GLACIAL-INTERGLACIAL CHANGES IN THE THERMOCLINE STRUCTURE OF THE MAKASSAR STRAITS: IMPLICATIONS FOR CHANGES IN THE INDONESIAN THROUGHFLOW

The Indo-Pacific Warm Pool exerts a strong influence on the global climate system. It is a major control on heat and moisture exchange between the oceans and the atmosphere, which in turn affect global precipitation and temperature. The Makassar Strait is the main passage for flow between the western Pacific Ocean and the Indian Ocean with implications for the Indonesian Throughflow. During the last deglaciation, the Makassar Strait likely experienced significant changes in throughflow that would affect the transport of heat and salt in the North Atlantic Ocean, and Atlantic meridional overturning circulation. We hypothesized that this change in throughflow would be evidenced by changes in thermocline depth. Here we present δ¹⁸O and Mg/Ca records from two sediment cores (MD98-2177 (01°24.20 N, 119°04.68 E, north Makassar Strait, and MD98-2160 (5°12.07 S, 117°29.20 E, south Makassar Strait) and reconstruct past water column temperature and salinity from three species of planktic foraminifera: G. ruber in the surface mixed layer, P. obliquiloculata in the thermocline, and G. mernardii in the sub-thermocline. The δ¹⁸O records show the transition from the last glacial maximum (LGM, 26.5 ka) into the Holocene as a decrease of ~2.0 ‰ in all species. Temperatures derived from shell Mg/Ca further allow us to distinguish between the contributions of temperature and δ¹⁸O_seawater to foraminifera δ¹⁸O. Coupled δ¹⁸O and Mg/Ca across species shows a change in thermocline depth across the Makassar Strait due to increased throughflow, which we hypothesize is due to sea-level rise.