The mangrove reactor: Fast clay transformation and potassium sink

Abstract Most known clay mineral reactions are slow. Clay formation by weathering is recognized as faster (hundreds of thousands to few million years) than clay reverse weathering (few to tens My), even if the latter takes place in deep diagenetic conditions at temperatures above 100 °C. Identifying hot spots of fast clay retrograde reactions acting as effective potassium sinks would contribute to eliminating the present imbalance of the potassium budget towards release into the oceans. We have identified and modeled the reaction kaolinite + Fe + cations → Fe - illite occurring in Brazilian mangroves, which takes place through kaolinite-smectite and illite-smectite intermediates. The reaction is very fast, transforming 72–154 g m − 2 y − 1 of kaolinite into Fe-illite, or 16–38% of the newly sedimented kaolinite each year. This kaolinite-to-illite transformation is 10s–100s times faster than kaolinite formation by weathering. Extrapolation of the calculated potassium consumption to mangrove forests worldwide produces 0.6–3 × 10 12 g y − 1 , or 1–6% of the yearly potassium riverine input into the oceans.