CGRG Bibliography of Canadian Geomorphology
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Author : Abbott, M.; Finney, B.; Edwards, M.; and Anderson, L.
Date : 2000.
Title : Lake level reconstructions from sites in Central Alaska, the Brooks Range, and the Yukon Territory
Publication : 30th International Arctic Workshop, Program and Abstracts, 2000. Institute of Arctic and Alpine Research, University of Colorado at Boulder
Issue :
Page(s) : 1.
Abstract
Our ongoing research is aimed at documenting the regional pattern of P-E change from the late Pleistocene to present using multi-proxy methods at a network of lakes from central and northern Alaska to the Yukon Territory. We have used seismic surveys and core transects to identify transgression and regression sequences associated with water-level changes. Laboratory work includes sedimentological, geochemical, oxygen isotope, and palynological analyses. Results from Birch Lake in central Alaska show a pronounced period of aridity ended around 15.3 ka B.P. (12.7 14C ka B.P.) (Abbott et al., 2000). Sediments in Jan Lake also show the same general pattern. Records older then this from central Alaska are rare because the dry lake basins were deflated and the sediment record lost. To date we have not identified any sites with records older than 15.3 ka B.P. in central Alaska. However, at Burial Lake in the Noatak Valley of northwestern Alaska we have a 42 14C ka B.P. record. If Burial Lake remained filled throughout the late Pleistocene it suggests western Alaska was not as arid as the interior. Work is in progress on a transect of cores from Burial Lake. In the eastern and central interior of Alaska we have also shown that the two most prominent regional vegetation changes: from herb to shrub tundra and the expansion of spruce-dominated boreal forest, were both coincident with regional increases in effective moisture. Results from Meli and Tangled Up lakes in the central Brooks Range indicate there have been both temperature and P-E balance shifts during the Holocene. A long term millennial scale trend towards increased effective moisture since ~8 ka B.P. is indicated by sediment cellulose del18O in Meli Lake. High-resolution del18O analyses of authigenic carbonate from Tangled Up Lake show decadal to century scale temperature variability. Combined, these records reveal climatic changes throughout the region at a variety of temporal scales that create a foundation for future research investigating the timing, spatial extent, and magnitude of these events. Preliminary results from a transect of eight sediment cores from Jackfish Lake in the Yukon Territory document a complex Holocene lake level history. Jackfish is a small (<1 km 2 ), shallow (<10 m deep) closed basin lake with a relatively high E/I ratio (2.2) and a low watershed to lake area ratio (3.1). Isotope analyses of surface water samples indicate it is sensitive to changes in the P-E balance (see poster by Anderson et al., this session). Basal radiocarbon dates indicate the lake basin was dry prior to 10.6 ka B.P. with water levels remaining low until after 7.1 ka B.P. After 7.1 ka B.P. shallow water cores contain multiple transgression/regression phases suggesting lake levels were lower than present until the latest Holocene. Stable isotope analyses on authigenic carbonate is in progress and combined with lake level, pollen, and geochronological studies will provide a powerful tool for identifying the timing, direction, magnitude, and rate of water balance changes in the region.
Bibliography of Canadian Geomorphology