Accumulation, storage and release of atmospheric mercury in a glaciated Arctic catchment, Baffin Island, Canada

Abstract

Part of the mercury (Hg) entering Arctic ecosystems is believed to be delivered from the atmosphere in snow but this source is difficult to quantify due to limited spatial coverage of Hg data in snow. Here we evaluate the atmospheric deposition, storage and release of total Hg (THg) and monomethyl mercury (MeHg) on Penny ice cap, Baffin Island. This is the first such study in the Baffin region. THg levels in snow and firn (mean=0.61ngL−1) are comparable to those on High Arctic glaciers but MeHg levels are noticeably higher (mean=0.11ngL−1). We find little evidence of springtime enhancement of Hg deposition in snow attributable to atmospheric mercury depletion events. Estimated accumulation rates of THg and MeHg in firn are ∼0.33 and 0.03μgm−2a−1, higher than on High Arctic glaciers, possibly due to higher precipitation on southern Baffin Island. The estimated net annual release of THg by glacial snow and ice melt is small (THg: 1.86kg; MeHg: 0.18kg). In the study area, geogenic Hg contributions from sediment-loaded glacial meltwater could be as large or larger than those from melting ice. MeHg levels are very low in meltwater-fed streams and lakes (⩽0.01ngL−1), suggesting that MeHg is released early in the snowmelt season and/or quickly removed from meltwater by various processes. Summer melt and percolation on Penny ice cap remobilise Hg in firn after deposition, and this imposes resolution limits of at least 3years on depositional trends inferred from ice cores.