Abstract
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 (δ18OCc) 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 δ18OCc are not fully understood. Part of the challenge arises from the fact that speleothem δ18OCc depends on not only the δ18O of precipitation but also temperature and kinetic isotope effects. Here we quantitatively deconvolve these parameters affecting δ18OCc 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.
Highlights
The Asian monsoon provides fresh water for a densely populated region and plays a major role in global climate as a conveyor of latent and sensible heat[1]
Changes in the cross-equatorial ocean energy transport driven by the Atlantic Meridional Overturning Circulation (AMOC) play a fundamental role in the monsoon system through its impact on the interhemispheric temperature gradient and the latitudinal position of the intertropical convergence zone (ITCZ)[2]
Palaeo-climate records offer a unique opportunity to study the links between changes in AMOC strength and the Asian monsoon system during periods of the past when the AMOC was substantially weaker or even completely collapsed[4,5], but there is no general consensus about the dominant mechanisms
Summary
The Asian monsoon provides fresh water for a densely populated region and plays a major role in global climate as a conveyor of latent and sensible heat[1]. The oxygen isotopic composition of speleothem calcite from East Asia suggests that rapid changes in the strength of the AMOC and the Asian monsoon were tightly linked[3,10,11,12,13,14,15]. An abrupt shift towards more positive δ18OFl is only observed around 133 ka, coinciding with the peak of MWP 2B (Fig. 2 and Supplementary Data Table 1g).
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