Low‐Latitude Forcing and High‐Latitude Response of the South Asian Summer Monsoon Through the Pliocene

Abstract

AbstractPrecipitation carried by the Asian summer monsoon influences the livelihoods of millions of people, and there has been a great deal of work trying to reveal the driving mechanisms behind past changes. Compared to the widely studied East Asian summer monsoon, the behavior of the South Asian summer monsoon (SASM) in the Pliocene is still not well known. Here, we present new high‐resolution geochemical (Rb/Sr and Ti) data from the lacustrine Yuanmou Basin (Southwest China) spanning the Pliocene to early Pleistocene (4.30–2.0 Ma) that permit detailed analysis of hydroclimate changes related to orbital‐scale SASM variability. We find a clear weakening of the SASM at 2.9–2.75 Ma, which may be related to warming in the high‐latitude southern hemisphere and a weakening of atmospheric circulation at low latitudes over the Indian Ocean. Our results highlight that 405‐ and 100‐Kyr eccentricity forcing had a dominant role in driving climate change in the Yuanmou Basin during the Pliocene to early Pleistocene. Based on analysis of our data from the Yuanmou Basin, coupled with marine data from the Arabian Sea, we suggest that orbital‐scale SASM variability during the Pliocene was mainly controlled by changes in low‐latitude insolation. In addition, oscillations of the West Antarctic ice sheet after ∼3.5 Ma also significantly influenced the evolution of the SASM on orbital time scales.