Mathematical modeling of diffuse flow in seafloor hydrothermal systems: The potential extent of the subsurface biosphere at mid-ocean ridges

•We model diffuse flow at mid-ocean ridges using a variety of approaches.•The models provide useful estimates the potential depth of the subsurface biosphere.•Estimates range from centimeters to hundreds of meters depending on flow regime.•Model results allow quantification of methane flux at the EPR 9°50′N.