Japan Geoscience Union Meeting 2016

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS17] Paleoclimatology and paleoceanography

Mon. May 23, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Tomohisa Irino(Faculty of Environmental Earth Science, Hokkaido University), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Akira Oka(Atmosphere and Ocean Research Institute, The University of Tokyo), Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), Ikuko Kitaba(Research Centre for Palaleoclimatology, Ritsumeikan University), Akihisa Kitamura(Institute of Geosciences, Faculty of Science, Shizuoka University), Masaki Sano(Research Institute for Humanity and Nature), Ryuji Tada(Department of Earth and Planetary Science, Graduate School of Science, The Univeristy of Tokyo), Takeshi Nakagawa(Ritsumeikan University), Akira Hayashida(Department of Environmental Systems Science, Doshisha University)

5:15 PM - 6:30 PM

[MIS17-P07] Pleistocene deep-sea ostracodes at IODP Site U1426 and their implication for paleoenvironments

*Tatsuhiko Yamaguchi1, Kentaro Kuroki2, Katsura Yamada2 (1.Center for Advanced Marine Core Research, Kochi University, 2.Shinshu University)

Keywords:Sea of Japan, Ostracoda, Pleistocene, Deep sea

In the Sea of Japan, the Quaternary glacial-interglacial climate changes have affected deep ocean floor environments as well as coastal environments and biota [e.g., Kitamura and Kimoto, 2006, Palaeogeogra., Palaeoclim., Palaeoeco., 236: 355–366; Watanabe et al., 2007, Palaeogeogra., Palaeoclim., Palaeoeco., 247, 50 – 64]. Little is known about the Pleistocene deep-sea ostracodes and their response to environmental changes. We present Pleistocene ostracodes at IODP Site U1426 (37°2.00′N, 134°48.00′E; 903 m water depth). Twenty-one taxa were obtained from 87 Pleistocene (2.0–1.2 Ma) sediments of the interval between 123.50 and 218.14 mcd. Ostracodes occur from sediment samples with L* values of more than 33. Benthic ostracode accumulation rates (BOARs) exhibit less than 14 ind/cm2/kyr. At 180 mcd, BOARs show a change: BOARs indicates maxima of 0.6–4.2 ind/cm2/kyr above 180 mcd (~1.7Ma), whereas BOARs show maxima of 1.7–14 ind/cm2/kyr below 180 mcd. Acanthocythereis dunelmensis, Krithe antiswanensis, Krithe hemideclivata, Krithe reversa, and Robertsonites tabukii are found ubiquitously. The ostracode fauna indicates oxic condition, alternation of export productivity, and possibly warm water-mass. Generally ostracodes are sensitive to oxygen contents. Their population vanishes in condition with oxygen contents of less than 0.4 ml/l O2[Dingle, 1995, Mar. Geol., 122, 207–225]. We infer that the sediments with high L* values (>33) were deposited at oxic condition (> 0.4 ml/l O2). Because BOARs are influenced by export productivity [Yasuhara et al., 2012, Paleobiol., 38, 162–179], the change in BOAR at 180 mcd suggests alternation of export productivity. According to Kitamura (2009, J. Quat. Sci. 24, 880–889), who discuss the surface and intermediate water-masses during the Pleistocene, the flow of the Tsushima current was intensified after 1.7 Ma. The change in surface water-mass probably made effects on surface productivity and benthic ostracodes. R. tabukii [= R. reticuliforma of Ozawa, 2003, Paleontol. Res., 7, 257–274], that lives in seafloor environments with water depth of 150–250 m and temperature of 2–5°C, indicates a warmer water-mass that the modern intermediate water with 0–1°C temperature.