Reconstructing past ice sheets and paleotopography using observations of past sea level and glacial geology

During the Quaternary, large ice sheets repeatedly formed and retreated over continental North America and northern Europe, which in turn caused fluctuations in global sea level by up to 120 m. This caused substantial changes to the Earth's surface, changing the distribution of land, continental ice sheets, and ocean. I demonstrate a technique we use to reconstruct ice sheets and paleotopography, and its application for the past 800000 years. I show that with the use of observations from glacial geology and ice extent chronology, it is possible to determine the history of the ice sheet configuration even prior to the Last Glacial Maximum (19000-26000 years ago). During Marine Isotope Stage 3 (57000-27000 years ago), when there are few constraints on sea level, we determined that sea level was between about 25-50 m lower than present, substantially higher than estimates based on marine benthic oxygen proxies. We also determined that global sea level during the Last Glacial Maximum was about -115 m, about 15 m higher than previous estimates. This shows that it is possible that, given the current constraints on sea level, that past ice sheet configuration may be an non-unique problem. The growing community efforts to standardize and compile datasets on past sea level bring an opportunity to reduce the uncertainty on ice sheet configuration, and extend our reconstructions further into the past (such as the last interglacial).