The International Polar Year (IPY) Circumpolar Flaw Lead (CFL) System Study: The Importance of Brine Processes for α- and γ-Hexachlorocyclohexane (HCH) Accumulation or Rejection in Sea Ice

We present evidence that both geophysical and thermodynamic conditions in sea ice are important in understanding pathways of accumulation or rejection of hexachlorocyclohexanes (HCHs). alpha- and gamma-HCH concentrations and alpha-HCH enantiomer fractions have been measured in various ice classes and ages from the Canadian High Arctic. Mean alpha-HCH concentrations reached 0.642 +/- 0.046 ng L-1 in new and young ice (<30 cm), 0.261 +/- 0.015 ng L-1 in the first-year ice (30-200 cm) and 0.208 +/- 0.045 in the old ice (>200 cm). Mean gamma-HCH concentrations were 0.066 +/- 0.006 ng L-1 in new and young ice, 0.040 +/- 0.002 ng L-1 in the first-year ice and 0.040 +/- 0.007 ng L-1 in the old ice. In general, alpha-HCH concentrations and vertical distributions were highly dependent on the initial entrapment of brine and the subsequent desalination process. gamma-HCH levels and distribution in sea ice were not as clearly related to ice formation processes. During the year, first-year ice progressed from freezing (accumulation) to melting (ablation). Relations between the geophysical state of the sea ice and the vertical distribution of HCHs are described as ice passes through these thermodynamic states. In melting ice, which corresponded to the algal bloom period, the influence of biological processes within the bottom part of the ice on HCH concentrations and a-HCH enantiomer fraction is discussed using both univariate and multivariate approaches.