Oceania is the collective name for a vast cluster of islands and atolls in the central and western Pacific Ocean. The boundaries of Oceania are conditional. The western border is considered to be the island of New Guinea, the eastern - Easter Island. As a rule, Oceania does not include Australia, as well as the islands and archipelagos of Southeast Asia, the Far East and North America. In the section of geography, country studies, Oceania is studied by an independent discipline - oceanics.

The term "Oceania" was first used by geographer Conrad Malt-Brune.

Oceania is the world's largest cluster of islands located in the southwestern and central Pacific Ocean, between the subtropical latitudes of the Northern and temperate Southern Hemispheres. When dividing the entire land mass into parts of the world, Oceania usually unites with Australia into a single part of the world Australia and Oceania, although it is sometimes separated into an independent part of the world.

Geographically, Oceania is divided into several regions: Micronesia (in the northwest), Melanesia (in the west), and Polynesia (in the east); New Zealand is considered separately.

The total area of the islands of Oceania, the largest of which is New Guinea, is 1.26 million km², the population is about 15 million people. (2013). Oceania in terms of total area and total population is comparable to the African state of Chad.

The islands of Oceania are washed by numerous seas of the Pacific (Coral Sea, Tasman Sea, Fiji Sea, Coro Sea, Solomon Sea, New Guinea Sea, Philippine Sea) and Indian Oceans (Arafura Sea).

The equator and the international date change line pass through Oceania. It is broken, most of which runs along the 180° meridian.

Sea currents
Through the whole of Oceania, along the equator, there are warm North Trade Wind and South Trade Wind Currents and Inter-Trade Winds. In the southwestern part of Oceania, the warm East Australian Current passes. Characteristic of Oceania is the absence of cold sea currents (with the exception of the Pacific Ocean zone southeast of New Zealand), which largely determines the climate of this region.

Islands and atolls
  
Mount Jaya in Western New Guinea (Indonesia) – the highest point of Oceania
Oceania is not a continent: only New Caledonia, New Zealand, New Guinea and Tasmania are of continental origin, formed on the site of the hypothetical continent of Gondwana. In the past, these islands were a single land, but as a result of the rise in the level of the World Ocean, a significant part of the surface was under water. The relief of these islands is mountainous and strongly dissected. For example, the highest mountains of Oceania, including Mount Jaya (5029 m), are located on the island of New Guinea.

Most of the islands of Oceania are of volcanic origin: some of them are the peaks of large underwater volcanoes, some of which still show high volcanic activity (for example, the Hawaiian Islands).

Other islands are of coral origin, being atolls that were formed as a result of the formation of coral structures around submerged volcanoes (for example, the Gilbert Islands, Tuamotu). A distinctive feature of such islands are large lagoons, which are surrounded by numerous islets, or motu, the average height of which does not exceed three meters. In Oceania, there is an atoll with the largest lagoon in the world - Kwajalein in the archipelago of the Marshall Islands. Although its land area is only 16.32 km² (or 6.3 sq mi), the lagoon has an area of 2174 km² (or 839.3 sq mi). The largest atoll by land area is Christmas Island (or Kiritimati) in the Line Archipelago (or central Polynesian Sporades) – 322 km². However, among the atolls there is also a special type - a raised (or raised) atoll, which is a limestone plateau up to 50-60 m above sea level. This type of island has no lagoon or traces of its past existence. Examples of such atolls are Nauru, Niue, Banaba.

The relief and geological structure of the bottom of the Pacific Ocean in the Oceania region has a complex structure. From the Alaska Peninsula (part of North America) to New Zealand, there are a large number of basins of marginal seas, deep-sea oceanic trenches (Tonga, Kermadec, Bougainville), which form a geosynclinal belt characterized by active volcanism, seismicity and contrasting relief.

On most islands of Oceania, minerals are absent, only on the largest of them are mined: nickel (New Caledonia), oil and gas (the island of New Guinea, New Zealand), copper (Bougainville Island in Papua New Guinea), gold (New Guinea, Fiji), phosphates (on most islands deposits are almost or already produced, for example, in Nauru, on the islands of Banaba, Makatea). In the past, many islands in the region have been actively mined for guano, a decomposed litter of seabirds that has been used as nitrogen and phosphorus fertilizer. On the ocean floor of the exclusive economic zone of a number of countries there are large accumulations of iron-manganese nodules, as well as cobalt, but at the moment no development is being conducted due to economic inexpediency.

