Tropical warming in the Timor Sea led deglacial Antarctic warming and atmospheric CO2 rise by more than 500 yr

On the basis of the radiocarbon (14C) plateau-tuning method, a new age model for Timor Sea Core MD01-2378 was established. It revealed a precise centennial-scale phasing of climate events in the ocean, cryo-, and atmosphere during the last deglacial and provides important new insights into causal linkages controlling events of global climate change. At Site MD01-2378, reservoir ages of surface waters dropped from 1600 yr prior to 20 cal ka to 250–500 yr after 18.8 cal ka. This evidence is crucial for generating a high-resolution age model for deglacial events in the Indo-Pacific Warm Pool. Sea-surface temperatures (SST) started to change near 18.8 cal ka, that is ~ 500 yr after the start of, presumably northern hemispheric, deglacial melt and sea level rise as shown by the benthic foraminiferal oxygen isotope ratio (δ18O). However, the SST rise occurred 500–1000 yr prior to the onset of deglacial Antarctic warming and the first major rise in atmospheric carbon dioxide at about 18 ka. The increase in SST may partly reflect reduced seasonal upwelling of cold subsurface waters along the eastern margin of the Indian Ocean, which is reflected by a doubling of the thermal gradient between the sea surface and the thermocline, a halving of chlorin productivity from 19 to 18.5 cal ka, and in particular, by the strong decrease in surface water reservoir ages. Two significant increases in deglacial Timor Sea surface salinities from 19 to 18.5 and 15.5 to 14.5 cal ka, may partly reflect the deglacial increase in the distance of local river mouths, partly an inter-hemispheric millennial-scale see-saw in tropical monsoon intensity, possibly linked to a deglacial increase in the dominance of Pacific El Niño regimes over Heinrich stadial 1.

Research Highlights
► New age model with centennial-scale resolution of deglacial sediments in Timor Sea.
► Precise phasing of deglacial events in the tropical ocean, cryo- and atmosphere.
► Northern hemispheric ice melt preceded tropical SST rise at 18.8 ka by about 500 yr.
► Coastal upwelling off N.W. Australia during Last Glacial Maximum summer.
► Interhemispheric see-saw of tropical monsoon intensity over deglacial times.