Soil and permafrost distribution, soil characterisation and soil vulnerability to human foot trampling, Wright Valley, Antarctica

Soils and shallow permafrost in Wright Valley, Antarctica were mapped at a scale of 1:50 000 to depict their spatial distribution, and sampled to determine the main drivers for the soil classification. In the cold desert of Wright Valley the Gelisol order of Soil Taxonomy was used to classify the soils. Soils on younger surfaces, associated with Lower Wright Glacier, Upper Wright Glacier and alpine glaciers, contain massive ice within 100 cm of the soil surface and are classified as Glacic Haplorthels or Glacic Haploturbels where there is field evidence of cryoturbation. As a generalization, at either end of the valley, soil moisture recharge from moist coastal air masses (eastern end) and blowing snow drifts maintain the depth to permafrost in which ice-cement occurs at <70 cm. The resulting shallow effective soil depth restricts soil development. Soils associated with the Onyx River and those receiving overland or subsurface flow also have a shallow depth to ice-cemented permafrost. Where there is permafrost in which the depth to ice-cement is <70 cm the soils are classified as Typic Haplorthels, or Haploturbels where there is field evidence of cryoturbation. Field evidence of cryoturbation includes patterned ground, sand wedges, or post-depositional distorted layering within the soil. Soils near central Wright Valley often show more development compared with those at the eastern or western ends of the valley and, where permafrost without ice-cement extends to >70 cm, are classified as Salic or Typic Anhyorthels or, where there is field evidence of cryoturbation, Anhyturbels. While mapping soils in Wright Valley, the distribution and nature of the shallow permafrost were also investigated. Three classes of permafrost were established to coincide with definitions or conditions within Soil Taxonomy viz: permafrost with ice-cement at <70 cm, dry permafrost to a depth of >70 cm, and massive ice. A definition for a petrosalic horizon is proposed based on the properties of a salic horizon and the indurated nature of petrocalcic/petrogypsic horizons. The horizon is likely to occur only in the cold desert climate zones of Antarctica. A rapid method to determine soil vulnerability to human foot traffic was developed. As vulnerability is the product of disturbance and rehabilitation, the method is based on the disturbance of 10 foot prints at a site multiplied by a soil rehabilitation factor based on the soil weathering stage. Although fine-grained aeolian sands are easily disturbed they also rehabilitate rapidly in the windy conditions of Wright Valley. In contrast, old stable soils have a tight cobbly desert pavement with reddish desert varnish and often show less foot print disturbance. When cobbles are overturned, however, fresh rock with thick salt accumulations and without desert varnish is exposed. It takes much time for the desert varnish to re-establish. The spatial distribution of Soil Taxonomy soil classes, nature of the permafrost and soil vulnerability to human traffic are presented as three separate maps at 1:50 000 scale and as live GIS files