Seasonal variations of biogenic and anthropogenic halocarbons in seawater from a coastal site

Abstract

Volatile halocarbons were measured weekly throughout 13 months in seawater sampled at a station on the western coast of Sweden. Samples were taken in a macroalgal belt among the submerged thalli of the dominating brown seaweed Fucus vesiculosus and compared to those taken from a nearby jetty that extended into a shallow bay and allowed water sampling at a total depth of 3.5 m. With regard to their seasonality, at least three different groups of halocarbons could be distinguished and suggested different sources. The polybrominated substances CHBr3, CH2Br2, and CHBr2Cl showed summer maxima and winter minima, and the concentrations were generally higher in the algal belt, indicating their macroalgal origin. CH2I2 and CH2ClI showed distinct concentration maxima in spring and fall that were similar in the algal belt and at the jetty. These substances are most likely produced by planktonic organisms. Finally, airborne contaminants such as CCl4 occurred at higher concentrations in winter and decreased with increasing water temperature in summer.