Long-term vegetation change and controlling factors in Donghae area, Korea, over the past 40,000 years

Determining the effect of climate change since the last glacial maximum (LGM) in the East Sea (Sea of Japan) coastal region of Korea has been difficult owing to a dearth of suitable paleoclimate proxies. A 40,000-year carbon isotope (δ13C) record from cave deposits collected from Cheongok Cave, Korea reveals both long-term change and superimposed shorter-term isotopic excursions. The δ13C value of the sedimentary organic matter, a proxy for past vegetation change, varied from − 25‰ to − 21‰, with lower values during the LGM and higher values during the Holocene, a pattern that is generally consistent with trends in total organic carbon content (TOC%) and magnetic susceptibility. From the LGM to the late Holocene, the C4 plant abundance (mainly grasses), estimated using a simple binary mixing model, increased from 15% to 45%. This long-term change resembles trends in biogenic opal production in the East Sea, sea-surface temperature, and global sea level more than it does Asian summer monsoon strength. Long-term changes in C4 plant abundance in eastern coastal areas of Korea over the last 40,000 years were probably affected most strongly by sea level-driven ocean circulation changes in the East Sea coupled with continental ice-volume changes; low pCO2 during the LGM was not sufficient to cause the expansion of C4 plant coverage without favorable climatic conditions.

► Cave sediments reveal significant variations in the organic carbon isotopic values.
► C4 plant changes were affected strongly by sea level-driven ocean circulation.
► Low pCO2 during the LGM was not sufficient to cause the C4 plant expansion.