Submarine groundwater discharge is an important source of REEs to the coastal ocean

Tuesday, 16 December 2014
Karen Haley Johannesson1, Darren Andrew Chevis1, C. Dianne Palmore1, Katherine Telfeyan1, David Burdige2, Jaye Ellen Cable3, Sidney R Hemming4, Troy Rasbury5, S Bradley Moran6, Nancy Prouty7 and Peter W Swarzenski8, (1)Tulane Univ Earth&Environ Sci, New Orleans, LA, United States, (2)Old Dominion University, Dept. of Ocean, Earth and Atmospheric Sciences, Norfolk, VA, United States, (3)University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, (4)Lamont-Doherty Earth Observ, Palisades, NY, United States, (5)Stony Brook University, Stony Brook, NY, United States, (6)University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States, (7)USGS, Pacific Coastal and Marine Science Center, Baltimore, MD, United States, (8)USGS, Pacific Coastal and Marine Science Center, Santa Cruz, CA, United States
Rare earth element (REE) concentrations of submarine groundwater discharge (SGD) were measured in three subterranean estuaries (i.e., Indian River Lagoon, Florida; Pettaquamscutt estuary, Rhode Island; Kona Coast, Hawaii). Using site-specific SGD estimates previously obtained by a variety of techniques (e.g., seepage meters, Ra, and Rn), we estimated SGD-derived fluxes of REEs to the coastal ocean using simple, one-dimensional modeling techniques. Our results indicate that the SGD fluxes of REEs are either of the same magnitude as riverine REE fluxes (Indian River Lagoon; Pettaquamscutt estuary), or far exceed surface runoff sources of REEs to the coastal ocean (Kona Coast). At each site important biogeochemical reactions occurring in the subterranean estuary, such as redox reactions, sediment bioirrigation, mineral dissolution and re-precipitation, and salt-induced mobilization from “nano-colloids”, appear to facilitate release of REEs into solution, which are then advected to the coastal ocean via SGD. Neodymium isotope analysis of SGD and aquifer sediment are consistent with sediment diagenesis and redox transformations of Fe(III) oxides/oxyhydroxides, as well as preferential weathering of REE-bearing minerals like apatite, as being important sources of REEs to coastal seawater. Our investigations demonstrate that geochemical reactions occurring in the studied subterranean estuaries represent a net source of light and middle REEs to coastal seawater, whereas the heavy REEs appear to be sequestered in the subterranean estuary sediment.