Tropical Climate Variability from the Last Glacial Maximum to the Present

Kristina Dahl, Ph.D., 2005
Delia Oppo, Advisor

This thesis evaluates the variability of two tropical climate phenomena over the past 20,000 years. The first phenomenon is the migration of the Intertropical Convergence Zone (ITCZ) within the tropical Atlantic region. Using both a coupled ocean-atmosphere general circulation model and phytoplankton biomarkers contained within Cariaco Basin sediments, we find that the ITCZ migrates southward in response to Northern Hemisphere cooling. The second phenomenon examined is the Indian Monsoon. We find that terrestrial plant waxes within Arabian Sea sediments can be used to reconstruct southwest monsoon winds. In addition, we use planktonic foraminiferal Mg/Ca ratios to reconstruct sea surface temperature (SST) patterns associated with monsoon-induced upwelling. We find that summer monsoon upwelling was reduced during the last glacial period and enhanced during the Early Holocene. The SST changes associated with variability in upwelling are, however, super-imposed upon larger-scale temperature changes, reflecting the competing effects of global and local climate processes.