RECONSTRUCTING EL NIÑO-SOUTHERN OSCILLATION VARIABILITY OVER THE LAST 60 KYR USING INDIVIDUAL FORAMINIFERA ANALYSES

The El Niño/Southern Oscillation (ENSO) is the largest natural interannual signal in the Earth’s climate system and has widespread effects on global climate that impact millions of people worldwide. A series of recent research studies predict an increase in the frequency of extreme El Niño and La Niña events as Earth’s climate continues to warm. In order for climate scientists to forecast how ENSO will evolve in response to global warming, it is necessary to have accurate, comprehensive records of how the system has naturally changed in the past, especially across past abrupt warming events. Nevertheless, there remains significant uncertainty about past changes in tropical Pacific climate and how ENSO variability relates to the millennial-scale climate events of the last 60 kyr, known as Heinrich and Dansgaard-Oeschger Events.

In this talk, I will describe a recently developed analytical technique, known as individual foraminifera analysis (IFA), that has the ability to reconstruct past ENSO variability. The IFA technique is based on the idea that an individual planktic foraminifer lives 2-4 weeks, and that by analyzing the temperature of many shells in a discrete sediment horizon, you can gain vital information about temperature variability over the time period of that sediment interval. I will present records of ENSO variability over the last 60 kyr reconstructed from a sediment core recovered from the Eastern Equatorial Pacific (EEP) cold tongue (MV1014-02-17JC, 0°10.8'S, 85°52.0'W, 2846 m water depth). In this region, thermocline temperatures are significantly correlated with ENSO variability, and thus, ENSO variability is determined from individual foraminifera analyses of the thermocline dwelling foraminifera Neogloboquadrina dutertrei.

Our preliminary results suggest that millennial-scale cold intervals of the last 60 kyr are characterized by reduced ENSO variability, while the opposite is true for warm intervals. The period of greatest ENSO reduction occurred during Heinrich Stadial 2 (~25 kyr), a millennial-scale cold event in the North Atlantic that occurred during the peak of the Last Glacial Maximum. Overall, we find that ENSO variability in the tropical Pacific is driven by both orbital forcing and mean climate state conditions that are predominantly forced from the North Atlantic.