Presentation Information
[U11-08]Extreme Impact: Glacial-to-Anthropocene monsoon swings & Bay of Bengal stratification★Invited Papers
*Kaustubh Thirumalai1 (1.University of Arizona)
Keywords:
ocean,biogeochemistry,monsoon,tropical hydroclimate
Quaternary archives from the Bay of Bengal provide a powerful test of how Indian Summer Monsoon (ISM) hydroclimate extremes reshape upper-ocean structure and marine ecosystems, with direct relevance for Anthropocene risk. Here, I focus on the high-resolution planktic foraminiferal geochemical record from IODP Site U1446 (Mahanadbi Basin, Bay of Bengal) spanning the last ~22 kyr. Paired Mg/Ca and stable oxygen-18 measurements constrain sea-surface temperature and salinity variability, capturing large swings in freshwater input and the physical conditions that regulate mixing and nutrient resupply. To place these changes in a mechanistic oceanographic framework, I map reconstructed surface conditions into temperature-salinity (T-S) space and evaluate shifts relative to isopycnals (density surfaces), separating thermally versus haline controlled buoyancy regimes and diagnosing stratification-relevant state changes. The record highlights contrasting monsoon extremes: reduced runoff during Heinrich Stadial 1 and enhanced freshwater outflow in the early Holocene, both of which coincided with reduced primary productivity, revealing nonlinear coupling between monsoon forcing, stratification, and biogeochemical response. When interpreted alongside transient deglacial simulations and CMIP6 projections, these results provide a Quaternary benchmark for how hydrological variability, atmospheric circulation, and greenhouse-gas-driven warming may combine to favor persistent stratification and diminished nutrient supply in a region central to South Asian food security. More broadly, the study demonstrates how natural archives can constrain coupled atmosphere-ocean mechanisms and sharpen expectations for future hydroclimate variability and extremes under continued anthropogenic forcing.