A two-dimensional model of the methane cycle in a sedimentary accretionary wedge

A two-dimensional model of sediment column geophysics and geochemistry has been adapted to the problem of an accretionary wedge formation, patterned after the margin of the Juan de Fuca plate as it subducts under the North American plate. Much of the model description is given in a companion paper about the application of the model to an idealized passive margin setting; here we build on that formulation to simulate the impact of the sediment deformation, as it approaches the subduction zone, on the methane cycle. The active margin configuration of the model shares sensitivities with the passive margin configuration, in that sensitivities to organic carbon deposition and respiration kinetics, and to vertical bubble transport and redissolution in the sediment, are stronger than the sensitivity to ocean temperature. The active margin simulation shows a complex sensitivity of hydrate inventory to plate subduction velocity, with results depending strongly on the geothermal heat flux. In low heat-flux conditions, the model produces a larger inventory of hydrate per meter of coastline in the passive margin than active margin configurations. However, the local hydrate concentrations, as pore volume saturation, are higher in the active setting than in the passive, as generally observed in the field.