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Permafrost

V. E. Romanovsky1, S. L. Smith2, H. H. Christiansen3, N. I. Shiklomanov4,
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 Department of Geosciences, University of Oslo, Norway
4Department of Geography, George Washington University, Washington, DC, USA
5Earth Cryosphere Institute, Tyumen, Russia
6MIRECO Mining Company, Syktyvkar, Russia

November 28, 2011

Highlights

  • In 2011, new record high temperatures at 20 m depth were recorded at all permafrost observatories on the North Slope of Alaska, where measurements began in the late 1970s.
  • During the last fifteen years, active-layer thickness has increased in the Russian European North, northern East Siberia, Chukotka, Svalbard and Greenland.
  • Active-layer thickness on the Alaskan North Slope and in the western Canadian Arctic was relatively stable during 1995-2008.

The most direct indicators of permafrost stability and changes in permafrost state are the permafrost temperature and the active layer thickness (ALT). Permafrost temperature measured at the depth where the seasonal variations in ground temperature cease to exist is best to use as an 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-around temperature measurements are available, the mean annual ground temperature (MAGT) at any depth within the upper 15 m can be used as a proxy of the permafrost temperature. The recently concluded International Polar Year (IPY 2007-2009) resulted in significant enhancement of the permafrost observing system in the Arctic; there are now ~575 boreholes (Fig. HTC23; Brown et al. 2010; Romanovsky et al. 2010a). A borehole inventory, including mean annual ground temperatures for most of these boreholes, is available online (http://nsidc.org/data/g02190.html).

Fig. 23 -- Mean annual ground temperature
Fig. HTC23. Circum-Arctic snapshot of mean annual ground temperature (MAGT) in permafrost during the International Polar Year (2007-2009; from Romanovsky et al. 2010).

Permafrost temperatures in the Arctic and sub-Arctic lowlands generally follow a latitudinal gradient, decreasing northward. Higher ground temperatures are found in the southern discontinuous zone, where MAGT is above 0°C at many locations (Fig. HTC23). The temperature of warm permafrost in the discontinuous zone generally falls within a narrow range, with MAGT at most sites being > -2°C (Christiansen et al. 2010; Romanovsky et al. 2010a; Smith et al. 2010) (Fig. HTC24). Temperatures as low as -3°C or even -4°C, however, may be observed in some specific ecological or topographic conditions (Jorgenson et al. 2010). A greater range in MAGT occurs within the continuous permafrost zone, from >-1°C at some locations to as low as -15°C (Christiansen et al. 2010; Romanovsky et al. 2010a; Romanovsky et al. 2010b; Smith et al. 2010). MAGT > 0°C is observed at some locations near the southern boundary of the continuous zone (Fig. HTC23), which may indicate that this boundary is shifting northward (Romanovsky et al. 2010b). Permafrost temperatures <-10°C are presently found only in the Canadian Arctic Archipelago (Smith et al. 2010) and near the Arctic coast in Siberia.

Systematic observations of permafrost temperature in Alaska, Canada and Russia since the middle of the 20th Century provide several decades of continuous data from several sites. The data allow assessment of changes in permafrost temperatures on a decadal time scale. A general increase in permafrost temperatures is observed during the last several decades in Alaska (Romanovsky et al. 2007; Osterkamp 2008; Smith et al. 2010; Romanovsky et al. 2010a), northwest Canada (Smith et al. 2010) and Siberia (Oberman 2008; Drozdov et al. 2008; Romanovsky et al. 2010b).

At most Alaskan permafrost observatories there was substantial warming during the 1980s and especially in the 1990s (Fig. HTC24). The magnitude and nature of the warming varies between locations, but is typically from 0.5°C to 2°C at the depth of zero seasonal temperature variations over this 20 year period (Osterkamp 2008). However, during the 2000s, permafrost temperature has been relatively stable on the North Slope of Alaska (Smith et al. 2010) (Fig. HTC24a), and there has been a slight decrease (by as much as 0.3°C) at some locations in Interior Alaska during the last three years (Fig. HTC24b). During the last decade, continuous warming has been observed only at near-coastal sites, where there has also been an increase in "greenness" of tundra vegetation (see the essay on Vegetation) and the area of open ocean in summer (see the essay on Sea Ice). The latest data may indicate that the observed warming trend along the coast has begun to propagate south towards the northern foothills of the Brooks Range, where a noticeable warming in the upper 20 m of permafrost has become evident since 2008 (Romanovsky et al. 2011). In 2011, new record high temperatures at 20 m depth were measured at all permafrost observatories on the North Slope of Alaska, where measurements began in the late 1970s (Fig. HTC24a). These distinct patterns of permafrost warming on the North Slope and a slight cooling in Interior Alaska are in good agreement with the Arctic/sub-Arctic air temperature differences described in the essay on Temperature and Clouds. These patterns may also be a result of differences in snow distribution (see the essay on Snow).

