Physical and optical properties of snow covering Arctic tundra on Svalbard

Abstract

Snow thickness, duration of snow coverage and amount of ice covering the soil are crucial for the development of biota in the Arctic tundra environment. The snow thickness and optical properties control the amount of Photosynthetically Active Radiation (PAR) that is available for vegetation. A late snow cover may prevent birds from nesting on the ground. Furthermore, ice at the snow/soil interface can be an obstacle for grazing of Svalbard reindeer and affect the microfauna population. Snow and ice thickness, and the physical and optical properties of snow covering Arctic tundra were measured on the Broggerhalvoya peninsula on western Svalbard in spring of 1997. Additionally, thicknesses of ground-covering ice were measured in spring of 1998. The initial maximum thickness of snow in the observed areas varied from 0.4 to 0.9 m. The snow around Ny-Alesund began to disappear by the beginning of June, with the entire snow pack disappearing within 2-3 weeks. At the bottom of the snow pack, there was a soil-covering ice layer between 0.05 and 0.1 m thick. We obtained radiation and reflectance parameters (spectral albedo, attenuation of PAR and global radiation) as well as physical properties of snow (e.g. temperature and density) over six weeks from early May to late June. Electrolytic conductivity of melted snow samples from snow pits shows clearly different conductivity for different stratigraphic sections within the snow pack in early June. Later on, these contrasts disappeared as internal ice layers melted and the snow pack underwent percolation. The albedo maximum before melt onset exceeded 0.9, whereas in the later phase of melting snow surfaces exhibited significantly lower albedo due to metamorphosis, thinning, and blackening by soil-particle contamination. However, even an apparently clean' snow surface had about 30% lower albedo in mid-June than in mid-May. Observations from under-snow PAR measurements are verified using a physically based radiative transfer model. This comparison indicates that scattering features that are smaller than the bulk-grain size may contribute significantly to the interaction between radiation and snowpack.