Document: FEN-3-41-14

Geomorphic and climatic controls over Holocene soil development in the arctic foothills of Alaska.

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

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

Abstract:
Quaternary glacial advances resulted in several geomorphic units of contrasting soil and vegetation within a similar regional climate in the arctic foothills of northern Alaska. Red Green Lake (RG; 68 39' N, 149 41' W) represents a young land surface (<15,000 years old) exposed by recession of the last glacial episode, whereas Upper Capsule Lake (UC; 68 38' N, 149 25' W) represents an old surface (>500,000 years old) unglaciated during the late Quaternary. We analyzed sediment cores from these two lakes for a suite of organic and inorganic geochemical indicators to assess Holocene soil development in relation to climatic and geomorphic variation. Overall the atomic ratios of carbon to nitrogen (C:N) and total concentrations of lignin-derived phenolic compounds (Lambda) are greater for UC than for RG, suggesting that the UC sediments are more enriched in terrestrial organic matter than those of RG. This difference probably reflects greater carbon fluxes from soil and vegetation within the UC watershed and higher aquatic productivity within RG Lake. At RG, increases in the content of organic carbon (OC%), C:N ratio, and Lambda together suggest that soil OC accumulation occurred gradually between 7000 and 2500 yr BP. The watershed soils of RG were mineral-rich prior to 7000 yr BP and organic-rich after 2500 yr BP. A marked increase in the Fe:Mn ratio of the RG sediments suggests that the onset of organic matter accumulation at 7000 yr BP was caused by the development of waterlogged, sub-oxic conditions that retarded the degradation of soil organic matter. Within the UC watershed, soil carbon storage probably also increased between 9000 yr BP and the late Holocene, as indicated by a doubling of sedimentary OC that is mainly of terrestrial origin. However, in contrast to RG, high OC% values, C:N ratios, and lignin-phenol concentrations at UC suggest that soils within the UC watershed were most likely organic-rich throughout the Holocene. The Fe:Mn ratios of the UC sediment core are relatively high without any stratigraphic variation, suggesting that waterlogged conditions existed throughout the Holocene. A regional climatic cooling ca. 7000 yr BP resulted in much greater edaphic alterations at RG than at UC, implying that sensitivity to climate forcing differs between the two geomorphic units represented by these two lakes.

Keywords: soil development, climate change, geomorphic control, Holocene, lake sediments, biogeochemistry

This abstract is being presented at: 4:15 PM in session:
Oral Session #32: Paleoecology.