Warming permafrost and active layer variability at Cime Bianche, Western European Alps

Abstract

The objective of this paper is to provide a first synthesis on the state and recent evolution of permafrost at the monitoring site of Cime Bianche (3100 m a.s.l.) on the Italian side of the Western Alps. The analysis is based on 7 years of ground temperature observations in two boreholes and seven surface points. The analysis aims to quantify the spatial and temporal variability of ground surface temperature in relation to snow cover, the small-scale spatial variability of the active layer thickness and current temperature trends in deep permafrost. Results show that the heterogeneity of snow cover thickness, both in space and time, is the main factor controlling ground surface temperatures and leads to a mean range of spatial variability (2.5 ± 0.1 °C) which far exceeds the mean range of observed inter-annual variability (1.6 ± 0.1 °C). The active layer thickness measured in two boreholes at a distance of 30 m shows a mean difference of 2.0 ± 0.1 m with the active layer of one borehole consistently deeper. As revealed by temperature analysis and geophysical soundings, such a difference is mainly driven by the ice/water content in the sub-surface and not by the snow cover regimes. The analysis of deep temperature time series reveals that permafrost is warming. The detected trends are statistically significant starting from a depth below 8 m with warming rates between 0.1 and 0.01 °C yr^-1

Soil Moisture Data for the Validation of Permafrost Models Using Direct and Indirect Measurement Approaches at Three Alpine Sites

“…The bedrock surface is highly weathered resulting in a layer of coarse-debris ranging from a few centimeters to several meters depth. The surface aspect is locally very heterogeneous with an alternation of visible bedrock outcrops, coarse-grained material, and fine-grained material (Pogliotti et al, 2015). As for Schilthorn, no vegetation is present at the site (see Figure 2B).…”

“…As the field site on Cime Bianche is located on an only slightly inclined mountain plateau, we interpret this difference to Schilthorn as being a consequence of topographic conditions, which facilitate the storage of snow melt water. Furthermore, the permafrost at Cime Bianche is colder than at Schilthorn (−1.25 • C at Cime Bianche in contrast to −0.5 • C at Schilthorn at the depth of zero annual amplitude, respectively) and the active layer is shallower (1.9-3.6 m for the period 2007-2013, Pogliotti et al, 2015) indicating slower advance of the thawing front and thus limiting the amount of water infiltration in the ground. The decrease of VWC during the summer is consistent with the active layer thickening period.…”

“…Measurements at the site include: ground temperature monitoring in two boreholes (41 and The permafrost at Cime Bianche is characterized by a temperature of around −1.2 • C and the active layer thickness varies between 1.9 and 3.6 m at the shallow borehole and between 3.8 and 5.4 m at the deep one. These strong spatial differences are most likely due to difference in ice content between the two boreholes (Pogliotti et al, 2015).…”

“…As for Schilthorn, no vegetation is present at the site (see Figure 2B). In situ records for the 2010-2013 period show a mean annual precipitation of 1200 mm and a mean annual air temperature of −3.2 • C (Pogliotti et al, 2015).…”

“…The instrumentation of the site started in 2005 and was progressively developed until 2008 (Pogliotti et al, 2015). Measurements at the site include: ground temperature monitoring in two boreholes (41 and The permafrost at Cime Bianche is characterized by a temperature of around −1.2 • C and the active layer thickness varies between 1.9 and 3.6 m at the shallow borehole and between 3.8 and 5.4 m at the deep one.…”