Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7 The transition zone of mountain permafrost on Dovrefjell, southern Norway J.L. Sollid Department of Physical Geography, University of Oslo, Norway K. Isaksen Norwegian Meteorological Institute, Oslo, Norway T. Eiken Department of Physical Geography, University of Oslo, Norway R.S. Ødegård Gjøvik University College, Gjøvik, Norway ABSTRACT: A monitoring programme was started in the autumn 2001 on Dovrefjell, southern Norway, to measure ground temperatures in 11 boreholes approximately 9 m deep along an altitudinal transect across the mountain permafrost transition zone. This is the first transect of this type set up in Scandinavia. Borehole tem- peratures are highly correlated with elevation. Measurements of mean ground temperatures at 8.5 m depth on exposed sites show that the lower limit of the mountain permafrost is on the high side of 1300 m a.s.l. The mean ground temperature elevation gradient was found to be Ϫ0.7°C/100 m. This gradient was not dependent on snow depth, and differs from the mean annual air temperature lapse rate (Ϫ0.44°C/100 m). The gradient differences may be due to stronger turbulent fluxes at high elevations during the snow-free period. 1 INTRODUCTION Dovrefjell (62°15ЈN, 9°20ЈE) is a mountainous area situated in southern Norway with Snøhetta (2286 m a.s.l.) as the highest mountain (Figures 1 and 2). Dovrefjell is an area rich in deglaciation terrain forms. There are well developed moraines (the Knutshø moraine-system) dating from about 9600 BP and gen- erated by the last activity of the Weichselian ice sheet in southern Norway (Sollid, 1964). The thickness of surficial materials (till and glacio-fluvial deposits) is variable in the region. Weathered regolith and block- fields dominate the summit areas. The mean annual air temperature (MAAT) at Fokstua Figure 1. Location map. Dovrefjell (62°15ЈN, 9°20ЈE), meteorological station (972 m a.s.l.), Dovrefjell, southern Norway. Study area shown by black rectangle. is Ϫ0.1°C and the mean annual precipitation is 435 mm Fokstua meteorological station is located approximately (1961–1990). A mean air-temperature lapse rate of 20 km SW of study area. Juvvasshøe (1894 m a.s.l.) in Ϫ0.44°C/100 m was calculated for the area using Jotunheimen is marked by a dot. regression and data from 18 climate stations in the region (Aune, 1993; Tveito et al., 2000). A 10 m deep borehole (DB1) in debris was drilled The lower limit of the mountain permafrost on on Dovrefjell (1505 m a.s.l.) in September 2001. A Dovrefjell, mapped using the BTS (Bottom Tempera- measurement setup with 11 thermistors from 0.2 m to ture of Snow) method, is about 1500 m a.s.l. (Ødegård 6.7 m depth with data recording every six hours was et al., 1996; Isaksen et al., 2002). This limit is repre- installed. Ten more boreholes (1481–1039 m a.s.l.), sentative for areas with a stable snow cover of 1–2m. 9 m deep were drilled in October 2001 (Table 1). The Sporadic permafrost is present at elevations down to boreholes were cased and instrumented with two 1000 m a.s.l. in some palsa bogs. During the Little Ice miniature-dataloggers (UTL1), reading ground temper- Age the lower limit of palsa bogs was 900 m a.s.l. atures at 0.2 m depth and 8.5 m depth every six hours. (Sollid & Sørbel, 1998). In the mountain permafrost Air temperatures (2 m) were measured at the high- area there is no palsa bogs due to a scarcity of sphag- est drill site (DB1) and close to the lowest drill site num moss. (DB11). The present paper examines the first year of 1085 1086 Figure 2. Map of the investigated area on Dovrefjell. The locations of boreholes DB1–DB10 are shown. An additional borehole DB11 is located about 1 km southeast of DB10. Permafrost distribution is according to earlier BTS results (Isaksen et al., 2002). The dark shaded and light shaded areas represent possible and probable permafrost occurrence, respectively, based on a linear correlation of the BTS classes. Table 1. Annual temperatures and key information measured at the Dovrefjell DB1–DB11 borehole sites during the first year after drilling (observation period is 17.10.01–16.10.02). Bh.nr. is borehole number (see Figure 2 for Locations), Depth is depth of boreholes, MGT