A model of methane concentration profiles in the open ocean

Methane-bearing particulate matter formed in the upper ocean layer is allowed to settle and degrade, releasing methane into the water column as a source in one-dimensional advection-diffusion equations. Predicted carbon and methane particulate fluxes are in good agreement with sediment trap data, using parameters of expected magnitude and particulate methane production well within the mixed layer. This suggests a rapid pathway to the atmosphere and reduced effects on methane concentrations below. Vertical advection rates yielding a good fit between methane concentration calculations and data are larger than expected unless methane oxidation is included. This confirms the significance of methane oxidation in shaping open-ocean methane concentration profiles in spite of turnover times of decades. Predictions of the isotopic composition of dissolved methane δ13 C with the one-dimensional model are more difficult, although trends in measured vertical profiles can be reproduced. While this work does not shed light on the purported mechanism of methane generation in the upper ocean, it shows that methane of particulate origin is sufficient to explain observed open-ocean methane concentrations