Assessing export production on millennial timescales in the eastern equatorial Pacific Ocean

The eastern equatorial Pacific Ocean (EEP) serves as a significant source of CO₂ to the atmosphere and accounts for a substantial portion of global new export productivity, making it an important player in global climate. While ocean dynamics have been shown to serve as the dominant control on equatorial Pacific export production on glacial-interglacial timescales¹, the relative roles of delivery of the micronutrient Fe via atmospheric dust deposition and/or upwelling of Southern Ocean sourced waters and their effect on productivity on millennial timescales is less understood given a paucity of high-resolution ocean sediment records from this region. Past work in the EEP on core MV1014-17JC (17JC)², has highlighted the potential for iron fertilization via enhanced delivery of atmospheric dust on millennial timescales contributing to enhanced drawdown of atmospheric CO₂ by biological producers in this region evidenced from the correlation between xsBa (biological productivity proxy) and ²³²Th mass accumulation rates (MARs) during several Heinrich Stadial events. xsBa, however, has the potential to be mobilized under reducing conditions in the sediment column³, leading to poor preservation of this proxy signal when bottom water oxygen is low which is the case for several time periods throughout the 17JC record. We will present high-resolution (²³¹Pa/²³⁰Th)xs measurements, a proxy insensitive to diagenetic effects, for the past 100kyr from the same site, with other trace element and radiogenic isotope records at 17JC in order to assess more clearly the nature of the relationship between export production, dust, and bottom water oxygen on millennial timescales for the EEP.

1 Winckler, G., Anderson, R. F., Jaccard, S. L. & Marcantonio, F. Ocean dynamics, not dust, have controlled equatorial Pacific productivity over the past 500,000 years. Proceedings of the National Academy of Sciences 113, 6119-6124 (2016).

2 Loveley, M. R. et al. Millennial-scale iron fertilization of the eastern equatorial Pacific over the past 100,000 years. Nature Geoscience 10, 760 (2017).

3 McManus, J. et al. Geochemistry of barium in marine sediments: implications for its use as a paleoproxy. Geochimica et Cosmochimica Acta 62, 3453-3473, doi:https://doi.org/10.1016/S0016-7037(98)00248-8 (1998).