Boundary condition controls on the timing and extent of Pleistocene glaciations in Yukon

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The CIS was an important component of Earth's past climate system: it responded to orbital induced climate forcing during repeated growth and decay and provided meltwater to adjacent oceans, which can influence climate. Precipitation limited means that glacier extents are mainly controlled by the amount, distribution, timing and type of effective precipitation. These precipitation limited glacier systems are of particular interest in paleoclimate studies because the marine isotope record, commonly used as a proxy for the relative global mass of glaciers, may not accurately reflect all glacier limits. This proposal will focus on the Yukon Territory, which has been repeatedly affected by the northern Cordilleran Ice Sheet (CIS). Although termed an ice sheet, it is better described as an ice complex, comprised of a series of coalescing valley glaciers and piedmont lobes whose ice flow was strongly controlled by topography. This ice complex produced irregular, digitate horseshoe-shaped glacial limits on the plateau area of central Yukon. Many of these ice flows had separate source areas, reflecting differences in the regional accumulation zones and the nature of the underlying topography. This ice complex produced three irregular, mappable, digitate horseshoe-shaped chrono-geomorphic regions on the plateau area of central Yukon ranging in age from 2.6 Ma to 12 ka. These three limits were thought to represent regionally coherent advances of the Cordilleran Ice Sheet. Our work, however, shows that regional ice expansion neither correlates across Yukon nor to peaks in global ice volume. Factors that could explain this varied response of the northern sector of the CIS across time and space will be tested and include changes in local topography, glacier dynamics, and climate. The primary objective of this proposal is to elucidate the varying forcing conditions that affect the extents and timing of Pleistocene glaciation in Yukon. An important dataset required for this objective includes a robust chronology of ice expansion to correlate to the marine isotope record and other similar glacier systems. Yukon is a perfect location to do this as it contains one of the oldest and richest terrestrial records of Arctic Quaternary climate change. With active volcanism, especially the presence of volcanic ashes, there is the potential for numerous dating methods to improve the chronology.My research in Yukon will significantly contribute to our understanding of the roles that climatic and non-climatic factors play in the response of high latitude glacier systems to climate change. Results will have an affect on research in other precipitation limited systems throughout the Arctic. These systems represent an important benchmark for climate models who will use that require data fro this study for validation. Careful study of deglaciation of the CIS also provides one analogue for current ice sheets such as Greenland.