| environ. | deep sea mining The most valuable of the marine mineral resources is petroleum. About 15% of the world's oil is produced offshore, and extraction capabilities are advancing. One of the largest environmental impacts of deep sea mining are discharged sediment plumes which disperse with ocean currents and thus may negatively influence the marine ecosystem. Coal deposits known as extensions of land deposits , are mined under the sea floor in Japan and England | Tiefseebergbau |