Vegetation Development and Variation in Near-Surface Ground Temperatures at Illisarvik, Western Arctic Coast

摘要

The Illisarvik Lake basin was experimentally drained in 1978 to study growth of permafrost in the lake-bottom sediments ab initio. Ground freezing began during the first winter after drainage and led to the development of permafrost throughout the lake basin, except beneath a residual pond. This paper reports the range in near-surface ground temperatures in the basin 40 years after drainage. In summer 2016, vegetation and soil characteristics were determined throughout the basin. Snow surveys were conducted in April 2017. Since drainage, seven principal vegetation communities (units) have developed in the basin: bare ground, sparsely vegetated soil, grass meadow, sedge marshes, and three shrub types. Characteristic snow depths in these units and in tundra surrounding the basin were 16, 27, 38, 62, 52-127, and 47 cm, respectively. Illisarvik's coastal location ensures that there is abundant snow to fill the high snow retention capacity created by tall shrubs and basin topography. Mean annual ground temperatures (T_g) at 25 cm depth were recorded by miniature data loggers in 2016-18 in the different vegetation units at 10 sites within the basin and the surrounding tundra. T_g in 2016-18 ranged from -0.1 ℃ beneath tall dense willows to -5.6℃ in bare ground. T_g in tundra surrounding Illisarvik was -5.2℃. The factors most strongly associated with the variations in temperature were snow depth and soil moisture. Although near-surface ground temperatures at Illisarvik initially decreased as permafrost was established after drainage, the basin soils are no longer cooling due in part to increases in snow depth with the growth of vegetation.