Trond Eiken

Climate variables along a traverse line in Dronning Maud Land, East Antarctica

Temperature, density and accumulation data were obtained from sha]low firn cores, drilled during an overland traverse through a previously unknown part of Dronning Maud Land, East Antarctica. The traverse area is characterised by high mountains that obstruct the ice flow, resulting in a sudden transition from the polar plateau to the coastal region. The spatial variations of potential temperature, ncar-surface firn density and accumulation suggest that katabatic winds are active in this region. Proxy wind data derived [rom fim-density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope. The high elevation of the ice sheet south of the mountains makes for a dry, cold climate, in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance. A simple katabatic-wind model is used to explain the variations o[ accumulation along the traverse line in terms o[ divergence/convergence of the local transport o[ drifting snow.The resulting windand snowdrift patterns are c1ose]yconnected to the topography of the ice sheet: ridges are especially sensitive to erosion, while ice streams and other depressions act as collectors of drifting snow.

Svalbard surge dynamics derived from geometric changes

Abstract Geometric changes on a sample of Svalbard glaciers were studied using subtraction of repeat digital terrain models to determine early surge-stage dynamics. Changes in surface features were also analyzed. A number of new surges were found for glaciers not known to have surged previously. The surge development could be followed through three stages, of which the first two had not been previously described in Svalbard. The first two stages are mainly identified from glacier thickness changes and showed little visual evidence. In stage 1, initial surface lowering was found in the upper part of the glacier, followed by a thickening further down-glacier in stage 2. Stage 3 represents the period of well-developed surge dynamics that is usually reported. Some surges ceased at stage 2 as a partial surge and never developed into a fully active surge. These partial surges could be misinterpreted as rapid response to climate change. The results of this study further support previous findings that the majority of Svalbard glaciers are of surge type.

A mean net accumulation pattern derived from radioactive layers and radar soundings on Austfonna, Nordaustlandet, Svalbard

We present the snow-accumulation distribution over Austfonna, Nord-austlandet, Svalbard, based on 29 shallow ice cores that were retrieved from this ice cap during 1998 and 1999. Mean annual net accumulation is deduced from radioactive layers resulting from the 1954-74 atmospheric nuclear tests (maximum in 1963) and the Chernobyl accident (1986). The Chernobyl layer was located in 19 ice cores in the accumulation area, and the nuclear test layer was located in two deeper ice cores. In addition, the spatial variation of the depth of winter 1998/99 snowpack was mapped using snow probing, ground-penetrating radar methods and pit studies. The altitudinal gradient of the mean annual net mass balance and the altitude of the mean equilibrium line are determined along five transects ending at the top of the ice cap. The mean annual net mass balance and the equilibrium-line altitudes show a high degree of asymmetry between the western and eastern parts of Austfonna, in accordance with the distribution of winter accumulation. Large interannual variations of the accumulation exist. However, the study of the mean annual net mass balance shows no trend for two different time periods, 1963-86 and 1986 to the date of the drillings (1998/99).

Calibrating a surface mass-balance model for Austfonna ice cap, Svalbard

Abstract Austfonna (8120km2) is by far the largest ice mass in the Svalbard archipelago. There is considerable uncertainty about its current state of balance and its possible response to climate change. Over the 2004/05 period, we collected continuous meteorological data series from the ice cap, performed mass-balance measurements using a network of stakes distributed across the ice cap and mapped the distribution of snow accumulation using ground-penetrating radar along several profile lines. These data are used to drive and test a model of the surface mass balance. The spatial accumulation pattern was derived from the snow depth profiles using regression techniques, and ablation was calculated using a temperature-index approach. Model parameters were calibrated using the available field data. Parameter calibration was complicated by the fact that different parameter combinations yield equally acceptable matches to the stake data while the resulting calculated net mass balance differs considerably. Testing model results against multiple criteria is an efficient method to cope with non-uniqueness. In doing so, a range of different data and observations was compared to several different aspects of the model results. We find a systematic underestimation of net balance for parameter combinations that predict observed ice ablation, which suggests that refreezing processes play an important role. To represent these effects in the model, a simple P MAX approach was included in its formulation. Used as a diagnostic tool, the model suggests that the surface mass balance for the period 29 April 2004 to 23 April 2005 was negative (–318mmw.e.).

Geometry changes on Svalbard glaciers: mass-balance or dynamic response?

Abstract The geometry of glaciers is affected by both the mass balance and the dynamics. We present repeated GPS measurements of longitudinal altitude profiles on three glaciers in Svalbard and show that surface altitude changes alone cannot be used to assess the mass balance. The three measured glaciers are in different dynamic modes, and the observed changes in geometry are strongly affected by the dynamics. Nordenskiöldbreen shows no significant change in the geometry, indicating that the mass balance is in steady state with the dynamics. On Amundsenisen the surface has lowered by 1.5–2.0 ma–1 in the lower part of the accumulation area at 520–550m a.s.l., indicating that the ice flux is higher than the mass-balance input, probably due to a surge advance of the glacier further downstream affecting the higher part of the drainage area. On Kongsvegen the opposite situation was found. Here the geometry of the profile showed a clear build-up of 0.5 ma–1 in the accumulation area and a lowering of 1 ma–1 in the lower part of the ablation area. The ice velocity is very low, giving a negligible vertical velocity component and an ice flux that is far smaller than the mass-balance flux, indicating that the glacier is building up towards a surge advance. Our results show that if mapping of height changes is to be used to monitor the response of the glaciers to climate change, both surface net mass-balance data and dynamic data are needed.

