Export Production Fluctuations in the Eastern Equatorial Pacific during the Pliocene-Pleistocene: Reconstruction Using Barite Accumulation Rates

Abstract:

Over the last 5 million years, Earth has experienced a transition from warmer climates to cooler climates. It is not clear how these changes affected export productivity in the Equatorial Pacific (EEP) and what are the potential feedbacks between ocean productivity and climate? To address these questions we use barite accumulation rates to reconstruct export productivity in the eastern equatorial Pacific (ODP Site 849) and compare the record to sea surface temperature (SST) fluctuations and other productivity proxies over the past 5.3 Ma. We find that export productivity fluctuated considerably on multiple time scales. During the Pliocene between 4.5 and 3 Ma, export productivity was on average higher (~50 g C m^-2 yr^-1) than during the Pleistocene (~ 35 g C m^-2 yr^-1). In the Pleistocene a trend of decreasing export production occurred between 3 Ma and 1 Ma (from ~60 to ~20 g C m^-2 yr^-1) followed by an increase over the last million years. Our record reveal decoupling between export productivity and SST on long (million year) time scales as previously suggested. Throughout this time interval shorter orbital-scale large amplitude fluctuations (between 10 and 100 g C m^-2 yr^-1) in export productivity are observed and export production was generally higher during cold periods or during transitions. Results from this study suggest that in the EEP mechanisms that affect carbon export on orbital time scales differed from those operating on longer time scales.