CALM at 21: Results of long-term monitoring of the active layer/upper permafrost system.

Abstract:

The Circumpolar Active Layer Monitoring network, comprised of more than 200 sites, represents the only coordinated and standardized program of observations designed to observe and detect decadal changes in the dynamics of seasonal thawing in high-latitude soils. It provides long-term time series of active layer thickness, ground temperature, and thaw settlement measurements at the same locations and across diverse terrain types and regions to establish trends and validate models. In this study we report long-term active layer trends for characteristic regions of the circumpolar Arctic, with specific emphasis on northern Alaska. We used data from 21 (1995-2015) years of extensive, spatially oriented field observations at Alaskan CALM sites to examine landscape-specific temporal and spatial ALT variability and its relation to climatic forcing and heterogeneity of edaphic properties. Soil consolidation accompanying penetration of thaw into an ice-rich stratum at the base of the active layer may obscure active-layer measurements, resulting in underrepresentation of the overall response of the active layer- upper permafrost system to climatic forcing. Here we provide results of long-term simultaneous monitoring of elevational position of the ground surface and thaw depth at representative Alaska landscapes to evaluate the impact of surface heave and subsidence on traditional active-layer observations.