Temporal and spatial trends in the distribution of 137Cs in surface waters of Northern European Seas—a record of 40 years of investigations

The distribution of anthropogenic 137Cs in surface waters of the NE Atlantic Ocean resulting from discharges from European nuclear reprocessing plants, the Chernobyl accident, and global fallout has shown decreasing concentrations in most regions in the past 2 decades, in proportion to the lessening of its release rates from the Sellafield and La Hague reprocessing plants. In contrast, concentrations increased significantly in the Baltic Sea in 1986, as a result of the Chernobyl accident. The average 137Cs concentrations in surface water have been estimated for the year 2000 to be 60±50 Bq m−3 for the Irish Sea, 3±1 for the Celtic Sea, 2.1±1.2 for the English Channel, 4±2 for the North Sea, 50±20 for the Baltic Sea, 2±1 for the Norwegian Sea, 2.4±0.5 for the Barents Sea, and 4±1 Bq m−3 for the Kara Sea. On the basis of time series data, the corresponding effective half-lives of 137Cs in surface water have been estimated to be 4±1 years for the Irish Sea, 2±1 for the Celtic Sea, 1.2±0.5 for the English Channel, 3±1 for the North Sea, 13±2 for the Baltic Sea, 4±1 for the Norwegian Sea, 5±1 for the Barents Sea, and 13±4 years for the Kara Sea. The mean transit times of water masses have been estimated to be 0.5±0.1 year from the Irish Sea to the North Channel, 2±0.2 years to the north of Scotland, 2.5±0.2 to the east coast of England, 3±0.5 to the southern North Sea, 4±0.5 to the central and eastern North Sea, 1.5±0.2 to the Celtic Sea, 2±0.2 to the English Channel, 5±1 to the Baltic Sea, 4.5±0.5 to the Norwegian Sea, 5±1 to the Barents Sea, and 6±1 years to the Kara Sea.