NOAA/WDS Paleoclimatology - Equatorial Pacific Line Islands 282ka Individual Foram Mg/Ca SST Data

The El Nino Southern Oscillation (ENSO) is highly dependent on coupled atmosphere-ocean interactions and feedbacks, suggesting a tight relationship between ENSO strength and background climate conditions. However, studies of ENSO variability over the past 25,000 years disagree on the extent to which background climate state determines ENSO behavior. Here we present reconstructions of El Nino amplitude from individual foraminifera distributions at discrete time intervals over the past ~285,000 years across widely varying atmospheric CO2 levels, global ice volume and sea level, and orbital insolation forcing. Our results show a strong correlation between El Nino amplitude and tropical Pacific Ocean mixed-layer thickness, indicating upwelling feedbacks are the key factor controlling ENSO strength on these time scales. We observe reduced El Nino amplitude only during May-July high-insolation intervals, suggesting insolation-forced warming of tropical Pacific thermocline source waters in the southern hemisphere weakens the upwelling feedback and El Nino strength. Our results indicate the primacy of the upwelling feedback in shaping ENSO behavior across many different background states, suggesting accurate modeling of this