A cold seep ( sometimes called a cold vent ) is an area of the ocean floor where hydrogen sulfide , methane and other hydrocarbon-rich liquids leak out of the Earth 's crust , often in the form of a brine pool . A cold seep ( sometimes called a cold vent ) is an area of the ocean floor where hydrogen sulfide , methane and other hydrocarbon-rich fluid seepage occurs , often in the form of a brine pool .