Global Controls on the Carbon Isotopic Composition of Carbonate Platforms: Unrelated to the Glocal Carbon Cycle

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The PI will test the hypothesis that over the past 25 yrs the variations in the carbon isotopic composition of marginal platform carbonates are not related to changes in the global carbon cycle as widely believed, but are instead related to the variations in global sea-level fluctuations and reflect the relative input of isotopically enriched carbonate produced in shallow water on the adjacent platforms. This hypothesis will be tested by analyzing the ä13C in bulk carbonate material sampled from DSDP and ODP sites cored adjacent to modern carbonate platforms. PI?s preliminary data has shown that (i) the ä13C of bulk carbonate sediments retrieved from such sequences cored at a number of sites adjacent to carbonate platforms such as the Bahamas can be correlated with each other, but that these variations are unrelated to changes in the global carbon cycle, and (ii) similar change can be recognized at locations in the Maldives and Australia over the past 10myrs. The PI will further investigate this phenomenon, by (i) extending the study to additional sites, (ii) extending the time range of samples back to 25 Ma, (iii) investigating the phenomenon over high amplitude glacio-eustatic changes in sea level, (iv) adding variations in the ä13C of organic material as a proxy of production from shallow-water carbonate platforms, and (v) developing a model combining the notion that input from shallow marine carbonate platforms alters the ä13C with changes in calcite-aragonite seas, and the varying burial of organic material. Broader Impacts: Recognition that other factors than the carbon cycle can control the ä13C of carbonates will improve the understanding of the history of the burial of organic carbon, but also lead to understanding of how such records relate to the present anthropogenic experiment of increasing the pCO2 of the atmosphere and transferring carbon from the organic to inorganic reservoirs. The project will support a Ph.D. thesis as well as the interaction of undergraduates, high-school students, and high-school teachers in the geochemical laboratories at RSMAS.