INVESTIGATING THERMOCLINE CONTROL OF ENSO ACTIVITY AND TROPICAL VARIABILITY IN THE EASTERN EQUATORIAL PACIFIC USING FORAMINIFERA GEOCHEMISTRY

The El Niño Southern Oscillation (ENSO) is an important climate phenomenon that is strongly expressed in the Eastern Equatorial Pacific (EEP). ENSO events alter temperature, precipitation, and weather patterns across the globe. However, the mechanisms that control tropical variability and by extension ENSO are not well understood, especially on centennial to millennial timescales. Here we reconstruct changes in the subsurface of the EEP over the course of the climatically relevant Holocene to investigate how tropical variability relates to changes in the region’s thermocline. We analyzed trace elements from the subsurface foraminifera species Neogloboquadrina dutertrei, which lives within the thermocline at the deep chlorophyll maximum, to reconstruct subsurface temperature. Coupling this data with foraminiferal temperature records of the upper water column, we assessed sea surface and subsurface temperature data from the last ~10,000 years. We found recognizable differences between the surface and subsurface temperature trends in the EEP, with a notable minimum in subsurface temperature occurring during the mid-Holocene. We investigate the implications of changes in the subsurface data over time in the context of surface temperature data sets from the mixed layer dwelling species Globigerinoides ruber. We investigate shifts in the surface/subsurface thermal gradient during this period. We use this data in addition to existing records of ENSO variability to determine how subsurface changes align with changes in ENSO, and investigate possible mechanisms of thermocline control.