East Asian monsoon forcing of suborbital variability in the Sulu Sea during Marine Isotope Stage 3: Link to Northern Hemisphere climate

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Abstract

[1] We have generated a new high-resolution record of variations in planktonic foraminiferal oxygen isotopes (δ18O) and Mg/Ca from a sediment core (IMAGES 97-2141) in the Sulu Sea located in the Philippine archipelago of western tropical Pacific. This record reveals distinct, suborbital-scale δ18O changes, most notably during Marine Isotope Stage 3 (MIS3) (∼30,000 to 60,000 years B.P.). The amplitudes of these δ18O fluctuations (0.4 to 0.7‰) exceed that which can be attributed to sea level changes and must be due to changes in sea surface conditions. In the same interval, variations in planktonic foraminifera Mg/Ca suggest that suborbital surface ocean temperature variations of 1 to 1.5°C in the Sulu Sea were not in phase with δ18O. Combined, this evidence indicates that the MIS3 millennial δ18O events in the Sulu Sea were primarily the result of changes in surface water salinity, which today is directly related to the East Asian Monsoon (EAM) and its influence on the balance between surface water contributions from the South China Sea and Western Pacific Warm Pool (WPWP). Within dating uncertainties the MIS3 Sulu Sea δ18O suborbital variability indicates that times of fresher surface conditions in the Sulu Sea coincide with similar conditions in the WPWP [Stott et al., 2002] and also with intensifications of the summer EAM as recorded in the U-Th dated Chinese (Hulu Cave) speleothem δ18O record [Wang et al., 2001] and thus by inference with interstadials in the Greenland Ice core records. Combined, these results indicate that pronounced suborbital variability in the summer EAM and Intertropical Convergence Zone (ITCZ) during MIS3 was tightly coupled with climate conditions in the northern high latitudes.

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