Uvigerina-based d18O and Mg/Ca data together with a new Japan Sea core-top Mg/Ca-temperature calibration for temperatures below 5 degrees C from IODP Site 346-U1427 (Japan Sea)

Using the sediments of Integrated Ocean Drilling Program (IODP) Site U1427, a shallow-water site in the southern Japan Sea, we present a continuous foraminiferal (Uvigerina spp.-based) d18O record encompassing the mid-Pleistocene transition (MPT).

Using Uvigerina spp. Mg/Ca ratios and a new core-top Mg/Ca-temperature calibration for the Japan Sea (see supplementary material to main manuscript) it is revealed that the d18O record shows the Japan Sea-typical low glacial d18O values in the late phase of the MPT, across Marine Isotope Stages (MIS) 24-17, while earlier MPT glacials, across MIS 39-25, are characterised by high d18O values. We propose that high glacial d18O values are the result of an improved connection between the shallow, southern Japan Sea and adjacent seas during early MPT glacials.