The influence of the atmosphere-snow-ice-ocean interactions on the levels of hexachlorocyclohexanes in the Arctic cryosphere

The alpha-and gamma-hexachlorocyclohexanes (HCHs) are being scavenged from the atmosphere by falling snow, with the average total scavenging ratios (W-T) of 3.8 x 10(4) and 9.6 x 10(3), respectively. After deposition, HCH snow concentrations can decrease by 40% because of snowpack ventilation and increase by 50% because of upward migration of brine from the ice. HCH vertical distribution in sufficiently cold winter sea ice, which maintains brine volume fractions < 5%, reflects the ice growth history. Initially, the entrapment of brine (and HCHs) in ice depends on the rates of ice growth and desalination. However, after approximately the first week of ice formation, ice growth rate becomes dominant. Deviations of HCH concentrations from the values predicted by the ice bulk salinity (rate of brine entrapment) can be explained by spatial variability of HCHs in surface water. HCH burden in the majority of the ice column remains locked throughout most of the season until the early spring when snow meltwater percolates into the ice, delivering HCHs to the upper ocean via desalination by flushing. Percolation can lead to an increase in alpha-and gamma-HCH in the sea ice by up to 2%-18% and 4%-32%, respectively.