Thermal state of permafrost in North America: a contribution to the international polar year

TLDR

Permafrost in northern North America ranges from above −3 °C in discontinuous zones to −15 °C in continuous zones, with temperature envelopes shaped by substrate and latent heat effects that allow persistence near 0 °C under warming conditions. The study aimed to produce a snapshot of the thermal state of permafrost across northern North America during the International Polar Year using ground temperature data from 350 boreholes. Ground temperature data were collected from 350 boreholes, more than half established during IPY to expand monitoring in sparsely covered areas, covering diverse ecoclimatic and geological settings and elevations across the continent. New mountain sites in Yukon indicate limited permafrost extent, and overall warming trends across North America over recent decades—especially north of the treeline—have reduced spatial diversity of permafrost thermal conditions. © 2010 Crown in the right of Canada and John Wiley & Sons, Ltd.

Abstract

Abstract A snapshot of the thermal state of permafrost in northern North America during the International Polar Year (IPY) was developed using ground temperature data collected from 350 boreholes. More than half these were established during IPY to enhance the network in sparsely monitored regions. The measurement sites span a diverse range of ecoclimatic and geological conditions across the continent and are at various elevations within the Cordillera. The ground temperatures within the discontinuous permafrost zone are generally above −3°C, and range down to −15°C in the continuous zone. Ground temperature envelopes vary according to substrate, with shallow depths of zero annual amplitude for peat and mineral soils, and much greater depths for bedrock. New monitoring sites in the mountains of southern and central Yukon suggest that permafrost may be limited in extent. In concert with regional air temperatures, permafrost has generally been warming across North America for the past several decades, as indicated by measurements from the western Arctic since the 1970s and from parts of eastern Canada since the early 1990s. The rates of ground warming have been variable, but are generally greater north of the treeline. Latent heat effects in the southern discontinuous zone dominate the permafrost thermal regime close to 0°C and allow permafrost to persist under a warming climate. Consequently, the spatial diversity of permafrost thermal conditions is decreasing over time. Copyright © 2010 Crown in the right of Canada and John Wiley & Sons, Ltd.