The Baltic Sea is a unique sea area. Even though the Danish straits connect it to the Atlantic Ocean, its salinity is very low (only about one fifth of the salinity of the oceans). The Baltic Sea is also shallow. Its average depth is about 54 metres, whereas the average depth of oceans can be several kilometres.
Because of its northern location, the Baltic Sea freezes during the winter, at least partially. This has a substantial impact on maritime nature and transportation.
The size of the Arctic sea areas is determined on the basis of the ice cover in winter. The Northern Polar Region is an ocean surrounded by land areas. About 40 per cent of it is land and 60 per cent ocean. The Arctic areas covered by sea and ice are important habitats for a large number of species.
Climate change has a major impact on the Arctic region: during the past fifty years temperatures in the region have risen twice as fast as the average Earth's temperature and the area covered by ice has become smaller. As the ice melts, economic activities and traffic in the Arctic sea areas increases, which will bring new challenges.
Oceans cover about 71 per cent of the Earth's surface and contain 97 per cent of the Earth's water resources. However, only about five per cent of the oceans have been explored.
Ocean currents balance Earth's temperatures between the Equator and Polar Regions and they are an important factor influencing the Earth's climate. This means that the oceans are also an important factor in the Earth's energy, water and carbon cycle.
About half of all forms of life on the Earth are directly dependent on oceans. Oceans are a source of food, medicines and minerals and oceans also provide transport routes for goods and people.
Oceans are explored with the help of advanced technology, which includes satellites and underwater research equipment.