Seasonal variations in the soluble ion content of snow at Summit. Greenland: Constraints from three years of daily surface snow samples

Daily samples of the surface snow at Summit, Greenland were collected from June 1997 to April 1998 and then from August 2000 to August 2002. Concentrations of nine soluble ions (only eight in the first year) were determined in order to assess the validity of seasonal variations in snow composition at this site inferred from earlier snowpit and core studies. Strong and consistently sharp spring (April) peaks in dust, and broader summer (June–August) enhancements of NH4+ and excess Cl-Cl- in the surface snow fully support the timing of these signals inferred from the pit profiles. Sea-salt reached maximum concentrations in the surface snow in late winter (February–March), based on averaging all three years of monthly means, but showed different patterns in winter each of the years. This is also consistent with the variable late-winter to spring timing inferred from pits. Simulated snowpit profiles constructed from the surface snow samples compared well with the ion profiles recovered from well dated snowpits sampled in this investigation, suggesting that early postdepositional changes do not greatly impact the glaciochemical records preserved at Summit. Nitrate in the real snowpits was approximately 25% lower than in simulated pits, this was the worst agreement for any ion but is consistent with several processes being known to deplete NO3- from near-surface snow.