Seasonal and annual dynamics of frozen ground in the Central Highland of Iceland

Abstract

A 9-yr study (1983-1991) was carried out in Thjórsárver, central highland of Iceland, to investigate the seasonal and annual dynamics of frozen ground and explore the relationship with environmental factors. The presence/absence of frozen ground and active layer thickness were recorded three times over the growing season (4-7 July, 1-4 August, and 20-24 August) at 51 permanent points in different plant communities and on 12 palsas. There were large annual fluctuations in the proportion of frozen ground, varying from about 20-100% in 4-7 July and from 0-50% in 20-24 August. The incidence of frozen ground in early summer was related to conditions in the previous early winter. The combination of a wet (high water availability) and mild weather (allowing percolation) in September to November may maximize soil moisture content at the onset of winter, facilitating frost penetration through higher conductivity of wet rather than dry soil, and lead to widespread frozen ground in early July. In contrast to frozen ground, active layer depth showed very little annual variation. This indicates that much of the frozen ground melts from below. Widespread frozen ground in early August was primarily associated with a dry July although a correlation with cold weather in July was also found. Both indicate the importance of water in melting seasonally frozen ground, probably by heat transported by flowing groundwater. The wide annual variation in frozen ground incidence in late August supports earlier notions about the marginal nature of permafrost in Iceland. The results indicate that changes in the amount and seasonal pattern of precipitation may be more important than summer temperatures in influencing the aggradation and degradation of permafrost in the central highland of Iceland. © 1996 Regents of the University of Colorado.