Rare earth element concentrations and Nd isotopes in the Southeast Pacific Ocean

Three vertical profiles of rare earth element concentrations and Nd isotopic compositions have been measured in the remote southeast Pacific Ocean. The three stations represent contrasting environments: the oligotrophic center of the gyre (station GYR), the "transition zone" east of the South Tropical Front (station EGY), and the Peru-Chile upwelling marked by a pronounced oxygen minimum (station UPX). Rare earth concentrations display nutrient like vertical profiles except at UPX where surface waters are enriched. At this station Nd isotopic compositions are clearly more radiogenic than in the open ocean, suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic Andes. Unexpected radiogenic values (epsilon(Nd) reaching -3.7) are also observed at 2000 m at station GYR in the Upper Circumpolar Deep Water that commonly have epsilon(Nd) values around -6. Exchange processes related to hydrothermal activity are suspected to produce this increase in epsilon(Nd) in the vicinity of the East Pacific Rise. These results provide some guidance for higher resolution studies planned in this region by the international GEOTRACES program.