(Table S1) Stable oxygen isotopic values and Mg/Ca ratios of Globigerinoides ruber w from sediment core AAS9_21@en

Variations in sea surface temperature (SST), d18O of sea water (δ18Ow), and salinity were reconstructed for the past 68 ka using a sediment core (AAS9/21) from the eastern Arabian Sea (EAS) in order to understand the changes in evaporation and precipitation associated with the monsoon system. The Mg/Ca-derived SST record varies by ~4°C; it shows that marine isotope stage (MIS) 4 was warmer than MIS 3, that the Last Glacial Maximum was 4°C cooler than the present, and that there was a 2°C increase within the Holocene. MIS 4 records higher d18Ow and salinity values than MIS 2, suggesting variable flow of low-salinity Bay of Bengal flow into the EAS during glacial periods. The transition from MIS 4 to MIS 3 was marked with a conspicuous shift from higher to lower d18Ow values, which reflects a decrease in the evaporation-precipitation budget in the EAS, perhaps due to the strengthening of southwest monsoon. Monsoon reconstructions based on d18Ow reveal that monsoon-driven precipitation was higher during MIS 3 and MIS 1 and was lower during MIS 2 and MIS 4. This is consistent with earlier monsoon reconstructions based on upwelling indices from the western Arabian Sea. However, the amplitude of monsoon fluctuations derived through upwelling indices and d18Ow varies significantly, which may indicate spatial variability of monsoon rainfall.

本研究利用取自阿拉伯海东海域（eastern Arabian Sea, EAS）的沉积物岩芯（AAS9/21），重建了过去68 ka以来的海表温度（sea surface temperature, SST）、海水δ18O（δ18Ow）与盐度变化，旨在揭示与季风系统相关的蒸发与降水演变过程。基于Mg/Ca比值重建的海表温度记录波动幅度约为4℃，结果显示海洋同位素阶段（marine isotope stage, MIS）4的温度高于MIS3，末次冰盛期（Last Glacial Maximum）较现代低4℃，全新世（Holocene）期间海表温度上升了2℃。MIS4时期的δ18Ow与盐度值均高于MIS2，表明冰期期间低盐度的孟加拉湾（Bay of Bengal）海水流入阿拉伯海东海域的通量存在显著变化。从MIS4向MIS3的过渡以δ18Ow值从高到低的显著转变为标志，这反映了阿拉伯海东海域的蒸发-降水收支减少，这可能与西南季风（southwest monsoon）的增强有关。基于δ18Ow的季风重建结果显示，季风驱动的降水在MIS3与MIS1时期较高，而在MIS2与MIS4时期较低。该结果与此前基于阿拉伯海西部上升流指数（upwelling indices）的季风重建结果一致。不过，基于上升流指数与δ18Ow得到的季风波动幅度存在显著差异，这可能指示了季风降雨的空间异质性。