Central Europe during the period of 'Subboreal' was about 2~3℃ cooler, it is supposed that the sea level in Korean Peninsula was relatively higher than the present. The sea level at 2,300 yr BP might be similar to that of the present, which was the lowest level since the mid-Holocene. From the fact, climatic environment during the cold period might not be reflected exactly in the sea level.

• Economic and Environmental Geology
• /
• v.56 no.5
• /
• pp.581-588
• /
• 2023

This study reports depth-dependent elemental distribution and mineral abundance of the oceanic sediment sample (WP21GPC04) near the Mariana Trench collected during the WP21 expedition in 2021. The elemental distribution determined by μ-XRF shows no significant differences with varying depth, with an average SiO₂ 53.91 wt%, FeO 4.48 wt%, Al₂O₃ 16.56 wt%, MgO 2.56 wt%, CaO 4.79 wt%, Na₂O 3.52 wt%, K₂O 5.48 wt%, similar to the average chemical composition of global subducting sediments (GLOSS). The mineral abundances analyzed using synchrotron XRD, however, vary with depth. While quartz, mica, and plagioclase were identified at all depths, chlorite was found at shallow depths, and zeolite group minerals, phillipsite and heulandite, showed a gradual change in phase fraction with depth. This suggests a change in sedimentation and alteration environments in the region, or the potential for coexistence emerges due to similar sediment stability. Overall, this study will provide a basis for the future investigations on the evolution of sedimentary environment near the Mariana Trench in the western Pacific Ocean and the phase distribution and the behavior of subducting oceanic sediments, which will affect the lithological and geochemical characteristics of the Mariana susduction system.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.14 no.3
• /
• pp.181-188
• /
• 2009

The macro tidal flat of the Gochanggun Myongsasipri, located on the southwestern coast of Korea, is studied in terms of seasonal variations of surface sediment and sedimentary environment. Surface sediments of 45 sites in the winter (February) and the summer (August) are sampled across three survey lines (15 sites in each survey line), respectively. The tidal flat of open-coast Myongsasipri is mainly composed of fine to medium sand, the distribution of which shows a coast-parallel trend. Grain-size distribution has a bi-modal trend, and grain size in the winter is coarser than that in the summer. During the winter, the upper tidal flat is dominated by medium sand, while the lower tidal flat is dominated by find sand. Such a feature is attributed to wave-dominated sedimentation in the winter. The finer grains of the summer rather than that of the winter and relationship between texture parameters suggest that tidal energy plays an important role in tidal-flat sedimentation during the summer. This study represents an environmental change from wave-dominated conditions in the winter to tide-dominated conditions in the summer as a result of the seasonal variation in the intensity of onshore-directed winds and waves in the Myongsasipri tidal flat.

• Korean Journal of Environment and Ecology
• /
• v.24 no.3
• /
• pp.249-257
• /
• 2010

The purpose of this paper is to weigh the possibility of endangered Jang-hang wetland at the estuary of Han River to be included on the Ramsar List of Wetlands of International Importance and come up with ways to manage the wetland depending on its biotope patterns. The target area is located between Gimpo bridge and Isanpo I.C. with about $2.7km^2$ area. Through the analysis of RIS(Information Sheet for Ramsar Wetlands), it was known that the wetland is located on the sedimentary topography and formed as a result of sediment at the estuary of the river owing to the concentration of rainfall during summer. The vegetation environment in the area is divided into brackish water and fresh water areas depending on salinity. Rhizosphere soil(RS) of the area was analyzed to be Silt loam while bottom RS to be Sand loam. The plant ecology was composed of 52 families 135 species and 11 varieties and 146 types. Among indigenous species found are Salix koreensis, Phragmites communis and Miscanthus sacchariflorus. The analyzed results of the actual vegetation showed that willow community accounts for 37% of the area and rice field is 13.5%. As for animal ecology, total of 62 species and 25,977 individual wild birds were observed. After comparing and analyzing the RIS we compiled with the Ramsar Site designation standards, it turns out that the Jang-hang wetland meets criteria 1(biographic region), criteria 2,3 and 4(species and ecological communities) and criteria 5 and 6(water birds). Thus, Jang-hang wetland is eligible for the Ramsar site. As a result of establishing and evaluating the biotope types for setting management areas, Jang-hang wetland has a total of 13 different types, and the grade I represents 75.4% of the area while the grade III 0.8% of the land status. We categorized four management zones for the wetland depending on the biotope patterns - preservation, restoration, use and buffer zones and suggested management methods for each zone.

• 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.

• Economic and Environmental Geology
• /
• v.56 no.6
• /
• pp.729-744
• /
• 2023

The value of lithium has significantly increased due to the rising demand for electric cars and batteries. Lithium is primarily found in pegmatites, hydrothermally altered tuffaceous clays, and continental brines. Globally, groundwater-fed salt lakes and oil field brines are attracting attention as major sources of lithium in continental brines, accounting for about 70% of global lithium production. Recently, deep groundwater, especially geothermal water, is also studied for a potential source of lithium. Lithium concentrations in deep groundwater can increase through substantial water-rock reaction and mixing with brines. For the exploration of lithim in deep groundwater, it is important to understand its origin and behavior. Therefore, based on a nationwide preliminary study on the hydrogeochemical characteristics and evolution of thermal groundwater in South Korea, this study aims to investigate the distribution of lithium in the deep groundwater environment and understand the geochemical factors that affect its concentration. A total of 555 thermal groundwater samples were classified into five hydrochemical types showing distinct hydrogeochemical evolution. To investigate the enrichment mechanism, samples (n = 56) with lithium concentrations exceeding the 90th percentile (0.94 mg/L) were studied in detail. Lithium concentrations varied depending upon the type, with Na(Ca)-Cl type being the highest, followed by Ca(Na)-SO₄ type and low-pH Ca(Na)-HCO₃ type. In the Ca(Na)-Cl type, lithium enrichment is due to reverse cation exchange due to seawater intrusion. The enrichment of dissolved lithium in the Ca(Na)-SO₄ type groundwater occurring in Cretaceous volcanic sedimentary basins is related to the occurrence of hydrothermally altered clay minerals and volcanic activities, while enriched lithium in the low-pH Ca(Na)-HCO₃ type groundwater is due to enhanced weathering of basement rocks by ascending deep CO₂. This reconnaissance geochemical study provides valuable insights into hydrogeochemical evolution and economic lithium exploration in deep geologic environments.