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RISS 인기검색어
- 검색키워드
- 저자 : B.K. Khim (검색결과 37 건)
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Khim, B.K.,Shim, J.,Yoon, H.I.,Kang, Y.C.,Jang, Y.H. Academic Press in association with the Estuarine a 2007 Estuarine, coastal and shelf science Vol.73 No.1-2
<P><B>Abstract</B></P><P>Particulate suspended material was recovered over a 23-month period using two sediment traps deployed in shallow water (∼30m deep) off the King Sejong Station located in Marian Cove of King George Island, West Antarctica. Variability in seasonal flux and geochemical characteristics of the sediment particles highlights seasonal patterns of sedimentation of both lithogenic (terrigenous) and biogenic particles in the coastal glaciomarine environment. All components including total mass flux, lithogenic particle flux and biogenic particle flux show distinct seasonal variation, with high recovery rates during the summer and low rates under winter fast ice. The major contributor to total mass flux is the lithogenic component, comprising from 88% during the summer months (about 21gm<SUP>−2</SUP>d<SUP>−1</SUP>) up to 97% during the winter season (about 2gm<SUP>−2</SUP>d<SUP>−1</SUP>). The lithogenic particle flux depends mainly on the amount of snow-melt (snow accumulation) delivered into the coastal region as well as on the resuspension of sedimentary materials. These fine-grained lithogenic particles are silt-to-clay sized, composed mostly of clay minerals weathered on King George Island. Biogenic particle flux is also seasonal. Winter flux is ∼0.2gm<SUP>−2</SUP>d<SUP>−1</SUP>, whereas the summer contribution increases more than tenfold, up to 2.6gm<SUP>−2</SUP>d<SUP>−1</SUP>. Different biogenic flux between the two summers indicates inter-annual variability to the spring–summer phytoplankton bloom. The maximum of lithogenic particle flux occurs over a short period of time, and follows the peak of biogenic particle flux, which lasts longer. The seasonal warming and sea-ice retreat result in change in seawater nutrient status and subsequent ice-edge phytoplankton production. Meanwhile, the meltwater input to Marian Cove from the coastal drainage in January to February plays a major role in transporting lithogenic particles into the shallow water environment, although the tidal currents may be the main agents of resuspension in this kind of sheltered bay.</P>
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Khim, B.K.,Bahk, J.J. Pergamon Press 2014 Quaternary international Vol.344 No.-
A piston core (EBP-3) collected from the South Korea Plateau in the East Sea (Japan Sea) preserved typical alternations of thick, dark laminated mud layers and bioturbated hemipelagic mud layers, but included several intercalated volcanic lapilli layers. The age estimate of core EBP-3 was aided by correlation of biostratigraphic radiolarian data, the abundance of microfossils (warm-water radiolarians), and geochemical properties (CaCO<SUB>3</SUB>) with the proxies of the well-dated core MD01-2407 obtained from the Oki Ridge. A part from the Marine Isotope Stage (MIS) 11 to MIS 9 in the middle of core EBP-3 was missing, presumably because of erosion following the abrupt deposition of a volcanic lapilli layer. Despite some uncertainty, the age estimate of core EBP-3 revealed that the lower part of core EBP-3 represents MIS 13, as was also evident from a comparison with the oxygen isotope stratigraphy. Downcore biogenic opal and CaCO<SUB>3</SUB> variations in core EBP-3 exhibited less distinct orbital-scale cyclic changes than cores from other areas in the East Sea (Japan Sea). However, differences in features were discernible between MIS 2 and MIS 12 in terms of their lithology and CaCO<SUB>3</SUB> constituent, although both periods were characterized by relatively high levels of CaCO<SUB>3</SUB> (about 30% for MIS 2 and about 50% for MIS 12). MIS 2 preserved a typical thick, dark laminated mud layer, whereas MIS 12 preserved a distinctly light mud layer with thin parallel laminations. This difference of the lithologic facies between MIS 2 and MIS 12 highlighted a discrepancy among the major constituents, indicating that planktonic foraminifera were dominant in MIS 2, whereas coccolithophores were dominant in MIS 12. Our results suggest that the thinly-laminated light mud layer, which is characterized by a high CaCO<SUB>3</SUB> content primarily composed of coccolithophores in MIS 12, can be used as a reliable time marker for the establishment of chronostratigraphy in the East Sea.
