The fractionation of sea salt and acids during transport across an Antarctic ice shelf

Analyses of Cl−, NO3−, SO42−, Na and Mg made on a series of surface snow samples, collected at 4 km intervals along a 116 km traverse of the Fimbul Ice Shelf in Dronning Maud Land, show that fractionation of some of the sea salt species has taken place. There is depletion of Mg compared to Na in the coastal part of the traverse, but the bulk sea water ratio is maintained further inland. Evidence for Cl− fractionation is less clear, with a depletion in some sections and an enrichment in others compared to Na. Taken over the whole data-set of 120 samples, the bulk sea water ratio between the marine ions Na, Mg and Cl appears to be conservatively maintained. For all of the sea-salt components, the general trend in concentration was an increase from the ice shelf front to a maximum value approximately 45 km inland, before decreasing to a value of 10% of the maximum by the end of the traverse. Non sea-salt sulphate followed a similar trend to 45 km, but the subsequent decrease in concentration was less rapid, suggesting a greater residence time for sulphate derived from marine biogenic activity than for sea-salt aerosol. Relatively high concentrations of nitrate were found in all of the surface snow samples in comparison to samples taken from shallow pits at each end of the traverse. This may be an indication of a post depositional loss of nitrate from the snow surface.

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