Background

About 5% of the total area of the Antarctic continent is ice-free permafrost terrain. The special climatic conditions, with very low temperatures and little precipitation, lead to permafrost with a very low moisture content and a thin active layer. The Antarctic environment therefore offers unique opportunities to study geomorphological processes in a setting very different from the northern polar region. Permafrost research has so far been concentrated to the northern hemisphere and therefore the understanding of how climate and permafrost interact on Antarctica is very limited. Since permafrost is now recognized as an important part of the global cryosphere there are also new demands for more knowledge on permafrost conditions in the southern hemisphere.

The research undertaken during the SWEDARP expedition to Dronning Maud Land (DML) in 2004/05 is part of an ongoing project initiated during the DML-expedition 2003/04. During the expedition 2003/04, which was concentrated to Wasa and Fossilryggen, ground temperatures and soil moisture conditions were found to enable active layer processes and generate a rich variety of patterned ground landforms. The same process was also confirmed at Svea, during the expedition 2004/05, where patterned ground phenomena were observed (picture 1). A climate station for measurements of ground temperatures and other climate parameters was also installed at the Finnish base Aboa close to Wasa in 2003/04.

Objectives

The principal aim during the expedition 2004/05 was to install data loggers for long-term measurements of ground temperatures at Fossilryggen and Svea, forming a temperature monitoring transect from the coast to the inland escarpment (picture 2). Furthermore different climatic parameters, such as soil moisture, ground and air temperatures, incoming radiation and wind speed, were also measured in relation to frost heave landforms. The objective of these measurements is to see how ground micro-climate drives and inhibits soil movement in the active layer and landform generation.

Long-term monitoring of ground temperatures

Two loggers were installed at Fossilryggen and Svea respectively. These loggers measure ground temperatures at depths of 2, 10, 30 and 60 cm and contribute data to the Circumpolar Active Layer Monitoring (CALM) programme. The loggers remain at the mentioned sites for year-round monitoring and data from them should be downloaded annually. The data set will be integrated in the snapshot documentation of the global state of permafrost during the International Polar Year 2007–2008.

Short-term micro-climate observations at sorted patterned ground

Short-term measurements were made for 12 days in proximity to a frost heavegenerated landform during a period of initial thaw after the winter freeze-up of the ground. The measured parameters were soil moisture and ground temperatures at depths of 5 and 10 cm, incoming shortwave radiation on the ground surface, wind speed close to the ground surface and air temperatures at heights of up to 1 m (picture 3). The latter were measured to test wind cooling effects on ground surface temperatures under different vertical temperature gradients. Soil moisture was measured with delta-T TDR-probes.

Results

Data from the loggers located at Fossilryggen and Svea will not be available until after the SWEDARP 2006/07 expedition. However the data from the short-term measurements is of great interest, especially with respect to soil moisture and ground temperatures (figure 4). There is a clear relationship between temperature and soil moisture. The near-surface soil moisture (at a depth of 5 cm) shows a decrease during the measurement period, while the soil moisture further down (at a depth of 10 cm) increases during the period. The high salt content causes a distinct freezing point depression of the soil water. This results in diurnal water melt and refreezing, even though the temperature is not above zero. These preliminary results suggest that surface release of soil moisture commences as soon as ice melts, even at sub-zero temperatures. Antarctic soils are known to be highly saline and this appears to play an important role in the freeze-thaw dynamics of the active layer. The origin of ice in the soils needs further study but field observations suggest crystalline pore ice development by direct atmospheric precipitation in the pores.

Data from the air and ground temperature profiles are still under analysis. Analysis of similar measurements made during SWEDARP 2003/04 at a rock surface illustrates some principles. Diurnal radiational heating commonly results in rock surface temperatures far exceeding those in the air and at deeper levels in the rock material. However low air temperatures, especially in association with strong winds, result in effective surface heat loss and rock surface temperature depression. Porous media such as soils, with lower heat conductivity, are expected to show even stronger surface cooling. This mechanism is expected to be an important driving factor for the very high frequency of diurnal frost cycles in the maritime Antarctic (Boelhouwers et al. 2003). The temperature profiles measured during the cruise and reported here are expected to provide further insights into the importance of convective heat loss in freeze-thaw processes.

Preliminary conclusions

• An active layer monitoring network has been installed along the Wasa, Fossilryggen and Svea transect. Data will be used during the International Polar Year 2007/08 and submitted on an ongoing basis to the CALM/GTN-P programme.
• Ground temperature and soil moisture measurements show that ground water is present in the form of both pore and segregation ice, but is rapidly released during the short thawing period during summer.
• The high salinity of Antarctic soils plays an important role in freeze-thaw dynamics and needs further understanding. As a first result, diurnal freeze-thaw cycles occur even where temperatures remain sub-zero.
• Clearly soil moisture and temperature fluxes need to be followed throughout the whole thaw season for a better understanding of active-layer dynamics.
• The low absolute soil moisture content limits the potential frost activity and the landforms are therefore believed to result from a very slow process activity during the Holocene.