China's manned submersible Shenhai Yongshi (Deep Sea Warrior) carries out a night dive in the South China Sea, May 19, 2018. The submersible Deep Sea Warrior returned to the oceanic research vessel Tansuo-1 on Sunday morning after carrying out a night dive of about 1,400 meters deep in the Haima Cold Seep area in the Pearl River mouth basin in the South China Sea. (Xinhua/Zhang Jiansong)

Staff members of China's manned submersible Shenhai Yongshi (Deep Sea Warrior) prepare to carry out a night dive in the South China Sea, May 19, 2018. The submersible Deep Sea Warrior returned to the oceanic research vessel Tansuo-1 on Sunday morning after carrying out a night dive of about 1,400 meters deep in the Haima Cold Seep area in the Pearl River mouth basin in the South China Sea. (Xinhua/Zhang Jiansong)

Staff members of China's manned submersible Shenhai Yongshi (Deep Sea Warrior) prepare to carry out a night dive in the South China Sea, May 19, 2018. The submersible Deep Sea Warrior returned to the oceanic research vessel Tansuo-1 on Sunday morning after carrying out a night dive of about 1,400 meters deep in the Haima Cold Seep area in the Pearl River mouth basin in the South China Sea. (Xinhua/Zhang Jiansong)

China's manned submersible Shenhai Yongshi (Deep Sea Warrior) prepares to carry out a night dive in the South China Sea, May 19, 2018. The submersible Deep Sea Warrior returned to the oceanic research vessel Tansuo-1 on Sunday morning after carrying out a night dive of about 1,400 meters deep in the Haima Cold Seep area in the Pearl River mouth basin in the South China Sea. (Xinhua/Zhang Jiansong)

China's manned submersible Shenhai Yongshi (Deep Sea Warrior) prepares to carry out a night dive in the South China Sea, May 19, 2018. The submersible Deep Sea Warrior returned to the oceanic research vessel Tansuo-1 on Sunday morning after carrying out a night dive of about 1,400 meters deep in the Haima Cold Seep area in the Pearl River mouth basin in the South China Sea. (Xinhua/Zhang Jiansong)