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Khim, B.K.,Tada, R.,Itaki, T. Pergamon Press 2014 QUATERNARY INTERNATIONAL Vol.333 No.-
Two piston cores (PC-05 and PC-08) were collected on the Yamato Rise in the East Sea/Japan Sea during the KR07-12 cruise. Both cores showed typical alternations of light (high L*) and dark (low L*) layers, which are characteristic in the hemi-pelagic sediment deposited in the deep part of the East Sea/Japan Sea. A composite core was achieved with the successful replacement of almost half of the upper part of core PC-05 by the entirety of core PC-08 based on the co-equivalence of L* values and the dark layers, because an interval (170 cm-410 cm) of core PC-05 was considerably disturbed due to fluidization during the core execution. Chronostratigraphy of the composite core was constructed by the direct comparison of L* values to the well-dated core MD01-2407 that was obtained in the Oki Ridge. The lower-bottom of the composite core extended to Marine Isotope Stage (MIS) 14, based on the age estimate by LR04 stacks. Downcore opal variation of the composite core exhibited the distinct orbital-scale cyclic changes; high during the interglacial and low during the glacial periods. However, downcore CaCO<SUB>3</SUB> variation showed no corresponding orbital-scale cyclic change between glacial and interglacial periods. Some intervals of both periods were high in CaCO<SUB>3</SUB> content. Frequent and large fluctuations in CaCO<SUB>3</SUB> content seemed to be more related to the presence of dark layers containing thin lamination (TL) within the glacial and interglacial intervals. It is worthy to note that MIS 2 and MIS 12 are characterized by distinctly high CaCO<SUB>3</SUB> content, showing up to 18% and 73%, respectively, among the glacial periods. Furthermore, in terms of lithology, MIS 2 was characterized by a thick dark layer (low L* values) with TL, whereas MIS 12 preserved the distinctly light layer (high L* values) with parallel laminations. Another remarkable dissimilarity between MIS 2 and MIS 12 was the nature of their CaCO<SUB>3</SUB> constituent; the CaCO<SUB>3</SUB> constituent of MIS 2 consisted of mostly planktonic foraminifera, whereas that of MIS 12 was mostly dump of coccolithophorids, regardless the presence of planktonic foraminifera. The distinctness of the CaCO<SUB>3</SUB> constituents between MIS 2 and MIS 12 indicates that the preservation of CaCO<SUB>3</SUB> contents was different temporarily during the glacial periods in the East Sea/Japan Sea. Enhanced CaCO<SUB>3</SUB> preservation in MIS 2 is attributed primarily to less dissolution during the sinking through the water column or at the seafloor, but increased CaCO<SUB>3</SUB> preservation in MIS 12 is mainly due to the high primary production in the surface water. With respect to the different function of the biological pump which controls CO<SUB>2</SUB> cycles, the East Sea/Japan Sea clearly experienced carbonate-ocean-like state during MIS 12, despite normally silica-ocean-like state.
