Active‐layer spatial and temporal variability at European Russian Circumpolar‐Active‐Layer‐Monitoring (CALM) sites

Three 100 × 100 m grids were established in European Russia in the framework of the Circumpolar‐Active‐Layer‐Monitoring (CALM) project. Records range from 4 to 7 years in length. The grids are in mineral soils with mean annual permafrost temperature from −0.5 to −2.5°C. The sites are known to be sensitive to decadal‐scale climatic changes. The grids differ in mean annual air temperature, but have similar thawing indices (DDT). Two grids with deeper annual thaw, separated by 400 km, reveal remarkable similarity in thaw depths, seasonal dynamics and interannual variability. All grids respond to thermal forcing rather consistently, although thaw increments caused by similar increases in DDT are smaller at the grid with the shallowest annual thaw. Stepwise multiple regression and other statistical analyses identified organic‐layer thickness and some, but not all, topographic features as the variables having explanatory power with respect to thaw‐depth variability. These and other variables examined do not, however, explain all the variability in the thaw depth. The effects of organic‐layer thickness on thaw depth are shown to change during the warm season. Copyright © 2004 John Wiley & Sons, Ltd.