| Summary: | Methanesulfonic acid (MSA), an oxidation product of DMS, is used as a biogenic sulfur tracer in deposited snow layers to better understand the relative importance of various sulfur inputs (biogenic, volcanic and anthropogenic sulfur) to both polar regions in the past.The ice cores and snowpit samples were collected from the 20D site (Greenland) and the Dominion Range site (Antarctica). A suppressed ion chromatographic method was used to measure MSA in snow and ice. The mean concentration of MSA in the 20D ice core is 3.30 ppb ($\sigma$ = 2.38 ppb, n = 1134). The MSA concentrations have decreased since 1900. The ratios of MSA/total S(VI) in the 20D ice core ranged from 15% before 1900 to 5% after 1900. These results suggest a non-biogenic sulfate source to the Greenland ice sheet at the present time. Based on the assumption that the pre-industrial ratios reflect the biogenic sulfur component in the sulfur burden, we estimate that, at the present time, approximately 80% of sulfur input to Greenland is contributed to non-biogenic sulfur.Seasonal variations of MSA in ice are observed in many but not all years. The seasonality in the 20D ice core is consistent with aerosol MSA data from high latitude stations which confirms that ice records that atmospheric changes. Complications of meterological conditions are believed to be responsible for the lack of seasonality of MSA in ice.The mean concentrations of MSA in the Dominion Range snowpit and ice core are 2.76 ppb ($\sigma$ = 2.36, n = 199) and 0.94 ppb ($\sigma$ = 0.56, n = 258), respectively. The mean MSA/total S(VI) ratio is below 1% at the Dominion Range site. These data confirm that the MSA fraction in the high plateau is considerably lower than in coastal Antarctica and in the low- and the high-latitude marine boundary layer. Possible causes include volcanic sulfate input, long range transport of low-latitude biogenic sulfur, and additional stratospheric sulfate input.In summary, all of the above suggest that transport related sulfur source changes may primarily control the atmospheric chemistry, and consequently the ice chemistry, in both polar regions.
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