Atmospheric Processes and the Chemistry of Snow on the Ross Ice Shelf, Antarctica

Abstract

Correlations between chemical profiles (Na, K and Mg) in three 2 m deep pits, separated by hundreds of kilometers on the Ross Ice Shelf, suggest that the passage of major storm systems is often recorded as peaks in cationic concentration in the snow-pack on the Ice Shelf. The magnitude of the peaks appears to be a function of both storm intensity and the extent of sea ice adjoining the Ross Ice Shelf. Samples were collected from a network of 21 shallow pits on the Ice Shelf. Although concentration of impurities in the snow varies as a function of distance from the sea on northern portions of the Ross Ice Shelf, a more complex relationship exists in the interior of the Shelf. A distinct chemical zone south of Roosevelt Island may reflect the presence of a "cyclone graveyard". Non-marine cationic ratios in the southern portion of the Ice Shelf suggest the significant influence of a fractionated marine aerosol and the presence of a second, continental aerosol source. Ionic ratios in rime deposited on the Ross Ice Shelf during periods of fog are interpreted as reflecting the production of fog droplets from the chemically-enriched surface microlayer of the ocean. Diffusionally grown snow crystals also have non-marine ratios. In contrast, snowfall associated with peaks in chemical concentration in particular, and the snow-pack on northern portions of the Ross Ice Shelf in general, yield near-marine ionic ratios. This indicates that the chemistry of snow which is near the coast and snow from major storms is dominated by large droplet riming and the associated presence of a high proportion of sea-salt particles.