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 tvariation was 20 cm in ZC1, but only 10 cm in ZC2, whenexcluding the 1999 snowdrift-affected year. This shows thatthe influence of the snowdrift seems to be larger than anyother meteorological factor in this type of landscape setting,where the combination of topography and meteorology leadto snowpatch accumulation. The snowdrift size is controlledby the amount of winter snow, but mainly by the late winterwind activity causing snowdrifting (Christiansen 2004).Comparing the ZEROCALM sites with the UNISCALMsite in Svalbard, the nearest CALM site on the oppositesite of the Greenland Sea is interesting. There is no simplecorrelation of ALT between the two CALM sites. Thedeepest thaw in Svalbard occurred in 2007 (Christiansen& Humlum 2008), while this was in 2005 for both sites innortheast Greenland (Fig. 1). In 2005, Svalbard actuallyexperienced the shallowest active layer since measurementsstarted in 2000.Air Temperature Control on Active LayerThicknessesTraditionally, the relationship between ALT and TDDof the thaw period is established using the Stefan solutionto investigate the influence of air temperature forcing orother factors on ground thawing (Hinkel & Nelson 2003).Just 10 m south of the ZC1 site, the ZEROCALM officialmeteorological station is located. Air temperature is a standardparameter measured at this station, enabling calculations ofthawing degree-days (TDD) of the thaw period.The correlations between ALT and the square root of theTDD are shown for the entire 12-year period for both ZC1and ZC2 in Figure 2. Clearly, ZC1 has a relatively highcorrelation to positive air temperatures in the thawing season,but also ZC2 has some correlation. Interestingly, both siteshave a significantly better correlation than what has beenfound for a flat site in neighboring Svalbard based on 8years of data (r 2 = 0.004) (Christiansen & Humlum 2008).Previously, based on the 7 first years of observations in theZC1 and ZC2 sites, reduced correlations (ZC1: r 2 = 0.53 andZC2: r 2 = 0.00) were also found for these sites (Christiansen2004). This indicates that longer data series, such as the 12-year record from Zackenberg, must be collected to analyzewith confidence the air temperature influence on groundthawing.AcknowledgmentsThe data collection of thaw depths is the responsibility ofthe Zackenberg Ecological Research Operations monitoringprogramme GeoBasis, to which we extend our sincere thanksfor keeping this basic monitoring running and thus providinga rather unique CALM data series from Greenland.ReferencesBrown, J., Hinkel, K.M. & Nelson, F.E. 2000. TheCircumpolar Active Layer Monitoring (CALM)Program: Research designs and initial results. PolarGeography 24: 165-258.Christiansen, H.H. 2004. Meteorological control oninterannual spatial and temporal variations insnow cover and ground thawing in two northeastGreenlandic Circumpolar-Active-Layer-Monitoring(CALM) sites. Permafrost and Periglacial Processes15: 155-169.Christiansen, H.H., Sigsgaard, C., Humlum, O., Rasch, M.& Hansen, B.U. In press. Permafrost and periglacialgeomorphology at Zackenberg. Advances inEcological Research 40.Christiansen, H.H. & Humlum, O. 2008. Interannualvariations in active layer thickness in Svalbard.Proceedings of the <strong>Ninth</strong> <strong>International</strong> <strong>Conference</strong>on Permafrost, Fairbanks, Alaska, June29–July 3,2008.Hinkel, K.M. & Nelson, F.E. 2003. Spatial and temporalpatterns of active layer thickness at CircumpolarActive Layer Monitoring (CALM) sites in northernAlaska, 1995–2000. Journal of Geophysical Research108: D2: ALT 9, 1-13.Figure 2. ZEROCALM-1 and ZEROCALM-2 active layer thicknesscorrelated to the square root of the thawing degree-days until thetime of the active layer measurement in the 1996–2007 period.46