Active Layer Thickening and Thaw Progression Variability in Central Svalbard

Thaw progression and active layer thickness (ALT) have been monitored since 2000 at a loess-covered terrace in Adventdalen, central Svalbard, as part of the Circumpolar Active Layer Monitoring (CALM) program. Ground temperature measurements are made adjacent to this site, which is called UNISCALM, allowing for the comparison of ALT determination via ground temperature interpolation and mechanical probing. Nearby meteorological stations allow for the comparison of ALT with parameters including summer air temperature, cloud cover, and precipitation. The 17 years of mechanical probing data demonstrate an increase in ALT over the study period. During the first six years of measurements, ALT remained less than 1 m and had a minimum of 74 cm in 2005. Since 2006, ALT has been 1 m or greater. Thaw progression at the beginning of summer is primarily controlled by the timing and duration of snowmelt, while ALT is largely controlled by air temperature and solar insolation. Interannual variability in ALT at UNISCALM is significant, and is greater than at other Nordic CALM sites.