Arctic Circle level, although in mountainous regions there is often no direct view of the true horizon. Only four million people live north of the Arctic Circle due to the severe climate; nonetheless, some areas have been settled for thousands of years by indigenous peoples, who today make up 10% of the region's population. Tens of thousands of years ago, waves of people migrated from eastern Siberia across the Bering Strait into North America to settle. The largest communities north of the Arctic Circle are situated in Russia, Norway and Sweden: Murmansk (population 307,257), Norilsk (175,365), Tromsø (71,295), Vorkuta (59,231) and Kiruna
Arctic Ocean () on Svalbard, a Norwegian archipelago, next to Fram Strait. In Russia, major ports sorted by the different sea areas are: The ocean's Arctic shelf comprises a number of continental shelves, including the Canadian Arctic shelf, underlying the Canadian Arctic Archipelago, and the Russian continental shelf, which is sometimes simply called the "Arctic Shelf" because it is greater in extent. The Russian continental shelf consists of three separate, smaller shelves, the Barents Shelf, Chukchi Sea Shelf and Siberian Shelf. Of these three, the Siberian Shelf is the largest such shelf in the world. The Siberian Shelf holds large oil and