The geochemistry of rare earth elements (REE) in estuarine and coastal waters, sediments, and pore waters in the main focus of this renewal proposal. The Chesapeake Bay and Amazon River shelf will be the main study areas. Based on the P.I.'s current grant, the flux, cycling and fractionation of REE undergo major biogeochemical perturbations in the estuarine zone. Results from the Cheseapeake Bay show that light REE as being enriched in the dissolved phase during the development of anoxic conditions in the deep basins. In the proposed research, a time-series study in a Chesapeake Bay seasonally anoxic basin (water column and sediments) will be carried out to quantify the extent and kinetics of such fluxes and fractionation. Incubation experiments will also follow the diagenesis of REE. Collaboration with a large multi-disciplinary study ("AmasSeds" project) of the Amazon shelf is also proposed. A seasonal study of the Amazon estuary will focus on the remineralization and removal of REE in the estuarine waters and REE diagenesis in the sediments associated with dynamic cycling of Fe and organic matter. The Amazon River estuary study will provide much needed data on REE for a major river/estuary system.
