Oxygen Stable Isotope Values from the Holocene and Last Glacial Maximum in the Eastern Equatorial Pacific

The mean state and variability of the tropical Pacific is influenced by the depth of the thermocline. During the Last Glacial Maximum (~21,000 years ago), the zonal sea surface temperature gradient across the equatorial Pacific was reduced and productivity was lower than modern. To understand the thermocline depth's role in determining the Last Glacial Maximum tropical mean state, here we reconstruct the upper ocean d18O profile from multiple species of planktic foraminifera. We synthesize existing records of surface and subsurface dwelling foraminifera to reconstruct the vertical d18O gradient throughout the eastern equatorial Pacific. We find the thermocline was deeper during the Last Glacial Maximum than the Holocene throughout the eastern equatorial region. The thermocline depth's role in the dynamic forcing of the cold tongue contributed to the reduced zonal SST gradient across the equatorial Pacific, decreased productivity and reduced El Niño-Southern Oscillation variability relative to the Holocene.