Title: Sustained Tropical Pacific Productivity During Pliocene Warmth

Speaker: Kristin Kimble, Ph.D., Postdoc in the Robinson Biogeochemistry Lab at GSO

Abstract: During the permanent El Niño-like mean state of the Pliocene (5.3-2.6 Ma), surface and thermocline waters in the eastern equatorial Pacific Ocean were ~2°C warmer than present. Despite the strong relationship between warm and unproductive waters observed during modern El Niño events, biomarker records preserved in marine sediment cores suggest high biological productivity during the warmer Pliocene. We measured biomarker concentrations and planktic foraminiferal stable oxygen and carbon isotopes along east-west and surface-subsurface transects to address the mechanisms that allowed warmer Pliocene waters to support high productivity. Water that upwells in the tropical Pacific originates in mid to high latitudes, and changes in extratropical sea surface temperature and biogeochemistry over the last 3.5 Myr governed tropical Pacific temperature and productivity evolution. Progressive planktic δ18O enrichment and increasing subsurface δ13C toward modern suggest that as high latitude waters cooled over the Plio-Pleistocene, cooler but less nutrient-rich water traveled from extratropical formation regions through the deeper ocean and emerged in the subsurface tropical Pacific.