Detecting Spatial Variability in the Ground Temperature in a Discontinuous Permafrost Region and Attributing it to the Physical and Biological Parameters

Recent observations indicate a warming of permafrost in many northern and mountain regions with a resulting degradation of ice-rich and carbon-rich permafrost. Permafrost temperature has increased by 1 to 2°C in northern Russia during the last 30 to 35 years. This observed increase is very similar to what has been observed in Alaska where the detailed characteristic of the warming varies between locations, but is typically from 0.5 to 2°C. In the last 30-years, warming in permafrost temperatures observed in the Russian North and Alaska has resulted in the thawing of permafrost in natural, undisturbed conditions in areas of the discontinuous permafrost zone. However, high spatial variability in ground surface conditions in the discontinuous permafrost zone produce a very diverse physical environment where mean annual ground temperatures (MAGT) may vary spatially by 5 to 6°C in the same climatic region. In this presentation, we will analyze ground temperature data collected during the last several years in an area north of Fairbanks in central Alaska. The observational sites were established along a profile across a small valley and encompass different topographic, hydrologic, and vegetation conditions and include sites where near-surface permafrost is present as well as the sites where permafrost is absent in the upper several meters. We found that the most pronounced difference in permafrost conditions along this profile is related to the site's elevation. Even if the difference in elevation between the ridge crest (338 m) and the valley bottom (175 m) is relatively small, the difference between mean annual air temperatures at these sites during the 2008-2010 period was about 3.4°C with higher temperature at the crest (-0.4°C) and lower at the valley bottom (-3.8°C). Well known winter temperature inversion effect is responsible for this difference. As a result, permafrost is generally absent at the higher elevations (MAGT at 1.2 m depth is +1.7°C at the crest site) and present in the lower elevations in this valley (MAGT at 1.2 m depth is -0.9°C at the valley bottom). However, other ecological conditions such as vegetation, soil moisture, and slope orientation are also play a very important role in forming the ground temperature regime. A complex interplay of these conditions will be illustrated in our presentation based on collected ground temperature data. Detection of permafrost presence or absence in the discontinuous permafrost zone using temperature measurements in shallow (0 to 1.5 m) boreholes will be also discussed.