Rare earth elements in deep-water articulated brachiopods: An evaluation of seawater mass

• REE distribution coefficients of modern Rhynchonellids and Terebratulids shells
• Open water brachiopods display vertical Ce/Ce* profiles similar to that of seawater.
• HREESN values define a seawater–depth relationship trend.
• REEs in deep-water brachiopods are a robust paleoceanographic proxy.

Modern articulated brachiopods of the orders Rhynchonellids and Terebratulids were obtained from below the neritic zone of the Caribbean Sea, North Atlantic, South Pacific and Southern Oceans to evaluate the proxy potential of their rare earth element (REE) contents. Shells of the two orders display similar REE distribution coefficients that vary consistently within the series in response to changes in ionic radii relative to that of the Ca2 + cation, which, in turn, excludes the possibility of a biological control on their REE incorporation. The calculated log KD values for the brachiopods are similar to those documented in other investigations, and as a consequence, shell calcite is enriched in REE concentrations relative to ambient water masses by an average of 0.81 × 105.Brachiopods from the four areas yielded LREESN and MREESN characteristics of their ambient water mass, exhibiting gradual enrichments with increasing atomic number as well as negative CeSN excursions. Their HREESN values, on the other hand, define a trend that varies with water depth. Overall, the Ce/Ce* profile of open-water deep-sea brachiopods is coupled with that of the ambient seawater. Our study confirms the robustness of REEs in deep-water (> 500 m) articulated brachiopods and supports their use as a proxy of paleo-oceanography, specifically water mass and redox.