Permafrost and Frozen Ground Assessments


The Recent State of Permafrost, 2012


V.E. Romanovsky1, S.L. Smith2, H.H. Christiansen3, N.I. Shiklomanov4, D.A. Streletskiy4, D.S. Drozdov5, N.G. Oberman6, A.L. Kholodov1, S.S. Marchenko1

1Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA
2Geological Survey of Canada, Natural Resources Canada, Ottawa, Ontario, Canada
3Geology Department, University Centre in Svalbard, UNIS, Norway
and Institute of Geography and Geology, University of Copenhagen, Denmark
4Department of Geography, George Washington University, Washington, DC, USA
5Earth Cryosphere Institute, Tyumen, Russia
6MIRECO Mining Company, Syktyvkar, Russia


04 July 2013

(This article is an abbreviated version of the material in the 2012 Arctic Report Card. It appears here by permission of the authors. [Edited by Michael Key.])

The most direct indicators of permafrost stability and changes in permafrost state are the permafrost temperature and the active layer thickness (ALT). The ALT is the top layer of soil and/or rock that thaws during the summer and freezing again during the fall, i.e., it is not permafrost. Permafrost temperature measured at a depth where seasonal variations in ground temperature cease to occur is the best indicator of long-term change. This depth varies from a few meters in warm, ice-rich permafrost to 20 m and more in cold permafrost and in bedrock (Smith et al., 2010; Romanovsky et al., 2010a). However, if continuous year-round temperature measurements are available, the mean annual ground temperature (MAGT) at any depth within the upper 15 m can be used for detection of changing conditions.

In 2012, new record high temperatures at 20 m depth were measured at most permafrost observatories on the North Slope of Alaska, i.e., north of the Brooks Range, where measurements began in the late 1970s (Figure 1b). The exceptions were West Dock and Deadhorse, where temperatures in 2012 were the same as the record-high temperatures observed in 2011. Record high temperatures were also observed in 2012 in the Brooks Range (Chandalar Shelf) and in its southern foothills (Coldfoot). These distinct patterns of permafrost warming on the North Slope and a slight cooling in the Alaska Interior in 2010-2011 are in good agreement with air temperature patterns observed in the Arctic and the sub-Arctic and might also be a result of snow distribution variations.

Figure 1
Figure 1: Time series of annual permafrost temperatures (b and c) measured from north to south across Alaska (a) in the continuous and discontinuous permafrost zones.

A similar temperature increase in colder permafrost during the last 40 years in northwest Canada was determined by comparison of measurements made between 2003 and 2007 with those made in the late 1960s and early 1970s (Burn and Kokelj, 2009). In the discontinuous zone of western Canada, the increase in permafrost temperature continues to be small, e.g., not exceeding 0.2°C per decade in the central and southern Mackenzie Valley (Figure 2, Norman Wells and Wrigley) (Smith et al., 2010; Derksen et al. 2012). In the eastern and high Canadian Arctic, greater warming has been observed, and since 2000 there has continued to be a steady increase in permafrost temperature (Figure 2, Alert). Significant increases in winter air temperature appear to be largely responsible for the recent increases in permafrost temperature in northern Canada, particularly at polar desert sites where snow cover is minimal (Smith et al., 2012). These changes in permafrost conditions are consistent with the recent observed reduction in spatial extent and mass of the cryosphere across the Canadian Arctic (Derksen et al., 2012).

Figure 2
Figure 2: Time series of mean annual permafrost temperature at 12 m depth at Norman Wells and Wrigley in the discontinuous permafrost zone of the central Mackenzie Valley, Northwest Territories, Canada and at 15 m and 24 m depth at CFS Alert, Nunavut, Canada (updated from Smith et al., 2010, 2012). The method described in Smith et al. (2012) was used to address gaps in the data record and produce a standardized record of mean annual ground temperature. Note the large temperature difference between the low (a) and high (b) latitude sites.

