[M-IS04] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS04-P03] Major re-organisation in marine ecosystem during the Late Miocene Global Cooling caused by changes in major monsoonal mode

*Kenji Matsuzaki¹, Masayuki Ikeda², Ryuji Tada² (1.Atmosphere and Ocean Research Institute, The university of Tokyo, 2.Graduate School of Science, The University of Tokyo)

Keywords:Summer Monsoonal Rainfalls, Japan Sea, Ecosystem response

The Late Miocene Global Cooling (LMGC) between 7.6 and 5.8 Ma corresponds to a shift from an East Asian Summer Monsoon (EASM) dominated climate to an East Asian Winter Monsoon (EAWM) dominated one. In the Japan Sea, one of the dominant plankton groups of the Neogene, radiolarians, is of interest because an endemic species dominate its assemblages, the species Cycladophora nakasekoi. This species occurred between 10 and 7.3 Ma and during the LMGC, co-existed for 500 kyr with a species of the same Genus Cycladophora sphaeris. Here, using sediment cores collected at Site U1425 of the Integrated Ocean Drilling Program (IODP) Expedition 346, we estimated C. nakasekoi and C. sphaeris accumulation rates for a better understanding on the variation of their fluxes during the LMGC and clarify the relationship between C. nakasekoi and C. sphaeris ecology and the LMGC. We interpreted changes in sediment physical properties collected at Site U1425 of the IODP Expedition 346 for reconstructing local hydrography. It is probable that under an EASM domination, strong summer monsoonal rainfalls caused a stratification of the water column in the Japan Sea by a strong riverine run-off delivering high amount of nutrient and dissolved silica to the shallow water, and favoured the blooming of C. nakasekoi. During the LMGC the EAWM strengthened likely because of both the establishment of an east Greenland Ice-sheet and decrease in height of the Iran Plateau, which would have strengthened the Siberian High and affected the path of tropical moist air respectively. Strong EAWM intensifies northerlies, and it is likely that the water column of the Japan Sea was well mixed during the LMGC and promoted the blooming of diatoms and C. sphaeris. In addition, the great marine predator, the shark Carcharocles megalodon, steadily disappears from the seas around Japan during the LMGC as well. Thus, the major re-organization in climate and marine nutrient systems during the LMGC is of a broad impact on marine micro to macro fauna.