Monitoring Active Layer Thickness and Temperatures, a CALM-project
Ole Humlum, UNIS, Department of Geology, Svalbard, Norway
Background
Permafrost is widespread on Svalbard and mean annual air temperatures at sea level ranges from about -4oC to -9oC. The active layer is the zone above the permafrost that experiences seasonal freezing and thawing, and is considered to be the locus of several important sets of dynamic processes, including biological, pedologic, geomorphic, biogeochemical, and hydrologic. Despite its importance to a wide variety of physical and biological investigations, information about development of the active layer has rarely been collected in a systematic, standardized fashion over large areas.
Should the annual thaw depth increases due to some future climatic change in air temperature, precipitation or wind, carbon and water currently stored in the permafrost below could be released. Interannual variations in the active layer thickness is therefore now monitored on a hemispheric scale, so as to better understand the roles of cold soils in global climatic change.
To achieve this goal, the CALM (Circumpolar Active Layer Monitoring) program has been established. It currently consists of more than 100 research sites in both hemispheres operated by researchers from Austria, Canada, China, Denmark/Greenland, Kazakstan, Poland/Svalbard, Russia, Sweden/Svalbard, Switzerland, and United States. Although the CALM program began as a voluntary effort in 1991, it has recently been formalized with a 5-year grant from the U.S. National Science Foundation (NSF). Investigators at these sites measure the seasonal thaw depth across plots using a standard protocol. Soil and air temperature, and soil moisture content, are also measured at many sites. If these areally averaged measurements are combined with site-specific information on soil, landscape, vegetation, and measurements of air and soil temperature, the stability and projected changes in regional thaw depth and the spatial patterns can be more realistically modeled and validated.
The KINGSCALM-site at Ny-Ålesund, August 2001, about 140 km NW of Longyearbyen (see also picture at the top of this page). Thaw depth is probed with a thin metal rod. Temperatures are measured with dataloggers (hidden by the stones; see also picture below). This CALM-site is established and operated by UNIS.
Available evidence indicates that trends of active-layer thickness are spatially and temporally variable, but are generally consistent with contemporary climate. In general, the active layer responds consistently to forcing by air temperature on an interannual basis, although at some sites it exhibits a more complicated behavior over longer (decadal) timescales. The relatively few long-term data sets available from the northern high latitude sites demonstrate substantial interannual and interdecadal fluctuations over the past forty years. The amount and timing of snow cover in winter exert important influences over ground temperature and thaw in the subsequent summer. Increased thaw penetration, thaw subsidence and development of thermokarst have been observed at some sites, indicating degradation of warmer permafrost.
Type of datalogger used for measurement of temperatures in UNIS-driven CALM-sites.
The CALM network is now part of the WMO Global Terrestrial Network for Permafrost (GTN-P). The GTN-P observations consist of both the active layer measurements and the permafrost thermal state measured in boreholes. The CALM program requires additional multi-decadal observations and boreholes for thermal measurements in the upper layers of the permafrost.
THAW OBSERVATIONS
UNIS are presently operating two CALM sites on Svalbard, UNISCALM and KINGSCALM (se descriptions below). At both sites the thaw depth is measured at each grid point with a metal rod, which is pushed vertically into the soil to the depth at which ice-bonded soil provides firm resistance. At one vertical profile located within each net ground temperatures are registered hourly on a year-round basis by Gemini dataloggers of the type shown above. Click here for more information on these dataloggers.
An example of active layer depths and ground temperatures are shown below (KINGSCALM).
Maximum thawing depths (cm's) in KINGSCALM 2001, measured by Hanne H. Christiansen (IPA) and Jack Kohler (NP) 3. September 2001. The maximum average thawing depth 2001 was 69 cm. The red dot shows the location of the vertical temperature profile (see readings in diagram below). North is towards the top.
Air and ground temperatures at KINGSCALM, 10. August - 3. September 2001. The air temperature is measured about 5 cm above the ground surface, at a wind exposed site shortly west of the CALM-site. Surface and ground temperatures are measured inside the CALM-net (location shown by yellow dot in diagram above).
UNIS-operated CALM-sites on Svalbard
1: UNISCALM
At Longyearbyen a 100x100 m CALM-site was established in July 2000, near the old airport in lower Adventdalen, on a terrace consisting of c. 3 m loess deposits accumulated since about 3000 BP. The site is almost horizontal and is subdivided into a 10x10 m grid. The photo above shows the UNISCALM site in early October 2002, looking towards E. The person in the background is standing at the eastern corner of the site, while the western corner is in the foreground.
Position: N78o12'03.5''; E015o50'10.6''
Altitude: 10 m asl.
Terrain surface slope: almost horizontal
Maximum average thawing depth in UNISCALM; year 2000: 96 cm, year 2001: 99 cm, year 2002: 96 cm.
The mean annual air temperature at Longyearbyen is about -6.0oC (1961-1990). The number of thawing degree days (DDT) is about 650, calculated from air temperatures measured shortly (20 cm, June-August) above the ground surface. If one instead uses standard 2 m air temperatures the average 30-yr DDT is 435 (1973-2002).
Click here for current meteorological conditions at the UNISCALM site.
By clicking on the green links below, you will be presented to diagrams showing conditions at the UNISCALM site since 2001.
2: KINGSCALM
About 140 km NW of Longyearbyen, shortly NW of Ny-Ålesund a CALM-site (45x45 m) named KINGSCALM was established August 2001 on a terrace consisting of raised coastal sands, sloping gently towards SE. The site is subdivided into a 5x5 m grid (see photo at the top of this page). The photo above shows the KINGSCALM site (arrow) in August 2001, looking towards SE.
Position: N78o56'18.0''; E011o50'40.0''
Altitude: 10 m asl. (center of site)
Slope: 2 deg. SE.
Maximum average thawing depth in KINGSCALM; year 2001: 69 cm, year 2002: 64 cm..
The mean annual air temperature at Ny-Ålesund is about -6.3oC (1961-1990). The number of thawing degree days (DDT) is about 590, calculated from air temperatures measured shortly (20 cm, June-August) above the ground surface. If one instead uses standard 2 m air temperatures the average 30-yr DDT is 334 (1973-2002).
Click here for current meteorological conditions in Ny Ålesund, 2 km SE of KINGSCALM. (data measured by the Koldeway-Station (Alfred Wegener Institute).
Click here for access to web cameras in Ny Ålesund.
By clicking on the green links below, you will be presented to diagrams showing conditions at the KINGSCALM site since 2001.
Relevant LINKS
Below you will find some links to web sites with information about permafrost, active layer, etc:
The International Permafrost Association
Circumpolar Active Layer Monitoring (CALM)
Global Terrestrial Network-Permafrost (GTN-P) - borehole monitoring
Permafrost and Climate in Europe (PACE)
Latest update: 5. April 2005.