Interception of atmospheric fluxes by Arctic sea ice: Evidence from cosmogenic 7Be

The natural cosmogenic radionuclide Be-7 (T-1/2 = 53.4 d) is supplied to the surface ocean from the atmosphere and, in the Arctic Ocean, can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species. Analyses of Be-7 in samples of surface water, surface sea ice, water beneath the ice, sea ice sediments, and precipitation from the Eurasian Basin of the Arctic Ocean show that the fraction of sea ice coverage determines the amount of Be-7 in the surface water. When sea ice coverage is <40%, the Be-7 inventory in the upper ocean (130 +/- 19 Bq m(-2)) is in good agreement with that expected from the inventory from Be-7 atmospheric flux (128 +/- 21 Bq m(-2)). In contrast, when ice coverage is >80%, the water column inventory drops to 58 +/- 20 Bq m(-2). The Be-7 inventory in sea ice is 39 +/- 23 Bq m(-2), and mass balance calculations show that sea ice can intercept 30 +/- 18% of the atmospheric flux of Be-7 during the studied period. We suggest that other atmospherically transported contaminants should be similarly intercepted. Be-7 in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the Fram Strait is similar to 500 g m(-2), a value comparable to previously measured fluxes in sediment traps deployed in the area.