Ocean Acidification- Category 1: Real time assessment of ocean acidification proxies and their incorporation in the marine sediment record

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The large and rapid release of CO2 into the atmosphere over the past two centuries and resultant uptake of a significant fraction of this by the oceans have resulted in measurable changes in ocean chemistry, most notably decreases in both pH and carbonate ion concentration. This change in atmospheric CO2 during the last 200 years and its concomitant effect on seawater chemistry are not unique but rather have occurred frequently throughout geologic history. Quantifying the response of the oceans to such naturally occurring changes in atmospheric CO2 provides valuable insights for modeling and predicting future changes in ocean chemistry associated with anthropogenic increases in CO2. This work examines three carbonate ion and pH proxies (weight, B/Ca and boron isotope composition of planktonic foraminiferal shells) using the 15-year time series of sediment trap samples and water column chemistry measurements collected biweekly as part of the Cariaco Basin ocean time series. These results will be compared to monthly measurements of upper water column carbonate ion and pH made at the time series site. High deposition rate, laminated sediments accumulating in the Cariaco Basin will be used to make a direct comparison between changes in these three foraminiferal pH proxies and the atmospheric CO2 record for the last two centuries, a period during which CO2 has increased by ~100 ppmv. The end product of the research will be an in-depth field-calibration of these widely used pH proxies. Funding supports a graduate student, and provides opportunities for undergraduate involvement in research.