Session: Benchmarking & cross-cutting Group 1 (Isotope modelling, COMPARE)
Author: Kaustubh Thirumalai / email@example.com / The University of Texas at Austin
Co-author: Martin Puy, The University of Texas at Austin;
Pedro DiNezio, The University of Texas at Austin;
Jessica E Tierney, The University of Arizona;
Mahyar Mohtadi, MARUM, University of Bremen;
Models project increased year-to-year climate variability in the equatorial Indian Ocean in response to greenhouse gas warming. This response has been attributed to changes in the mean climate of the Indian Ocean associated with the zonal sea-surface temperature (SST) gradient. According to these studies, air-sea coupling is enhanced due to a stronger SST gradient driving anomalous easterlies that shoal the thermocline in the eastern Indian Ocean. We propose that this relationship between the variability and the zonal SST gradient is consistent across different mean climate states. We test this hypothesis using simulations of past and future climate performed with the Community Earth System Model Version 1 (CESM1). We constrain the realism of the model for the Last Glacial Maximum (LGM) where CESM1 simulates a mean climate consistent with a stronger SST gradient, agreeing with proxy reconstructions. CESM1 also simulates a pronounced increase in seasonal and interannual variability. We develop new estimates of seasonal-to-interannual climate variability at the LGM using δ18O analysis of individual foraminifera which indicates a marked increase in δ18O-variance during the LGM and strongly supports the simulations. This agreement further supports the dynamics linking year-to-year variability and an altered SST gradient, increasing our confidence in model projections.