High-resolution neodymium characterization along the Mediterranean margins and modelling of εNd distribution in the Mediterranean basins.

An extensive compilation of published neodymium (Nd) concentrations and isotopic compositions (Nd IC) was realized in order to establish a new database and a map (using a high-resolution geological map of the area) of the distribution of these parameters for all the Mediterranean margins. Data were extracted from different kinds of samples: river solid discharge deposited on the shelf, sedimentary material collected on the margin or geological material outcropping above or close to a margin. Additional analyses of surface sediments were done in order to improve this data set in key areas (e.g. Sicilian strait). The Mediterranean margin Nd isotopic signatures vary from non-radiogenic values around the Gulf of Lion, (^εNd values ~-11) to radiogenic values around the Aegean and the Levantine sub-basins up to +6. Using a high-resolution regional oceanic model (1/12° of horizontal-resolution), "Nd distribution was simulated for the first time in the Mediterranean Sea. The high resolution of the model provides a unique opportunity to represent a realistic thermohaline circulation in the basin and thus apprehend the processes governing the Nd isotope distribution in the marine environment. Results are consistent with the preceding conclusions on boundary exchange (BE) as an important process in the Nd oceanic cycle. Nevertheless this approach simulates a too-radiogenic value in the Mediterranean Sea; this bias will likely be corrected once the dust and river inputs will be included in the model. This work highlights that a significant interannual variability of ^εNd distribution in seawater could occur. In particular, important hydrological events such as the Eastern Mediterranean Transient (EMT), associated with deep water formed in the Aegean sub-basin, could induce a shift in ^εNd at deep/intermediate depths that could be noticeable in the eastern part of the basin. This underlines that the temporal and geographical variations of ^εNd could represent an interesting insight of Nd as tracer of the Mediterranean Sea circulation, in particular in the context of palaeo-oceanographic applications. [ABSTRACT FROM AUTHOR]