Ground Truthing the Boron Isotope Paleo-pH Proxy

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ABSTRACTOCE-0326952Boron isotopes in marine carbonates may provide information about past ocean chemistry because the inclusion of this isotope into carbonates is controlled primarily by the carbonate chemistry of the ocean. However, to date no systematic, global evaluations of this proxy have been carried out. For this reason, a PI from Queens College plans to test the utility of the boron isotope paleo-pH proxy by analyzing planktonic and benthic formaminifera obtained from surficial sediments recovered globally from regions with well-defined water chemistries. Results from this study will provide an opportunity to document potential deviations from predicted isotopic compositions in response to species effect, temperature and alkalinity. In addition, the PI will carry out laboratory calcite growth experiments to determine the influence of pH, temperature, pressure, salinity and growth rate on the boron isotope composition of calcite. Foraminifera culture experiments with Orbulina universa and Globigerina bulloides (species with and without symbionts, respectively) also will be done under controlled water composition and temperature to assess boron fractionation in response to symbiont density and other variables. Lastly, the effect of diagenesis (dissolution and recrystallization) on the boron isotope composition will be evaluated. Broader impacts. Results from this study will determine whether boron isotopes can be used as a paleo-pH proxy to obtain information on ancient climate change in lieu of direct evidence. An understanding of past natural fluctuations in the earth's climate is essential to comprehending and evaluating current pattern of, and anthropogenic impacts on, global climate change.