Created: 2014-01-23 10:47:38
Modified: 2014-01-23 13:35:06
Years of record (a)
Min Thaw (cm)(b)
Max Thaw (cm)(b)
Thawing Degree Days (c)
DESCRIPTION OF AREA CONTAINING SITES, SAMPLING DESIGN AND METHOD:
The active layer monitoring system extends from Fort Simpson, Canada in upper Mackenzie River valley to the Beaufort Sea coast at North Head, Richards Island, Canada. Records start in 1991, 92 or 93 and continue.
Maximum annual thaw penetration and maximum heave and subsidence of the ground surface is measured using a modified version of a frost tube developed by Mackay (1973). The device is a removable water-filled clear plastic observation tube, 2 cm in diameter, and ~2.5 m long inside a ~2.5 cm diameter, heave resistant access tube (Tarnocai et al 2004) long enough (~4 m) to be anchored in permafrost upon installation. The ice-water interface in the observation tube corresponds to the frost table in the surrounding ground. A 3 mm diameter coloured glass marker, dropped into the tube each year prior to time of maximum thaw, rests on the ice surface, descending during the thaw season to be trapped at maximum depth on freeze back in late summer or fall. Maximum heave and subsidence is recorded between observations by a scriber attached to a weighted sleeve around the outside of the access tube, scratching a painted surface either side of a reference mark (renewed at each visit). Tubes were installed using a light weight pump (~10 kg, maximum discharge 100 litres/min). The active layer is defined as the thaw recorded in the thaw tube, minus the height of the tube above the ground surface at maximum surface subsidence, assumed to occur about the time of maximum thaw.
Snow pack observations were taken during March or April, and are reported as a range of values from all the observations at the site.
Many of the thaw tube sites are also instrumented with automatic air and ground temperature loggers (Tarnocai et al 2004). At some 40 sites, a 6-plate 12 cm diameter radiation shield (R.M. Young, model 41301-5) was mounted 1.5 m above the ground surface and air temperatures are measured by a thermistor in the shield that is connected to a single channel miniature data logger in the lower part of the mast (see Fig. 5 in Nixon et al., 1995). A similar miniature data logger with internal sensor is buried near the base of the air temperature mast at a nominal depth of 3-7 cm to measure near-surface ground temperatures. Two types of miniature data loggers have been used: HOBO loggers (Onset Computer Corp, USA.), range -37o to 46oC, resolution 0.25oC and Minilog loggers (Vemco Ltd., Canada), -50o to 40oC, resolution 0.3oC. Temperatures are recorded every 2 to 6 hours for a year or more before servicing.
Data provided are from 10 IPA Circumpolar Active Layer Monitoring sites.
Additional metadata, data, and maps are available through Canadian National Permafrost Databases
CALM Canada Geological Survey
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