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 alpha-HCH and gamma-HCH, were 18% and 24% lower than values found on a 1988 cruise. Mean concentrations in ocean air were 91 pg m(-3) alpha-HCH. and 23 pg m(-3) gamma-HCH, a decrease since 1988. The water/air fugacity ratio of alpha-HCH averaged 1.86 over all stations, compared to 0.74 from 1988 measurements. A fugacity ratio greater than unity implies volatilization and reversal of the net gas exchange direction since 1988. The 1993 fugacity ratios for gamma-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 gamma-HCH was depositional at all stations. Mean fluxes on BERPAC-93 estimated from the two-film model were 30 for alpha-HCH and -1.5 for gamma-HCH (ng m(-2) day(-1), positive indicates volatilization).