Laboratory study of the migration of methane sulphonate in firn
Two 10cm lengths of firn core from the Dyer Plateau (700° 3l'S, 65°0l'W), Antarctic Peninsula, were used to carry out a laboratory experiment to investigate the migration of methane sulphonate, the anion of methane sulphonie acid (MSA), in natural fim. Each length was cut vertically into tour pieces, and a dopant solution containing Cl-, NO3,-, SO4 2, F and MSA pipetted onto the top of three sections, the fourth being kept as a blank. The doped sections were stored vertically, with the doped end uppermost, for R months at a range of temperatures (nominally -5°, -10° and -22°C) before subsampling at 1em resolution and analysis by ion chromatography. The two firn lengths were treated identically and the results were consistent. Profiles of the doped fim sections showed that Cl-, NO3,-, SO4 2, remained in the uppermost subsample, although the NO3 concentrations were variable compared to the blank. The yo profile shows slightly elevated concentrations in the second sample down compared to the blank, at temperatures of -l0°C and above. The MSA- showed higher concentrations in the second, third and fourth samples down at -10°C and above, which indicates that some percolated downwards from its original position at the top of the core. This experiment shows that MSA is mobile in warm fim even over a short period of time. We propose that the mechanism tor the mobility of MSA in natural fim is via liquid MSA drainage, though we cannot yet discount vapour phase transport.