Permafrost and snow monitoring at Rothera Point (Adelaide Island, Maritime Antarctica): Implications for rock weathering in cryotic conditions

Abstract

In February 2009 a new permafrost borehole was installed close to the British Antarctic Survey Station at Rothera Point, Adelaide Island (67.57195°S 68.12068°W). The borehole is situated at 31 m asl on a granodiorite knob with scattered lichen cover. The spatial variability of snow cover and of ground surface temperature (GST) is characterised through the monitoring of snow depth on 5 stakes positioned around the borehole and with thermistors placed at three different rock surfaces (A, B and C). The borehole temperature is measured by 18 thermistors placed at different depths between 0.3 and 30 m. Snow persistence is very variable both spatially and temporally with snow free days per year ranging from 13 and more than 300, and maximum snow depths varying between 0.03 and 1.42 m. This variability is the main cause of high variability in GST, that ranged between − 3.7 and − 1.5 °C. The net effect of the snow cover is a cooling of the surface. Mean annual GST, mean summer GST, and the degree days of thawing and the n-factor of thawing were always much lower at sensor A where snow persistence and depth were greater than in the other sensor locations. At sensor A the potential freeze–thaw events were negligible (0–3) and the thermal stress was at least 40% less than in the other sensor locations. The zero curtain effect at the rock surface occurred only at surface A, favouring chemical weathering over mechanical action. The active layer thickness (ALT) ranged between 0.76 and 1.40 m. ALT was directly proportional to the mean air temperature in summer, and inversely proportional to the maximum snow depth in autumn. ALT temporal variability was greater than reported at other sites at similar latitude in the Northern Hemisphere, or with the similar mean annual air temperature in Maritime Antarctica, because vegetation and a soil organic horizon are absent at the study site. Zero annual amplitude in temperature was observed at about 16 m depth, where the mean annual temperature is − 3 °C. Permafrost thickness was calculated to range between 112 and 157 m, depending on the heat flow values adopted. The presence of sub-sea permafrost cannot be excluded considering the depth of the shelf around Rothera Point and its glacial history

Recent shallowing of the thaw depth at Crater Lake, Deception Island, Antarctica (2006–2014)

“…40 cm and a thermal offset of 0.8°C. The zero annual temperature depth is shallow and should be just below 4.5 m depth in contrast to other sites in the Western Antarctic Peninsula in high diffusivity bedrock settings (Ramos and Vieira, 2009;Bockheim et al, 2013;Guglielmin, et al, 2014). These characteristics are strongly influenced by the high porosity pyroclastic debris of Deception Island, which show a high ice-content at the base of the active layer.…”

Effect of Snow Cover on the Active‐Layer Thermal Regime – A Case Study from James Ross Island, Antarctic Peninsula

“…TDD g values calculated for JRI (496.1°C day in 2011–12 and 358.3°C day in 2012–13) are significantly higher than those for Livingston Island (98 to 257°C day; De Pablo et al ., ) and Signy Island (2 cm TDD g ranged between 260.5 and 378.0°C day for the period 2006–09; Guglielmin et al ., ). An even higher TDD g value of 618°C day has been recorded at Rothera Point, Adelaide Island (Guglielmin et al ., ).…”

“…A number of studies have suggested that the effect of air temperature on ground temperature is highly variable in the AP region (Cannone et al ., ; Guglielmin et al ., ). Whereas a relatively weak correlation (r = 0.58 to 0.82) between air and ground temperatures was reported from King George Island and Signy Island (Cannone et al ., ) in areas covered by different types of vegetation, a stronger relationship (r > 0.90) was described in areas of bare ground at Rothera Point (Guglielmin et al ., ).…”

Discussion on ‘Active Layer Thickness Prediction on the Western Antarctic Peninsula’ by Wilhelmet al. ()

“…() show the opposite tendency when compared to those of other locations with larger temperature amplitudes and similar mean annual ground surface temperatures (e.g. Guglielmin et al ., , ), which is hard to explain by differences in ground material properties. In fact, the surface thawing degree‐days are substantially lower on Amsler Island than at other sites within the Antarctic Peninsula (e.g.…”

“…In fact, the surface thawing degree‐days are substantially lower on Amsler Island than at other sites within the Antarctic Peninsula (e.g. Guglielmin et al ., , ; Hrbáček et al ., ) or the northern hemisphere (e.g. Christiansen et al ., ), where thinner active layers have been reported.…”