			Home About us Contact

Thaw Depth (thaw + depth)

Distribution by Scientific Domains

Humanities and Social Sciences	57%

Selected Abstracts

Estimating the Variability of Active-Layer Thaw Depth in Two Physiographic Regions of Northern Alaska

GEOGRAPHICAL ANALYSIS, Issue 2 2001
Claire E. Gomersall
The active layer is the zone above permafrost that experiences seasonal freeze and thaw. Active-layer thickness varies annually in response to air and surface temperature, and generally decreases poleward. Substantially less is known about thaw variability across small lateral distances in response to topography, parent material, vegetation, and subsurface hydrology. A graduated steel rod was used to measure the 1998 end-of-season thaw depth across several transects. A balanced hierarchical sampling design was used to estimate the contribution to total variance in active-layer depth at separating distances of 1, 3, 9, 27, and 100 meters. A second sampling scheme was used to examine variation at shorter distances of 0.3 and 0.1 meter. This seven-stage sample design was applied to two sites in the Arctic Foothills physiographic province, and four sites on the Arctic Coastal Plain province in northern Alaska. The spatial variability for each site was determined using ANOVA and variogram methods to compare intersite and inter-province variation. Spatial variation in thaw depth was different in the Foothills and Coastal Plain sites. A greater percentage of the total variance occurs at short lag distances (0,3 meters) at the Foothills sites, presumably reflecting the influence of frost boils and tussock vegetation on ground heat flow. In contrast, thaw variation at the Coastal Plain sites occurs at distances exceeding 10 meters, and is attributed to the influence of well-developed networks of ice-wedge polygons and the presence of drained thaw-lake basins. This information was used to determine an ongoing sampling scheme for each site and to assess the suitability of each method of analysis. [source]

Shrub expansion may reduce summer permafrost thaw in Siberian tundra

GLOBAL CHANGE BIOLOGY, Issue 4 2010
D. BLOK
Abstract Climate change is expected to cause extensive vegetation changes in the Arctic: deciduous shrubs are already expanding, in response to climate warming. The results from transect studies suggest that increasing shrub cover will impact significantly on the surface energy balance. However, little is known about the direct effects of shrub cover on permafrost thaw during summer. We experimentally quantified the influence of Betula nana cover on permafrost thaw in a moist tundra site in northeast Siberia with continuous permafrost. We measured the thaw depth of the soil, also called the active layer thickness (ALT), ground heat flux and net radiation in 10 m diameter plots with natural B. nana cover (control plots) and in plots in which B. nana was removed (removal plots). Removal of B. nana increased ALT by 9% on average late in the growing season, compared with control plots. Differences in ALT correlated well with differences in ground heat flux between the control plots and B. nana removal plots. In the undisturbed control plots, we found an inverse correlation between B. nana cover and late growing season ALT. These results suggest that the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw. Increased shrub growth may thus partially offset further permafrost degradation by future temperature increases. Permafrost models need to include a dynamic vegetation component to accurately predict future permafrost thaw. [source]

Measuring thaw depth beneath peat-lined arctic streams using ground-penetrating radar

HYDROLOGICAL PROCESSES, Issue 14 2005
John H. Bradford
Abstract In arctic streams, depth of thaw beneath the stream channel is likely a significant parameter controlling hyporheic zone hydrology and biogeochemical cycling. As part of an interdisciplinary study of this system, we conducted a field investigation to test the effectiveness of imaging substream permafrost using ground-penetrating radar (GPR). We investigated three sites characterized by low-energy water flow, organic material lining the streambeds, and water depths ranging from 0·2 to 2 m. We acquired data using a 200 MHz pulsed radar system with the antennas mounted in the bottom of a small rubber boat that was pulled across the stream while triggering the radar at a constant rate. We achieved excellent results at all three sites, with a clear continuous image of the permafrost boundary both peripheral to and beneath the stream. Our results demonstrate that GPR can be an effective tool for measuring substream thaw depth. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The n-factor of nonsorted circles along a climate gradient in Arctic Alaska

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2006
A. Kade
Abstract Three study sites were selected on zonal sites from north to south along a climate gradient in Arctic Alaska. Air and mineral soil surface temperatures of nonsorted circles and adjacent well-vegetated tundra plots were monitored from September 2003 through September 2004, and the depths of vegetation, soil organic horizons and snow were measured. N-factors, the ratio of ground-surface temperature to air temperature, were determined for the summer and winter seasons. N-factors and thaw depths were greater for relatively barren nonsorted circles than for adjacent well-vegetated tundra. Along the climate gradient, the thickness of vegetation, soil organic layer and snow increased from north to south, while n-factors and thaw depths decreased at bare circles from 1.43,±,0.02 to 0.74,±,0.01 and from 81.2,±,1.4,cm to 59.5,±,2.4,cm, respectively, and at the tundra from 0.99,±,0.02 to 0.17,±,0.01 and from 62.6,±,1.4,cm to 21.0,±,2.8,cm, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source]