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Katsuki, Kota,Nakanishi, Toshimichi,Lim, Jaesoo,Nahm, Wook‐,Hyun Blackwell Scientific 2017 The island arc Vol.26 No.6
<P><B>Abstract</B></P><P>Detailed diatom records within core sediments from Maeho Lagoon along the Eastern coast of South Korea revealed that the ecological dynamics of the lagoon during the Holocene were associated with relative sea level and regional precipitation. Accelerator mass spectrometry (AMS) <SUP>14</SUP>C dating indicates that sediment accumulation began prior to 8300 cal. year BP, and that the lagoon formed around 8000 cal. year BP. The salinity level of the lagoon increased until 5000 cal. year BP, and then decreased. Long‐term trends in salinity were dependent upon changes in sea level: periods of high salinity in the lagoon were generally coincident with periods of high sea levels along the east coasts of Korea and Japan. On the other hand, multicentennial‐scale fluctuations in diatom assemblages and magnetic susceptibility (MS) suggest that a 400 year fluctuation in salinity was regulated by changes in precipitation in the area of this lagoon. Changes in the westerly jet stream, controlled by variation in solar irradiance, had an important influence on precipitation volume in South Korea, suggesting that the patterns of the westerly jet stream fluctuate on a 400 year cycle.</P>
Land—sea linkage of Holocene paleoclimate on the Southern Bering Continental Shelf
Katsuki, Kota,Khim, Boo-Keun,Itaki, Takuya,Harada, Naomi,Sakai, Hideo,Ikeda, Tomonori,Takahashi, Kozo,Okazaki, Yusuki,Asahi, Hirofumi SAGE Publications 2009 The Holocene Vol.19 No.5
<P>Detailed diatom records within surface and core sediments from the Southern Bering Continental Shelf (SBCS) reveal that the Holocene evolution of sea-ice distribution is associated with low pressure patterns. Holocene sea-ice distribution over the SBCS was mainly controlled by the location of the Aleutian Low. The corresponding paleoceanographic and paleoclimate conditions can be divided into three stages: (1) the early Holocene (before 7000 cal. yr BP) was characterized by extensive sea-ice distribution under two low-pressure cells, which covered the western Bering Sea and the Gulf of Alaska, respectively. (2) Between 3000 and 7000 cal. yr BP, the low-pressure system over the Gulf of Alaska became weak, causing total sea-ice mass over the SBCS to retreat. (3) In the past 3000 years, prevailing southwesterly winds over the SBCS due to the developing Aleutian Low have reduced further sea-ice cover on the SBCS. These paleoclimatic changes were probably a response to ENSO variation. The timings of water mass exchanges on the SBCS coincided with sea-level change along the Alaskan Peninsula. As a result, subsequent morphologic alterations have also influenced the paleoceanographic condition of the SBCS. The effect of the surface coastal water and bottom marine water on the SBCS intensified about 6000 cal. yr BP when sea level increased.</P>
Multi-centennial-scale changes in East Asian typhoon frequency during the mid-Holocene
Katsuki, Kota,Yang, Dong-Yoon,Lim, Jaesoo,Lee, Jin-Young,Asahi, Hirofumi,Han, Min Elsevier 2017 Palaeogeography, palaeoclimatology, palaeoecology Vol.476 No.-
<P><B>Abstract</B></P> <P>This study reconstructs a record of typhoon frequency over the Korean Peninsula during the mid-Holocene using mineral components and diatom assemblages in deposits of Lagoon Hyangho, located on the east coast of the peninsula. The lagoon deposits confirm the occurrence of cyclical, multi-centennial scale episodes of low salinization induced by typhoon-derived heavy rain. Although shifts in typhoon frequency broadly follow El Niño/Southern Oscillation (ENSO) conditions during the Holocene, evidence from the typhoon-induced deposits in Hyangho Lagoon suggests that the path of the polar westerly jet controls the effect of ENSO on multi-centennial-scale typhoon patterns across the mid-latitude region of East Asia. The influence of ENSO is limited when the westerly jet passes through low latitudes. Fluctuations in solar activity play a key role in regulating movement of the westerly jet. Multi-centennial scale changes in typhoon frequency in mid-latitude East Asia are, therefore, influenced by changes in solar activity and ENSO conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Typhoon records for the mid-Holocene are reconstructed using lagoon sediments. </LI> <LI> Typhoon frequency in East Asia is synchronous with changes in solar irradiance. </LI> <LI> The effect of ENSO on typhoon paths is regulated by westerly jet stream conditions. </LI> </UL> </P>
지난 70만 년 동안 동남극 Lützow-Holm만 주변 해역의 생물기원 퇴적물 함량 변화
김여훈,Kota Katsuki,Yusuke Suganuma,Minoru Ikehara,김부근 한국해양과학기술원 2011 Ocean and Polar Research Vol.33 No.3
Contents of biogenic components [opal, CaCO3, TOC (total organic carbon)] were measured in Core LHB-3PC sediments collected off Lützow-Holm Bay, in order to understand glacial-interglacial cyclic variation of the high-latitude surface-water paleoproductivity, in the Indian Sector of the Southern Ocean. An age model was established from the correlation of ARM/IRM ratios of Core LHB-3PC with LR04 stack benthic δ18O records, in complement with radiocarbon isotope ages and biostratigraphic Last Appearance Datum (LAD). The core-bottom age was estimated to be about 700 ka. Although the CaCO3 content is very low less than 1.0% throughout the core, the opal and TOC contents show clear glacial-interglacial cyclic variation such that they are high during the interglacial periods (7.2-50.3% and 0.05-1.00%, respectively)and low during the glacial periods (5.2-25.2% and 0.01-0.68%, respectively). According to the spectral analysis, the variation of opal content is controlled mainly by eccentricity forcing and subsequently by obliquity forcing during the last 700 kyrs. The opal contents of Core LHB-3PC also represent the apparent Mid-Pleistocene Transition (MPT)-related climatic variation in the glacial-interglacial cycles. In particular, the orbital variation of the opal contents shows increasing amplitudes since marine isotope stage (MIS) 11, which defines one of the important paleoclimatic events during the late Quaternary, called the “Mid-Brunhes Event”. Based on the variation of the opal contents in Core LHB-3PC, we suggest that the surfacewater paleoproductivity in the Indian Sector of the Southern Ocean followed the orbital (glacial-interglacial)cycles, and was controlled mainly by the extent of sea ice distribution during the last 700 kyrs.