Air flow and dry deposition of non-sea salt sulfate in polar firn: Paleoclimatic implications

Abstract

Non-sea salt sulfate aerosol (NSS) is an important factor for the Earth's albedo because it backscatters solar radiation and is the major cloud condensation nucleus over oceans. At Vostok, Antarctica, NSS concentration shows an increase in glacial period ice of 20–46% that cannot be attributed to changes in accumulation rate. The additional NSS may be due to enhanced dry deposition of NSS by topographic windpumping during the windy glacial periods. We model the volume flux of air into snow due to barometric pressure changes and air flow over surface microrelief. The Gormley-Kennedy equation approximately describes how aerosols advected into the snow pack are removed from the air by diffusion to the snow matrix. Barometric pressure and wind speed data from several polar sites have been used to quantify the vertical volume flux of air and mass flux of NSS. Model results indicate that air flow over small sastrugi, wind carved snow dunes commonly found on ice caps, is the dominant dry deposition mechanism for NSS. Paleo wind speed and surface roughness can significantly influence the aerosol record in ice cores.