The Variable and Changing Carbonate Chemistry of the Southern Ocean

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The Southern Ocean is a source of great uncertainty and large potential change in predictions of the future carbon-climate system. In this project, a research team at the University of Colorado at Boulder will develop improved numerical models to better predict the rate of Southern Ocean carbon uptake over the next several decades to centuries. This will require a thorough understanding of the variable and changing carbonate chemistry of the Southern Ocean, including better constraints on the present-day mean state and seasonal cycle, quantification of past variability, and characterization of key processes driving change in the future. The primary numerical tool for this project will be the Community Earth System Model (CESM), a state-of-the-art Earth system model with fully interactive marine ecosystem and global carbon modules. Output from hindcast and 21st century CESM simulations, hydrographic data, and satellite data products will be used to understand model biases, interpret variability, and quantify carbon-climate feedback strength. The specific objectives are to: (1) analyze biases in, and guide improvement of, the Southern Ocean alkalinity cycle in the CESM; (2) quantify multi-decadal changes in modeled Southern Ocean carbonate chemistry over the last 60 years, and validate these trends with satellite and hydrographic data sets; (3) identify drivers of interannual to multi-decadal variability in Southern Ocean carbonate chemistry; and (4)quantify carbon feedbacks in the Southern Ocean due to changes in acidification, stratification, and wind-driven circulation. By quantifying past variability in the inorganic carbonate chemistry of the Southern Ocean, and identifying the physical and ecological processes that modify carbonate chemistry here, this project will offer new insights into the changing rate of Southern Ocean carbon uptake and acidification. The vast user base of the CESM stands to benefit from the proposed improvements in the representation of biogeochemistry and ecology in the CESM. Broader Impacts: This research will lead to a better understanding of the future evolution of the global carbon-climate system, which is of direct benefit to society. Results from this work will be widely disseminated in the scientific community through publication in peer-reviewed journals and presentation at scientific meetings. It will support an early-career scientist and the development of her research group. The PI is a mentor for the Summer Multicultural Access to Research Training program at her home institution, which aims to provide hands-on experience in research and an introduction to graduate education to undergraduate students who are members of racial/ethnic groups severely underrepresented in science, math, and engineering. The project will support the education and training of two graduate students. Significant research findings from this project will be incorporated into the curriculum of four courses at the University of Colorado.