Effects of Past Nd Seawater Concentrations on Nd-Isotope Paleocirculation Reconstructions: A Bayesian Approach

Abstract

Neodymium (Nd) isotope ratios are potentially valuable for paleo-ocean circulation reconstructions because they trace water-mass transport and mixing in the present-day oceans. Moreover, the Atlantic and Pacific global end-member Nd-isotope values can be constrained through time, and at in-between sites their proportions vary with past climate changes. However, an important source of uncertainty about Nd-isotopes' applicability for paleo-circulation studies arises from the inability to constrain past Nd-concentrations of the end-members. Here we address this “paleo-[Nd] problem” through a Bayesian analysis. Results show that even large variability in end-member Nd-concentrations over the Pleistocene is unlikely to significantly impact their concentration ratio, therefore end-member concentration changes likely have only small impacts on Nd-isotope ratios at in-between locations. The results support their applicability to reconstruct past Atlantic paleo-circulation. In addition, a Nd-isotope mass balance for Antarctic Bottom Water shows that its present-day Nd-isotope values are consistent with the input from its sources.