Beryllium-7 and lead-210 in aerosol and snow in the dye 3 gas, aerosol and snow sampling program

Abstract

Concentrations of cosmogenic ⁷Be and the radon daughter ²¹⁰Pb were determined in surface-level aerosols and fresh and aging snow throughout DGASP. The distinct sources, yet common association with submicron aerosols, of these atmospheric radionuclides makes them valuable tracers of the transport, depositional and post-depositional processes leading to incorporation of submicron aerosols (and associated species) into the Greenland Ice Sheet.

The aerosol concentrations of atmospheric radionuclides tended to covary on the 1–7 day time scale of individual samples (r = 0.57, n = 114, p = 0.001) and were also highly correlated when averaged by month (r = 0.80, p = 0.002). The year-long time series of both ⁷Be and ²¹⁰Pb showed concentration peaks in spring (April) and fall (September–October) and minima in summer (July) and winter (November–February). This finding is in stark contrast to results from other arctic sites, where both radionuclides, but particularly ²¹⁰Pb, show pronounced concentration peaks in the winter. This indicates that the air masses over the Greenland Ice Sheet may be distinct from the air in the polar basin, or boundary layer processes strongly bias surface-level aerosol characteristics over the ice sheet, or, likely, some combination of these factors are operating.

The concentrations of ⁷Be and ²¹⁰Pb in fresh snow at Dye 3 show wide variability between snow fall events. The lack of any obvious correlation between concentrations in aerosol and fresh snow support the contention that surface-level air at this site is often not reflecting air aloft. Aging snow studies did not reveal consistent trends in concentration, suggesting important heterogeneity in the initial concentrations of ⁷Be and ²¹⁰Pb in surface snow over small spatial scales. Poor agreement between the ²¹⁰Pb profile in a 2 m snowpit sampled at the end of the project and the observed deposition of ²¹⁰Pb through the year indicate the potential importance of post-depositional processes in modifying the atmospheric “signals” preserved in the snowpack.