Fluid seepage velocities through marine sediments constrained by a global compilation of interstitial water SO42-, Mg2+, and Ca2+ profiles

The depth dependence of the SO42-, Mg2+, and Ca2+ contents of interstitial waters extracted from sediments in 140 Deep Sea Drilling Project/Ocean Drilling Program/Integrated Ocean Drilling Program drill holes on oceanic crust has been fit using a model of transport (advection and diffusion) and reaction. These drill holes come from a range of crustal ages, sediment types, sediment thicknesses, and sediment accumulation rates. The best fitting specific discharge through the sediment at these locations is estimated to be generally <500mMyr(-1) (0.05cmyr(-1)), where sediments are thicker than 100m, although an order of magnitude faster seepage is estimated for some locations with sediment tens of meters thick. Assuming that the drill holes are globally representative, then seepage of fluids through marine sediments at specific discharges of a few hundred mMyr(-1) is estimated to be only a few percent of the total ridge flank hydrothermal fluid flux. This is consistent with the previous suggestion that hydrothermal fluid exchange between the ocean and the crustal aquifer primarily occurs through basement outcrops. Chemical fluxes of SO42-, Mg2+, and Ca2+ across the sediment-water interface globally (excluding continental margins) are estimated to be less than 10% of the riverine input to the ocean.