Millennial-scale hydroclimate variations in southwest China linked to tropical Indian Ocean since the Last Glacial Maximum

Abstract

Indian summer monsoon (ISM) variations have been linked to the orbital-scale boreal summer insolation and millennial-scale North Atlantic climates. Recent studies show the critical role of Indian Ocean sea-surface temperatures (SSTs) in affecting deglacial millennial-scale monsoon oscillations. However, it is unclear whether SSTs can affect monsoon rainfall and terrestrial hydroclimate during the Holocene. Here we report multiproxy evidence of hydroclimate changes in southwest China since the Last Glacial Maximum. Similar to the often-documented gradual decrease in Holocene monsoon rainfall with superimposed millennial-scale variations, our records particularly show pronounced hydroclimate fluctuations including wet conditions at ∼5000-4000 yr ago, and perhaps over the past 1000 yr. We also find coherent variations between our records and sea-surface salinities in the eastern Indian Ocean, suggesting that terrestrial hydroclimate and resultant continental drainage have affected surface ocean conditions. These fluctuations are likely linked to changes in SSTs downstream of the monsoon source in the tropical western Indian Ocean, i.e., a warmer ocean and more monsoon rainfall. We conclude that the influence of both insolation and tropical SSTs on the ISM has persisted from the last deglaciation into Holocene.