Neodymium concentration and isotopic composition distributions in the southwestern Indian Ocean and the Indian sector of the Southern Ocean

Abstract

Neodymium concentration and isotopic composition profiles were determined for two stations in the Crozet Basin in the southwestern Indian Ocean and one station in the Indian sector of the Southern Ocean. The station located in the northern part of the Crozet Basin showed very similar Nd concentrations, SiO2, and dissolved oxygen profiles to those previously reported for the closest station in the Madagascar Basin. However, the station in the northern part of the Crozet Basin and the previously studied station in the Madagascar Basin exhibited clearly different Nd isotopic values at water depths of approximately 400 m, which was attributed to a strong influence of the Agulhas Return Current on the Crozet Basin station and/or a large contribution of the South Equatorial Current to the Madagascar Basin. The Nd isotopic profile at ER-14 in the Indian sector of the Southern Ocean was similar to those of stations in the Atlantic sector of the Southern Ocean at depths above 2000 m. Conversely, variable Nd isotopic compositions were observed in the Indian and Atlantic sectors of the Southern Ocean at depths below 2000 m, suggesting the importance of local Nd to determination of the Nd isotopic composition of deeper depths.The Pb isotopic compositions, which are strongly controlled by anthropogenic Pb, showed different features in vertical profile from Nd isotopic compositions at all stations. The Nd isotopic composition profiles of stations from the Crozet Basin showed a clear peak corresponding to Antarctic Intermediate Water, whereas a clear peak corresponding to Subantarctic Mode Water was observed for Pb isotopic vertical profiles. A combined Nd and Pb isotopic composition study of seawater may clarify the contribution of natural and anthropogenic sources to Pb in the ocean.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.