Russia formally staked its claim Tuesday to a large portion of the Arctic Ocean that includes the North Pole, even planting a flag on the floor of the ocean below the area to exercise its control. If the United Nations committee that arbitrates sea boundaries accepts Russia’s claim, the waters will be subject to Moscow’s oversight on economic matters, including fishing and oil and gas drilling, though Russia will not have full sovereignty. Under a 1982 United Nations convention, the Law of the Sea, a nation may claim an exclusive economic zone over the continental shelf abutting its shores. If...