Collaborative Research: Refining foraminiferal I/Ca as a paleoceanographic oxygenation proxy for the glacial Atlantic Ocean

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This collaborative project seeks to refine the use of I/Ca ratios in fossil foraminifera from marine sediments as a proxy for reconstructing past dissolved oxygen levels in the ocean, a fundamental variable because of the role oxygen plays in the biogeochemical cycle of carbon and in controlling the distribution of marine life. The present oceans because of warming and eutrophication are on a trajectory to lower oxygen contents and future expansion of marine "dead zones" - regions where waters have oxygen levels below the threshold necessary for life. Ocean-wide changes in dissolved oxygen levels that are projected to occur over the next century are expected to have magnitudes similar to those that occurred over the natural glacial-interglacial cycles of the last few millions of years. A better understanding of the ocean's oxygen history in the past, especially the geographic and bathymetric extent of oxygen depletion, can help improve future forecasts. While a number of geochemical proxies are available to reconstruct extreme oxygen changes that affected the whole or large parts of the global ocean in the distant geological past, proxies sensitive to the subtler oxygen fluctuations expected to occur in the near-future have been lacking. Measurements of foraminiferal I/Ca in preliminary studies have shown excellent potential to differentiate and reconstruct intermediate oxygen levels in the water column. This project will further evaluate and refine I/Ca as a quantitative proxy for reconstructing hypoxic and suboxic conditions, oxygen levels most relevant to future threats to marine ecosystems on a human time scale. Broader impacts of the project include the support of an early career scientist and two senior PIs, as well as two graduate students and several undergraduates. Public outreach will be through collaboration with the local Syracuse Science Museum and through the mainstream media. The project team will conduct I/Ca analyses of foraminifera from a large suite of core top samples from the west Africa margin to further develop empirical calibrations between iodine and subsurface oxygen levels. They will compare I/Ca data with two independent oxygen proxies (nitrogen isotope data and carbon isotope gradients in benthic foraminifera), targeting both the upper and deep oceans. The team will then apply I/Ca measurements to downcore planktic and benthic foraminifera from a variety of regions in the Atlantic and Southern Ocean to quantitatively reconstruct past variations in the distribution and intensity of the oxygen minimum zone (OMZ), with a focus on changes in the glacial ocean at different depths and in different parts of the Atlantic basin. In addition, a representation of the marine iodine cycle will be incorporated into a widely-used Earth System Model (cGENIE), enabling explicit data-model comparisons for the first time. Graduate and postgraduate training in earth system modeling will be provided through a two-day workshop to be held at Syracuse University. This project will lead to further develop of a promising proxy (I/Ca) for hypoxic and suboxic conditions, investigate the variability of ocean oxygenation with climate change, and advance the capacity for future integration between proxy oxygen data and earth system models.