Collaborative Research: Remote Observations of Ice Sheet Surface Temperature: Toward Multi-Proxy Reconstruction of Antarctic Climate Variability

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This project will develop spatially extended and statistically reliable estimates of Antarctic surface temperature variations over the past several centuries, using a multi-proxy calibration/verification approach that combines the climate signal in ice core, satellite remote sensing, and weather station data. Antarctica has been problematic from the point of view of large-scale paleoclimate reconstruction because of the paucity of long-term instrumental data, and the relatively low resolution of most ice cores. Several new developments, particularly the network of shallow (~100 meter) ice cores from the ongoing International Trans-Antarctic Scientific Expedition (ITASE) project will yield broad spatial coverage of annually resolved ice core physical properties, chemistry, and stable isotope data over more than a hundred years. Second, there are now over twenty years of microwave and infrared brightness temperatures available from satellites covering virtually all of Antarctica with seasonally resolved information that has been demonstrated to record the ice surface/near surface temperature with very reasonable precision and accuracy. Finally, higher quality microwave emission data from Advanced Microwave Scanning Radiometers (AMSR) with much finer spatial resolution and radiometric fidelity than those from previous sources will offer an improved view of longer term mean temperatures in Antarctica.The 40-year instrumental record and the shorter but spatially more comprehensive Automatic Weather Station network will be combined with seasonally-resolved 37-gigahertz satellite-based ice surface temperature estimates to reconstruct Antarctic-wide temperature patterns during the past forty years. The sparser Antarctic instrumental surface temperature data available back nearly to the beginning of the century will be added for longer-term, though quite spatially-restricted, cross-validation of these reconstructions. This cross-validation procedure has been used successfully with roughly century-long instrumental records at locations primarily in the Northern Hemisphere. The longer time scale will be approached through a cross-validation of the proxy-based pre-20th century surface temperature reconstructions using information on thermal emission from deeper in the firn that is contained in low-frequency passive microwave satellite measurements. The low-frequency estimates, supplemented by borehole thermometry, will provide important independent verification of the long-term averages of the annual surface temperature reconstructions.