The Mid Pleistocene Transition diatom record from the Japan Sea

The East Asian Monsoon (EAM) is not only one the most important climate phenomena in Asia, but also plays a significant role in the global climate system. Aiming to better understand if and how the EAM patterns will be impacted by future climate changes, we have studied how diatoms behaved during the Mid Pleistocene Transition (MPT, 700 ka to 1.25 Ma), a major natural climate reorganization due to changes in Earth's orbital cycles. The shift from the 41ka obliquity to 100 ka eccentricity increases long term average global ice volume and establishes a strong asymmetry in global ice volume cycles This transition has been recognized in diatom records from the North Atlantic and Pacific oceans. However, this is one to the first diatom records to be produced for this area.

In here we present two diatom records through MPT: Site U1427 is located in the Yamato Basin, under the influence of the Tsushima Warm Current, affected by the sea level difference between the East China Sea and Japan Sea and the river runoff that is controlled by the monsoon behavior. Site U1423 is key for the MPT studies because it is being used by the IODP Expedition 346 scientific collaborators for glacial and ice presence (oxygen isotopes study) and Ice Raft Debris (IRD) signals (key features for recording the orbital cycles). The IRD study will be complemented by the presence of ice and freshwater diatoms.

First results show that the MPT in our study area is marked by a decrease of diatoms at the end of MPT, given by the abundance of marine diatom species. However freshwater diatoms do not appear to respond to this event, implying no significant changes in the monsoon patterns.