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Khim, B.K.,Park, Y.H.,Bahk, J.J.,Jin, J.H.,Lee, G.H. Pergamon Press 2008 Quaternary international Vol.176 No.-
Geochemical (opal, total organic carbon (TOC), and CaCO<SUB>3</SUB>) analyses of three sediment cores from the South Korea Plateau in the East Sea (Japan Sea) revealed that the late Quaternary (<190kyr BP to the present) paleoceanographic conditions are characterized by the orbital variations of geochemical properties that have recorded the changes of surface- and bottom-water conditions. Chronostratigraphy of the sediment cores was accomplished by the direct correlation of L<SUP>*</SUP> values to the well-dated core MD01-2407 in Oki Ridge, supplement to the AMS <SUP>14</SUP>C dates, well-known lithostratigraphic and tephrostratigraphic markers. Biogenic opal concentrations are high during Marine Isotope Stage (MIS) 1 and MIS 5.5, and low during the glacial period, suggesting that diatom production was enhanced during the warm period when the surface-water exchange between the East Sea and adjacent marginal seas was active. In contrast, glacial opal paleoproductivity appears to have been depressed, probably because of insufficient nutrient availability, resulting from limited vertical ventilation. Overall TOC contents follow the orbital variations; high during the interglacial and relatively low during the glacial time. However, high-resolution TOC fluctuations are independent of opal concentration, which may be attributed more to the preservation of organic matter rather than to the surface-water production. The high TOC contents in the thin dark mud (i.e., TL) layers may be due to the enhanced surface-water production as well as the intensified bottom-water anoxia. On the other hand, high CaCO<SUB>3</SUB> contents associated with the TL layers during the glacial and stadial period may be attributed to the reduced dissolution. The temporal variations of these geochemical properties are likely to follow the global orbital cycles, indicating the significant changes of surface- and bottom-water properties due to the eustatic sea-level fluctuations between the interglacial and glacial period. The comparable values of these geochemical properties among the sediment cores suggest that the spatial paleoceanographic conditions in the South Korea Plateau were consistent and uniform during the late Quaternary, in spite of a little local discrepancy in amounts of properties and timing of events.
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Lee, B.,Khim, S.,Jeon, B.J.,Park, J.Y.,Lee, S.H.,Choi, K.Y.,Stewart, G.R.,Kim, K.H. North-Holland 2013 Physica. C, Superconductivity Vol.495 No.-
Single crystals of Li(Fe<SUB>1-x</SUB>Co<SUB>x</SUB>)As (x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.1) were grown by the Sn-flux method and their resistivity behaviors were investigated. As the Co concentration x increased, the superconducting transition temperature T<SUB>c</SUB> as well as the residual resistivity ratio systematically decreased, indicating a monotonic doping of electron carriers. Upon the analysis of the Fermi-liquid behavior of the resistivity and by using the Kadowaki-Woods relation, the T<SUP>2</SUP> coefficient of the resistivity A and the Sommerfeld coefficient γ<SUB>N</SUB> were found to increase abruptly near x=0.06. This is the point in the phase diagram at which the density of states at the Fermi energy (proportional to γ<SUB>N</SUB>) is expected to be enhanced due to the collapse of the small hole-pockets. This result suggests that the Li(Fe<SUB>1-x</SUB>Co<SUB>x</SUB>)As series at least up to x=0.08 remain as compensated metals and their transport properties are determined by multi-band effects.
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Katsuki, K.,Seto, K.,Nomura, R.,Maekawa, K.,Khim, B.K. Academic Press in association with the Estuarine a 2009 Estuarine, coastal and shelf science Vol.81 No.2
Diatom assemblages of the surface and in core sediment samples from Lake Saroma (Japan) were examined for the purpose of evaluating anthropogenic effect on the coastal environmental changes. Before the first inlet excavation, the lake's water quality and ecology were controlled by water exchange with the Okhotsk Sea as well as lake-level variation. However, large-scale ecological modification occurred, mainly due to artificial excavation and shellfish industrial farms. A distinct record of the succession of the dominant diatom taxa was preserved in core sediments. Low-oxygen water was prevalent in the lake in 1929, before the first inlet excavation. Immediately after the first inlet excavation, the low-oxygen water in the western basin of the lake began to disappear, in a trend that became increasing transparent, which has been attributed to an increasing rate of water exchange. However, the lacustrine environment of bottom sediments resumes deterioration 20years after since the first artificial excavation: the resultant deposition of river-mouth materials into the deep basin caused eutrophication and environmental disturbance of the lake bottom. At the same time, the eutrophication of surface water became intensified with the onset of intense scallop culturing beginning in 1966. Increasing organic loads deposited onto the bottom layer in the form of excreta from the scallop nursery led to more oxygen deficiency and the elution of nitrogen and phosphorus from the sediment, which again brought about eutrophication of the surface layer. Such environmental change was reflected in a decrease of benthic diatom taxa and an increase of planktonic taxa, trends which have continued until today. Particularly, the numbers of diatom assemblage have been decreasing all over the lake during the last 10years, which suggests that Lake Saroma's present-day deterioration and eutrophication will continue or become even worse.
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