CAREER: South Greenland's Holocene Climate History Reconstructed Using Three Paleolimnological Approaches

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This NSF CAREER award to Yarrow Axford at Northwestern University would support a multi-pronged effort at deciphering and understanding the climate history of southern Greenland over the last eleven thousand years, and an educational effort focused on public communication of science and K-12 science literacy. Paleoclimate data provide our only empirical observations of how the arctic system responds to major sustained climate change. It is especially urgent to understand how past climate change unfolded on Greenland, because mass loss from the Greenland Ice Sheet will drive a large fraction of future sea level rise. Existing data from south Greenland hint that climate trends there may differ from trends observed elsewhere in the Northern Hemisphere on a range of timescales, with potential consequences for future temperature change and thus for ice sheet mass balance. The proposed research will assess the apparent divergence through the Holocene (the last 11,000 years), by developing a suite of climate reconstructions from lakes in southernmost Greenland. Climate records to be generated include quantitative temperature reconstructions based on insect (chironomid) assemblages and reconstructions of precipitation isotopes (reflecting changes in atmospheric circulation) using an emerging method based on chironomid oxygen-18. A third approach -- reconstructions of alpine glacier fluctuations using sediments from glacial threshold lakes -- will constrain local ice mass balance and help to further characterize local atmospheric climate through the Holocene, especially its influence on the ice sheet. This work would double the number of continuous, quantitative Holocene terrestrial temperature reconstructions available from Greenland beyond the ice sheet, thus contributing to community-wide efforts to understand how the arctic system responds to sustained climate change. Data will be incorporated into paleodata syntheses, in keeping with the PI's track record of participation in such efforts, and will allow for better tests of climate and ice sheet models. Independent reconstructions of Holocene precipitation isotopes will be used to assess whether changes in atmospheric circulation accompanied past climate change, and thus might accompany future climate change. By constraining summer temperatures and local glacier mass balance, and comparing results with glacial geologic studies, this work will help clarify the role of atmospheric climate at the ice sheet margin in driving ice sheet changes. This work will also advance two methods: It will validate and apply an emerging isotopic proxy with potential for widespread application, and the PI will lead international collaborative development of a new calibration dataset for the chironomid paleothermometer. This grant will train at least two Ph.D. students and at least five undergraduates in international polar research, and will advance the professional development of a pre-tenure geoscientist who has a demonstrated commitment to the broader impacts of her research. Multiple collaborations, including with glacial geologists and paleoecologists at five foreign institutions, will be advanced. A new seminar will train graduate students in sustainability-relevant STEM fields in skills for communicating science beyond academia, contributing to broad training of the future STEM workforce. This project will provide sustained professional development for K-12 teachers, who in turn will bring climate and energy science to Chicago-area classrooms, promoting innovative STEM education for students in one of the largest U.S. urban school districts (Chicago's District 299).