Penultimate deglaciation Asian monsoon response to North Atlantic circulation collapse

During glacial terminations, massive iceberg discharges and meltwater pulses in the North Atlantic triggered a shutdown of the Atlantic Meridional Overturning Circulation (AMOC). Speleothem calcium carbonate oxygen isotope records (δ¹⁸O_Cc) indicate that the collapse of the AMOC caused dramatic changes in the distribution and variability of the East Asian and Indian monsoon rainfall. However, the mechanisms linking changes in the intensity of the AMOC and Asian monsoon δ¹⁸O_Cc are not fully understood. Part of the challenge arises from the fact that speleothem δ¹⁸O_Cc depends on not only the δ¹⁸O of precipitation but also temperature and kinetic isotope effects. Here we quantitatively deconvolve these parameters affecting δ¹⁸O_Cc by applying three geochemical techniques in speleothems covering the penultimate glacial termination. Our data suggest that the weakening of the AMOC during meltwater pulse 2A caused substantial cooling in East Asia and a shortening of the summer monsoon season, whereas the collapse of the AMOC during meltwater pulse 2B (133,000 years ago) also caused a dramatic decrease in the intensity of the Indian summer monsoon. These results reveal that the different modes of the AMOC produced distinct impacts on the monsoon system.