 Some of the most important discoveries were finding the deep-water Lomonosov Ridge, which crosses the Arctic Ocean, other large features of the ocean bottom's relief, the discovery of two systems of the drift (circular and "wash-out"), the fact of cyclones' active penetration into the Central Arctic.The last Soviet "NP" station, North Pole-31, was closed in July 1991.In the post-Soviet era, Russian exploration of the Arctic by drifting ice stations was suspended for twelve years.