Millennial-scale variability of East Asian summer monsoon inferred from sea surface salinity in the northern East China Sea (ECS) and its impact on the Japan Sea during Marine Isotope Stage (MIS) 3

Color alternations in deep-sea sediment in the Japan Sea have been thought to be linked to millennial-scale variations in the East Asian summer monsoon (EASM), associated with the Dansgaard-Oeschger (D-O) cycles and Heinrich events in the high-latitude North Atlantic during Marine Isotope Stage 3 (MIS 3). In this study, we investigate the variability of sea surface salinity (SSS) in the northern East China Sea (ECS) to evaluate the EASM precipitation in South China and its linkage to the sediment color of the Japan Sea during MIS 3. High time resolution (< 100 years) SSS along with sea surface temperature (SST) records were reconstructed using paired Mg/Ca and the oxygen isotope of planktic foraminifera Globigerionoides ruber sensu stricto from core KR07-12 PC-01 recovered from the northern ECS. The results indicate that millennial-scale variability of the SSS is observed with the amplitude of ~ ± 1 during MIS 3. The variations in SSS are well correlated to D-O cycles and Heinrichs. The EASM precipitation decreases in association with the southward shift of the westerly jet in D-O stadials and Heinrichs, suggesting suppressed moisture convergence along the EASM front associated with weakened North Pacific subtropical high in response to the slow-down of the Atlantic Meridional Overturning Circulation. In a comparison between the SSS in the ECS and the color alternation in the Japan Sea, closely correlated variations between the two records in the interval 44–34 ka indicate that the SSS in the ECS plays a crucial role in regulating nutrient and salinity inflow into the Japan Sea. However, the linkage becomes ambiguous, especially after ~ 30 ka, when the sea level falls toward the level of the last glacial maximum. This shift is associated with changes in sediment facies, confirming that the underlying mechanism in regulating the sedimentary change in the Japan Sea depends on the sea level.