An underwater load-carrier is disclosed that includes an underwater-balloon detachably attached to a container that is loaded with ballast. The underwater load-carrier is lowered into the water of an ocean and allowed to descend to the ocean bottom and there connected a mining-vehicle. The mining-vehicle loads mined nodules into the container while the container ejects ballast to maintain the container at a specified altitude above the ocean bottom. When nodule loading is complete, nodules and/or ballast is ejected to allow underwater load-carrier to rise to the ocean surface where mined nodules is unloaded from the container.