The Arctic Ocean is the smallest of the world's oceans, located around the North Pole. Approximately half of it is frozen over year-round, while the rest freezes in the winter for several months. Countries with Arctic coastline, in order of length, are Russia, Canada, Denmark, Norway and the United States. Though historically the ocean has not seen much ship traffic, global climate change has allowed parts of it to stay navigable for a significant part of the year. This has finally allowed ships to access the Northwest Passage between Europe and Asia, and shipping traffic is set to further increase. In addition, areas of the ocean and its surrounding coast have been found to contain reserves of oil and natural gas, which has led to various seabed claim disputes. The prospect of mineral wealth has led the five Arctic Ocean nations to compete for claims outside their Exclusive Economic Zones, which must be approved by the United Nations per the United Nations Convention on the Law of the Sea.