ANTARCTIC LINK WITH EAST ASIAN SUMMER MONSOON VARIABILITY DURING THE HEINRICH STADIAL-BøLLING INTERSTADIAL TRANSITION

Previous research has shown a strong persistence for direct teleconnections between the East Asian Summer Monsoon (EASM) and high northern latitude climate variability during the last glacial and deglaciation, in particular between monsoon weakening and reduced Atlantic meridional overturning circulation (AMOC). However, less attention has been paid to EASM strengthening as AMOC was reinvigorated following peak Northern Hemisphere (NH) cooling episodes. Moreover, climate model simulations have suggested a strong role for Antarctic meltwater discharge in modulating northward heat transport and hence NH warming, yet the degree to which SH climate anomalies impacted the Asian monsoon region is still unclear.

Here we present a new high-resolution stalagmite oxygen-isotope record from the EASM affected region of central China, which documents two prominent stages of increased ¹⁸O-depleted moisture delivery to the region during the transition from Heinrich Stadial 1 (HS1) to the Bølling-Allerød (B-A) interstadial, in general agreement with the Greenland ice core records. We propose that the two-stage EASM intensification observed in our speleothem records were linked with two massive Antarctic meltwater discharge events at 16.0 ka and 14.7 ka, immediately following the peak HS1 stadial event, through novel comparisons with a recent ice-berg rafted debris (IBRD) record from the Southern Ocean. The mechanistic explanation for these teleconnections can best be explained by Antarctic freshwater input to the Southern Ocean cooling the surrounding surface waters and, through resultant sea ice expansion, causing the SH Westerlies and ITCZ to shift northward. Moreover, increased meltwater during the two IBRD events would have freshened the source of Antarctic Intermediate Water (AAIW), stimulating the formation of North Atlantic Deep Water (NADW) and reinvigorating the AMOC into full swing during the HS1- Bølling transition. The result of this sequence-of-events would have been warming in the North Atlantic whilst at the same time cooling in the Antarctic; the ensuing interhemispheric temperature gradient would have acted to push the ITCZ northward, weakening the Australian-Indonesian summer monsoon (AISM) whilst enhancing the EASM.