HR: 0800h
AN: C21C-1135    [Abstracts]
TI: The Effect of Vegetation, Soil Organic Layer and Snow on the Modified N-Factor in Patterned-Ground Ecosystems
AU: * Kade, A
EM: ftank@uaf.edu
AF: Biology and Wildlife Department, 211 Irving I University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Walker, D A
EM: ffdaw@uaf.edu
AF: Institute of Arctic Biology, P.O. Box 757000 University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Romanovsky, V E
EM: ffver@uaf.edu
AF: Geophysical Institute, P.O. Box 757320 University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AB: The vegetation and soil patterns in arctic tundra are influenced by the distribution of nonsorted circles, which are patterned-ground features caused by differential frost heave that occurs when ice lenses form in soils during winter. Compared to the surrounding tundra areas, nonsorted circles have typically no or little vegetation cover, coarser soil texture, deeper thaw depth and greater frost heave, and their morphology changes along a climate gradient. This study examines the insulation effect of the vegetation and soil organic layer on mineral soils in the summer and the insulation effect of snow in the winter by determining the modified n-factor (n'-factor) for nonsorted circles and the surrounding tundra along a climate gradient. The n'-factor is a simple indicator of the energy balance at the mineral soil surface, and it is defined as the ratio of seasonal degree-day sums at the mineral soil surface to that in the air. The study was conducted along a bioclimate gradient from the coast of the Arctic Ocean to the Arctic Foothills along the northern segment of the Dalton Highway, Alaska. From north to south, three study sites were selected in bioclimate subzones C (Howe Island), D (Franklin Bluffs), and E (Happy Valley). Mineral soil-surface and air temperatures of nonsorted circles and adjacent stable tundra plots were monitored from September 2003 through 2004, and the thickness of the vegetation and soil organic horizons, thaw depth, snow depth and soil moisture of each study plot were measured. The nonsorted circles have warmer summer and cooler winter soil temperatures, deeper thaw depths, drier soils, shallower snow depth and greater snow densities than the surrounding tundra. The summer n'-factor is greater for nonsorted circles (Howe Island n'=1.4; Franklin Bluffs n'=1.0; Happy Valley n'=0.7) than for the adjacent stable tundra (Howe Island n'=1.0; Franklin Bluffs n'=0.4; Happy Valley n'=0.2). The difference in the winter n'-factor is not as pronounced between nonsorted circles (Howe Island n'=0.9; Franklin Bluffs n'=0.7; Happy Valley n'=0.4) and the surrounding tundra (Howe Island n'=0.9; Franklin Bluffs n'=0.5; Happy Valley n'=0.3). Along the climate gradient, the n'-factor declines from north to south with increasing thickness of the vegetation and soil organic layer and snow depth, which insulate the mineral soil. The summer n'-factor is closely tied to active layer-depth. From north to south, thaw depth decreases from 81 cm to 60 cm at the nonsorted circles and from 63 cm to 21 cm at the stable tundra. Increased vegetation growth and snow depth associated with a warming climate might decrease the n'-factor and active-layer depth in the northern subzones, and the morphological differences between nonsorted circles and the surrounding tundra might become less pronounced.
DE: 0704 Seasonally frozen ground
DE: 0706 Active layer
DE: 0718 Tundra (9315)
DE: 0768 Thermal regime
DE: 9315 Arctic region (0718, 4207)
SC: Cryosphere [C]
MN: Fall Meeting 2005