Temperature-Dependent Ocean-Atmosphere Equilibration of Carbon Isotopes in Atlantic Thermocline and Surface Waters

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The stable isotopes of carbon can provide clues about the processes by which carbon moves through the earth system. Researchers at Georgia Institute of Technology will use carbon isotope and nutrient reconstructions in the upper ocean, in combination with existing atmospheric carbon isotope reconstructions from ice cores, to better understand why and how atmospheric carbon dioxide rose at the end of the last ice age. This work will help further the understanding of the controls and feedbacks on atmospheric carbon dioxide concentrations. The possibility of reconstructing past surface ocean temperatures from the air-sea carbon isotope difference will also be explored. The investigators will assess whether the upper ocean carbon isotope changes seen over the deglaciation in the North Atlantic primarily reflect biological cycling or air sea exchange processes. A detailed record of seawater cadmium (Cd, related to the nutrient phosphate in today's ocean) from Cd/Ca measurements in benthic foraminifera will be constructed. These measurements will help to pinpoint what mechanism was responsible for the transition to a less efficient biological carbon pump over the deglaciation. The investigators will also reconstruct the carbon isotopic composition of well equilibrated, low nutrient surface waters in the North Atlantic using carbon isotopic measurements on large planktonic foraminifera. The carbon isotope ratio in these waters will reflect the changes in the atmospheric ratio and the temperature of equilibration, potentially providing information on past surface ocean temperature changes. In addition to the societal relevance of better understanding the relationship between carbon dioxide and climate, this grant will support the training of several students from under-represented groups. The data will be made available to the community and will be contributed to an international effort to synthesize and interpret carbon isotope records over the deglaciation.