Air-sea exchange of halocarbons: the influence of diurnal and regional variations and distribution of pigments

Journal article, 2004

Diurnal cycles of halocarbons, except methyl bromide and methyl chloride, were observed at six 24-h stations occupied in three different regions, the Summer Ice Edge, the Winter Ice Edge, and the Antarctic Polar Front, in the Atlantic sector of the Southern Ocean during a Swedish-South African expedition in 1997/1998. The diurnal cycles contained three phases; a productive phase, a phase of losses and a phase with steady state. The duration of the different phases varied for the different stations as well as for individual compounds. The measured production and losses of organo-halogens in the Antarctic Ocean based on values from each station, were in the order of a few to hundreds of Tg yr(-1). Bromochloromethane, tribromomethane, trichloroethene and diiodomethane were the four compounds found in highest concentrations throughout the investigation, and they were found to be the major contributors of organohalogens. Only the presence of the photosynthetic pigment 19'-hexanoyloxyfucoxanthin, biomarker pigment of haptophytes, could explain some of the variations in the distribution and production of halocarbons, and then only for iodinated compounds. The flux of organo-halogens from the oceans to the atmosphere was estimated in two ways, either based on calculations according to models or based on the measured concentrations. Large discrepancies were found, which could not be explained by chemical or biological degradation or adsorption to particles. This investigation, therefore, shows the need for assessing the rates of degradation and the air-sea exchange more accurately. (C) 2004 Elsevier Ltd. All rights reserved.