NSFGEO-NERC: Collaborative Research: Understanding the Drivers of Inert Gas Saturation to Better Constrain Ice Core-Derived Records of Past Mean Ocean Temperature

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). The integrated heat content of the global ocean is a fundamental climate variable for understanding Earth’s energy balance. Accurate estimates of past changes in the global energy budget are essential for understanding the inherent sensitivities of the Earth system. This project will address the accuracy of these estimates by carrying out computer simulations of dissolved gases in the ocean. By analyzing the outcomes of these simulations, the team aims to refine ice-core-based reconstructions of ocean heat content that rely on measurements of gases (Xenon, Krypton, and Nitrogen) in ancient air bubbles preserved in ice cores. The project aims to produce the first estimates and uncertainty ranges of saturation anomalies of Xenon, Krypton, and Nitrogen in the glacial ocean during the Last Glacial Maximum. Recent analytical advances have permitted measurement of ratios of Xenon to Nitrogen and Krypton to Nitrogen in ice cores at sufficient precision to resolve whole-atmosphere changes in these ratios that reflect warming and cooling of the global ocean at the 0.1ºC level. However, to quantitatively constrain past ocean heat content using inert gas measurements requires assumptions about long-term changes in the global ocean saturation state of these gases, which remains an entirely open problem. Consequently, the team will use the Transport Matrix Method for biogeochemical tracer simulations. They will build on a suite of previously conducted simulations of oxygen and carbon dioxide in the glacial ocean with the University of Victoria Earth System Climate Model to quantitatively constrain the glacial-interglacial change in inert gas saturation state and understand its physical drivers. In addition, the team will add independent experiments using a second model (the MIT global circulation model) and carry out several future warming experiments to consider how ongoing changes in the Earth system may affect physical air-sea gas transfer. Finally, the team will reevaluate existing ice-core inert gas records to produce best estimates of changes in ocean heat content during the Last Glacial Maximum and periods of abrupt warming throughout the last deglaciation. This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) (U.S. participants) and the Natural Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own investigators and component of the work.The NSF award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2)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.