When will α-HCH disappear from the western Arctic Ocean?

Water column concentrations of α-HCH were measured in the southern Beaufort Sea as part of the Canadian Arctic Shelf Exchange Study (CASES; 2003–04), the Circumpolar Flaw Lead System Study (CFL; 2007–08), and in the Mackenzie River during the 2008 NAHIDIK program. Atmospheric α-HCH concentrations were measured during CASES program. Inventories of α-HCH in the Polar Mixed Layer (PML) and the Pacific Mode Layer (PL) of the Beaufort Sea were calculated between 1986 and 2007 based on the available data. Between 1986 and 1993, there was a significant loading of α-HCH to the Beaufort Sea via the ocean currents. About 12% of the loading to the PML could be explained by the combined effect of the air–water gas exchange and the river runoff. After 1993, α-HCH inventories started decreasing, and could be well predicted exclusively by degradation. Ice formation was shown to be a solvent depleting process leading to a significant increase in the α-HCH concentration in the water just beneath the ice. Associated low α-HCH concentrations in the ice and relatively low ice export from the Beaufort Sea resulted in negligible influence of this output route on the inventories in the PML. The majority of α-HCH in the Beaufort Sea could be eliminated due to degradation by 2020, with concentrations in 2040 dropping to < 0.006 and < 0.004 ng L− 1 in the PML and PL, respectively. Elimination of α-HCH from sea water takes significantly longer than from the atmosphere, with a lag of about two decades.

► The evolution of the α-HCH inventory in the PML and PL of the Beaufort Sea is shown.
► Between 1986 and 1993, the inventories increased due to loading via ocean currents.
► Degradation could explain the decrease of α-HCH concentrations between 1993 and 2007.
► Gas exchange, river inflow and ice export are negligible α-HCH input/output routes.
► The majority of the α-HCH could be degraded in the Beaufort Sea by 2020.