THERMOCLINE CONDITIONS IN THE EASTERN EQUATORIAL PACIFIC DURING THE LAST GLACIAL MAXIMUM

The El Niño Southern Oscillation (ENSO) is a powerful climate phenomenon that influences temperature, precipitation, and global weather patterns. Climate background state, orbital alterations, and tropical Pacific surface and subsurface conditions, specifically the warmth and depth of the thermocline in the Eastern Equatorial Pacific (EEP), have been proposed as potential influences on ENSO. However, there is sparse evidence for EEP thermocline conditions during the Last Glacial Maximum (LGM) and thus a complete understanding of the relationship between ENSO and the EEP thermocline is elusive. Here we explore this relationship during the LGM from 22-24 thousand years ago (ka). Climate background conditions during the LGM are dissimilar to today, with large ice sheets and very different hemispheric temperature gradients, but with similar precessional forcings. We reconstruct the surface and subsurface conditions of the EEP using trace elemental ratios in foraminifera. We analyze Mg/Ca in the subsurface species Neogloboquadrina dutertrei and surface-dwelling Globigerinoides ruber. Our approach allows us to determine the difference between surface and subsurface temperatures and how this varies through time. We analyze these results in the context of existing records of EEP variability to determine whether thermocline conditions are related to ENSO change during the LGM. Our results provide key insights into the nature of the EEP thermocline - ENSO relationship during different climate background states, which can clarify the mechanisms controlling these phenomena and allow the development of future projections of ENSO behavior.