Oceanic Tunnel Controls of Eastern Equatorial Pacific Surface Temperature and Productivity Over the Past 3.6 Myr

Abstract

Abstract Robust modern gradients in sea surface temperature (SST) and biological productivity across the eastern equatorial Pacific (EEP) Ocean between 80° and 140°W derive from vigorous upwelling of cold and nutrient‐rich waters. However, during the mid‐Pliocene warm period (3.0–3.3 Ma), the zonal SST gradient within the EEP was reduced to <0.5°C while the productivity gradient remained as strong if not stronger than modern. We consider the oceanographic mechanisms and external climate forcings responsible for the evolution of the SST‐productivity coupling. We synthesize existing records and present new reconstructions of alkenone biomarker SST and productivity from four EEP sites. The progressive SST gradient strengthening over the Plio‐Pleistocene contrasted with the stronger Late Pliocene surface productivity gradient relative to modern. Dominance of the oceanic tunnel over surface forcings best explains these observations: SST changes reflect extratropical water masses cooling toward the present while productivity proxies suggest these waters became less nutrient‐rich.

Keywords

• alkenone paleothermometry
• sea surface temperature
• eastern equatorial Pacific