The five oceans from smallest to largest are: the Arctic, Southern, Indian, Atlantic and Pacific.
These five "oceans" are connected and are actually one huge body of water, called the global ocean or just the ocean. If you were to add the smaller seas like the Barents, Beaufort, Chukchi, Kara, Laptev, East Siberian, Lincoln, Wandel, Greenland and Norwegian, etc. you would have a total area of the ocean of about 361,000,000 km² (which is ~71% of the Earth's surface), a total volume of roughly 1,370,000,000 km³, and an average depth of 3,790 m. Our hydrosphere (ocean plus all freshwater in ground water, lakes, rivers, snow, ice and the atmosphere) makes up about 0.023% of the total mass of the Earth.
The word “Ocean” comes from Okeanos, the Greek god of the Ocean.
Terrigenous, pelagic, and authigeni materials composes most of ocean sediments. Erosion, weathering and volcanic activity on land washes out to sea and creates the sand, mud, and rock particles that make up terrigenous deposits. Consequently, terrigenous deposits are confined to narrow marginal bands close to land like continental shelves and are deepest near the mouths of large rivers or desert coasts. Pelagic deposits derived from seawater are red clays and the skeletal remains of organisms that have died and sunk to the ocean floor. These include pelagic red clays and globigerina, pteropod and siliceous oozes. Most of the ocean floor is actually covered in these organic remains with a depth ranging anywhere from 60 to 3,300 m deep, but they are thickest in convergence belts and upwelling zones. Authigenic deposits are made up of particles like manganese nodules and include montmorillonite and phillipsite and can be found in places where the sedimentation process occurs very slowly or currents sort out the deposits.
The Arctic Ocean
The Arctic Ocean is divided by an underwater ocean ridge called the Lomonosov ridge into the 4,000-4,500 m deep Eurasian or Nasin basin and the 4,000 m deep North American or Hyperborean basin. The topography of the Arctic Ocean bottom varies consisting of fault-block ridges, abyssal plains, and ocean deeps and basins that have an average depth of 1,038 m due to the continental shelf on the Eurasian side.
The greatest inflow of water to the Arctic Ocean comes from the Atlantic via the Norwegian Current, (which then travels along the Eurasian coast) although water also enters from the Pacific via the Bering Strait. The greatest outflow comes from the East Greenland Current. Ice used to cover most of the Arctic Ocean year round (this is now changing drastically due to global warming). When the ice melts, salinity and subfreezing temperatures vary. The subfreezing temperatures cool the air traveling towards the equator, mixing with warmer air at middle latitudes, resulting in rain and snow. Marine life is thought to be relatively scarce in the cold waters of the Arctic Ocean except in the open, southerly waters. Air traffic is common over the Arctic because it is the shortest route between the Pacific coast of North America and Europe. For boats, major ports are the Russian cities known as Murmansk and Arkhangelsk (Archangel).
The Southern Ocean
The Southern Ocean is the world's fourth-largest body of water. It encircles Antarctica and is actually divided among the Atlantic, Indian, and Pacific Oceans. Most people of North America and Continental Europe have no name for the area and regard the area as parts of the Atlantic, Pacific, and Indian Oceans simply extending to Antarctica. However, because mariners have long referred to this area as the “Southern Ocean” it was accepted as an ocean in 2000 by the International Hydrographic Organization. This ocean is predominantly deep water, averaging 4,000-5,000 m deep, and includes the Antarctic continental shelf, an unusually deep and narrow area with an edge of 400-800m deep (over 270-670 m deeper than average). The lowest point is 7,235 m deep at the southern end of the South Sandwich Trench. There is a seven-fold increase in the size of the Antarctic ice pack between March and September (though this is also changing due toglobal warming), ranging from 2,600,000 km² to 18,800,000 km². The world's largest ocean current, the Antarctic Circumpolar Current (21,000km in length) moves perpetually eastward here and transports 130,000,000 m³ of water per second—100 times the flow of all the world's rivers combined.
Current Environmental Issues
An increase in solar ultraviolet radiation originating from the Antarctic ozone hole is reducing marine primary productivity, or phytoplankton, by as much as 15% and is actually damaging the DNA of some fish.
Unregulated (5-6 times more than the regulated fishery) and unreported illegal fishing of Patagonian toothfishas been occurring, an activity that will have a long-term affect on the sustainability of the remaining stock. This illegal fishing also increases the mortality of seabirds who get caught in the long-lines used for toothfish.
The now-protected seal population is making a strong comeback after its severe overexploitation in the 18th and 19th centuries.
The Indian Ocean
The Indian Ocean is the third-largest in the world and makes up approximately 20% of the Earth's water surface. It is bounded by southern Asia in the north, the Arabian Peninsula and Africa in the west, the Malay Peninsula, Sundra Islands and Australia in the east and the Southern Ocean in the south. The 20° east meridian separates the Indian Ocean from the Atlantic Ocean and the 147° east meridian separates it from the Pacific Ocean. The Indian Ocean stretches to about 30° N latitude in the Persian Gulf at its northernmost extent. At the southern tips of Africa and Australia, it is almost 10,000 km (or 6,200 miles) wide and its area is 73,556,000 km² (or 28,400,000 sq miles) when the Red Sea and the Persian Gulf are included. The volume of this massive body of water has been estimated at 292,131,000 km³ (or 70,086,000 mi³). Other features include small islands around the continental rims such as Madagascar (the world's fourth largest island), Comoros, Seychelles, Maldives, Mauritius, Sri Lanka, and Indonesia. The Indian Ocean is an important transit route between Asia and Africa, a geographical feature that has fueled some strong historical conflicts. Because the Indian Ocean is so enormous, no nation had ruled it until the beginning of the 1800s when Britain was able to dominate much of the surrounding land.