| Project Detail |
Artificial fallout radionuclides from nuclear weapons testing and from nuclear power plant accidents are found ubiquitously in the environment around the world and they provide the privileged marker candidates (“golden spikes”) of the Anthropocene stratigraphic layers (Certini and Scalenghe, 2021). The onset of their emissions coincided with the period of the Great Acceleration after World War II which is characterized by an increase in soil degradation, mostly triggered by land use change (Ferraro et al., 2018; Wang et al., (in press)). Particle-bound radiocaesium and plutonium are widely used to date modern sediment archives and reconstruct soil redistribution rates. However, the fallout chronology is better constrained in the Northern Hemisphere, and much less is known regarding the timing and the spatial distribution of their deposition in the Southern Hemisphere (Foucher et al., 2021a). The Franco-Swiss AVATAR project consortium will therefore fill this knowledge gap through the compilation of all published data available including recently released declassified military archives and adding new measurements to the data base. Our main objectives are to (i) provide the first detailed reference map for land surface in the Southern Hemisphere of both cesium-137 (137Cs) and Plutonium-239 as well as Plutonium-240 (239+240Pu) fallout and the associated uncertainties, (ii) disentangle - through the use of rigorous end-member un-mixing models - fission product signatures of 137Cs and Pu isotopic ratios from different atmospheric nuclear tests conducted near the Equator and in the Southern Hemisphere and (iii) to apply the refined baseline data to reconstruct on-site soil erosion rates, validating soil erosion modelling assessments and dating of environmental archives during the Anthropocene in the Southern Hemisphere with focus on South America. A participative network to update and upgrade a fallout radionuclide database at the global scale will be launched as one major task of the project. While the meta-analysis (WP1) and the participatory network (WP5) will be a global approach, attribution of fission product signatures to specific locations (i.e. the proportion of global fallout due to USSR and USA atmospheric nuclear bomb tests with a peak in 1963 vs. the proportion of fallout due to French nuclear tests conducted between 1966 and 1974 in the South Pacific) will span over the entire Southern Hemisphere including South America, Africa, Australia and Southern Hemisphere Islands (WP3). However, the reconstruction of the baseline map will be focused on South America and the delineation of soil erosion rates during the Anthropocene to two South American catchments to ensure maximum feasibility of the approach (WP4). We will conduct soil and sediment sampling in zones identified as data gaps in the Southern Hemisphere in WP2. Spatial analyses will be conducted to provide the first reference map of radiocaesium and plutonium fallout in South America and to improve sediment core dating through the incorporation of additional time markers related to the late French atmospheric bomb tests in WP3 (1966-1974). The improved fallout distribution knowledge over space and time will be used to reconstruct soil redistribution during the Anthropocene through an innovative combination of conversion and erosion models in two large pilot river basins in South America. Finally, the compiled databases and maps will be shared with a wide community including atmosphere scientists, climatologists, radio-toxicologists, geo- and soil scientists. |
