Factors Affecting the Availability of Plant Nutrients on an Antarctic Island

Abstract

Continental Antarctica is predominantly an ice-covered cold desert with few habitats for living organisms. In contrast, the coastal zone and off-shore islands (the 'maritime Antarctic' of Holdgate 1964) have a milder climate, much ice-free lowland, and a variety of plant and animal life. This flora and fauna is undoubtedly influenced by many factors and one of them, chemical nutrient availability and circulation, is considered in the present paper. Although only one island has been studied it is considered sufficiently representative for the data to be fairly widely applicable. Signy Island (latitude 600 43' S, longitude 450 38' W) has an area of about 20 km2 and is one of the smaller members of the South Orkney group. It has been the site of a British scientific and meteorological station since 1947 (Holdgate 1965). The island is composed mainly of quartz-mica-schist with subsidiary amphibolites and scattered thin bands of marble (Matthews, Maling & Adie 1967). About half the surface is covered by permanent ice and snow, whilst much of the remaining area is mantled by glacial debris. The climate is of the cold oceanic type with monthly mean temperatures ranging from 10-5 to 0.8? C and an annual mean of 3.8? C. Precipitation occurs on about 335 days, and totals about 40 cm/annum. Cloudiness is high, evaporation low, and the ground is generally moist. With frequent freeze-thaw cycles and large areas of saturated fine mineral debris, solifluxion processes are widespread and many slopes show marked surface instability. Such areas are largely unvegetated, but the more stable ground supports a variety of cryptogamic communities dominated by bryophytes and lichens (Holdgate 1964). A general description of the soils of Signy Island has been given by Holdgate, Allen & Chambers (1967). The present paper is based on samples of these soils together with rock material and vegetation, all collected in February 1962 by M. W. Holdgate; also on water and vegetation samples obtained in March 1965 by personnel of the British Antarctic Survey Station. All samples were transported in cold storage to Merlewood Research Station, Grange-over-Sands, England, where they were analysed using the techniques summarized in the Appendix.