Evaluating drivers of Pleistocene eastern tropical Pacific sea surface temperature

Abstract

AbstractSea surface temperature (SST) of the eastern equatorial Pacific is a key component of tropical oceanic and atmospheric circulation with global teleconnections. Forcing factors such as local and high‐latitude insolation changes, ice sheet size and albedo feedbacks, and greenhouse gas radiation have been proposed as controls of long‐term eastern tropical Pacific SST, though the precise role each mechanism plays is not fully known on glacial‐interglacial or longer timescales. Here proposed mechanisms are evaluated by comparing orbital‐scale records of eastern Pacific SST with forcing variability over the past 1.5 Ma. The primary SST records are a compilation of new and existing data from Ocean Drilling Program Site 1239 at the northeastern margin of the modern eastern Pacific cold tongue and Site 846 SST within the cold tongue. Using time series analysis, we test previously proposed mechanisms for control of long‐term tropical SST change and SST gradients in the eastern Pacific. We find that within statistical uncertainties, in the precession band eastern Pacific SST is consistent with direct forcing by equatorial radiation changes in the tropical cold season (summer‐fall) rather than inversely correlated as previously suggested. In the obliquity band high‐latitude solar forcing leads or is in phase with eastern equatorial Pacific SST, while in the eccentricity band atmospheric greenhouse gas concentrations are closely associated with cold tongue SST. Pleistocene eastern Pacific SST gradients indicate that the gradient on the northern margin of the cold tongue strengthened through the mid‐Pleistocene transition, a result compatible with the cold tongue becoming more focused at ~900–650 ka.