Under 1980 DSMHRA Act, US citizens and corporations are fee to mine deep seabed regardless of whether US is party to UNCLOS

Indeed, this was the U.S. position prior to UNCLOS III. Years earlier, Congress made clear the U.S. position on the legality of deep seabed mining in the Deep Seabed Hard Mineral Resources Act of 1980 (DSHMRA):

[I]t is the legal opinion of the United States that exploration for and commercial recovery of hard mineral resources of the deep seabed are freedoms of the high seas subject to a duty of reason- able regard to the interests of other states in their exercise of those and other freedoms recognized by general principles of international law.¹⁰

The U.S. position set forth in 1980 in DSHMRA and again in 1983 at UNCLOS III remains the same today. According to the Restatement of the Law, Third, of the Foreign Relations Law of the United States, U.S. citizens and corporations may engage in seabed mining regardless of whether the U.S. accedes to UNCLOS, provided that they conduct such mining without claiming sovereignty over any part of the seabed and as long as the mining activities are exercised with due regard to the rights of other nations engaged in mining.¹¹ As related by the Restatement, “like the fish of the high seas the minerals of the deep sea-bed are open to anyone to take.”¹²