The relative age of mountain permafrost - estimation of Holocene permafrost limits in Norway

For Scandinavia in general and Norway in particular the regional distribution of mountain permafrost is reasonably well known, both through ground temperature measurements in boreholes, geophysical soundings and spatial modeling. However, the evolution of permafrost over longer time periods, such as the Holocene, is unknown, but is considered to have significance for landscape development and geomorphological processes in high mountain areas of Scandinavia. In this study two mean annual air temperature series covering the Holocene have been compiled to drive a 1D heat flow model over a 10 kyr period for several sites in Norway. At each site temperature-monitored boreholes exist, which were used to calibrate the model. In addition the spatial distribution of permafrost during selected time periods of the Holocene was addressed using a newly implemented version of an equilibrium permafrost model. The result of this study indicates an altitudinal zonation of relative permafrost age in Norway. We find that permafrost has existed continuously since the deglaciation at the highest altitudes, whereas in large areas where permafrost currently is present, it degraded during the Holocene thermal maximum (HTM). In all boreholes the coldest simulated permafrost occurred during the 'Little Ice Age' (LIA), and also the largest areal distribution of Holocene permafrost in Norway seems to be connected to the LIA. (C) 2012 Elsevier B.V. All rights reserved.