Water masses traced by neodymium isotopic compositions at an unprecedented level in the North Atlantic Ocean
As part of the Dutch GEOTRACES GA02 section, Myriam Lambelet analysed neodymium (Nd) isotopic compositions and concentrations at 12 profiles in the North West Atlantic Ocean, extending from the south of Iceland down to the Sargasso Sea.
The detailed discussion, allowed by the good quality of Lambelet’s data, reveals many new features, among them 3 are selected:
1) εNd values of the surface waters provide insight into the unradiogenic continental Nd inputs from Greenland and North America while the subtropical gyre is influenced by dust input from Africa (see figure, upper panel).
2) Exported NADW can be separated into upper- and lower-NADW, based on their distinct Nd isotopic compositions, which was never demonstrated before (see figure, lower panel).
3) Comparing dissolved seawater Nd concentrations and isotopic compositions confirms that the two parameters are decoupled, one of the most striking feature being that in the middle of the water column (1000–3000 m), strong lateral advection dominates the cycling of Nd in the western North Atlantic Ocean.
As a whole, their data support the idea that Nd isotopes can serve as an excellent water mass tracer, if sampled in areas away from oceanic margin, and particularly in areas of strong advection (i.e. deep western boundary current).
Figure: Upper panel: neodymium (Nd) isotopic composition for the surface North Atlantic Ocean (dots with black rim = this study). The coloured outlines of the coastlines represent the approximate Nd isotopic signature of the continents (purple = old; red = young). Lower panel: section of Nd isotopic composition for the western North Atlantic Ocean. The black lines are CFC concentrations (= water mass tracer). Click here to view the figure larger.
Reference:
Lambelet, M., van de Flierdt, T., Crocket, K., Rehkämper, M., Kreissig, K., Coles, B., Rijkenberg, M.J.A., Gerringa, L.J.A., de Baar, H.J.W., Steinfeldt, R. (2016). Neodymium isotopic composition and concentration in the western North Atlantic Ocean: results from the GEOTRACES GA02 section. Geochimica et Cosmochimica Acta, 177, 1–29. doi:10.1016/j.gca.2015.12.019