Observations on permafrost ground thermal regimes from Antarctica and the Italian Alps, and their relevance to global climate change

Abstract

Active-layer monitoring and the permafrost thermal regime are key indicators of climate change. The results of 3 years (1997–1999) of active-layer monitoring at one high-mountain site (La Foppa, 46°28′42″N; 10°11′18″E, 2670 m a.s.l.) and at one Antarctic site (Boulder Clay, 74°44′45″S; 164°01′17″E, 205 m a.s.l) are presented. The initial analysis of a thermal profile in a borehole (100.3 m deep) within mountain permafrost at Stelvio (3000 m a.s.l., 46°30′59″N; 10°28′35″E) is also presented. At the alpine site, the active-layer thickness variations (between 193 and 229 cm) relate to both the snow cover and to the air temperature changes. By contrast, at the Antarctic site, there is a strong direct linkage only between air temperature fluctuations and active-layer variations. At the alpine (La Foppa) site, the relationship between climate and active-layer thickness is complicated by thermal offset that is almost negligible at both the Stelvio and Antarctic sites. The permafrost temperature profile at Stelvio site contains a climate signal suitable for paleoclimate reconstruction. The permafrost at this site has a mean annual ground surface temperature (MAGST) of −1.9 °C (during 1998/1999), an active layer of about 2.5 m thick and a total thickness of ∼200 m. Analysis of the MAGST history, obtained by applying a simple heat conduction one-dimensional model, revealed the occurrence of a cold period from 1820 to 1940 followed by a warming period until 1978. Since the beginning of the 1980s, temperature dropped (less than 2 °C) until the middle 1990s, when a new period of warming started. All these climatic changes fit well with the glacial fluctuations in the area and with other paleoclimatic information derived from different proxy data.