PALEOCEANOGRAPHIC RECORDS OF INDONESIAN THROUGHFLOW AT ITS EXIT SINCE THE LAST GLACIAL AND THEIR SIGNIFICANCE

The Indonesian Throughflow (ITF), sole conduit between the Pacific and Indian Oceans, plays an important role in regulating heat and fresh water budgets between the two oceans, and in controlling the tropical and global climate. In this study, we investigated records from the Core SO18460 that was drilled at the exit of the ITF into the Timor Sea to reexamine their significance in reflecting the ITF since the last glacial. Records of temperature and salinity of surface and subsurface seawaters, and depth of thermocline (DOT) were reconstructed from δ¹⁸O and Mg/Ca ratio of the planktonic foraminifera of Globigerinoides ruber and Pulleniatina obliquiloculata and were then compared with regional paleoclimatic indices. The results show that salinity of both surface and thermocline seawaters co-varied with regional precipitation over the last glacial cycle, likely indicating transmission of precipitation signal by means of seawater salinity from sea surface to thermocline through upper ocean mixing. Sea surface temperature at the coring site of Core SO18460 oscillated centering at 28 ℃, possibly under influence of the Western Pacific Warm Pool since the early Holocene. In contrast, thermcoline seawater temperature (TWT) was always below 22 ℃, probably indicating that El Niño-Southern Oscillation was located in El Niño-like episodes. Decline of TWT and shoal of DOT might be, on the one hand, in response to more frequent El Niño-like events; and on the other hand, resulted from depression of ITF surface flow caused by increased precipitation due to southward shift of the Intertropical Convergence Zone, and/or by intensification of South China Sea surface flow driven by enhanced East Asian winter monsoon during Holocene. On glacial-interglacial timescale, TWT co-varied with the boreal summer insolation, possibly due to influence of North Pacific Tropical Water sourced waters that were carried by the Mindanao Current to the Sulawesi Sea and merged into the ITF.