Collaborative Research: Reconstructing the Meridional SST Gradient and Climate Conditions of the Early Pliocene

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The majority of proxy temperature records indicate that during the early Pliocene, roughly 3 to 5 million years ago, the tropical Pacific was characterized by a permanently warm El Niño-like mean state. Specifically, the sea surface temperature (SST) gradient along the equator was very small or nonexistent. At the same time, the meridional SST gradient from the equator to the subtropics was also reduced, implying that the ocean tropical warm pool extended much farther poleward than at present. Such climate conditions persisted even though external factors that control climate, such as atmospheric CO2 concentrations, were essentially the same as today. The goal of this study is to generate proxy SST data in several critical regions of the Pacific Ocean that would enable us to carefully reconstruct the latitudinal SST distribution in the Pacific and to investigate mechanisms that can explain climate observations in the early Pliocene. In parallel with generating new data, the PIs will reconstruct the thermal structure of the upper ocean and atmospheric circulation using calculations with atmospheric and ocean General Circulation Models (GCMs), and with coupled GCMs. The coupled experiments will use two complimentary approaches, constrained and unconstrained, and investigate the role of ocean vertical mixing in maintaining El Niño-like conditions and an expanded warm pool. The ultimate goal of the project is to create a comprehensive picture of the early Pliocene climate in the tropics and subtropics, identify the factors that will facilitate modeling this state with coupled GCMs, and link the Pliocene climate to contemporary climate change. A post-doctoral researcher and graduate student will be supported with this award.