Migration of methane sulphonate in Antarctic firn and ice

Abstract

We investigate the seasonal relationship of the sulphur‐bearing anions methane sulphonate (MSA−) and non‐sea‐salt sulphate (nssSO42−) in sections of firn and ice cores from the Antarctic Peninsula and Weddell Sea region of Antarctica. In cores from Dolleman Island and Berkner Island, MSA− has clearly migrated from the summer snow layer, where it is initially deposited, to become concentrated in the winter layer. A similar behavior is evident in a core from the Dyer Plateau, though in deeper layers. Cores from Gomez Nunatak and Beethoven Peninsula show little evidence of relocation of MSA−, though migration at greater depth in the ice sheet cannot be ruled out. In contrast, in all these cores, non‐sea‐salt sulphate remains in the summer layer. From comparisons between the ice core characteristics and the migration behavior at these sites, we conclude that the movement of MSA− does not occur via percolation and refreezing of meltwater. Simple concentration‐driven diffusion is also not a factor, as the MSA− peaks are sharp in the winter layer. The data presented indicate that the movement of MSA− in firn is likely to be linked to the concentration of other ionic species in the snowpack and to the snow accumulation rate. A possible mechanism for the migration of MSA− in the snowpack is via an initial diffusion in the liquid or vapor phase, which is halted by trapping in the winter layer when the MSA− forms a salt with a cation.