Interstadial coral reef terraces and relative sea-level changes during marine oxygen isotope stages 3-4, Kikai Island, central Ryukyus, Japan

摘要

Coral reef terraces are one of the best recorders of relative sea-level changes during the last glacial cycle. Thus far, knowledge of relative sea-level record based on coral reefs during the marine Oxygen Isotope Stage (OIS) 3 has been limited to studies of the Huon Peninsula, Papua New Guinea. High-precision a α-spectrometric ~(230)Th/~(234)U dating demonstrated an offlapping sequence of five coral reef complexes, ages of which are ～ 66, ～ 64, ～ 62, ～ 55 and ～ 52 ka, in the northern part of Kikai Island, central Ryukyus of Japan. Interstadial reefs, characterized by deepening-upward sequences of coral assemblages, recorded three hemicycles from transgression to highstand at ～52, ～62, and ～66ka, during which these reefs were drowned. These highstands in the relative sea-level record can be correlated with the eustatic record reconstructed from the Huon reef terraces and with the interstadials 14, 18, and 19 of the GISP 2 oxygen isotope record. This consistency confirms the Huon sea-level record of OIS 3 and implies that the eustatic sea level responded to the millennial-scale climate changes even during the glacial period of OIS 4.