Rapid clay mineral formation in Amazon delta sediments: Reverse weathering and oceanic elemental cycles

Formation of aluminosilicate minerals in marine sediments was proposed over 30 years ago as a potentially important control on the chemistry of the oceans. Until now, this reverse weathering process has been largely discounted because of insufficient direct evidence for its existence. Experiments with unaltered, anoxic, Amazon delta sediments showed that substantial quantities of K-Fe-Mg clay minerals precipitated on naturally occurring solid substrates over times of ∼12 to 36 months at ∼28°C. A range of pore-water, solute-flux, and solid-phase criteria indicates that comparable clay mineral precipitation processes occur throughout Amazon shelf sediments, contributing ≳3 percent of the weight of the deposits and consuming ∼10 percent of the global riverine K⁺ flux.