Variations of the Last Glacial Warm Pool: Sea surface temperature contrasts between the open western Pacific and South China Sea

Abstract

High‐resolution paleoceanographic records from the southern South China Sea (SCS) and the tropical open western Pacific reveal multicentennial‐ to millennial‐scale variations of the Western Pacific Warm Pool (WPWP) over the last 40 kyr. During the Last Glacial Maximum (LGM), in marine isotope stage (MIS) 2, planktonic Globigerinoides sacculifer δ18O in core NS93‐5 from the southern SCS and in core WP92‐5 from the central WPWP registered a similar average value of about −1.5‰. However, the average δ18O value was about 0.5‰ more negative in the SCS than in the central WPWP, as was their difference before and after the LGM in the later part of MIS 3 and early portion of MIS 1. These results indicate weaker monsoonal and fluvial effects on the southern SCS during the last glacial than during pleniglacial and postglacial periods owing to different oceanic circulation modes and regional topography. The calculated seasonal temperature differences of summer and winter sea surface temperatures (SSTs) between the open WPWP and the southern SCS were up to 3–4.5°C during the LGM but only slightly over 3°C in the southern SCS and less than 2°C in the open WPWP during other periods. From about 29 to 25 ka the MIS 2/3 transition was marked by a sudden SST increase in the southern SCS but a decrease in the open WPWP. Over this 4 kyr period the average annual SST appeared to be only 28°C in the central WPWP but more than 28°C in the southern SCS, indicating a shift of the central WPWP toward the far west during that time. Furthermore, our results imply a period of nearly 6 kyr from 22.5 to 16.5 ka without an apparent warm pool of 28°C in the western Pacific.