Collaborative Research: Studying Carbon Injection and the Silicate Weathering Feedback over the Paleocene Eocene Thermal Maximum Using Ca Isotopes and Modeling

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The Paleocene-Eocene Thermal Maximum (PETM) was a strong warming event that took place 55 million years ago. The PETM was driven by a large addition of carbon dioxide to the ocean and atmosphere at that time. This project will quantify the PETM carbon dioxide addition and document the response of the Earth’s carbon cycle to that addition. The study will explore how the Earth system responds to climatic perturbations, including the rates and mechanisms of that response. Events in the geologic record show the climatic, hydrological, and geochemical evolution of the Earth in response to rapid warming. Thus, this study will provide a valuable comparison with modern climate change and future climate. The project broader impacts include support for a graduate student and undergraduate researchers. The project will also create YouTube video content for use in undergraduate courses.This study will utilize Ca isotopes as recorders of the temporal evolution of bottom water calcite saturation state over the recovery interval of the PETM, an interval that has received less attention in comparison to the onset and ocean acidification phases. Understanding the dynamics of the recovery interval is critical because this is the time during which the silicate weathering response to climatic warming is expressed, primarily as an alkalinity 'overshoot'. This interval is a favorable focus for study because it is more likely than the interval of intense carbonate dissolution to be recorded, and preserved, in marine sediments. Complementary numerical modeling approaches – reactive transport (RTM) and intermediate complexity Earth System (cGENIE) modeling – and existing reconstructions of oceanic dissolved inorganic carbon (DIC) will be used to elucidate (i) the amount of C input to the ocean-atmosphere system, and (ii) the silicate weathering response. A significant advantage of this approach is that the interpretive framework is not impacted by the rate of carbon injection (i.e., for the most likely injection time scales 10 ka), removing a significant uncertainty in reconstructing the mass of carbon injection. The rate at which the Earth System recovers from hyperthermals depends critically on the rate at which the silicate weathering feedback operates and the strength of the feedback. Despite the significance of this knowledge, there are few constraints available to minimize uncertainties.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.