Developing a New Paleosalinity Proxy Based on Na/Ca Ratios in the Planktonic Foraminifera Trilobatus sacculifer and Globigerinoides ruber

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This project will develop a new method of estimating past ocean surface salinity. Salinity is used to understand ocean and atmospheric conditions as climate changes. It also allows scientists to predict how the climate will change in the future. Preliminary studies in the Atlantic Ocean show that sodium increases in the tiny shells of plankton as the salinity increases. This project will expand the range of study to include the Atlantic, Pacific, and Indian Oceans. To improve the accuracy of the calibration, this project will also study how the shells lose sodium as they partially dissolved when sinking to bottom of the ocean. The improved measurement will be tested on long sediment cores than span the last ice age. This project will support the educational and professional development of undergraduate and graduate students. The project will also produce professional quality YouTube videos aimed at educating the public on important climate change issues.This project will develop a new upper ocean paleosalinity proxy based on Na/Ca ratios in two species of planktic foraminifera, Trilobatus sacculifer and Globigerinoides ruber, from a suite of sediment core tops spanning the subtropical/tropical Atlantic, Pacific, and Indian Oceans. Based on initial results from nine Atlantic core tops, salinity is the dominant factor controlling shell Na/Ca ratios in T. sacculifer. However, the initial calibration needs to be expanded across a wider range of salinities and in other ocean basins. Because T. sacculifer is not always abundant in faunal assemblage at all locations, this project will also develop a calibration for G. ruber, a species with an even shallower depth habitat than T. sacculifer that is commonly utilized in studies reconstructing sea surface temperature (SST) and salinity. The major goal of this project, therefore, is to develop species-specific global calibrations that can be used at any location. This project will also investigate and quantify the effects of dissolution on shell Na/Ca ratios in the Atlantic and Indian Oceans, as a recently published study showed that dissolution significantly impacts shell Na/Ca ratios in the tropical Pacific. This will be achieved by measuring down-slope core tops from the tropical Atlantic and the south Indian Ocean. Finally, the newly developed calibrations will be used to generate a high-resolution record of Na/Ca-based salinity change in the Gulf Stream during Marine Isotope Stage 3 and compare it to a previously published salinity record based on the calculation of 18Oseawater using Mg/Ca-SST combined with 18O values in G. ruber. This project will support the educational and professional development of undergraduate and graduate students. The project will also produce professional quality YouTube videos aimed at educating the public on important climate change issues.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.