Over the past two decades radiogenic neodymium isotope compositions have been increasingly used as a proxy of present and past ocean circulation and water mass mixing. This application is based on the quasi conservative behavior of Nd isotopes in the open ocean and on the ability of Nd isotope compositions to fingerprint the contributions of distinct continental source areas. Weathering inputs label the water masses with distinct isotope compositions of the rocks on land in those areas where the waters were last in contact with land. In addition, the precise and accurate measurement of Nd isotopes in waters and sediments is comparably easy given the widely available TIMS or MC-ICPMS instruments, accepted standard values, and internationally intercalibrated techniques, such as in the frame of the international GEOTRACES programme for water samples. The wealth of seawater data that have now become available allows a detailed picture of the present day Nd isotope distribution, to which the sedimentary records can be directly compared.
In my presentation I will discuss successful examples for tracing water mixing but will focus on the pitfalls that may arise from non-conservative behavior of Nd isotopes in the water column of particular areas of the ocean. This will include the effects of particle inputs and dissolution, exchange with reactive margin sediments, as well as contributions from pore waters. Considering these processes there are clearly areas of the ocean where the Nd isotope signatures will not reflect ocean circulation but rather weathering inputs. To avoid such pitfalls it is evident that the Nd isotope method will deliver the most reliable records in areas where water mass exchange is rapid and which are not located close to reactive continental margins and the associated detrital particle fluxes. I will also discuss a recent successful application to reconstruct past ocean circulation.
