The Circumpolar Active Layer Monitoring (CALM) program, designed to observe the response of the active layer and near‐surface permafrost to climate change, currently incorporates more than 100 sites involving 15 investigating countries in both hemispheres. In general, the active layer responds consistently to forcing by air temperature on an interannual basis. The relatively few long‐term data sets available from northern high‐latitude sites demonstrate substantial interannual and interdecadal fluctuations. Increased thaw penetration, thaw subsidence, and development of thermokarst are observed at some sites, indicating degradation of warmer permafrost. During the mid‐ to late‐1990s, sites in Alaska and northwestern Canada experienced maximum thaw depth in 1998 and a minimum in 2000; these values are consistent with the warmest and coolest summers. The CALM network is part of the World Meteorological Organization's (WMO) Global Terrestrial Network for Permafrost (GTN‐P). GTN‐P observations consis...

The circumpolar active layer monitoring (calm) program: Research designs and initial results 1

Distribution of near-surface permafrost in Alaska: Estimates of present and future conditions

[1] The measurement of temporal changes in active layer thickness (ALT) is crucial to monitoring permafrost degradation in the Arctic. We develop a retrieval algorithm to estimate long-term average ALT using thaw-season surface subsidence derived from spaceborne interferometric synthetic aperture radar (InSAR) measurements. Our algorithm uses a model of vertical distribution of water content within the active layer accounting for soil texture, organic matter, and moisture. We determine the 1992–2000 average ALT for an 80 × 100 km study area of continuous permafrost on the North Slope of Alaska near Prudhoe Bay. We obtain an ALT of 30–50 cm over moist tundra areas, and a larger ALT of 50–80 cm over wet tundra areas. Our estimated ALT values match in situ measurements at Circumpolar Active Layer Monitoring (CALM) sites within uncertainties. Our results demonstrate that InSAR can provide ALT estimates over large areas at high spatial resolution.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2011JF002041

Estimating 1992-2000 average active layer thickness on the Alaskan North Slope from remotely sensed surface subsidence

Frost boils in northern Alaska vary from large, 2–3-m diameter, barren non-sorted circles to completely vegetated hummocks. Summer warmth increases southwards from the coast. Average thaw-layer thickness shows the opposite trend. Frost heave shows no trend along the climate gradient but is affected by soil texture. Heave is greatest on frost boils with fine-grained sediments. Biomass increases from 183 g m � 2 at the coast to 813 g m � 2 in the Arctic Foothills. An aggrading permafrost table is evident in most of the frost-boil soil profiles, indicating that, over time, accumulation of plant biomass leads to reduced thaw-layer thickness. A conceptual model suggests how vegetation affects the morphology of patterned ground forms. In the coldest parts of the High Arctic well-developed frost boils do not form and there is little vegetation on frost boils or the inter-boil areas. In the warmest parts of the Low Arctic, vegetation is usually sufficient to stabilize the frost boil soils. Frost boils play an important role in Arctic ecosystems functions, including the flux of trace gases to the atmosphere, flux of water and nutrients to streams, and the recycling of important nutrients to wildlife populations. Copyright # 2004 John Wiley & Sons, Ltd.

/pdf/frost-boil-ecosystems-complex-interactions-between-landforms-h18snjhctk.pdf

Frost‐boil ecosystems: complex interactions between landforms, soils, vegetation and climate

Active-layer thickness was determined in late August 1995 and 1996 at 100 m intervals over seven 1 km 2 grids in the Arctic Coastal Plain and Arctic Foothills physiographic provinces of northern Alaska. Collectively, the sampled areas integrate the range of regional terrain, soil, and vegetation characteristics in this region. Spatial autocorrelation analysis indicates that patterns of active-layer thickness are governed closely by topographic detail, acting through near-surface hydrology. On the coastal plain, maximum variability occurs at scales involving hundreds of meters, and patterns were similar in the two years. Substantially less spatial structure and interannual correspondence were found within the foothill sites, where high variability occurs over smaller distances. The divergence in patterns of thaw depth between the two provinces reflects the scale of local terrain features, which predetermines the effectiveness of fixed sampling intervals. Exploratory analysis should be performed to ascertain the scale(s) of maximum variability within representative areas prior to selection of sampling intervals and development of long-term monitoring programs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD00534

Active‐layer thickness in north central Alaska: Systematic sampling, scale, and spatial autocorrelation

Models of regional CO exchange processes in arctic tundra environ2 ments using landscape characteristics may need to incorporate spatial and temporal variations in the depth to the permafrost layer because it influences soil drainage, aeration, decomposition, and nutrient availability. However this depth, or the depth of the active layer (DAL), will have to be estimated indirectly since it is not practical to make a large number of ground measurements on a regular basis. Previous research has demonstrated that spatial variations in DAL are strongly related to aboveground vegetation production in sub-arctic tundra. Since aboveground vegetation production in Alaskan arctic tundra has been related to the Normalized Difference Vegetation Index (NDVI), it was hypothesized that spatial variations in NDVI would follow variations in DAL in these environments. Studies were conducted on the North Slope of Alaska during the summers of 1994 and 1995 to determine the feasibility of estimating DAL at multiple ...

The relation between active layer depth and a spectral vegetation index in arctic tundra landscapes of the North Slope of Alaska

Relating CO 2 fluxes to spectral vegetation indices in tundra landscapes: importance of footprint definition

Carbon flux and spectral reflectance data were collected on the North Slope of Alaska during the 1994 growing season. Observations were made at two sites in the coastal plain and two sites in the foothills of the Brooks Mountain Range. The relationship between the normalized difference vegetation index (NDVI) and daily gross primary production (GPP) was investigated. The daily gross primary production of tussock tundra was normalized for variations in photosynthetically active radiation (PAR) and was found to be linearly related to the NDVI. Seasonal changes in the vegetation and solar elevation, and variations in cloud cover conditions during radiometric observations did not have a significant effect on the relationship between GPP/PAR and the NDVI. The contrasting landscapes of the coastal plain and foothills regions (vegetation and moisture characteristics) and experimental manipulations that included changes in soil moisture conditions, illumination and temperature also did not appear to affect the relationship.

Direct estimates of CO/sub 2/ flux in Arctic environments using a spectral vegetation index

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The relation between active layer depth and a spectral vegetation index in arctic tundra landscapes of the North Slope of Alaska

Relating CO 2 fluxes to spectral vegetation indices in tundra landscapes: importance of footprint definition

Direct estimates of CO/sub 2/ flux in Arctic environments using a spectral vegetation index