JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS05] Cenozoic Evolution of the Asian Monsoon and the Indo-Pacific Paleoclimates

convener:Masanobu Yamamoto(Faculty of Environmental Earth Science, Hokkaido University), Steven C Clemens(Brown University), Hongbo Zheng(Research Center for Earth System Science, Yunnan University), Ryuji Tada(Department of Earth and Planetary Science, Graduate School of Science, The Univeristy of Tokyo)

[MIS05-04] Influences of East Asian summer and winter monsoons on the millennial-scale color alternation of Japan Sea sediment

★Invited Papers

*Takuya Sagawa1, Yusuke Narita2, Takuya Matsuzaki3, Masafumi MURAYAMA4, Takashi Hasegawa1, Akiko Goto1, Takeshi Nakagawa5 (1.Institute of Science and Engineering, Kanazawa University, 2.Graduate School of Natural Science and Technology, Kanazawa University, 3.Center for Advanced Marine Core Research, Kochi University, 4.Faculty of Agriculture and Marine Science, Kochi Univeristy, 5.Ritsumeikan University)

Keywords:Japan Sea, East Asian monsoon

Millennial-scale total organic carbon (TOC) content in the Japan Sea sediments is characterized by the Dansgaard-Oeschger (DO) event like variability. The DO-like pattern of TOC is thought to reflect the East Asian summer monsoon induced productivity and stratification change. However, TOC content is also influenced by changes in the oxygen content of the bottom water. Here, we conducted Br measurement of two sediment cores retrieved from close sites with different depth, 400 and 850 m water depths, off the Wakasa Bay in the southern Japan Sea. The deeper sediment core (WB6: 850 m) shows clear dark-light color alternations, and parallel laminations are observed in some dark layers. On the other hand, the shallower sediment core (WB4: 400 m) shows gradual color change and no lamination is observed throughout the core. Since the analyzed Br/Ti shows a strong positive correlation with the marine organic carbon (MOC) contents estimated by TOC and their carbon isotope, we use Br/Ti as a MOC content proxy. The MOC contents of two sediment cores show generally similar variations but details are not similar. The WB6 shows a larger MOC amplitude and higher frequency fluctuation than that of WB4. We infer that the MOC change in the shallower WB4 core mainly reflects primary productivity because no anoxic condition is indicated by sediment structures and that in the deeper WB6 core is influenced by both productivity and oxygen level of the bottom water, which is regulated by ventilation due to winter cooling. Since the MOC fluctuation of WB6 is more similar to the Greenland ice core isotope record than WB4, it is suggested that the MOC variation (alternation of dark and light color) in the deeper Japan Sea sediment is caused by both East Asian summer and winter monsoon variations.