Snowpack chemistry, nitrate stable isotopes and net deposition fluxes from the largest ice-free region in Greenland

Snowpack chemistry, nitrate stable isotopes and net deposition fluxes for the largest ice-free region in Greenland 15 were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at 8 locations within 3 lake catchments in each of 3 regions (ice sheet margin in the east, central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181 mm snow water equivalent (SWE), compared with 36 mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl-, other major cations), ammonium (regional means 1.4-2.7 µmol/l), total and non-sea salt sulfate (total 1.8-7.7, non-sea salt 1.0-1.8 µmol/l) than the two inland regions. Nitrate (1.5-2.4 µmol/l) showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in a strong deposition gradient for NO3- as well as NH4+ and non-sea salt sulfate (nss-SO4^2-) increasing from the inland regions to the coast (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17 and 11 mol/ha/yr of NO3-, NH4+ and nss-SO4^2- respectively). The d15N of snowpack NO3- shows a significant decrease from the ice sheet margin (-7.5 per mil) to the coast (-11.3 per mil). We attribute the spatial gradient of d15N in SW Greenland to post-deposition processing rather than differing sources because of 1) the climatic gradient from ice sheet margin to coast, 2) within catchment isotopic differences between terrestrial snowpack and lake-ice snowpack, and 3) similarities between fresh snow (rather than accumulated snowpack) at Kelly Ville and the coast. Hence the d15N of coastal snowpack is most representative of snowfall in SW Greenland, but after deposition the effects of photolysis, volatilization and sublimation lead 30 to enrichment of the remaining snowpack with the greatest effect in inland areas of low precipitation and high sublimation losses.