A common feature at Alaskan, Canadian and Russian sites is greater warming in relatively cold permafrost than in warm permafrost in the same geographical area (Romanovsky et al., 2010a). With a long-term warming at the ground surface, more constituent ice in fine-grained frozen sediment turns into water in the upper 5 to 15 m of permafrost, with little effect on permafrost temperature (Romanovsky and Osterkamp, 2000). In contrast, temperatures in colder permafrost are much more responsive to changes in temperature at the ground surface. This difference in the rate of permafrost warming is responsible for the fact that permafrost temperatures at such distant sites in Alaska as Chandalar Shelf in the Brooks Range and Birch Lake in Interior Alaska, which are 445 km apart, now have exactly the same permafrost temperatures. Another such example is the Old Man and College Peat sites, which are 225 km apart (Figure 1).

Long-term observations of changes in active-layer thickness (ALT) are less conclusive. Thaw depth observations exhibit substantial inter-annual fluctuations, primarily in response to variations in summer air temperature (e.g., Smith et al. 2009; Popova and Shmakin, 2009). Decadal trends in ALT vary by region. (Shiklomanov et al., 2012). A progressive increase in ALT has been observed in some Nordic countries, e.g., in the Abisko area of Sweden since the 1970s, with a faster rate after 1995 that resulted in disappearance of permafrost in several mire landscapes (e.g., Åkerman and Johansson, 2008; Callaghan et al., 2010). This increase in thaw propagation ceased during 2007-2010, coincident with drier summer conditions (Christiansen et al., 2010). Increases in ALT since the late 1990s have been observed on Svalbard and Greenland, but these are not spatially and temporarily uniform (Christiansen et al., 2010). Increase in ALT during the last fifteen years has been observed in the north of European Russia (Drozdov et al., 2012; Kaverin et al., 2012), in the north of East Siberia (Fyodorov-Davydov et al., 2008) and in Chukotka (Zamolodchikov, 2008), but ALT was relatively stable in the northern regions of West Siberia (Figure 3). Active-layer trends are different for North American sites, where a progressive increase of ALT is evident only at sites in Interior Alaska; there, the maximum ALT for the 18-year observation period occurred in 2007 (Figure 3). Active-layer thickness on the North Slope of Alaska is relatively stable, without pronounced trends during 1995-2008 (Streletskiy et al., 2008; Shiklomanov et al., 2010). Similar results are reported from the western Canadian Arctic. Smith et al. (2009) found no definite trend in the Mackenzie Valley during the last 15 years, with some decrease in ALT following a maximum in 1998. Although an 8 cm increase in thaw depth was observed between 1983 and 2008 in the northern Mackenzie region, shallower thaw has been observed since 1998 (Burn and Kokelj, 2009). In the eastern Canadian Arctic, ALT has increased since the mid-1990s, with the largest increase occurring in bedrock of the discontinuous permafrost zone (Smith et al., 2010).

Figure 3
Figure 3: Active-layer change in nine different Arctic regions according to the Circumpolar Active Layer Monitoring (CALM) program. The data are presented as annual percentage deviations from the mean value for the period of observations (indicated in each graph). Solid red lines show mean values. Dashed grey lines represent maximum and minimum values. Thaw depth observations from the end of the thawing season were used. Availability of at least ten years of continuous thaw depth observations through to the 2011 thawing season was the only criterion for site selection. For Greenland sites, 2011 data are not available. The number of CALM sites within each region varies and is indicated in each graph. Figure updated from Shiklomanov et al. (2012).

The last 30 years of ground warming have resulted in the thawing of permafrost in areas of discontinuous permafrost in Russia (Oberman, 2008; Romanovsky et al., 2010). This is evidenced by changes in the depth and number of taliks (a sub-surface layer of year-round unfrozen ground within permafrost), especially in sandy and sandy loam sediments compared to clay. A massive development of new closed taliks in the southern continuous permafrost zone, resulting from increased snow cover and warming permafrost, was responsible for the observed northward movement by several tens of kilometers of the boundary between continuous and discontinuous permafrost (Oberman and Shesler, 2009; Romanovsky et al., 2010).


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