The potential of anthropogenic 236-Uranium as a new and transient oceanographic tracer demonstrated in the North Atlantic

236-Uranium (236U) is present on Earth due to natural and anthropogenic production. However, the estimated inventory of anthropogenic 236U (106 kg) largely exceeds the natural one (30 kg). Releasing even a tiny fraction of this artificial isotope would drastically change the environmental 236U/238U ratio and therefore make this ratio a useful isotopic marker to trace such anthropogenic releases and to study seawater transport and mixing processes in the ocean.

Casacuberta and her colleagues took this premise to propose the first transect of 236U in the North Atlantic Ocean during the first two legs of the GEOTRACES GA02 cruise. Global fallout and the releases of the European reprocessing nuclear plants La Hague and Sellafield are the main sources of 236U to the ocean. Results of this transect showed that there is a North to South and surface to deep decreasing gradient of 236U/238U atomic ratio when moving from 64ºN to 2ºN mirroring the distribution of waters masses in this region. In particular, highest 236U contents are shown in the Labrador Sea Water and Denmark Strait Overflow Water, tracing the penetration of waters to the North Atlantic Ocean that carry the signal of 236U from the two European reprocessing plants. This pioneer work is proving that 236U can be an efficient water mass transient tracer.

14 Casacuberta
Figure: Distribution of 236U in the North Atlantic Ocean. Click here to view the figure larger.



Casacuberta, N., Christl, M., Lachner, J., Rutgers van der Loeff, M., Masqué, P., & Synal, H. -A. (2014). A first transect of 236U in the North Atlantic Ocean. Geochimica et Cosmochimica Acta, 133, 34–46. doi:10.1016/j.gca.2014.02.012. Click here to access the paper.

Latest highlights

Science Highlights

Thorium-Protactinium fate across the tropical Atlantic Ocean: what reveals the water column-sediment coupling

Twenty seawater profiles and twenty core-top 231-protactinium and 230-thorium analyses were realised by Ng and colleagues along five depth transects across the northern tropical Atlantic open ocean.


Science Highlights

Constraining Oceanic Copper Cycling through Artificial Intelligence and Ocean Circulation Inverse Model

Using available observations of dissolved copper, artificial neural networks, and an ocean circulation inverse model, authors calculated a global estimate of the 3-dimensional distribution and cycling of dissolved copper in the ocean


Science Highlights

Particulate rare earth elements distributions, processes and characterisation of nepheloids in the North Atlantic

Lagarde et al. realised the first basin scale section of particulate rare earth elements concentrations across the North Atlantic Ocean.


Science Highlights

Isopycnal mixing controls protactinium and thorium distributions in the Pacific Southern Ocean

Pavia and co-workers determined the physical and chemical speciation as well as the vertical distribution of Protactinium-231 and Thorium-230 at 12 stations across the Southern Pacific Antarctic Circumpolar Current…