RARE-EARTH ELEMENT COMPOSITION OF PRECIPITATION, PRECIPITATION PARTICLES, AND AEROSOLS

We report the rare earth element (REE) composition of aerosols and precipitation (dissolved and particle phases) from Bermuda, Lewes (Delaware), and Woods Hole (Massachusetts). There is large-scale fractionation of REEs between the continents, atmosphere, and the oceans. The REE compositions of atmospheric samples are highly fractionated relative to (1) each other (e.g., aerosol/precipitation pairs), (2) the upper crust of the Earth, and (3) seawater. Precipitation samples exhibit markedly convex-up shale-normalized patterns, large negative Eu anomalies and large and systematic depletions in the heavy REE (Lu > Yb > Er > Dy). Aerosols are strongly depleted in the heavy REE which dissolutions experiments show are attributable to the presence of HREE-enriched refractory minerals. We argue that in situ selective dissolution of mineral aerosol panicles is responsible for the unusual REE composition of precipitation. This has major implications for the interpretation of the biogeochemical cycles of REEs in the oceans, particularly the partitioning between solution and particle phases, residence times, and the composition of seawater.