Assessment of the status of the development of the standards for the Terrestrial Essential Climate Variables - T7 - Permafrost and seasonally frozen ground

• Main Authors: Smith, Sharon, Brown, Jerry
• Format: Text
• Language: English
• Published: 2009
• Subjects: Cryosphere; Active layer monitoring; Active layer thickness; Global Terrestrial Network for Permafrost; GTN-P; Ice; International Permafrost Association; International Polar Year; IPY; permafrost
• Online Access: http://library.arcticportal.org/668/; http://library.arcticportal.org/668/1/T07.pdf; http://www.fao.org/gtos

Decadal changes in permafrost temperatures and depth of seasonal freezing/thawing are indicators of changes in climate. Warming may result in an increase in active layer thickness, melting of ground ice and subsequent reduction in permafrost thickness and the lateral extent of permafrost. These changes can have an impact on terrain stability leading to ground subsidence or erosion, vegetation, ecosystem function and soil moisture and gas fluxes. Permafrost and seasonally frozen ground also influence surface and subsurface hydrology. Standardized in situ measurements are essential to understanding how permafrost conditions are changing, to improve predictions of future changes, and to calibrate and to verify regional and global climate change models. Long-term monitoring sites are contributing to the Global Terrestrial Network for Permafrost (GTN-P). These sites exist throughout the permafrost regions and have provided data that have facilitated the characterization of trends in permafrost conditions over the last two to three decades and in a few cases over much longer periods. Under the leadership of the International Permafrost Association a coordinated field campaign is under way during the International Polar Year to obtain a snapshot of global permafrost temperatures and active layer measurements. The main parameters and measurement methods are: Permafrost: sub-surface earth materials that remain continuously at or below 0°C for two or more consecutive years. Parameter is ground temperature (°C) at specified depths. Permafrost temperature measurements are obtained by lowering a calibrated temperature sensor into a borehole, or recording temperature from multi-sensor cables permanently or temporarily installed in the borehole. Measurements may be recorded manually or by data loggers. The depth of boreholes varies from less than 10m to greater than 100m. Data loggers may be utilized for daily measurements of shallow temperatures to reduce the frequency of site visits and provide a continuous record of ground temperatures. Ideally (although not always feasible at all sites), temperatures at shallow depths (upper 10 m to 20 m) should be collected at monthly or more frequent intervals as this allows the annual temperature envelope (i.e. range in temperatures at depth) and mean annual temperatures to be determined. Active layer: the surface layer of ground, subject to annual thawing and freezing in areas underlain by permafrost. Parameters are thickness (cm) and temperatures (°C). Several traditional methods are used to determine the seasonal and long - term changes in thickness of the active layer: mechanical probing annually, frost tubes, and interpolation of soil temperatures. The minimum observation required under the Circumpolar Active Layer Monitoring (CALM ) protocol is a late season mechanical probing of the thickness of the active layer on a gridded plot or transect. Interpolation of soil temperature measurements from a vertical array of sensors can be used to determine active-layer thickness at a point location (see www.udel.edu/Geography/calm/) Seasonally frozen ground: refers to soils without permafrost that are subjected to seasonal freezing and thawing. Parameters are depth (cm) and temperature (°C). Winter frost penetration in regions of seasonal ground freezing is determined by measuring soil temperatures or by use of frost tubes; similar to methods used for active layer measurements. The methods described above are presented in a combined draft manual developed for the International Polar Year Thermal State of Permafrost (IPY/TSP) which is available on the International Permafrost Association (IPA) Web site (www.ipa-permafrost.org/). Deriving ISO standards from this manual should encourage the adoption of these standard methodologies and promote the expansion of the observational networks. Unlike ice and snow covers, properties of permafrost terrain are currently not directly detected from remote sensing platforms. However, many surface features of permafrost terrains and periglacial landforms are observable with a variety of sensors ranging from conventional aerial photography to high-resolution satellite imagery in various wavelengths._1