Evolution of South Pacific Oxygen and Preformed Nutrient Changes over the Deglaciation

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Oxygen concentrations in the deep ocean, in combination with measurements of nutrients and seawater temperature, provide a powerful constraint for the understanding cycling of carbon in the ocean and the amount of atmospheric carbon dioxide. This research uses deep sea sediment cores as recorders of changes in these key environmental variables since the peak of the last ice age, a period encompassing a fundamental shift in the Earth's climate system. Funding supports training of a graduate student, along with a K-12 teacher and two of her high school students. The training activities will also include the participation of members of under-represented groups who have demonstrated interest in the Ocean Sciences. The data will be made available to the community and will be of broad interest to those seeking to understand the cycling of carbon in the ocean.More specifically, this research will further develop a promising method for the quantitative reconstruction of oxygen in the deep ocean-- the difference between carbon isotope values of epibenthic and deep infaunal foraminifera (Dd13C). Using this technique, the research team will generate records of oxygen concentrations in the South Pacific over the last 25,000 years. This time period covers a major climatic transition when atmospheric carbon dioxide concentrations rose from the low levels of glacial times to the higher values of the pre-industrial present. Estimates bottom water phosphate (using Cd/Ca in benthic foraminifera) and bottom water temperature (using Mg/Ca and Li/Ca in benthic foraminifera) will be made using in the same sediment cores. Combined with the oxygen reconstructions, phosphate and temperature information will be used to estimate the nutrient content in the regions where the deep water left the surface (preformed nutrients). The timing and magnitude of the changes in oxygen and preformed nutrients will help to understand how changes in ocean biology and circulation contributed to the lowering in carbon dioxide during the last ice age.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.