[M-IS12] Paleoclimatology and paleoceanography

[MIS12-P27] Orbital-scale flooding frequency inferred from Lake Biwa core for the past 1.8 million years

*Nodoka Kuramoto¹, Masayuki Ikeda¹ (1.The University of Tokyo)

Keywords:monsoon, Milankovitch cycle, Pleistocene, Lake Biwa

The East Asian summer monsoon (EASM) transfers huge amounts of heat and moisture from the ocean to the land and has direct impacts on global atmospheric circulation. The long-term EASM variability has been driven by local solar radiation and global ice volume dynamics, yet their relative impact varies by regions and periods based on various proxies and climate models. At Lake Biwa in Japan, which is under the influence of EASM, pollen-based precipitation has varied mainly with the 20-kyr insolation cycle for the past 450 ka, while the 100-kyr signal predominated in the same regions in some climate models. However, since the pollen record is also dominated by millennium cycles, despite an average interval of ~3,000 years, it is necessary to examine the precipitation record at a high temporal resolution. In this study, we attempted to reconstruct precipitation variations over the past 1.8 million years based on gravel frequency, grain size changes, and lake level variations estimated from sedimentary facies in the Karasuma core from the shore of Lake Biwa. While the lake level record was dominated by millennial-scale fluctuations probably influenced by tectonic-related changes in silk depth seismic, flood-related gravel frequencies were dominated by 20-, 40-, 100-, and 400-kyr orbital cycles. In particular, amplitude modulations of the 20-kyr cycle in gravel frequency show 100- and 400-kyr periodicities, which are consistent with those of pollen-based precipitation records. The 40- and 100-kyr cycles of gravel frequency were also found to be predominant similar to those of glacial cycle. Contrary to the climate model results, the 100-kyr signal was not as prominent. These results suggest that the precipitation change around Lake Biwa was strongly influenced by the solar radiation change in the climatic precession cycle in addition to glacial forcing.