Non-Fickian Diffusion Affects the Relation between the Salinity and Hydrate Capacity Profiles in Marine Sediments

On-site measurements of water salinity (which can be directly evaluated from the electrical conductivity) in deep-sea sediments is technically the primary source of indirect information on the capacity of the marine deposits of methane hydrates. We show the relation between the salinity (chlorinity) profile and the hydrate volume in pores to be significantly affected by non-Fickian contributions to the diffusion flux---the thermal diffusion and the gravitational segregation---which have been previously ignored in the literature on the subject and the analysis of surveys data. We provide amended relations and utilize them for an analysis of field measurements for a real hydrate deposit.