Determining the pathways, fate, and flux of atmospherically derived trace elements in the arctic ocean/ice system

International audienceAerosol deposition is an important pathway for delivering trace elements, including those of anthropogenic origin, into the Arctic. Assessment of this process is difficult in the harsh Arctic environment, and limited field studies have forced a reliance on poorly constrained models. Here we use the cosmic ray produced radioisotope, 7Be, to trace the atmospheric deposition of elements within the Arctic water/ice/snow system, and link aerosol concentrations to flux. Seawater, ice, snow, melt pond, and aerosol samples were collected during late summer 2011 as part of the RV Polarstern's ARK-XXVI/3 campaign. From the measured 7Be inventories we determined an average 7Be flux of 109 dpm/m2/d, which is consistent with results from previous studies in the region. Snow, ice and melt ponds represent significant reservoirs of 7Be, and the relative 7Be inventory in ice increased through late August, as melt pond inventories decreased with onset of freezing. The total (water/ice/snow system) inventory was relatively constant across our transect, but mixed layer inventories increased towards lower latitudes as ice-free, open water was approached. The latter gradient drives transport of 7Be, and presumably other atmospherically-derived species, towards the ice-covered ocean mixed layer. This is modeled by advective transport along the Transpolar Drift. The average 7Be aerosol concentration was 0.0182 dpm/m3. None of the lithogenic aerosol elements showed any significant enrichment above crustal composition, while the pollution-derived elements (Cr, Ni, Cu, Zn, Cd, Sb, Pb) showed varying degrees of enrichment relative to crustal values. Historical aerosol 7Be data was used to derive a seasonal cycle in the 7Be inventory that was calibrated to the inventory measured in this study, using an effective bulk (wet plus dry) deposition velocity of 1350 m/day. This deposition velocity was then used to estimate the seasonal atmospheric flux of aerosol trace elements