137Cs concentrations in Atlantic and western Antarctic surface waters: results of the 7th Ukrainian Antarctic Expedition, 2002

The latitudinal distribution of 137Cs in the Atlantic–western Antarctic surface waters was studied during the 7th Ukrainian Antarctic Expedition in January–May 2002. The 137Cs concentrations have also been measured in the upper ice of the coastal glacier Woozle Hill located near the Ukrainian Antarctic station “Akademik Vernadsky” (western Antarctica, 65°15′ S–64°16′ W). Comparison of these data with results of previous same-route expeditions SWEDARP (Swedish Antarctic Research Expedition, 1988/1989) and the French R/V “Jeanne dʹArc” (1992/1993), has shown practically parallel changes of 137Cs surface concentrations between 40° N and 20° S, pointing to decrease of 137Cs radioactivity at these latitudes with an apparent half-life of 10–15 years (12.5±2.1 years on average). This suggests that decrease of 137Cs surface concentration within this latitude band is controlled, besides the radioactive decay of 137Cs (half-life=30 years), by vertical mixing of the upper water masses. South of 20° S, the 137Cs concentrations in surface water have decreased more rapidly because of the influence of the less contaminated Antarctic waters. At 50–60° S and near the Antarctic coast, the 137Cs activity in 2002 was similar to those measured during the SWEDARP and “Jeanne dʹArc” expeditions, suggesting an additional input of 137Cs to these waters from the melted ice from the adjacent glaciers.