Antarctic soils are everywhere underlain by permafrost, which can be divided into a number of distinct types (Campbell and Claridge 2006). Ice-cemented or ice-bonded permafrost (Fig. 2.6) is easily recognized, and has an active layer that immediately overlies hard ice-bonded permafrost. The active layer depth varies according to mean annual temperature, moisture supply and the thermal radiation balance, but is usually deepest (up to 1 m) in warmer northern locations, and shallow (< 2 cm) in the coldest areas. A similar form is permafrost with massive ice
Fig. 2.6 Permafrost types in the Transantarctic Mountains region. The active layer thickness diminishes with increasing coldness and with increasing age and aridity, the permafrost changes from ice bonded to dry permafrost. 1: active layer over ice-bonded permafrost, 2: active layer over buried or massive ice, 3: active layer over dry permafrost over ice-bonded permafrost, 4: active layer over dry permafrost over buried or massive ice, 5: active layer over dry permafrost, 6: saline permafrost immediately below or at some depth below the active layer. This ice is typically stagnant or old residual glacial ice (Claridge and Campbell 1968; Sugden et al. 1993), commonly associated with patterned ground surfaces (Fig. 2.4) and younger land surfaces with thermokarst terrain (Campbell and Claridge 2003).
Ice-free or dry permafrost (Bockheim 1995) is distinguished by very low water content in both the active layer and the permafrost, which is loose and non-cohesive. Ice crystals, where present, may behave like sand grains. Our measurements indicate that a gravimetric water content of around 6-7% is required for ice bonding to occur in these sandy gravel materials. In ice-bonded permafrost, weathering is restricted to the active layer but in dry permafrost, weathering occurs into the permafrost, sometimes to a depth of several meters. Intermediate forms between ice-bonded and dry permafrost are also found with dry and weathered perennially frozen permafrost overlying at variable depth ice-bonded permafrost or ancient massive ice (Claridge and Campbell 1968; Sugden et al. 1999).
Saline permafrost is found in small depressions and salty hollows, and associated soils are highly saline. In summer months, the active layer frequently contains brine, usually at a temperature several degrees below 0°C, while the soil is characterized by abundant efflorescences of soluble salts.
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