Palsa development in Dovrefjell, southern Norwegian Mountains : Breakdown in a warming climate

Palsas are peat mounds with a perennially frozen core which are mainly formed due to ice segregation. They are located in bogs in warmer (sporadic and discontinuous) permafrost zones and they are therefore sensitive to environmental changes unfavourable for permafrost. In this study I have investigated a particular palsa in Haukskardsmyra, which is the largest palsa bog in the Dovre Mountains, southern Norwegian Mountains. Due to its southerly position, this mire is located on the climatic limit for palsa existence and therefore, can give valuable information about the reaction of palsas and the rate of degradation to climate amelioration. The palsa has been mapped and monitored over the period 2006-2007-2008 for change detection. The palsa surface height, depth of the thawed layer over the frozen ground and snow depths have been measured. To monitor the temperature at the study site, TinyTag data loggers have been used since 2006. The data loggers have been located on the palsa surface, at 10, 30 and 70 cm depths and 1.8 m above the surface. This data, combined with temperature data from a nearby weather station, has been used to back-calculate mean annual temperatures of the palsa site until 1865. Aerial photographs from 1963, 1979, 1992 and 2002 have been investigated to trace the palsa development over the last half century. Since 1865 the mean annual air temperature has increased by more than 1°C at the palsa site and the present mean annual air temperature is slightly above 0°C. Mean annual precipitation has increased by about 100 mm since 1923. Since 1963 the palsa bog has degraded significantly, as shown by repeated aerial photography and field studies. Over the period 2006-2008 the studied palsa has experienced a severe and violent degradation, with large parts falling into the water. Presently, both temperature and precipitation are likely too high to allow palsa development at Haukskardsmyra. Hence, the palsa bog is situated out of the climatic limit which favours palsa development. It is likely that the palsas at Haukskardsmyra will disappear within the next 30-50 years and, by inference that also other palsa bogs in Dovre will decrease substantially in size and distribution.