Lake-level responses to climate change in an inland basin in the Japanese Islands during the last 16 kyr

Abstract

During the last deglaciation and middle Holocene, rapid climatic changes occurred repeatedly. Previous research has primarily focused on investigating these periods in East Asia's coastal and inland regions of the Eurasian continent. In contrast, a limited number of studies have reported on climate change and its environmental impacts in island areas near the Pacific Ocean. This study aims to reconstruct paleosol drainage conditions and lake water level fluctuations in the Suwa Basin, an inland basin in central Japan, after the last deglaciation. We utilize the identification of paleosols and the geochemistry of lacustrine sediments to discuss climate change and its impacts on terrestrial environments in the East Asian coastal region. During the Last Glacial Maximum, the basin experienced a lowstand period; meandering fluvial systems led to the development of dry and well-drained paleosols. The lacustrine environment expanded between ca. 16 cal kyr BP and 5 cal kyr BP during a transgressive period. Short-term lake-level fluctuations were reconstructed by examining repeated paleosol development and changes in the bulk SiO2 content originating from biogenic silica in lacustrine sediments. Our data suggest that the lake's water level fell at ca. 12 cal kyr BP, 8 cal kyr BP, and 7 cal kyr BP. After 5 cal kyr BP, thin paleosols repeatedly formed during short exposure times due to the rapid sedimentation rate in the delta system, which corresponds to the highstand period. Short-term fluctuations between 16 kyr BP and 5 kyr BP, in the lake water level in the inland basin of the Japanese Islands was influenced by drying and cooling trends in the East Asian coastal region, as well as declines in sea surface temperatures in the western tropical Pacific Ocean. These fluctuations roughly synchronize with the Younger Dryas stadial and an 8.2 ka cooling event. Changes in precipitation, which responded to fluctuations in the East Asian summer monsoon intensity and tropical depressions, likely regulated the lake water level. These findings imply the predominant influence of paleoclimate fluctuations over thousands of years on the hydrological regime of lake systems across the island area of the East Asia.