a.
Fig. 24a -- Time series of permafrost temperature measured at 20 m below the surface North Slope of Alaska
b.
Fig. 24b -- Time series of permafrost temperature measured at 20 m below the surface Interior Alaska
c.
Fig. 24c -- Time series of permafrost temperature measured at 20 m below the surface map

Fig. HTC24. Time series of permafrost temperature measured at 20 m below the surface at locations (a, top) from north to south across the North Slope of Alaska in the continuous permafrost zone, and (b, middle) in Interior Alaska. Note the higher permafrost temperatures in Interior Alaska (b) than on the North Slope (a) The locations of sites named in (a) and (b) are shown in the map (c, bottom).

A similar permafrost temperature increase during the last 40 years was estimated for colder permafrost in northwest Canada (Burn and Kokelj 2009). In the discontinuous zone of western Canada, the increase in permafrost temperature has been smaller (Fig. HTC25a), with negligible change in recent years (Smith et al. 2010). In the eastern and high Canadian Arctic, greater warming has been observed, and since 2000 there has been a steady increase in permafrost temperature (Fig. HTC25b).

Fig. 25 top -- Time series of mean annual permafrost temperatures
Fig. 25 bottom -- Time series of mean annual permafrost temperatures

Fig. HTC25. Time series of mean annual permafrost temperatures at (top) 12 m depth at two sites in the discontinuous permafrost zone of the central Mackenzie Valley, Northwest Territories Canada and (bottom) 15 m depth at CFS Alert, Nunavut, Canada (updated from Smith et al. 2010). The method described in Throop et al. (2010) was used to address gaps in the data record and produce a standardized record of mean annual ground temperature.

Permafrost temperature has increased by 1°C to 2°C in northern Russia during the last 30 to 35 years (Drozdov et al. 2008; Oberman, 2008; Romanovsky et al. 2010b). An especially noticeable temperature increase was observed during the late 2000s in the Russian Arctic, where the mean annual temperature at 15 m depth increased by >0.35°C in the Tiksi area and by 0.3°C at 10 m depth in the European North of Russia during 2006-2009. However, relatively low air temperatures during summer 2009 and the following winter interrupted this warming trend at many locations in the Russian Arctic, especially in the western sector. A common feature at Alaskan, Canadian and Russian sites is more significant warming in relatively cold permafrost than in warm permafrost in the same geographical area (Romanovsky et al. 2010a).

Unlike the rest of the Northern Hemisphere, the Nordic area, including Greenland, does not have comparable long-term permafrost temperature data. The few sustained permafrost monitoring sites have significantly shorter records that begin at the end of the 1990s. However, these also show a recent decadal warming of 0.04 to 0.07°C/yr in the highlands of southern Norway, northern Sweden and Svalbard, with the largest warming in Svalbard and in northern Scandinavia (Isaksen et al. 2007; Christiansen et al. 2010).

Long-term observations of the changes in active-layer thickness (ALT) are less conclusive. The active layer is a layer of earth materials between the ground surface and permafrost that freezes and thaws on an annual basis. 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) (see the essay on Temperature and Clouds). Decadal trends in ALT vary by region. A progressive increase in ALT has been observed in some Nordic countries, e.g., in the Abisko area of Sweden since the 1970s, with an accelerated rate after 1995, resulting 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 over the last fifteen years has been observed in the Russian European North (Mazhitova, 2008), in the north of East Siberia (Fyodorov-Davydov et al. 2008), and in Chukotka (Zamolodchikov, 2008). Active-layer trends are different for North American sites, where a progressive increase of ALT is evident only at sites in Interior Alaska, where the maximum ALT for the 18 year observation period occurred in 2007. 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 increased since the mid-1990s, with the largest increase occurring in bedrock of the discontinuous permafrost zone (Smith et al. 2010).

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. 2010b). 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 of the boundary between continuous and discontinuous permafrost by several tens of kilometers (Oberman and Shesler 2009; Romanovsky et al. 2010b). The frequently-reported long-term permafrost thawing in the Central Yakutian area around the city of Yakutsk are directly related to natural (forest fire) or anthropogenic (agricultural activities, construction sites) disturbances (Fedorov and Konstantinov 2008) and are not significantly correlated with climate (Romanovsky et al. 2010b).

References

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