THERMAL ENVIRONMENTS OF ARCTIC SOIL ORGANISMS DURING WINTER

This paper compares winter soil temperatures at five high arctic sites (Ny Alesund, West Spitsbergen) and one subarctic site (Slattatjakka, Abisko) during 1992/93 and 1993/94. At the high arctic sites snow cove r afforded slight insulation where minimum air temperatures were as lo w as -32 degrees C (March 1993). However, snow did not accumulate sign ificantly until late winter, by which time the ground had cooled to ap proximately -20 degrees C. The polar night aided soil cooling by minim izing solar heat gain. Soil temperatures at 3 cm depth during the autu mn freeze were initially higher than surface temperatures, but once fr ozen, the zone inhabited by soil microarthropods (approximately 10 cm depth) remained isothermal and closely tracked air temperature. By con trast, throughout the spring thaw, the soil at 3 cm depth was cooler t han the surface. Hence, snow cover reduced absolute minimum temperatur es in late winter but prolonged the effective winter period. Hence soi l organisms may be inactive for up to 79% (289 d) of the year, owing t o the extended period that the ground is frozen. The incidence of dail y ground freeze/thaw events was reduced at high arctic sites compared with a subarctic location. Similarly, there were differences in temper ature means and minima at the adjacent high arctic sites dependent on location and topography; for example, on opposite coasts of the Brogge rhaloya, West Spitsbergen the minimum temperatures in 1993/94 were -15 .7 degrees C (Stuphallet) and -8.2 degrees C (Kjaerstranda). Terrestri al microarthropods inhabiting sites with late snow accumulation and co ld air temperatures experience extreme low soil temperatures and hence require effective cold-hardiness strategies.