Large-scale spatial trends in recent firn chemistry along an east-west transect through central Greenland

Abstract

Seventeen shallow firn cores drilled along an ∼ 1000-km-long east-west traverse through central Greenland (EGIG-line) and dated by annual δ 18 O H 2 O 2 stratigraphy have been evaluated in seasonal resolution for their nitrate, sulphate, chloride, sodium and calcium content covering the time span ∼ 1982–1992. Each component showed a geographically uniform seasonal input pattern along the EGIG-line corresponding to what is observed at other sites over the central Greenland Ice Sheet. Going across the main ice divide from west to east, the strong decline in the mean snow accumulation rate (associated with precipitating air masses advected from the west) causes a linear decrease in the average deposition rates of nitrate, sulphate and calcium with longitude. Sea-salt components, however, exhibit an exponential decline (scale length ∼ 320 km) from the west to the ice divide but constant rates in the eastern part. The mean firn concentrations of all ions show a systematic increase from west to east related to the concurrent snow accumulation decline. Only exceptionally high sea-salt concentrations at the western-most positions deviate from this picture. Including results from other drill sites all over the Greenland Ice Sheet, a geographically uniform linear relationship of accumulation and deposition rates for the non-sea-salt components is observed. For nitrate, sulfate and calcium average dry deposition fluxes of 1080, 610 and 156 ng cm −1a −1, respectively, are inferred which, depending on the local accumlation rate, may explain 20–40% of the total nitrate and sulphate but 40–80% of the total calcium deposition flux