Variation of the activity concentrations and fluxes of natural (210Po, 210Pb) and anthropogenic (239,240Pu, 137Cs) radionuclides in the Strait of Gibraltar (Spain)

Abstract The activity concentrations and fluxes of natural ( 210 Pb , 210 Po ) and anthropogenic ( 239,240 Pu , 137 Cs ) radionuclides have been determined in the different water masses crossing the Strait of Gibraltar. New data have been gathered during four multidisciplinary and multinational sampling campaigns, performed between 1997 and 1999 within the framework of the CANIGO-FLUGIST Project. Mean activity concentrations of 210 Po (1.53±0.34 Bq m −3 , n =30) and 210 Pb (1.16±0.50 Bq m −3 , n =31) in the Atlantic water entering the Mediterranean basin are about double those measured in the Mediterranean outflow, namely 0.84±0.34 Bq m −3 ( n =22) for 210 Po and 0.66±0.34 Bq m −3 ( n =22) for 210 Pb . The opposite trend is observed for 239,240 Pu , with average concentrations of 9.9±3.0 mBq m −3 ( n =29) in the incoming Atlantic flow and 22.0±3.0 mBq m −3 ( n =22) in the outpouring Mediterranean water. In the case of 137 Cs , the same concentrations were quantified in the waters moving inwards (2.52±0.28 Bq m −3 , n =27) and outwards (2.14±0.52 Bq m −3 , n =21) from the Mediterranean Sea. On this basis, the Mediterranean basin experiences a net annual input flux of 14 TBq of 210 Pb and 19 TBq of 210 Po , and a net annual loss of 0.34 TBq of 239,240 Pu , while—at present— 137 Cs input and output fluxes appear to be balanced.