Mechanisms and Implications of α-HCH Enrichment in Melt Pond Water on Arctic Sea Ice

During the summer of 2009, we sampled 14 partially refrozen melt ponds and the top 1 m of old ice in the pond vicinity for alpha-hexachlorocyclohexane (alpha-HCH) concentrations and enantiomer fractions (EFs) in the Beaufort Sea. alpha-HCH concentrations were 3 - 9 times higher in melt ponds than in the old ice. We identify two routes of alpha-HCH enrichment in the ice over the summer. First, atmospheric gas deposition results in an increase of alpha-HCH concentration from 0.07 +/- 0.02 ng/L (old ice) to 0.34 +/- 0.08 ng/L, or similar to 20% less than the atmosphere-water equilibrium partitioning concentration (0.43 ng/L). Second, late-season ice permeability and/or complete ice thawing at the bottom of ponds permit alpha-HCH rich seawater (similar to 0.88 ng/L) to replenish pond water, bringing concentrations up to 0.75 +/- 0.06 ng/L. alpha-HCH pond enrichment may lead to substantial concentration patchiness in old ice floes, and changed exposures to biota as the surface meltwater eventually reaches the ocean through various drainage mechanisms. Melt pond concentrations of alpha-HCH were relatively high prior to the late 1980-s, with a Melt pond Enrichment Factor >1 (MEF; a ratio of concentration in surface meltwater to surface seawater), providing for the potential of increased biological exposures.