Pleistocene Sea-Level and Glacial Fluctuations, Coastal Ahklun Mountains, Southwest Alaska

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Recent work in the south part of the west coast of Alaska (eastern Bristol Bay, 59oN) demonstrates that glaciers experienced extensive advances during the late Pleistocene. In northwestern Alaska (Seward Peninsula, 65oN, and western Brooks Range, 67oN), on the other hand, early Wisconsin glaciers were restricted to the highest mountain valleys and occupied an area approximately an order of magnitude less extensive than during middle and early Pleistocene advances. The most-recent major advance of glacier ice to the coast in southwestern Alaska was at least 300,000 yr younger than the last advance of ice to the coast in northwestern Alaska. To understand the cause and significance of this apparent glacial- geologic and paleoclimatological incongruity, the following must be addressed: (1) Where and over what distance along the coast between eastern Bristol Bay and Seward Peninsula does the cross-over between late Pleistocene glacial maxima and middle Pleistocene maxima occur? (2) To what extent to valley hypsometries control the extent of ice from the different source areas? (3) What does the geographic distribution of late-Wisconsin and pre-late-Wisconsin ice imply about equilibrium line altitude (ELA) lowering and equilibrium line altitude (ELA) gradients, and consequently, moisture sources and other climate variables? Solving these questions will require extensive field, aerial photographic, and geochronologic research in the only glaciated region between eastern Bristol Bay and Seward Peninsula-the Ahklun Mountains. It will depend on a multi-disciplinary effort to obtain numerical-age control on the deposits. State-of-the-art geochronologic and sedimentologic techniques will be applied to reconstruct the spatial and temporal pattern of Pleistocene sea-level and glacier fluctuations. This work will improve the understanding of the paleoclimatological controls of glaciation across western Alaska and their relation to the global climate system; should enable to address whether gl aciation in southwestern Alaska is synchronous with Northern Hemispheric ice-sheet fluctuations, or whether major glaciations here precedes ice build-up at lower latitude.