Nitrate stable isotopes and major ions in snow and ice from Svalbard

Sammanfattning: Increasing atmospheric reactive nitrogen (Nr), as consequence of human activities, has generated accumulation of nitrate (NO3-) in Arctic regions. The Arctic has fragile nitrogen limited ecosystems that can be altered by increases of dry or wet deposition of Nr. Ice cores have shown increments of twofold in nitrogen deposition over Greenland and Svalbard during the 20th century. Ice core NO3- stable isotopes, (?15N-NO3- and ?18O-NO3-), have the potential to serve as proxy of nitrogen oxides (NOx) sources and atmospheric oxidation pathways. NO3- is difficult to interpret in ice since it has several sources and experiences post-depositional processes, e.g. photolysis, relocation, evaporation and diffusion. The present work shows the results of NO3- and NO3- stable isotopes analyses of ice cores, snow and precipitation from Svalbard, in order to obtain records of natural and anthropogenic sources of NO3-. In addition, meltwater percolation effects on the snowpack ion content were also studied. A comparison between NO3- records from different Svalbard ice cores and NOx and SOx emission profiles from different regions shows that the major source regions affecting Svalbard are Western Europe and North America, followed by Central Europe and former USSR. Post-1950s ?15N-NO3- measured at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions, and forest fires. There is an east-west gradient in snow NO3- stable isotopes during 2010/2011, with lower ?15N-NO3- and higher ?18O-NO3- values at eastern sites; the results evidence differences in the origin of air masses arriving at Svalbard sites, mainly Eurasia, to the eastern sites, and Northern Europe to the western sites. The effects of post-depositional change on the ice core chemistry were studied, finding that 45% of annual snowpack suffers melt at Lomonosovfonna during the last 60 years. Percolation lengths were estimated as ?1 m for most of ions; therefore, it is expected that the atmospheric ionic signal is preserved at annual or bi-annual resolution within the last 60 years at the Lomonosovfonna summit. The results presented here suggest that NO3- stable isotopes from Svalbard ice cores are useful to describe different sources and source regions of NOx, contributing to the assessment of nitrogen enrichment for this region.