Collaborative Research: Paleoglaciology of Alaska -- Climate Parameters During the Last Glacial Maximum from GIS Determination of Equilibrium Line Altitudes

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AbstractOPP-9977972OPP-9977974This is a collaborative project with Principal Investigators from the University of Colorado and Northern Arizona University. One of the most effective means for better understanding the global climate system is to understand the conditions during the last ice age and Alaska is a pivotal area for such ice-age experiments. Environmental response in the Arctic is expected to amplify regional and global climate change through feedbacks of sea-ice extent, glacier/permafrost melting, carbon cycling, and albedo. Paleoclimate proxies are available for large areas of Alaska that escaped continental glaciation during the Last Glacial Maximum (LGM). Assessing terrestrial paleoenvironmental response to past climate forcing will enable the Principal Investigators to test and refine global and regional circulation models of climate change.Recent advances enable us to estimate past climate parameters from glacial-geological records on a regional scale and in a quantitative, spatial manner for direct comparison with climate models. Valley glaciers are relatively simple recorders of climate. Winter precipitation and summer temperature locally control the vertical position of the Equilibrium Line Altitude (ELA) for individual glaciers, where the sum of accumulation and ablation equals zero. Regional variations in ELA's primarily reflect spatial variability in winter precipitation. Climate dynamic activities responsible for glacial extents during the LGM in Alaska have previously been assessed qualitatively and have suggested that Alaska has experienced a significant reduction in precipitation relative to the present. However, none have used recent empirical regressions between precipitation and temperature for ELAs, and none have taken advantage of the Geographic Information System (GIS) to perform spatial calculations and to produce past climate grids.The Principal Investigators propose to use glacial-geologic evidence to further refine the record by compiling LGM glacier extents in Alaska and produce digital maps of ELA variation and winter precipitation anomalies. Aerial photography and published maps will be used to determine glacier outlines. For selected, poorly studied areas, they propose to conduct field research to constrain the limits of LGM valley glaciers and to evaluate their age. This work will focus on two statewide transects: one spanning west to east from the Kuskokwim Mountains to the Yukon-Tanana Upland, and the other extending south to north along the western coast of the state. They will use carbon14 and cosmogenic isotopes to determine the absolute and relative ages of LGM moraines when suitable rocks available. In conjunction with modern climate data and estimates of LGM temperature depression, the ELA's can then be used to calculate LGM winter precipitation. The statewide computations will be compared with output from circulation models and will provide an empirical basis for evaluating climate dynamics. The GIS has advanced far enough to where we can now bring empirical paleoclimate data to the scale and resolution of global circulation models.