Document: WYA-3-41-13

Climatic and geomorphic controls on Holocene vegetational changes in the arctic foothills of Alaska.

OSWALD, W.W.* ¹, F.SHENG HU ², L.B.BRUBAKER ¹ and G.W.KLING ³

University of Washington, Seattle, WA 98195 ¹
University of Illinois, Urbana, IL 61801 ²
University of Michigan, Ann Arbor, MI 48109 ³

Abstract:
The distribution of tundra plant communities in the arctic foothills of northern Alaska is strongly influenced by landform controls on soil properties and thaw depths. We analyzed pollen and lignin-derived phenolic compounds in sediment cores from 2 lakes on contrasting geomorphic units to understand Holocene vegetational changes in relation to climatic and geomorphic variation. Red Green Lake (RG; 6839'N, 14941'W) represents recently deglaciated land surfaces (<15,000 yr BP). Young geomorphic units are characterized by irregular topography, thin soils, deep thaw layers, and moist non-acidic tundra (MNT). Upper Capsule Lake (UC; 6838'N, 14925'W) represents landscapes that remained unglaciated during the late Quaternary (>500,000 yr BP). Old surfaces currently have little relief, thick organic soils, thin thaw layers, and moist acidic tundra (MAT). Quantitative analyses of the UC pollen record indicate a shift from MNT to MAT at 7000 yr BP in response to regional climatic cooling. Cinnamyl:vanillyl (C:V) ratios increase throughout the UC record, suggesting that non-woody tissue increased at the expense of woody tissue. Woody shrubs, e.g., Betula and Salix, may have decreased in abundance during this period. The RG pollen record also suggests a vegetational shift at 7000 yr BP, with sparse, xeric tundra changing to MNT. C:V ratios for RG increase from 8000 to 3000 yr BP, corresponding to a decrease in Betula pollen percentages. After 3000 yr BP, lower C:V and higher syringyl values suggest more terrestrial organic matter and possibly more woody tissue. Higher percentages of Artemisia and Selaginella rupestris also indicate that the vegetation near RG changed in response to climatic cooling at 3000 yr BP. Comparison of the UC and RG records illustrates the landscape level heterogeneity of vegetation during the Holocene, and improves our understanding of the controls on past tundra communities in the arctic foothills.

Keywords: Alaska, Arctic Foothills, Holocene, landform, lignin, paleoecology, pollen, Quaternary, tundra

This abstract is being presented at: 4:30 PM in session:
Oral Session #32: Paleoecology.