FLUORINE UPTAKE BY AMAZON CONTINENTAL-SHELF SEDIMENT AND ITS IMPACT ON THE GLOBAL FLUORINE CYCLE

Dissolved fluoride concentrations in sediment pore waters are below se awater throughout the Amazon continental shelf sedimentary environment . Calculations of mass fluxes of fluoride between seawater and mud dep osits, based on pore water gradients, reaction rate estimates, and sel ective chemical extraction of sediment, indicate an uptake of 0.2-0.6 x 10(10) moles F y(-1). The majority of this uptake is apparently due to alteration of detrital alumino-silicate debris or neoformation of a uthigenic alumino-silicate minerals within the sediment itself. Uptake of fluoride during diagenesis of Amazon River sediment on the Amazon continental shelf equals approximately 7% of the previously defined si nks in the marine environment. If this process occurs in other tropica lly-derived shelf sediments, then alumino-silicate reactions would rep resent the most important mechanism of fluoride removal in the sea.