Award: OCE-1923998

The goals of this project were to investigate the solubility of marine calcium carbonates in seawater through the development of a novel saturometer device, capable of incubating carbonates in natural seawater at in situ conditions (See attached Figure 1). We have now successfully deployed the saturometer, and gathered solubility data on two species of foraminifera and inorganic calcite. The main outcome of this work, in combination with laboratory experiments and associated analyses, is that foraminifera are more soluble than inorganic calcite in seawater, meaning that the reservoir of foraminifera tests on the seafloor is a much bigger and more reactive reservoir of alkalinity than previously thought. This result implies that the ocean can absorb more CO2 (likely upwards of 100 gigatons of carbon or more) than previously thought, and means that the ocean plays an even bigger role in mitigating the worst effects of climate change than previously thought. We are currently writing this work up for imminent publication (Subhas et al., in prep). Intellectual merit: In all, we have addressed the primary intellectual question posed by this project, and have now confirmed that foraminifera are more soluble than inorganic calcite. Moreover, we have developed a framework for interpreting this solubility, using first-principles relationships between mineralogy and solubility. This project has culminated in results from two research expeditions, including one led by PI Subhas, a suite of laboratory experiments, and the design, testing, and successful deployment of a novel in situ experimental device. To date, we have submitted two data sets to BCO-DMO under the project (https://www.bco-dmo.org/project/882852), with several more pending upon further manuscript submission. We have published one paper (Subhas et al., 2023) based on collaborations formed on the SR2113 expedition, led by PI Berelson. Two more manuscripts are in revision (Hashim et al., in revision, Dong et al., in revision) and a third is in preparation for imminent submission on the saturometer results, as mentioned above (Subhas et al., in prep). Additionally, through the EN665 expedition led by PI Subhas, we have an established collaboration with Erin Black at the University of Rochester, which will likely result in another publication and associated data sets on the flux of organic and inorganic carbon in the Gulf of Maine. Broader Impacts: The project has provided professional development for PI Subhas and PI Long, both of whom are early career scientists. This was the first project for PI Subhas, giving him experience in leading a research expedition, managing a project and a team of scientists, and building collaborations with other researchers along the way. The project has also supported the mentorship of Postdoctoral fellow Mohammed Hashim, who has since developed a model of calcium carbonate reactivity in Bahama Bank sediments, and who provided mineralogical analyses for the saturometer work. This work, and the saturometer work, has been presented at several international meetings (AGU, Goldschmidt), as well as invited seminars including at Penn State University, GEOMAR, University of Connecticut, Notre Dame University, and the Bermuda Institute of Ocean Sciences. References: Subhas, A. V., Pavia, F. J., Dong, S., & Lam, P. J. (2023). Global Trends in the Distribution of Biogenic Minerals in the Ocean. Journal of Geophysical Research: Oceans, 128(2). doi: 10.1029/2022jc019470 Hashim, M.S., Subhas, A.V., Kaczmarek, S.E., Naa, G.W., & Bish, D.L. A Process-based Geochemical Framework for Shallow-Marine Carbonate Sediments During Burial. In revision, Geochimica et Cosmochimica acta. Dong, S., Pavia, F.J., Subhas, A.V., Gray, W., Adkins, J.F., & Berelson, W.M. Composition and Biogeochemical Processes in Marine Particles Based on Inorganic and Organic Stable Carbon Isotopes. In preparation. Subhas, A.V., Hashim, M.S., Long, M.H., McCorkle, D.C., Gray, W.R., Berelson, W.M., & Adkins, J.F. Enhanced Solubility of Planktonic Foraminiferal Calcite in Seawater. In preparation. Last Modified: 03/29/2024 Submitted by: AdamSubhas