Hypersaline brine or a mixture of hydrocarbons that seeps from the ocean floor in a manner similar to that of a hydrothermal vent, but at about the ambient temperature. Cold seeps are rich in methane and support large and diverse communities sustained by the primary productivity of chemosynthetic bacteria; methane is taken up by the gills of the dominant mussels (Bathymodiolus), and is oxidized by intracellular bacteria to release energy.