EXTREME INDIAN MONSOON STATES AND STRATIFICATION-INDUCED PALEOPRODUCTIVITY COLLAPSES SINCE THE LAST ICE AGE (Invited Presentation)

Monsoon precipitation fuels biogeochemical cycling across Asia and exerts first-order controls on food security in Earth's most densely-populated regions. Despite projected greenhouse intensification, anthropogenic and internal Earth-system trajectories impose uncertainty in future monsoon evolution. Here we use foraminiferal geochemistry and assemblages to document centennially-resolved Indian monsoon runoff and productivity fluctuations across the last glacial transition, a period featuring extreme monsoon states. Our record reveals multi-centennial runoff deficits across the Holocene with peak runoff during 10-9 ka and abject monsoon failure during Heinrich Stadial 1, along with strong millennial-scale deglacial variability. Counterintuitively, we find that both extreme states of peak runoff and failure were associated with paleoproductivity collapses in the Bay of Bengal. Individual foraminiferal analyses pinpoint upper-ocean stratification as a persistent feature of both scenarios. Thus, despite substantial impacts on societies and civilizations across the subcontinent, monsoon variability for much of the Holocene was geologically medial and underscores efforts to constrain future extreme states and resultant biogeochemical implications.