Japan Sea oxygen isotope stratigraphy and global sea-level changes for the last 50,000 years recorded in sediment cores from the Oki Ridge

We obtained twenty AMS (Accelerator Mass Spectrometry) radiocarbon dates, 2 tephra layer chronologies, and a planktonic foraminiferal δ18O stratigraphy for the last 50,000 years from Japan Sea cores from the Oki Ridge. In this paper we report AMS 14C results that allow us to reconstruct a high-resolution chronology of the cores and discuss millennial scale climate changes recorded in Japan Sea sediments. The sedimentation rate for the site increased dramatically from the glacial stage to the Holocene as a result of significant hydrological changes associated with deglaciation and global sea-level rise. A lighter δ18O anomaly for the planktonic foraminifers was found during the LGM (Last Glacial Maximum). This shift corresponds to a freshening of the Japan Sea surface waters, and is mainly due to a global sea-level drop rather than anomalously warm SSTs (sea-surface temperatures) as previously reported. Our record combined with the global sea-level data suggests that the LGM started about 30 kyr ago and that the salinity of the Japan Sea became fresher than at present. The SSTs during MIS (Marine Oxygen Isotope Stage) 3 were relatively stable and global sea-level was not lower than ca. − 80 m. The surface water of the Japan Sea attained “normal” saline levels following the Younger Dryas cold event and reached the present-day δ18O values 7 kyr ago.