Abstract

To improve the knowledge about the 137Cs spatial distribution and vertical migration in soils of the Southern Hemisphere, the total areal activity density and the vertical transport parameters of this radionuclide were measured in an Antarctic region. For this purpose vegetation and incremental soil samples were collected at 21 representative sites located at 4 islands of the South Shetland Archipelago: King George, Robert, Greenwich and Snow (62-63°S and 58-62°W). The total 137Cs activity density varied considerably from 118 to 662 Bq m-2 (median 384 Bq m -2, reference date 1995), with a high percentage of the total activity retained in the vegetation cover (5-98% in moss, 3-20% in lichen and 4-12% in grass). At most sites, the maximum activity density in soil was observed in the top layer from where it decreased continuously. To evaluate the transport parameters of 137Cs from the activity-depth profiles, the classical convection-diffusion model was used based on the time-course of the annual deposition density of 137Cs at the studied region. The values for the diffusion coefficient Ds (median 0.043 cm2 year-1) and the convection velocity vs (median -0.012 cm year-1) of radiocesium observed under a polar climate are small compared to the transport parameters determined in temperate zones. The data also indicate that at these sites the convectional transport of 137Cs is almost negligible compared to the transport by diffusion. The high vulnerability of the Antarctic soils to 137Cs deposition, as a consequence of its very slow transport due to the extreme climatic conditions at these latitudes, has been confirmed.