TRANSFORMATION IN PHYTOPLANKTON ECOSYSTEMS CAUSED BY RAPID WARMING AND SEA LEVEL RISE IN THE PLEISTOCENE CARIACO BASIN (MIS 9-7)

Anthropogenic climate change has the potential to alter ocean nutrient circulation and affect the distribution of phytoplankton species, which could lead to species invasions and enhancement of harmful algal blooms. We evaluated the impact of 5 °C warming on tropical coastal environments using the MIS 7.5 (250 kya) warming as an analogue for future change. By combining calcareous nannofossils with sterol and alkenone biomarkers, we reconstructed water column structure, nutrient sourcing, and phytoplankton ecology in the Cariaco Basin (ODP Site 1002). Environmental and ecological variability increased during the rapid warming at the end of the MIS 8 glacial period, and coincided with the first significant abundance of the coccolithophore Emiliania huxleyi at this site. The distribution of the major phytoplankton groups (dinoflagellates, diatoms, and coccolithophores) was primarily driven by water column structure and nutrients consistent with the Margalef's Mandala model of plankton ecology. Using the coccolithophore and stratification proxy Florisphaera profunda, we found that stratification increased during warm periods, concurrent with increases in terrestrial inputs and enhanced production and preservation of organic matter, as shown by sterol proxies. These results suggest enhanced potential for eutrophication and disruption to planktonic ecosystems in high productivity tropical coastal waters with future warming.