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 (delta(13)C) record from cave deposits collected from Cheongok Cave, Korea reveals both long-term change and superimposed shorter-term isotopic excursions. The delta(13)C value of the sedimentary organic matter, a proxy for past vegetation change, varied from -25 parts per thousand to -21 parts per thousand, 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 C(4) 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 C(4) 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 C(4) plant coverage without favorable climatic conditions. (C) 2011 Elsevier B.V. All rights reserved.