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 tTable 1. Summary table of data values at BH4 and BH2.Year (Sept-Aug)MAATSnow DepthAverage (cm)Snow DepthMaximum (cm)MAGST BH4 MAGST BH2 Surface OffsetBH4Surface OffsetBH22002–2003 -10.5 18.0 33.2 -8.1 -0.1 2.4 10.42003–2004 -12.2 14.6 24.8 -7.6 -2.0 4.7 10.22004–2005 -11.5 12.6 36.3 -8.6 -0.9 2.9 10.62005–2006 -8.8 28.1 56.1 -5.2 -1.0 3.6 7.8this year had the most snow, the greatest surface offset wasin 2003–2004, and that at BH2 was noticeably less than inthe other years in 2005–2006.The result that the deep snowbank produces very largesurface offsets and substantially warms the ground surfaceon an annual basis was also found beneath a snow fenceinduced snowbank in Barrow, Alaska (Hinkel & Hurd 2006).Similarly, the shallower thaw depths produced by the latelyingsnow were observed in Alaska, where in one year theirsnowbank failed to melt completely.Figure 2. Maximum calculated thaw depths for BH2 and BH4 from1997 to 2005 using manual data taken approximately three timesper month during maximum thaw season.Lake weather station did not produce a significant linear fit(results not shown).Calculated maximum thaw depths at BH2 beneath thesnowbank averaged 1.67 m with a standard deviation of0.10 m, and range from a minimum of 1.48 m in September1997 to a maximum of 1.78 m in September 2001 (Fig. 2).Interannual variability in the thaw depth at this borehole,therefore, was only about 0.3 m, substantially less than atBH4.The average snow depth at BH4 from 2002–2006 rangedfrom 13 to 28 cm. The highest value occurred in the winterof 2005–2006, when the maximum depth reached 56 cm atthe end of April, at least 20 cm deeper than any of the otherthree years (Table 1).The year 2004 had the lowest TDD in the four years ofcontinuous monitoring at the site with a value of 843, whereas2003, 2005, and 2006 ranged between 947 and 1051.DiscussionThe effect of the snowdrift can be seen clearly in thetemperature envelopes in Figure 1. The amplitude of theenvelope is much greater at BH4, reaching much lowerminimum temperatures showing a more direct link to changesin air temperature. The small amplitude of the envelope andthe milder temperatures at BH2 illustrate the muting effectof the snowdrift, dampening the effect of air temperaturechanges.The decrease in thaw depth in 2004 reflects the low value ofthawing degree-days that year (843) compared to other years.There was not a clear link between interannual differencesin snow depths measured at BH4 and surface offsets. The2005–2006 winter at BH4 had more snow than other yearsalong with the highest MAGST and MAAT. Even thoughConclusionThe long-lasting snow fence induced snowbank at BakerLake results in the ground surface beneath being warmer thanthe surrounding area by 4–8°C on an annual basis. However,the snow is so deep that thaw is retarded significantly, andthaw depths average 17 cm less beneath its deepest sectionthan at the control site (BH4). Variability in depths of thawover 9 years was greater at the control site than beneath thesnowbank. There is no evidence from the ground temperaturedata that warming by the snowbank is causing thermokarstat the site.AcknowledgmentsSupport for this project has been provided by NaturalResources Canada, the Canadian Government’s ClimateChange Action Plan 2000, and <strong>International</strong> Polar YearProgram. Orin Durey, a Baker Lake resident, maintains thesite and collects the temperature data.ReferencesACIA 2005. Arctic Climate Impact Assessment. CambridgeUniversity Press.Hinkel, K.M. & Hurd, J.K. Jr. 2006. Permafrost destabilizationand thermokarst following snow fence installation,Barrow, Alaska, U.S.A. Arctic, Antarctic and AlpineResearch 38: 530-539.Smith, M.W. & Riseborough, D.W. 2002. Climate and thelimits of permafrost: a zonal analysis. Permafrost andPeriglacial Processes 13: 1-15.Smith, S.L., Burgess, M.M., Riseborough, D.W. & Nixon,F.M. 2005. Recent trends from Canadian permafrostthermal monitoring network sites. Permafrost andPeriglacial Processes 16: 19-30.314