长久性冻土监测

Campbell Scientific equipment helpsdetail global warming in Canada’s extreme north
Permafrost stations add to High Arctic Monitoring

Permafrost is a thermal condition—its formation, persistence, ordisappearance is highly dependent on climate. Its distribution,temperature, and thickness respond to natural environmental changesand anthropogenic disturbances that cause an alteration to theground thermal regime.  Changes in air temperature and/orprecipitation, or surface disturbances due to clearing ofvegetation, removal of insulating organic layer, forest fires,river channel migration, shoreline erosion all may produce amodification to the ground thermal regime.

The interaction between the climate above the ground and belowthe ground is complex, and dependent on several factors. Changes in climate above the ground are most often dampened belowthe ground due to the insulating effects of vegetation, organicmaterial, or snow cover.  There is generally a lag between atemperature change at the ground surface and a permafrost change atdepth.  For thick permafrost, this lag may be on the order ofhundreds to thousands of years, for thin permafrost, years todecades.

Author Sharon Smith makes a final inspection ofthe monitoring station before leaving Alert, Nunavut, Canada.

The Geological Survey of Canada's(GSC) ongoing monitoringprograms in the Mackenzie Region focus on studying the interactionbetween permafrost and climate.  Not all permafrost inexistence today is in equilibrium with the present climate. Offshore permafrost beneath the Beaufort Sea is several hundredmetres thick.  It was formed when the shelf was exposed tocold air temperatures during the last glaciation.  Thispermafrost is presently in disequilibrium with Beaufort Sea watertemperatures and has been slowly degrading.

General circulation models predict that, for a doubling ofatmospheric concentrations of carbon dioxide due to anthropogenicsources, mean annual air temperature may rise several degrees formuch of the Arctic.  In the discontinuous permafrost region,where ground temperatures are within 1 to 2 degrees of melting,permafrost will likely ultimately disappear as a result of groundthermal changes associated with global climate warming. Whereground ice contents are high, this permafrost degradation will haveassociated physical impacts.  Of greatest concern are soilswith the potential for instability upon thaw (thaw settlement,creep or slope failure).  Such instabilities may haveimplications for the land scape, ecosystems, andinfrastructure.  An assessment of the impact of climatechanges on permafrost is necessary to determine whether adaptationmeasures will be required.

Greely Fjord, on Ellesmere Island, Nunav at,Canada, is part of the Campbell Scientific network within the HighArctic Islands.

The Canadian Permafrost Monitoring Network provides long-termfield observations of active layer and permafrost thermalstate.  The observations are essential for understanding thepresent permafrost conditions and the detection of the terrestrialclimate signal in permafrost and its temporal and spatialvariability. This network contributes to the Global TerrestrialNetwork for Permafrost and Canada's obligations to providesystematic cryospheric observations under the World MeteorologicalOrganization's Global Climate Observing System.  The GSC isresponsible for coordinating and implementing the framework andinfra- structure for the network.  About 75 thermal monitoringsites are operated by government and University scientists.

The GSC maintains a network of over20 thermal monitoringsites.  The bore-holes are generally up to 20 m deep. Theywere established in the mid 1980s in the Mackenzie Valley andDelta, some of which operate in collaboration with EnvironmentCanada and Agriculture Canada.  The GSC also operates anet-work of 60 active layer monitoring sites in the Mackenzieregion using thaw tubes. The GSC maintains a network of High Arcticpermafrost temperature observatories, including five bore-holes atCanadian Forces Station (CFS)Alert.

In the late 1970's,five permafrost ground temperature boreholeswere instrumented at CFS Alert (82.5°N,62.4°W) on the northern tipof Ellesmere Island, Nunavut. Permafrost ground temperatures atdepths of up to 60 m have been measured manually at these sitessince 1978.The boreholes represent the most northerly permafrostthermal-monitoring site in the world, and are an importantcontribution to the recently established Global Terrestrial Networkfor Permafrost(http://sts.gsc.nrcan.gc.ca/per-mafrost/index.html).  The23-year data set is one of the longest records of permafrosttemperatures in Canada.  The boreholes are maintainedcollaboratively by the Department of National Defence (DND)and theGSC.

In 2002, GSC collaborated with Environment Canada's snowmonitoring network to install Campbell Scientific meteorologicalsensors.  These consisted of air temperature, wind speed, andultra-sonic snow depth sensors at GSC sites: three at the highArctic site at Alert, one at a low Arctic site at Baker Lake, andone at a Boreal forest site near Wrigley in the MackenzieValley.  The sensors are measured using a CR510 datalogger,and an external SM4M storage module pro-vides additional datastorage because the stations are visited infrequently.  Poweris supplied by a 26 Ahr battery charged by a10 W solar panel. The high storage of the High Arctic Islands, is cold and dry. Themean annual air temperature is -18.1°C and mean annual groundsurface temperature is about -16°C.  The 30-yearnormals forprecipitation show 16.2 mm of rainfall, with a mean total annualprecipitation of 153.6 mm.  Permafrost is over 600 m thick.

Although snow cover is generally thin to absent in this area, itexhibits high spatial and temporal variability.  The snowcover is an important factor influencing the response of shallowpermafrost temperatures to changes in air temperature. The weatherdata will aide the analyses of the local microclimate's role ininfluencing the permafrost response to air temperature changes.

For further information on permafrost research and monitoring,visit the GSC and the Global Terrestrial Network for Permafrost Websites:

GSC Permafrost Website:http://sts.gsc.nrcan.gc.ca/permafrost/

GTN-P Website:http://sts.gsc.nrcan.gc.ca/gtnp/