Reversal of the Air-Water Gas Exchange Direction of Hexachlorocyclohexanes in the Bering and Chukchi Seas: 1993 versus 1988.

In the summer of 1993, water and air samples were collected in the Bering and Chukchi Seas (BERPAC-93) to determine the air-water gas exchange of hexachlorocyclohexanes (HCHs). Average concentrations in the ocean surface water, 2.00 and 0.45 ng L -1 for α-HCH and γ-HCH, were 18% and 24% lower than values found on a 1988 cruise. Mean concentrations in ocean air were 91 pg m -3 α-HCH and 23 pg m -3 γ-HCH, a decrease since 1988. The water/air fugacity ratio of α-HCH averaged 1.86 over all stations, compared to 0.74 from 1988 measurements. Afugacity ratio greater than unity implies volatilization and reversal of the net gas exchange direction since 1988. The 1993 fugacity ratios for γ-HCH indicated volatilization in the Bering Sea (1.25), deposition in the Gulf of Anadyr and Chirikov Basin region (0.72), and near equilibrium in the Chukchi Sea (0.90-0.98). In 1988, the net exchange of γ-HCH was depositional at all stations. Mean fluxes on BERPAC-93 estimated from the two-film model were 30 for α-HCH and -1.5 for γ-HCH (ng m -2 day -1 , positive indicates volatilization).