title: The air-sea equilibrium and time trend of hexachlorocyclohexanes in the Atlantic Ocean between the Arctic and Antarctica.
abstract: Hexachlorocyclohexanes (HCHs) were determined simultaneously in air and seawater during two cruises across the Atlantic Ocean between the Arctic Ocean (Ny-Alesund/ Svalbard, 79 degrees N; 12 degrees E) and the Antarctic Continent (Neumayer Station/ Ekstroem Ice Shelf, 70 degrees S; 8.2 degrees W) in 1999/ 2000. The concentrations of alpha-HCH and gamma-HCH in air and surface waters of the Arctic exceeded those in Antarctica by 1-2 orders of magnitude. The gaseous concentrations of gamma-HCH were highest above the North Sea and between 20 degrees N and 30 degrees S. Fugacity fractions were used to estimate the direction of the air-sea gas exchange. These showed for alpha-HCH thatthe measured concentrations in both phases were close to equilibrium in the North Atlantic (78 degrees N-40 degrees N), slightly undersaturated between 30 degrees N and 10 degrees S and again close to equilibrium between 20 degrees S and 50 degrees S. Y-HCH has reached phase equilibrium in the North Atlantic as alpha-HCH, but the surface waters of the tropical and southern Atlantic were strongly undersaturated with y-HCH, especially between 30 degrees N and 20 degrees S. These findings are significantly different from two earlier estimates around 1990 as a result of global emission changes within the past decade. Therefore, we investigated the time trend of the HCHs in the surface waters of the Atlantic between 50 degrees N and 60 degrees S on the basis of archived samples taken in 1987-1997 and those from 1999. A decrease of alpha-HCH by a factor of approximately 4 is observed at all sampling locations. No decrease of gamma-HCH occurred between 30 degrees N and 30 degrees S, but there was a decrease in the North Atlantic, North Sea, and in the South Atlantic south of 40 degrees S. The constant level of gamma-HCH in the tropical Atlantic confirms the conclusion that the tropical Atlantic acts as a sink for y-HCH at present time. The measured alpha-HCH seawater concentrations were compared with results from a global multimedia fate and transport model. Whereas the time trend over 13 years and the latitudinal gradient were well reproduced by the model, the absolute levels were too high by a factor of 4.5. This may be explained by the zonal averaging employed in the model as well as uncertain emissions and degradation rates.
authors.affiliation: Alfred Wegener Institute Foundation for Polar and Marine Research, Bremerhaven, Germany. slakaschus@awi-bremerhaven.de
authors.forename: Sonke
authors.initials: S
authors.lastname: Lakaschus
authors.forename: Kurt
authors.initials: K
authors.lastname: Weber
authors.forename: Frank
authors.initials: F
authors.lastname: Wania
authors.forename: Regina
authors.initials: R
authors.lastname: Bruhn
authors.forename: Otto
authors.initials: O
authors.lastname: Schrems
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000864:Antarctic Regions; D001110:Arctic Regions; D001267:Atlantic Ocean; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004784:Environmental Monitoring; D001556:Hexachlorocyclohexane / Q000032:analysis* / Q000737:chemistry; D008962:Models, Theoretical; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D014874:Water Pollutants, Chemical; D001556:Hexachlorocyclohexane