HYDRAULIC AND THERMAL PROPERTIES OF MCMURDO DRY VALLEYS SOILS: WHAT ANTARCTIC LANDSCAPES ARE AT RISK?

Spatial variability in the hydraulic, physical, and thermal properties of active layer soils may reflect the fluvial and climatic history of cold-desert regions. In this study we measured the constant-head saturated hydraulic conductivity and grain-size-distribution of sixty-five soil samples taken from Taylor Valley, as well as the thermal diffusivity of twelve soil samples taken from met stations throughout the McMurdo Dry Valleys, Antarctica.

Both the hydraulic conductivity and grain size distribution of soils are spatially organized within Taylor valley. Soils collected down-valley near McMurdo Sound have a higher percentage of fine-sized sediments (silt, clay) and lower hydraulic conductivities than soils collected up-valley near Taylor Glacier. Soils collected mid-valley have intermediate amounts of fines and conductivity values consistent with a hydrogeologic gradient spanning the valley. Soil hydraulic conductivity is strongly dependent on the presence of fines, with lower conductivities associated with soils containing a higher percentage of fines. The spatial organization of these soil properties within the valley suggests an active fluvial history in which glacier-fed channels, perhaps aided by water tracks, have flushed fine sediments down into lake basins. Three samples taken from neighboring Garwood Valley by contrast have very low conductivities, perhaps reflecting the less active fluvial history in that region that has left till un-eroded resulting in a soil column clogged with fines throughout the valley.

Thermal diffusivity curves were created by measuring the thermal conductivity and heat capacity of soils collected from near Long Term Ecological Research project met stations. Soil thermal properties were measured over a range of water contents to provide a basis for interpreting the thermal history of Dry Valley soils and their stability under changing temperature and precipitation conditions. Three qualitative soil groups emerged from this analysis: soils with low diffusivities at all water contents, soils that slowly increase in diffusivity with increasing water content, and soils that exhibit high thermal diffusivity at low water contents. The first two groups are spatially correlated with ground ice, while the latter group is associated with thermokarst features.