Properties of a chronosequence of ultraxerous soils in the trans-antarctic mountains

Abstract

Cold desert soils were examined on 27 lateral moraines and on ground moraine in Arena Valley, Antarctica (77°50′S 161°E). The soils range in age from 200 000 to possibly 7–10 m.y. and have formed under virtually abiotic conditions, currently receiving less than 1 cm of water-equivalent precipitation per year. On 314 m2 circular plots, the frequency of surface boulders decreases and the frequencies of ventifacted boulders and pitted dolerite boulders increase with time. The desert pavement becomes more distinct with time, as manifested by an increase in rock types resistant to weathering, proximity of fragments greater than 15 mm, and number of coarse fragments which are stained and ventifacted. The thickness of solum and depth at which comminuted clasts occur increase with time. Whereas salt encrustations beneath clasts are prevalent in the youngest soils, the oldest soils contain a weakly cemented salt pan. Cracks measuring 1–5 cm intwidth, irregularly spaced at 15–50 cm intervals and extending to depths of 50 cm, occur primarily in older ultraxerous soils. Electrical conductivity and concentrations of sodium and nitrate in water extracts of the salt-enriched horizon increase with time. Concentrations of cations in water extracts are ranked: Na+ >Ca2+, Mg2+ ⪢ K+, whereas anions are ranked: NO3− >SO42− >Cl−. In the upper part of the solumn, the amount of gravel (76-2 mm) decreases and the amounts of silt (20-2 μm) and clay (< 2 μm) increase with time. The proportions of quartz and mica, the dominant minerals in the clay-size fraction, increase with time. Lesser amounts of vermiculite, montmorillonite and interstratified chlorite-vermiculite and mica-montmorillonite occur in the clay fraction.