One important variable that is bein

One important variable that is being closely monitored on a circum-Arctic basisis the depth of the active layer of the permafrost. Active layer depth (ALD) isthe depth to which thawing occurs each summer. Estimates are determinedfrom temperature profiles as the deepest level that warms to 0ºC, before againrefreezing. ALD is determined by finding the profile for the moment when soiltemperature reaches its maximum for the year. The depth where soil reaches0º and then begins to cool is the ALD for this year. Here is an example how thisis accomplished using graphical interpolation. Although ALDs are determined tothe nearest 1cm, profiles are not necessarily linear between 95 and 70 cmdepth so there is an uncertainty that has not been quantified, but is consideredsmall. Other years were analyzed consistently following this method. Theresults show that ALD stays the same over the years 2012-2014 at Flux towerand estimated at 43 cm. The soil temperature at wet, dry and mid soil siteswere measured only within the active layer and are insufficient for ALDestimation. This ALD estimation method was suggested by Robert Stone.