Shelf exposure influence on Indo-Pacific Warm Pool climate for the last 450,000 years

The Indo-Pacific Warm Pool is the largest source of heat and rainfall on Earth, but the mechanisms driving long-term climate variability in this region remain uncertain. Some studies suggest that precessional variations in insolation exert a primary role; alternatively, sea level change may be more important, with exposure of the Sunda and Sahul shelves leading to weakened Walker circulation across the Indian Ocean during glacial periods. The limited number of paleoclimate records from the warm pool that extend beyond the Last Glacial Maximum makes it difficult to test these competing hypotheses. Here, we present a 450,000-year long reconstruction of sea surface temperatures, sub-surface temperatures, and regional vegetation from southern Sumatra. We show that the dominant signal in each record is the 100 ky glacial cycle. We find that both surface and sub-surface temperatures cool during glacial periods, but the sub-surface cools more, reflecting a shoaling of the thermocline. Southern Sumatra and western Java consistently exhibit increased C ₄ grass coverage and an enhanced dry season during glacial periods. The observed changes in the thermocline and rainfall seasonality are consistent with the shelf exposure mechanism, suggesting that sea level changes exert a prominent role in warm pool climate over glacial-interglacial timescales.