Relationship between environmental change on Geoje Island, southern coast of Korea, and regional monsoon and temperature changes during the late Holocene

To reconstruct environmental change during the late Holocene, we investigated sedimentary δ13C values from an exposed section on Geoje Island, on the southern coast of Korea. The δ13C values ranged from −24.3‰ to −21.2‰ and were divided into five stages based on the average value (−22.5‰). A comparison with the regional climate index revealed that wet periods linked to intensified summer monsoon conditions occurred at Stage 1 (4500–3600 cal BP), Stage 3 (1350–900 cal BP), and Stage 5 (300 cal BP to present). Dry intervals were found at Stage 2 (3600–1350 cal BP) and Stage 4 (900–300 cal BP). We found two different vegetational responses to changes in regional temperature and summer monsoons. Stage 3, corresponding to the MWP, was characterized by an association between the δ13C values on the island and the regional temperature, but Stage 4, including the LIA interval, did not show such a relationship. Furthermore, based on comparison with the summer monsoon index, this study suggested that, on the southern coast of Korea, vegetational change was controlled by an MWP-like mode during the warm and wet periods following regional climate change, whereas a LIA-like mode showing independent climate change was dominant during the cold and dry periods. This difference in vegetational changes along the southern coast of Korea and regional (mainly terrestrial-signal based) climate change may be attributed to the influence of sea surface temperature changes in the tropical ocean through the transport of warming seawater by the Kuroshio and Tsushima currents on the East Asian coastal area, including this study area, than on the inner part of the East Asian continent.