Abstract. Sulfur stable isotopes from

[1] Sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples from Summit, central Greenland, covering the preindustrial (from the fourteenth to the eighteenth century) and industrial (from 1872 to 1969 A.D.) periods. Results have been used to estimate the different source contributions to the deposited sulfate and their evolution along the last centuries. They indicate that the preindustrial background sulfate budget is slightly dominated on a year-round average by marine biogenic emissions, amounting to close to half of the non-sea-salt sulfate (49%). The second contribution is provided by continental sources of secondary sulfate, including background volcanism and, to a lesser extent, continental biota (44% of the non-sea-salt sulfate). Sulfur emitted by relatively weak eruptions is found to be largely depleted in 34 S compared to bulk volcanic S, suggesting an efficient washout of the heavier isotope during the tropospheric transport. The impact of human-driven emissions on the sulfate deposited in central Greenland ice is visible in isotope data as early as 1870 A.D. The isotopic signature of anthropogenic sulfur deposited during the twentieth century is found to be constant (d 34 S % + 3.0 ± 1.5%), regardless of the changes of dominant source regions and emission processes. This signature is slightly but measurably lighter than the one reported for Arctic haze pollution events.

Abstract.A shallow ice core was extracted at the summit of Mera Peak at 6376 m a.s.l. in the southern flank of the Nepalese Himalaya range. From this core, we reconstructed the seasonal deposition fluxes of dust and refractory black carbon (rBC) since 1999. This archive presents well preserved seasonal cycles based on a monsoonal precipitation pattern. According to the seasonal precipitation regime in which 80 % of annual precipitation falls between June and September, we estimated changes in the concentrations of these aerosols in surface snow. The analyses revealed that mass fluxes are a few orders of magnitude higher for dust (10.4 ± 2.8 g m −2 yr −1 ) than for rBC (7.9 ± 2.8 mg m −2 yr −1 ). The relative lack of seasonality in the dust record may reflect a high background level of dust inputs, whether from local or regional sources. Over the 10-year record, no deposition flux trends were detected for any of the species of interest. The data were then used to simulate changes in the surface snow albedo over time and the potential melting caused by these impurities. Mean potential melting caused by dust and rBC combined was 713 kg m −2 yr −1 , and for rBC alone, 342 kg m −2 yr −1 for rBC under certain assumptions. Compared to the melting rate measured using the mass and energy balance at 5360 m a.s.l. on Mera Glacier between November 2009 and October 2010, i.e. 3000 kg m −2 yr −1 and 3690 kg m −2 yr −1 respectively, the impact of rBC represents less than 16 % of annual potential melting while the contribution of dust and rBC combined to surface melting represents a maximum of 26 %. Over the 10-year period, rBC variability in the ice core signal primarily reflected variability of the monsoon signal rather than variations in the intensity of emissions.