Structure, microphysics, and surface area of the Arctic snowpack near Alert during the ALERT 2000 campaign

The seasonal snowpack at Alert (North coast of Ellesmere Island, 82°29.94′N, 62°20.55′W) was studied in February and April 2000, on land and on sea ice. The stratigraphy was studied, and the density and specific surface area (SSA) of each snow layer were measured. SSA was measured by CH4 adsorption at 77 K using a volumetric method. On land, the snowpack was 10–50 cm thick and consisted of a depth hoar layer covered by one or more hard wind-packed layers with densities between 0.35 and 0.52. These were sometimes separated by soft layers of more or less faceted crystals. The surface was covered by recent precipitation and surface hoar. The stratigraphy on sea ice was more variable, with numerous hard wind-packed layers alternating with soft layers of depth hoar or faceted crystals. SSA values ranged from 125 cm2/g for depth hoar to 1500 cm2/g for diamond dust and dendritic snow. The total surface area of the snowpack was calculated from the thickness, density, and SSA of each layer, and ranged from 1160 to 3710 m2 of snow surface area per m2 of ground. These values were used to estimate the potential impact of the snowpack on atmospheric chemistry, by adsorption/desorption of trace gases. Using the example of acetone, whose adsorption behavior on ice is estimated, it is found that the snowpack may sequester most of the acetone of the (snow+boundary layer) system most of the year. The release during metamorphism of trace gases dissolved in snow is also discussed. We propose that the frequency and intensity of wind storms will strongly affect the release of trace gases, as this will determine whether intense metamorphism leading to depositional depth hoar can happen.