PP21A-06 Views into tropical Indian Ocean hydroclimate variability since the Last Glacial Maximum from Madagascar stalagmites (Invited)

Abstract: Stalagmites from northern Madagascar have provided much-improved records of the nature and causes of Last Glacial Maximum-to-recent summer monsoon variability in the western Indian Ocean region. Stable isotope and trace element records indicate a consistent relationship between monsoon strength in northern Madagascar and rainfall throughout eastern tropical Africa both north and south of the equator. Our results suggest that monsoon changes do not reflect north-south shifts of the regional tropical rainbelt. Rather, rainfall tracks changes in the east-west sea surface temperature (SST) gradient in the tropical Indian Ocean, a pattern observed on interannual timescales today. Over the last glacial period and deglaciation, this gradient appears to be tightly connected to the strength of the North Atlantic’s overturning circulation. Over the Holocene, existing and new records show a temporal pattern unexpectedly out of phase with Southern Hemisphere summer insolation, likely due to continued control by the east-west SST gradient in the Indian Ocean. We assess progress and challenges in robustly documenting centennial-to-millennial scale variability over the Holocene. Synthesizing climate model output and proxy data, we then explore the dynamics behind past east-west SST gradient changes and their relevance for future rainfall changes in northern Madagascar.