| Summary: | Summer thaw depths at eight monitoring sites in the Mackenzie Valley, determined from probing of grids and thaw tubes, are used to characterise the spatial and temporal variations in active‐layer thickness and to investigate linkages to climatic variations. Intra‐site variability in thaw depths is typically low where organic cover is thin and uniform. Higher variability occurs where moisture contents and organic cover are high and spatially variable. Grid‐mean thaw depths provide robust measures of the average site thaw depth, although they are less than annual maximum active‐layer thicknesses determined by thaw tubes. Values from both measurements correlate reasonably well, permitting estimates of the variations in active‐layer thickness from grid‐mean thaw depths. Active‐layer response to thermal forcing in various settings is well represented by grid‐mean thaw depths and the square‐root of late‐season thawing‐degree days. However, the effect of interannual climate variability on active‐layer thickness is better assessed by maximum tube thaw depths and the square‐root of total thawing‐degree days. Copyright © 2009 Her Majesty the Queen in right of Canada. Published by John Wiley & Sons, Ltd.
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