Nd isotopic composition of water masses and dilution of the Mediterranean outflow along South-West European margin

Kevin Copard (1, 2) , Christophe Colin (1) , Norbert Frank (3) , Catherine Jeandel (4) , Jean-Carlos Montero-Serrano (1, 2) , Gilles Reverdin (5) , Bruno Ferron (6)

1 GEOPS - Géosciences Paris Saclay
2 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
3 GEOTRAC - Géochrononologie Traceurs Archéométrie
4 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
5 SURF - Échanges dans la couche de surface : des pôles aux tropiques
6 LPO - Laboratoire de physique des océans

Nd isotopic compositions (ɛNd) of seawater profiles and deep‐sea corals collected off the coast of Iberia and from the Bay of Biscay were measured (1) to constrain the Nd isotopic composition of water masses along the southwest European margin, (2) to track the Mediterranean Outflow Water (MOW) during its northward propagation, and (3) to establish hydrological changes during the last 1500 years. The Eastern North Atlantic Central Water (ENACW) is characterized by Nd isotopic composition of around −12.0. Mediterranean Sea Water (MSW) is collected from 800 and 1200 m depth and is characterized by ɛNd values ranging from −10.9, off the coast of Iberia, to −11.6 in the Bay of Biscay. These ɛNd results suggest a strong dilution of the pure MOW at the Strait of Gibraltar (ɛNd −9.4) of approximately 40% and 30% along its northward circulation pathway essentially with a contribution from ENACW. At around 2000 m depth, ɛNd water profiles display the occurrence of a nonradiogenic water mass (ɛNd −13), originating from the Labrador Sea (Labrador Sea Water). Fossil deep‐sea corals, dated between 84 and 1500 years, display Nd isotopic compositions that vary moderately from present‐day seawater values, suggesting a weaker influence of MOW in the formation of MSW during the Dark Ages and the Little Ice Age. These recent cold events seem to be associated with a reduction in the northward penetration of MSW, which may result from a greater eastward extension of the middepth subpolar gyre and/or a reduction of MSW formation, likely tied to a variation in deep Mediterranean water production.

Mots clés: European margin; Nd isotopic composition; deep‐sea corals; water masses

Domaines: Sciences de la Terre

Kevin Copard, Christophe Colin, Norbert Frank, Catherine Jeandel, Jean-Carlos Montero-Serrano, et al.. Nd isotopic composition of water masses and dilution of the Mediterranean outflow along South-West European margin. Geochemistry, Geophysics, Geosystems, 2011, 12 (6), pp.Q06020. ⟨10.1029/2011GC003529⟩. ⟨hal-00627329⟩