Seasonal accumulation timing and preservation of nitrate in firn at Summit, Greenland

In a yearlong investigation of the air-snow transfer function for nitrate (NO3-) at the Greenland Environmental Observatory, Summit (3203 m above sea level), surface snow concentrations measured every other day were compared with levels measured in 10 snow pits dug adjacent to accumulation stakes. Concentrations in the surface snow ranged from 0.4 to 34 muM with a mean of 2.9+/-1.9 muM. Measured firn profiles in the snow pits had a maximum NO3- concentration of 12 muM and a mean of 2.7+/-0.5 muM. Reconstructed profiles from surface snow observations and accumulation data closely matched the observed profiles. The small difference in preserved concentrations from observed surface snow concentrations gives evidence of only 7% postdepositional loss at this site (mean annual accumulation similar to23 g cm(-2) yr(-1)). Removing the three highest outliers (which may originate from local sources) of surface snow concentration drops the mean to 2.7 muM, further demonstrating preservation. Results indicate that at this site accumulation is the most significant process affecting preservation of nitrate in the firn. Other rapid postdepositional processes may impact surface snow concentrations, but do not appear to significantly change the preserved record. The inverse analysis of converting preserved records to surface snow concentrations provides equivalent evidence of the same preservation.