Temporal variations and probable origins of hydrocarbons in the water column of Bedford Basin, Nova Scotia

Abstract

Hydrocarbons in Bedford Basin seawater were analysed on 33 dates between January 1975 and April 1976 by fluorescence spectroscopy and gas chromatography. Crude oil equivalent concentrations averaged 2.5 and 1.8 μg l −1 at 2 and 50 m, respectively, while total n-alkanes averaged 200 and 180 ng l −1 at the same depths. Crude oil equivalent concentrations were slightly higher than generally found in oceanic regions while total n-alkane concentrations were comparable. Hydrocarbon concentrations tended to be highest in the winter and lowest in the summer. Biosynthesis does not appear to be an important source of hydrocarbons since the concentration of only one hydrocarbon (retention index of 2052 and suspected to be a polyunsaturated olefin reported to be common in marine phytoplankton) increased during the spring phytoplankton bloom. The majority of hydrocarbons appear to be of anthropogenic origin and the increased use of fuel oils in the urban area surrounding Bedford Basin during the colder months can explain the higher winter-time concentrations. If biosynthesis is not an important hydrocarbon source in Bedford Basin, it can be argued that it is also unimportant in the ocean as a whole.