Sea-level variation during MIS 11 constrained by stepwise Osaka Bay extensions and its relation with climatic evolution

Abstract

Marine oxygen isotope stage (MIS) 11 has been described as a super-interglacial because of its long duration, more than 30 ka, but this view is often refuted by the observation that the peak sea level and maximum temperature did not surpass other interglacials, including the last interglacial. We address this problem using data from coastal sediments; we conducted diatom and sulfur analyses on two cores of high accumulation rate (0.52 m/ka) sediments from Osaka Bay, Japan. A linear age model applied to the diatom data shows that sea-level variations with precession cycles are correlated with oxygen isotopic events 11.3, 11.24, 11.23, 11.22, and 11.1. Diatom abundances reveal sea level increases and falls because of environmental changes caused by stepwise extension of the bay. This extension can be verified and mapped using data from 15 other drill cores. Sea level was above the sill for Osaka Bay during the marine interval in Osaka Bay, spanning 60 ka. It was above the sill for Kawachi Bay during the marine interval in Kawachi Plain for a duration of 44 ka, including events 11.3 and 11.23. The highest sea level was above the sill for Kyoto Bay during an interval of 16 ka centered at event 11.3. Estimates of sill elevations together with geological data suggest that the sea level of MIS 11 changed within a range from −60 m to +20 m. Palynological data from the same core show that the MIS 11 climate around Osaka Bay was divided into early warm-temperate and late cool-temperate times, with a boundary between events 11.3 and 11.24. During the marine interval in Kyoto, the climate was an extremely warm hypsithermal, almost coincided with the warmest interval in Antarctica where temperatures are >0 °C.