Fluorine uptake by Amazon continental shelf sediment and its impact on the global fluorine cycle

Dissolved fluoride concentrations in sediment pore waters are below seawater throughout the Amazon continental shelf sedimentary environment. Calculations of mass fluxes of fluoride between seawater and mud deposits, based on pore water gradients, reaction rate estimates, and selective chemical extraction of sediment, indicate an uptake of 0.2-0.6 × 10 10 moles F y −1. The majority of this uptake is apparently due to alteration of detrital alumino-silicate debris or neoformation of authigenic 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 sinks in the marine environment. If this process occurs in other tropically-derived shelf sediments, then alumino-silicate reactions would represent the most important mechanism of fluoride removal in the sea.