Oceania is located within several climatic zones: equatorial, subequatorial, tropical, subtropical, temperate. Most of the islands are dominated by a tropical climate. Subequatorial climate prevails on the islands near Australia and Asia, as well as east of the 180th meridian in the equator zone, equatorial - to the west of the 180th meridian, subtropical - to the north and south of the tropics, temperate - in most of the South Island in New Zealand.

The climate of the islands of Oceania is determined mainly by the trade winds, so most of them receive heavy rainfall. The average annual rainfall varies from 1500 to 4000 mm, although on some islands (in particular, due to the features of the relief and on the leeward side) the climate may be more arid or more humid. Oceania is home to one of the wettest places on the planet: on the eastern slope of Mount Waialeale on the island of Kauai, up to 11,430 mm of precipitation falls annually (the absolute maximum was reached in 1982: then 16,916 mm fell). Near the tropics, the average temperature is about 23 ° C, at the equator - 27 ° C, with a slight difference between the hottest and coldest months.

The climate of the islands of Oceania is also greatly influenced by such anomalies as the El Niño and La Niña currents. During El Niño, the intertropical zone of convergence moves north towards the equator, at La Niña - to the south away from the equator. In the latter case, there is a severe drought on the islands, in the first - heavy rains.

Most of the islands of Oceania are subject to the detrimental effects of natural disasters: volcanic eruptions (Hawaiian Islands, New Hebrides), earthquakes, tsunamis, cyclones, accompanied by typhoons and heavy rains, droughts. Many of them lead to significant material and human losses. For example, the tsunami in Papua New Guinea in July 1999 killed 2200 people.

On the South Island in New Zealand and on the island of New Guinea, there are glaciers high in the mountains, but due to the process of global warming, there is a gradual reduction in their area.

Due to the different climatic conditions, the soils of Oceania are very diverse. The soils of the atolls are highly alkaline, of coral origin, very poor. They are usually porous, which is why they retain moisture very poorly, and also contain very few organic and mineral substances with the exception of calcium, sodium and magnesium. The soils of volcanic islands are usually of volcanic origin and are characterized by high fertility. On large mountainous islands there are red-yellow, mountain lateritic, mountain-meadow, yellow-brown soils, yellow-earths, red earths.

There are major rivers only on the South and North Islands of New Zealand, as well as on the island of New Guinea, on which the largest rivers of Oceania, Sepik (1126 km) and Fly (1050 km) are located. The largest river in New Zealand is the Waikato (425 km). Rivers are predominantly rain-fed, although in New Zealand and New Guinea rivers are also fed by water from melting glaciers and snow. On the atolls, rivers are completely absent due to the high porosity of the soil. Instead, rainwater seeping through the soil forms a lens of slightly brackish water, which can be reached by digging a well. On larger islands (usually of volcanic origin), there are small streams of water that flow towards the ocean.

The largest number of lakes, including thermal ones, is located in New Zealand, where there are also geysers. On other islands of Oceania, lakes are a rarity.

Oceania is part of the Paleotropical vegetation region, with three subregions distinguished: Melanesian-Micronesian, Hawaiian and New Zealand.[4] Among the most widespread plants of Oceania are coconut palm and breadfruit, which play an important role in the lives of local residents: fruits are used for food, wood is a source of heat, a building material, from the oily endosperm of coconut palm nuts produce copra, which forms the basis of exports of the countries of this region. A large number of epiphytes (ferns, orchids) also grow on the islands. The largest number of endemics (both representatives of flora and fauna) is recorded in New Zealand and the Hawaiian Islands, while from west to east there is a decrease in the number of species, genera and families of plants.

The fauna of Oceania belongs to the Polynesian faunal region with a subregion of the Hawaiian Islands. The fauna of New Zealand is allocated to an independent region, New Guinea - to the Papuan subregion of the Australian region. The greatest diversity is distinguished by New Zealand and New Guinea. On the small islands of Oceania, primarily atolls, mammals are almost not found: on many of them only a small rat lives. But the local avifauna is very rich. On most of the atolls there are bird bazaars, where seabirds nest. Of the representatives of the fauna of New Zealand, the most famous are kiwi birds, which have become the national symbol of the country. Other endemics of the country are kea (Latin Nestor notabilis, or Nestor), kakapo (Latin Strigops habroptilus, or owl parrot), takahe (Latin: Notoronis hochstelteri, or wingless sultanka). All the islands of Oceania are home to a large number of lizards, snakes and insects.

During the European colonization of the islands, many of them were introduced alien species of plants and animals, which negatively affected the local flora and fauna.

On the territory of the region there is a large number of protected areas, many of which occupy significant areas. For example, the Phoenix Islands in the Republic of Kiribati have been the world's largest marine reserve since January 28, 2008 (with an area of 410,500 km²).