1. China University of Petroleum, Qingdao, China and Qingdao National Laboratory for Marine Science and Technology, Laboratory for Marine Mineral Resources, Qingdao, China.
2. China National Offshore Oil Corporation, Tianjin, China.
3. China University of Petroleum, Qingdao, China and Qingdao National Laboratory for Marine Science and Technology, Laboratory for Marine Mineral Resources, Qingdao, China. (corresponding author)