Holocene sea surface temperature variations recorded in corals from Kikai Island, Japan

Abstract

Understanding seasonal to interannual characteristics of the climate during the transition from the “Holocene Optimum” (7.0–5.0 kyr BP) to mid-Holocene cold and dry period (4.6–4.0 kyr BP) is important since it is related to the evolution and collapse of human civilization in East Asia. To investigate those characteristics, we reconstructed a seasonal scale sea surface temperature (SST) and measured oxygen isotope ratios (δ¹⁸O) in seawater (δ¹⁸O_seawater) using modern and fossil (4.9 kyr) corals from Kikai Island. Larger seasonal amplitudes observed among the reconstructed SST values and δ¹⁸O_seawater change at 4.9 kyr suggest that the East Asian Monsoon (EAM) circulation might be stronger than the present-day. Our compiled coral records, along with the previous studies from Kikai Island, also suggest that the largest SST amplitude during the Holocene Optimum was recorded at 4.9 kyr and an abrupt cold climate shift occurred during the Holocene Optimum and the Pulleniatina Minimum Event (PME) in the north-western Pacific.