Oceanic phosphorus imbalance: Magnitude of the mid‐ocean ridge flank hydrothermal sink

We present a new estimate for the crustal phosphorous sink that results from reactions among seawater, basalt, and sediment blanketing low temperature mid‐ocean ridge flank hydrothermal systems. New estimates for global hydrothermal power output, sediment thickness, and the dissolved phosphate concentrations in basement formation fluids indicate that fluid flow through ridge flanks removes 2.8 × 10 10 mol P yr −1 . This value is larger (130%) than the riverine dissolved flux of inorganic phosphate and is as much as 35% of the sedimentary P sink. The concordant seawater flux (2.1 × 10 16 kg yr −1 ) is 65% of the riverine fluid flux and circulates a fluid volume equivalent to the entire ocean in about 70,000 yr. Additional sampling of seafloor springs is required to further constrain the range of calculated phosphate fluxes; nevertheless the modern phosphorus budget is clearly unbalanced with total sinks outpacing sources.