Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tvalues exceed the 4-day temperature drop rate of 1.8°C/d,reported by Mackay (1993), which favored ice wedgecracking on the western Arctic coast. They also exceed themean drops of 7.9°C, over mean periods of 18 hours, at amean air cooling rate of -0.5°C/h measured before crackingevents by Fortier and Allard (2005), at Bylot Island in theeastern Canadian Arctic Archipelago.Ground temperatureThe mean annual ground surface temperature (MAGST)was -17.1°C at Baker Rocks and -20.4°C at BoomerangGlacier. The mean ground surface temperature, over an 11-month period, was -22.4°C at Mount Jackman.During winter seasons the mean ground surface temperature(MGST) was -28.6°C at Baker Rocks, -29.8°C at BoomerangGlacier, and -33.1°C at Mount Jackman. Temperatures withlows below -40°C were recorded at all sites.The mean annual temperature of the top of the ice wedgewas -15.3°C at Baker Rocks, -20.2°C at Boomerang Glacier.A mean value of -21.3°C was recorded at Mount Jackmanover an 11-month period. During the winter months, icewedge top temperatures were consistently below -20°C atBaker Rocks (mean value -21.7°C) and Boomerang Glacier(mean value -26.8°C), and below -25°C at Mount Jackman(mean value -28.4°C).The ground surface thermal regime closely follows that ofthe air, with similar large and rapid fluctuations in temperature.Mean ground cooling rates (MGCR) of -28.6°C/d, -4.8°C/d,and -12.4°C/d at the surface, and of -0.4°C/d, -0.5°C/d, and-1.3°C/d at the ice wedge tops were obtained, respectively,at Baker Rocks, Boomerang Glacier, and Mount Jackman.These rates exceed the MGCR before frost-cracking episodesof -0.3°C/d at the surface and -0.2°C/d at the permafrosttable, reported by Fortier & Allard (2005).DiscussionThe analysis of the thermal regime at the ice wedgepolygon sites revealed that, in winter, the temperatures of theair and on the tops of the ice wedges fell below -30°C and-20°C, respectively. These values exceed the limits at whichthermal-contraction cracking is known to occur in the Arctic(Lachenbruch 1966, Allard & Kasper 1998, Fortier & Allard2005). Comparison of the cooling rates of the air and groundwith those measured by Mackay (1993) and Fortier & Allard(2005) at the time of cracking events shows that thermalconditions at the study sites are more severe than thoseidentified in the Arctic areas, and they most likely can triggerice wedge cracking. This is also supported by the existenceof open cracks observed, both in the ice wedges discussedin this article and in many others excavated during summerfield surveys in northern Victoria Land (Raffi 2003).At present, no field data of snow cover are available;however, we can infer that there was no thick snow cover atthe three sites because throughout winter seasons, the dailyground surface temperatures were almost always lower thanthe daily air temperatures. When the opposite occurred, dailyground surface temperatures only remained higher than theair temperature for very brief periods (from a few hours to afew days), and then quickly decreased. The strong katabaticwinds, with gusts reaching speeds of more than 200 km/h inwinter, prevent snow accumulation and its insulating effecton the ground.AcknowledgmentsThis research was carried out within the Italian AntarcticNational Research Program. Thanks are due to Dr. R. Bono,CNR-ISSIA of Genova, I, and to Dr. U. Gentili, ClimateProject, ENEA, Roma, I, for the field maintenance of thethermometric stations.ReferencesAllard, M. & Kasper, J.N. 1998. Temperature conditions forice-wedge cracking: field measurements from Salluit,northern Québec. In: A.G. Lewkowicz & M. Allard(eds.), Proceedings of the Seventh <strong>International</strong>Permafrost <strong>Conference</strong>, Yellowknife, Canada, June23-27, 1998. Centre d’études nordiques, Québec:Université Laval, Collection Nordicana 57: 5-12.Burn, C.R. 1990. Implications for palaeoenvironmentalreconstruction of recent ice-wedge development atMayo, Yukon Territory. Permafrost and PeriglacialProcesses 1(1): 3-14.Fortier, D. & Allard, M. 2005. Frost-cracking conditions,Bylot Island, Eastern Canadian Arctic Archipelago.Permafrost and Periglacial Processes 16(2): 145-161.Lachenbruch, A.H. 1966. Contraction theory of ice-wedgepolygons: a qualitative discussion. Proceedings of theFirst <strong>International</strong> Permafrost <strong>Conference</strong>, Lafayette,Indiana, November 11-15, 1963. Washington, DC:National Academy of Sciences-National ResearchCouncil, publication no. 1287: 63-71.Mackay, J.R. 1993. Air temperature, snow cover, creep offrozen ground, and the time of ice-wedge cracking,western Arctic coast. Canadian Journal of EarthSciences 30: 1720-1729.Raffi, R. 2003. Ice wedges in the Terra Nova Bay region(northern Victoria Land, Antarctica). Distributionand morphological features. Terra Antartica Reports8: 143-148.250