| Summary: | Thesis (Ph.D.)--University of Washington, 2022 This dissertation describes three research projects investigating changes in polar climate and the ice sheets during the last deglaciation. The first project, Chapter 2, reconstructs the past 20,000 years of Greenland temperature and precipitation to learn about their relationship and influences on the ice sheet. The reconstruction method, paleoclimate data assimilation, uses oxygen-isotope ratios of ice and accumulation rates from long ice-core records and extends this information to all locations across Greenland using spatial relationships derived from a transient climate-model simulation. Evaluations against out-of-sample proxy records indicate that the reconstructions capture the climate history at locations without ice-core records. The reconstructions show that the relationship between precipitation and temperature is frequency dependent and spatially variable, suggesting that thermodynamic scaling methods commonly used in ice-sheet modeling are overly simplistic. Overall, the results demonstrate that paleoclimate data assimilation is a useful tool for reconstructing the spatial and temporal patterns of past climate on timescales relevant to ice sheets. To learn how these climate reconstructions relate to the behavior of the ice sheet, we must also reconstruct the history of the ice sheet. Most observational data of the past ice sheet geometry, however, is at the margins of the ice sheet, while the ice core climate records are located in the interior. The second project, Chapter 3, investigates a common paleoaltimetry method that reconstructs elevation from temperature records. This method suggests the climate and elevation signals contained within an ice-core temperature record can be disentangled by comparing two proxy locations with similar climates. The difference between the records is assumed to be due to elevation, which is estimated by scaling the temperature difference by a lapse rate. I investigate the errors associated with this approach using the ...
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