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$\varepsilon_{Nd}$ (i. e. the relative deviation of $\frac{^{143}Nd}{^{144}Nd}$ from a standard) is often used as a proxy in paleoceanography to identify the basin of origin of oceanic currents.

But what is the model behind this idea? Is this proxy purely empiric?
Why would the Neodymium isotopic ratio vary among basins and why would this variation be stable in (geological) time?

plannapus
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A part answer to your question.

According to the article Palaeoceanography: The briny deep (Martin, 2008), explains the reason for the use of the neodymium ratio as being

The isotopic signature of a water mass is imparted from weathering of continental material in the region where the water mass sinks below the surface. Radiogenic Nd isotope values reflect a contribution from relatively young volcanic material, whereas non-radiogenic values are a consequence of inputs from old continental crust. The water mass carries its distinctive signature as it circulates through the oceans.

Its stability is described in the paper Temporal stability of the neodymium isotope signature of the Holocene to glacial North Atlantic (de Flierdt et al. 2006), as being due to the observations that Nd isotopes

are not thought to be altered in any significant way by biological processes, and thus can serve as a quasi-conservative water mass tracer.

  • Ok, that explains indeed the main idea behind the isotope. But then it's only "stable through time" as long as the source of continental weathering doesn't change. Anyway: thanks for the answer, a good base to start reading from! – plannapus Sep 30 '14 at 06:25
  • @plannapus you're welcome, this is just a part answer - a starting point - but that point you made could probably be an intriguing question in itself. –  Sep 30 '14 at 06:27