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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), εNd 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.

An interdisciplinary study was conducted to evaluate the relationship between geological and paleontological parameters and the bacterial and archaeal community structure of two contrasted subseafloor sites in the Western Mediterranean Sea (Ligurian Sea and Gulf of Lions). Since both depositional environments were well-documented in this area, large data-sets were available and allowed to calibrate the investigated cores with several reference and dated cores previously collected in the same area, and notably correlated to Quaternary climate variations. Molecular-based fingerprints showed that the Ligurian Sea sediments, characterized by an heterolithic facies with numerous turbidites from a deep-sea levee, were unexpectedly dominated by Betaproteobacteria (more than 70 %), at the base of the core mainly below five meters in the sediment. Analysis of relative betaproteobacterial abundances and turbidites frequency indicated that the microbial diversity was controlled by the important climatic changes occurring during the last 20 ka. This result was supported by statistical direct multivariate canonical correspondence analyses (CCA). In contrast, the Gulf of Lions core, characterized by a homogeneous lithology of upper-slope environment, was dominated by the Bacteroidetes group and in a lesser extent, by the Betaproteobacteria group. At both sites, the dominance of Betaproteobacteria coincided with increased terrestrial inputs, as confirmed by the geochemical measurements (Si, Sr, Ti and Ca). In the Gulf of Lions, geochemical parameters were also found to drive microbial community composition. Taken together, our data suggest that the palaeoenvironmental history of erosion and deposition recorded in the Western-Mediterranean Sea sediments has left its imprint on the structure/composition of the microbial communities during the late Quaternary.