INVESTIGATION OF CENTRAL TROPICAL PACIFIC VARIABILITY DURING THE LAST GLACIAL MAXIMUM THROUGH ANALYSIS OF TRACE ELEMENTS IN INDIVIDUAL FORAMINIFERA

The El Nino Southern Oscillation (ENSO) is characterized by variations in winds, subsurface and surface temperatures in the eastern and central tropical Pacific Ocean. It is the expression of strong coupled atmosphere-ocean interactions and feedbacks in the tropical oceans. While ENSO has a profound impact on global climate, the observational record is relatively short and its long-term behavior is only partially understood. Recent observations suggest that the spatial pattern of ENSO variability, known as ‘flavors’, may vary. These different patterns, or ‘flavors’, are characterized by the location of the strongest sea surface temperature anomalies, in either the eastern or central equatorial Pacific. Here we reconstruct central equatorial variability and ENSO through analysis of individual foraminifera at discrete intervals during the last glacial maximum (LGM, 20-25 thousand years ago). During this time the sea level was lower and meridional temperature gradients were larger, but precessional forcing was similar to today. We use trace elemental ratios, specifically Mg/Ca, in individual specimens of the mixed-layer species Trilobatus sacculifer from a central equatorial Pacific sediment core to reconstruct tropical variability during the LGM. By analyzing multiple individuals from a sediment interval, we generate a distribution of temperatures representing the variability of climate conditions during that time. By comparing distributions from multiple intervals, we can assess changes in central equatorial Pacific variability. We compare our results with existing eastern Pacific records to determine how the pattern of variability compares with today, and whether ENSO ‘flavors’ differed during the LGM. These results will further our understanding of the nature of ENSO’s response to background climate conditions and provide context for ENSO behavior in the future.