Doctoral Dissertation Research: Late Pleistocene Glaciation in Southeastern Alaska: Assessing the Sensitivity of a Marine-Terminating Ice Sheet to Changing Environmental Conditions

This doctoral dissertation research project will integrate glacial geology, detailed ice-margin mapping, and high-resolution geochronology to assess the influence of climate and topography on the extent and retreat of a marine margin of the Cordilleran Ice Sheet is southeastern Alaska. This project will provide new insights into the processes that control the stability of marine ice-sheet margins. It will yield a direct chronology of a western Cordilleran Ice Sheet retreat along a marine margin, thereby facilitating reconstructions of this part of the ice sheet and adding to knowledge about the spatial and temporal relationships among climate, topography, and ice-sheet extent. This project will generate new insights into the processes that control the stability of marine ice sheet margins and provide empirical constraints to improve predictive models of the ice sheet-climate system. In addition, the project will provide direct evidence of ice-free conditions in previously proposed coastal ice-free areas along the Pacific Rim of North America that will have important implications for analyses of human migrations into the Americas. Project results will be incorporated into an outreach program conducted in concert with the Buffalo Museum of Science that synthesizes current research in geography, paleoclimatology, anthropology, and paleontology to educate the public about the causes and consequences of changing environmental conditions. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career. Marine ice-sheet margins, including those in present-day Greenland and Antarctica, are thought to be highly sensitive to climatic variation, but the effects of environmental change on marine ice sheet margins are still poorly understood. During the Last Glacial Maximum (roughly 26,000 to 19,000 years ago), the Cordilleran Ice Sheet covered much of western North America, stretching from southern Alaska to the Pacific Northwest of the U.S. Relatively little is known about Cordilleran Ice Sheet behavior during this time period, particularly along the west coast where it terminated in the ocean. This project will focus on three sets of research questions concerning the behavior of the western Cordilleran Ice Sheet during and following the Last Glacial Maximum: (1) How extensive was the Cordilleran Ice Sheet in southeastern Alaska during the Last Glacial Maximum, and did any areas of southeastern Alaska remain ice-free? This question will be addressed using cosmogenic exposure dating of the beryllium-10 isotope bedrock and boulder surfaces in previously proposed ice-free areas. Together with detailed mapping of the paleo-ice margin from publicly available topographic data and aerial imagery, exposure ages from these locations will allow the doctoral student to reconstruct the maximum extent of the western Cordilleran Ice Sheet. (2) What was the timing and pace of retreat of the western Cordilleran Ice Sheet? Cosmogenic beryllium-10 dating of rock surfaces along coast-to-inland transects will be used to resolve this question, which has implications for basic understanding of the sensitivity of marine-terminating ice sheets to climate change. (3) What environmental factors, such as ocean warming, atmospheric warming, and sea-level rise, influenced ice-sheet retreat? The retreat chronology developed in this study will be correlated with existing climate and sea-level records to test the hypothesis that ocean warming was the primary factor influencing marine ice-sheet collapse in southeastern Alaska.