Using a cesium-137 (137Cs) sedimentary fallout record in the South Atlantic Ocean as a supporting tool for defining the Anthropocene

•The 137Cs maximum can work as a stratigraphic marker in the Anthropocene.•1963 can be found with the horizon of maximum 137Cs activity in cores.•The past nuclear fallout is the only source of 137Cs for the South Atlantic.•The modeling of 137Cs behavior estimates its past activity from the fallout.•There is a latitudinal pattern of fallout 137Cs on South Atlantic sediments.

Human civilization is causing many changes to the global environment, such as the widespread presence of coastal cities and air, soil and water pollution. A new stratigraphic term for the current age, the Anthropocene, has been proposed and is differentiated from the Holocene by anthropogenic alterations. This study evaluated the occurrence and distribution of an artificial radionuclide, cesium-137 (137Cs), in coastal sediments of the South Atlantic Ocean through analysis of a large number of sediment cores covering a wide latitudinal band (0°–35°S). The age of this radionuclide’s horizon of maximum activity is validated with unsupported lead-210 (210Pb) dating and its use is directly related to the peak of the past atmospheric fallout from nuclear tests in 1963, showing its radioactive record to be a short- to mid-term chronostratigraphic marker in helping to define the beginning of the Anthropocene. The presence of fallout 137Cs follows a latitudinal pattern with a mid-latitude maximum at approximately 35°S and lower values toward the equator. This result agrees with observations reported in the international literature regarding the deposition of fallout radioactivity.