A Coral Skeleton P/Ca Proxy for Surface Ocean Phosphate: Testing and calibration

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A direct record of past nutrient concentrations in the surface ocean would add considerably to our understanding of the links between ocean circulation, climate, and air-sea carbon fluxes, and in coastal waters would allow reconstructions of upwelling and eutrophication histories. The calcium carbonate skeleton of a single colony of coral can provide a continuous record of ocean surface conditions, including phosphate concentrations, over hundreds of years. For this reason, an investigator from Rutgers University plans to develop, calibrate, and apply a new coral proxy for surface ocean phosphate based on promising preliminary data from a Gulf of Panama coral indicating skeletal P/Ca quantitatively record variations in surface water phosphate in a seasonal upwelling regime. This project will focus on calibration of the P/Ca proxy against in situ time-series surface water chemistry data, to test the following hypotheses based on findings from the preliminary data: (1) skeletal P/Ca in recent corals quantitatively reflects documented time-series surface water phosphate variations at relatively high (Panama Bay: 0.2-0.8 M) and low (Gulf of Eilat, Red Sea: 0.01-0.1M) seawater phosphate values; (2) the P/Ca surface water phosphate proxy can be applied in Pavona and Porites, and inter- and intra-colony replication would allow reconstruction of seasonal scale surface water phosphate variations; (3) coralline phosphorous is incorporated as a combination of inorganic and organic species that allow total P/Ca to be resistant to diagenetic alteration, permitting application of P/Ca to long cores and fossil corals; and (4) the organic component of skeletal phosphorous largely comprises phospholipids distributed at the sub-micron scale in biogenic aragonite and provide a window into incorporation mechanism. As regards broader impacts, the scientist would collaborate with the COSEE-MA office at Rutgers University to develop coral and paleoceanography teaching materials. One graduate student would be supported and trained as part of this project.