Japan Geoscience Union Meeting 2015

Presentation information


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

[M-IS34] Paleoclimatology and paleoceanography

Wed. May 27, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Kazuyoshi Yamada(Museum of Natural and Environmental history, Shizuoka), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Tomohisa Irino(Faculty of Environmental Earth Science, Hokkaido 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), Takeshi Nakagawa(Ritsumeikan University), Akira Hayashida(Department of Environmental Systems Science, Doshisha University)

6:15 PM - 7:30 PM

[MIS34-P04] Variations in sedimentary environments around the Ryukyu Arc since 25 kyr based on CNS elements

*Atsuko AMANO1, Takuya ITAKI1 (1.Geological Survey of Japan, AIST)

Keywords:CNS elements, deposition process, sea level change, Kuroshio Current, Ryukyu Islands

In this study, we analyzed 14C dates, grain size, and CNS element contents using sediment cores collected at the eastern edge of the backarc and forearc of the Ryukyu Arc, and demonstrated different temporal variations in CaCO3 contents and C/N ratios compared with previous studies of the Okinawa Trough cores. Increases in CaCO3 contents and decreases in C/N ratios, from the Last Glacial Maximum to the Holocene, in the Okinawa Trough backarc basin correspond with sea-level changes. These results demonstrate that the sedimentary environment in the Okinawa Trough is influenced by sediment supply from mainland China, and reveal temporal variations reflecting changes in the Yangtze River mouth that accompany sea-level changes. In contract, CaCO3 contents of cores in this study are double those in the Okinawa Trough cores, and show an increasing trend at 7.5-6.0 cal kyr BP. Additionally, in the forearc core, the profile of CaCO3 content decreases at 11.5-8.1 cal kyr BP. These variations of CaCO3 contents suggest that marine productivity changed with trophic conditions in sea surface. In addition, the lateral transport of terrigenous sediment by the Kuroshio and Ryukyu currents might contribute to an increased CaCO3 content by reducing the influence of dilution. Variations in the C/N ratio after 7.8 cal kyr BP suggest that the Kuroshio Countercurrent has varied in strength at 1-2 kyr intervals since the early Holocene, influencing the deposition of terrigenous organic matter from the Okinawa Islands in the deeper parts of the east backarc.