Dating of marine sediments and time evolution of heavy metal concentrations in the Bay of Cádiz, Spain.

In this paper the time evolution of heavy metal concentration of Pb, Zn, Cd and Hg, in the sediments of the Bay of Cádiz (southwest of Spain) is studied during the past century, as a result of the industrial influence in the zone. The study has been performed using sedimentary profiles that have been extracted from the seabed. The measurement of 210Pb and 137Cs radionuclides has provided the dating of the sediment layers, up to a depth corresponding to the age of 115 years. The relative sedimentation rates obtained are around 0.2 cm/year. The 137Cs activity profile reflects the concentration of this radionuclide in the atmosphere and into aquatic systems during the second half of the twentieth century. This profile has been used to ratify the results provided by the 210Pb dating method.