Natural and artificial radionuclides in a marine core. First results of 236U in North Atlantic Ocean sediments

Publication date: Available online 20 October 2017
Source:Journal of Environmental Radioactivity
Author(s): M. Villa-Alfageme, E. Chamizo, F.J. Santos-Arévalo, J.M. López-Gutierrez, I. Gómez-Martínez, S. Hurtado-Bermúdez
There are very few data available of ²³⁶U in marine sediment cores. In this study we present the results from the first oceanic depth profile of ²³⁶U in a sediment core sampled in the North Atlantic Ocean, at the PAP site (4500 m depth, Porcupine Abyssal Plain (PAP) site, 49°0′ N, 16°30′ W). Additionally, the sediment core was radiologically characterized through the measurement of anthropogenic ¹³⁷Cs, ²³⁹Pu, ²⁴⁰Pu, ¹²⁹I and ¹⁴C and natural ²¹⁰Pb, ⁴⁰K and ²²⁶Ra.The measured ²³⁶U concentrations decrease from about 90·10⁶ at g⁻¹ at the seafloor down to 0.5·10⁶ at g⁻¹ at 6 cm depth. They are several orders of magnitude lower than the reported values for soils from the Northern Hemisphere solely influenced by global fallout (i.e. from 2700·10⁶ to 7500·10⁶ at g⁻¹). ²³⁶U/²³⁸U atom ratios measured are at least three orders of magnitude above the estimated level for the naturally occurring dissolved uranium. The obtained inventories are 1·10¹² at m⁻² for ²³⁶U, 80 Bq m⁻² for ¹³⁷Cs, 45 Bq m⁻² for ^239+240Pu and 2.6·10¹² at m⁻² for ¹²⁹I. Atomic ratios for ²³⁶U/²³⁹Pu, ¹³⁷Cs/²³⁶U and ¹²⁹I/²³⁶U, obtained from the inventories are 0.036, 0.11 and 2.5 respectively. Concentration profiles show mobilization probably due to bioturbation from the abundant detritivore holothurian species living at the PAP site sea-floor. The range of ²³⁶U, ¹³⁷Cs, ^239+240Pu and ¹²⁹I values, inventories and ratios of these anthropogenic radionuclides are more similar to the values due to fall-out than values from a contribution from the Nuclear Fuel Reprocessing Plants dispersed to the south-west of the North Atlantic Ocean. However, signs of an additional source are detected and might be associated to the nuclear wastes dumped on the Eastern North Atlantic Ocean.



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