Recent fluctuations in the extent of the firn area of Austfonna, Svalbard, inferred from GPR

Abstract In spring during 2004–07 we conducted ground-penetrating radar (GPR) measurements on the Austfonna ice cap, Svalbard, with the original aim of mapping the thickness and distribution of winter snow. Here, we further exploit the information content of the data and derive a multi-year sequence of glacier-facies distribution that provides valuable spatial information about the total surface mass balance (SMB) of the ice cap, beyond the usually evaluated winter balance. We find that following an initial decrease in the extent of the firn area (2003–04), the firn line lowered within two subsequent years by ∼40–100m elevation in the north and west and 150–230m in the south and east of the ice cap, corresponding to a lateral expansion of the firn area along the profiles by up to 7.3 and 13.3 km, respectively. The growth of the firn area is in line with stake measurements from Etonbreen that indicate a trend towards less negative SMB over the corresponding period.

The distribution of snow accumulation across the Austfonna ice cap, Svalbard: direct measurements and modelling

We present an analysis of the spatial variability in the snow accumulation on the Austfonna ice cap in Svalbard, Norway, based on the results of field investigations conducted in the spring of 1999, 2004 and 2005. During the campaigns ground penetrating radar measurements at 500 and 800 MHz were collected along profiles, along with additional manual snow sounding and pit stratigraphy work. The analysis of the data reveals a consistent pattern in the spatial distribution of the snow accumulation over the ice-cap, and therefore enables the compilation of a multiple regression model of the snow distribution across the ice cap. Once validated, the results of the model complement the information derived from direct measurements, with an accumulation index for every point on the ice cap, thus enhancing the accuracy of future mass balance studies and dynamic modelling of Austfonna. As very few direct meteorological measurements are performed in the eastern part of Svalbard, the accumulation measurements on the Austfonna ice cap provide valuable integrated information about winter precipitation in this region.

Geometry and dynamics of two lobe-shaped rock glaciers in the permafrost of Svalbard

Photogrammetric measurements of geometry, thickness changes and horizontal movements over time periods of more than 20 years were performed for two rock glaciers in western Svalbard. The results for Brøggerbreen rock glacier revealed no significant thickness changes (i.e. <1 cm a -1 ) and horizontal velocities in the range of a few cm a -1 . No significant horizontal or vertical changes over the observation period were detected for a rock glacier at Nordenskiöldkysten. A number of observations, however, indicate slow deformation and advance of the body. Under this assumption, the age of the rock glacier can be estimated in the order of 50 ka, which implies potential impact on the rock glacier by (de-)glaciations and sea level changes. While rock glaciers on Svalbard represent creep of cold and continuous polar permafrost, those in the European Alps are an expression of warm and discontinuous mountain permafrost creep. From inter-comparison of the above results with two rock glaciers in the Swiss Alps, we conclude that the observed differences in creep speed and surface micro-topography could, to a large extent, be explained by the substantial differences in ground thermal regime.

Mass Balance Methods on Kongsvegen, Svalbard

On the glacier Kongsvegen (102 km2) in northwest Spitsbergen, Svalbard, traditional mass balance measurements by stake readings and snow surveying have been conducted annually since 1987. In addition, repeated global positioning system (GPS) profiling, shallow core analysis and ground-penetrating radar (GPR) surveying have been applied. The purpose of this paper is to evaluate the input from the different methods, especially the GPS profiling, using the results from the traditional direct method as a reference. The annual flow rate on Kongsvegen is low (2 − 3 m a−1), and the emergence velocity is almost negligible. Thus the geometry changes of the glacier, i.e. the change in altitude per distance from the head of the glacier, should reflect the change in net balance of the glacier. The mean annual altitude change from the longitudinal, centreline GPS profiles was compared to the direct stake readings and showed a very good agreement. On Kongsvegen the measured actual ice flux is so low that the mass transfer down-glacier at the mean equlibrium line altitude is less than 10% of what is needed to maintain steady-state geometry. This is clearly shown in the changing altitude profiles. GPS profiling can be used on large glaciers in remote areas to monitor geometry changes, ice flow and net mass balance changes. However, it requires that the centreline profile changes are representative for the area/altitude intervals, i.e. that the accumulation and ablation pattern is evenly distributed. For this purpose the GPR surveying quickly gave the snow distribution variability over long distances. Shallow cores drilled in different altitudes in the accumulation area were analysed to detect radioactive reference layers from the fallout after the Chernobyl accident in 1986, and showed very good agreement to the direct measured net balance. Thus older reference horizons from bomb tests in 1962 could be used to extend the net balance series backwards.

Measuring coastal cliff retreat in the Kongsfjorden area, Svalbard, using terrestrial photogrammetry

As part of the international project Arctic Coastal Dynamics, results from two sites for measuring coastal cliff retreat in the Kongsfjorden area in Svalbard (79 ° N, 13 ° E) are presented. The two sites were established in August 2002 and revisited in August 2004. Photographs with stereo coverage were taken at distances of 7 and 15 m from the cliff walls with a 60-mm Hasselblad camera mounted on a theodolite. Fixed points were established by drilling bolts into the cliff wall and were then surveyed. These fixed points were used as control points for orientation of the photogrammetric models. Digital photogrammetry applied to scanned photographs of the sites resulted in a detailed digital terrain model (DTM) for each site and year. The coastal cliff retreat rates were found by differencing the DTMs of 2002 and 2004. As a result of the short distance between camera and cliff, the DTM differencing was accurate down to 10 mm at least. The results show a yearly retreat of 2.7 and 3.1 mm. These rates are taken to be significant as most of the retreat takes place within small areas with rates well above the accuracy limits of the technique. The results are analysed and discussed in light of earlier rock-wall retreat studies in the same area.