Understanding Southern Ocean heat uptake and redistribution in a warming climate

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The Southern Ocean plays a dominant role in uptake of anthropogenic atmospheric heat. Observations have suggested a rapid interior warming in the Southern Ocean over the past several decades, which has been attributed primarily to greenhouse gases increases and stratospheric ozone depletion. Nevertheless, the physical mechanisms and processes under either forcing could be distinct. Moreover, the impacts of both forcings on Southern Ocean temperature may change during the twenty-first century, especially when considering the projected stratospheric ozone recovery. The goal of this project is to obtain an in-depth understanding of physical mechanisms on Southern Ocean heat uptake and redistribution under various anthropogenic forcings. The work will clarify the importance of well-mixed greenhouse gases and stratospheric ozone in climate change as shown by the Southern Ocean warming, broaden the recognition of the role of ocean circulation in Southern Ocean heat redistribution, and is relevant to understanding of regional sea level change. This project will support an early career investigator and the training of two Ph.D. students and enhance modeling capabilities at UC Riverside, one of the most ethnically diverse research universities in the country. Outreach activities through Museum of Riverside will include public lectures and teacher development workshops. Proposed work will address the following questions: (1) What are the physical processes driving the Southern Ocean warming during the past few decades under GHG increases and stratospheric ozone depletion, respectively? (2) How will the projected ozone hole recovery in the twenty-first century affect the Southern Ocean heat uptake? (3) What are the effects of ocean eddies on Southern Ocean heat uptake and redistribution? To answer these questions, the proposal outlines plans to: (i) analyze available CESM1 large ensemble simulations and accompanying fixed-ozone and fixed-GHGs simulations; (ii) conduct single forcing experiments with CESM1 in which the model is only forced with historical integrations under GHGs or ozone forcing; (iii) conduct overriding experiments based on CESM1 single forcing simulations to explore the roles of ocean circulation in Southern Ocean warming under GHGs and ozone forcings, respectively; (iv) analyze CMIP6 historical and SSP simulations and accompanying GHGs-only, ozone-only, aerosol-only and natural-forcing-only simulations, with a particular focus on the effect of projected stratospheric ozone recovery on future Southern Ocean heat uptake; (v) comparison between historical and Shared Socioeconomic Pathways (SSPs) simulations with two versions of CMIP6 climate models—eddy-resolved and eddy-parameterized—to examine the effect of ocean eddies in Southern Ocean heat uptake and redistribution.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.