is mean ground temperature measured at 8.5 m depth, GTmax is maximum ground temperature (8.5 m), GTmin is minimum ground temperature (8.5 m), MGST is mean ground surface temperature measured 0.2 m below surface, GSTmax is maximum ground surface temperature (0.2 m), GSTmax is minimum ground surface temperature (0.2 m), MAT is mean air temperature during the observation period. MAAT is mean annual air temperature (see text). Snow depth (m) indicates late winter snow depth and was measured at sites DB1–DB4 at 19.03.02. At sites DB5–DB11 snow depths are based on visual field observations in March. No surface temperatures were measured at DB9, DB10 and DB11. Ground temperatures Surface temperatures Air temperatures Depth Altitude MGT GTmax GTmin MGST GSTmax GSTmin MAT MAAT Surface Snow depth Bh.nr. (m) (m) a.s.l. (°C) (°C) (°C) (°C) (°C) (°C) (°C) (°C) material (m) DB1 10.0 1505 Ϫ0.4 Ϫ0.2 Ϫ0.4 Ϫ0.3 17.4 Ϫ18.7 Ϫ0.8 Ϫ2.5 Debris 0.1–0.2 DB2 9.0 1481 Ϫ0.3 Ϫ0.2 Ϫ0.4 Ϫ0.5 14.1 Ϫ17.4 Ϫ0.7* Ϫ2.4 Debris 0.1–0.2 DB3 9.0 1477 0.2 0.5 Ϫ0.1 1.1 12.3 Ϫ3.6 Ϫ0.7* Ϫ2.4 Debris 1.5–2.0 DB4 9.0 1467 0.0 0.0 0.0 1.0 11.8 Ϫ4.1 Ϫ0.7* Ϫ2.4 Debris 3.0–4.0 DB5 9.0 1458 0.4 0.6 0.3 Ϫ0.2 12.9 Ϫ15.0 Ϫ0.6* Ϫ2.3 Debris 0.5–1.0 DB6 9.0 1402 Ϫ0.5 Ϫ0.4 Ϫ0.6 Ϫ0.2 14.1 Ϫ16.9 Ϫ0.4* Ϫ2.1 Debris Ͻ0.1 DB7 9.0 1344 1.4 2.1 0.8 1.0 12.1 Ϫ6.1 Ϫ0.1* Ϫ1.8 Debris 1.0–1.5 DB8 9.0 1254 1.9 3.3 0.9 0.9 13.1 Ϫ12.2 0.3* Ϫ1.4 Bedrock 0.3–1.0 DB9 9.0 1178 1.8 3.4 0.9 –– – 0.6* Ϫ1.1 Bedrock 0.3–0.5 DB10 9.0 1094 2.5 3.9 1.3 –– – 1.0* Ϫ0.7 Bedrock 0.3–0.5 DB11 9.0 1039 2.1 3.0 1.1 –– – 1.3 Ϫ0.4 Bedrock Ͻ0.1 * Values are interpolated from DB1; lapse rate is Ϫ0.44°C/100 m. borehole-temperature data to locate the transition zone results of the BTS measurements, which indicate of mountain permafrost in the area. The results are com- a lower mountain permafrost limit of approximately pared to the earlier BTS measurements. 1500 m a.s.l. (Figure 2). The mean ground temperature (MGT, cf. Figure 3) elevation gradient (Ϫ0.7°C/100 m) of snow-covered 2 RESULTS AND DISCUSSION sites is equal to the elevation gradient of sites with- out snow (e.g. DB6 and DB11), but differs from the Borehole temperatures (Table 1) are highly correlated mean annual air temperature (MAAT) lapse rate with elevation (Figure 3). Based on the results of the (Ϫ0.44°C/100 m). The gradient differences could be borehole temperature measurements, the mountain per- due to increasing winds with altitude, or changes in mafrost transition zone is located at approximately surface cover due to vegetation, block fields etc. On 1300–1550 m a.s.l. Snow depth controls mountain per- Juvvasshøe 1894 m a.s.l. in Jotunheimen, the MGT mafrost distribution within this zone (Figure 4). In the is Ϫ3.0°C (Isaksen et al., 2001) and the lower limit of lower part of the zone, permafrost is found only beneath mountain permafrost is around 1450 m a.s.l. (Isaksen local convexities strongly exposed to winds, while in et al., 2002; Ødegård et al., 1992). The MGT elevation the higher part, permafrost is also found beneath flat gradient above the mountain permafrost limit at areas and local depressions where snow depths are Juvvasshøe is thus approximately Ϫ0.7°C/100 m. On greater. The results suggest that the lower limit of moun- Dovrefjell, no boreholes have been drilled to investi- tain permafrost on Dovrefjell corresponds to a MAAT gate permafrost above 1505 m a.s.l. Conditions above of approximately Ϫ1.6°C for locations with thin or no the lower limit of mountain permafrost, however, are snow cover. For comparison, Etzelmüller et al. (1998) expected to be similar to those on Juvvasshøe (cf. used a MAAT of Ϫ4°C as the lower limit of mountain Isaksen et al., 2002). permafrost distribution in southern Norway. The extent of mountain permafrost, therefore seems to be greater than that suggested by Etzelmüller et al. (1998). 3 CONCLUSIONS AND PERSPECTIVES BTS-measurements were performed in areas with a stable winter-snow cover of 1–2m (Ødegård et al., The lower limit of mountain permafrost on Dovrefjell 1996; Isaksen et al., 2002). Temperature measure- southern Norway, based on borehole temperature meas- ments in boreholes at snow-covered sites indicate the urements at exposed sites, is approximately 1300 m a.s.l.