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남극해 인도양 해역에 위치한 콘래드 해령 지역의 마지막 빙하기 이후 생물기원 오팔 생산의 변화
양주연,Minoru Ikehara,최혁,김부근 한국해양과학기술원 2023 Ocean and Polar Research Vol.45 No.3
Biological pump processes generated by diatom production in the surface water of the Southern Ocean play an important role in exchanging CO2 gas between the atmosphere and ocean. In this study, the biogenic opal content of the sediments was measured to elucidate the variation in the primary production of diatoms in the surface water of the Southern Ocean since the last glacial period. A piston core (COR-1bPC) was collected from the Conrad Rise, which is located in the Indian sector of the Southern Ocean. The sediments were mainly composed of siliceous ooze, and sediment lightness increased and magnetic susceptibility decreased in an upward direction. The biogenic opal content was low (38.9%) during the last glacial period and high (73.4%) during the Holocene, showing a similar variation to that of Antarctic ice core ΔT and CO2 concentration. In addition, the variation of biogenic opal content in core COR-1bPC is consistent with previous results reported in the Antarctic Zone, south of the Antarctic Polar Front, in the Southern Ocean. The glacial-interglacial biogenic opal production was influenced by the extent of sea ice coverage and degree of water column stability. During the last glacial period, the diatom production was reduced due to the penetration of light being limited in the euphotic zone by the extended sea ice coverage caused by the lowered seawater temperature. In addition, the formation of a strong thermocline in more extensive areas of sea ice coverage led to stronger water column stability, resulting in reduced diatom production due to the reduction in the supply of nutrient-rich subsurface water caused by a decrease in upwelling intensity. Under such environmental circumstances, diatom productivity decreased in the Antarctic Zone during the last glacial period, but the biogenic opal content increased rapidly under warming conditions with the onset of deglaciation.
Thermal Analysis on MnBi in High Magnetic Fields up to 45 T
Yoshifuru Mitsui,Yuki Ikehara,Kazuo Watanbe,Eun Sang Choi,Eric C. Palm,Keiichi Koyama 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
Differential thermal analysis (DTA) equipment for utilization in a high magnetic field of 45 T wasdeveloped. From the DTA experiments, the decomposition temperature (MnBi ! Mn1.08Bi+liquid:632 K at zero field) Tt was found to increase linearly at a rate of 2 KT−1 in fields up to 18 T andto deviate from that linear increase above 20 T. In addition, the peritectic temperature (Mn1.08Bi! Mn + liquid: 721 K at zero field) Tm was slightly increased by applying a magnetic field. At amagnetic field of 45 T, Tt and Tm reached 714 K and 726 K, respectively. The behaviors of Tt andTm for MnBi and Mn1.08Bi under high magnetic fields are discussed, and the magnetic energies arecalculated on the basis of mean field theory.
Takata, Hiroyuki,Nishida, Naohisa,Ikehara, Ken,Katsuki, Kota,Khim, Boo-Keun Elsevier 2018 QUATERNARY INTERNATIONAL Vol.482 No.-
<P><B>Abstract</B></P> <P>We investigated fossil benthic and planktonic foraminifera in sediment cores FV10-05 and FV10-06-2, off Fukuoka, southwestern Japan to evaluate the impact of the Tsushima Warm Current on coastal environments around the strait between southeastern Korea and southwestern Japan during the early to middle Holocene. A cluster analysis of benthic foraminifera in these cores established four sample clusters (A, B, C, and D), which are interpreted as indicators of relatively high energy condition due to wave/current processes. Clusters A and C, characterized by attached taxa, became dominant at ∼6.6 ka. Such faunal changes are consistent with the current-influenced sedimentation, confirming that the Tsushima Warm Current reached its present-day distribution at that time. A hiatus at ∼8–7 ka has been reported in cores from deeper water off Fukuoka, whereas our shallow core shows deposition under high energy conditions was continuous even at ∼8–7 ka near the coast off river mouth. Across the strait, the maximum landward extent of benthic foraminifera occurred in the Nakdong River delta (southeastern Korea) in ∼8–7 ka, and an outer bay fauna of benthic foraminifera with seagrass beds occurred transiently in the restricted bay of the San-in district (southwestern Japan) at that time. The evolution of the Tsushima Warm Current during the early to middle Holocene thus appears to play an important role in coastal environments not only in the strait areas between southeastern Korea and southwestern Japan, but also in the San-in district.</P>