Oceans

The earth’s oceans have been a mystery for many centuries. Combined, they cover 71% of the planet’s surface or an area of some 361 million square kilometers. Nearly half of the world’s marine (oceanic) waters are over 3,000 meters (9,800 feet) deep.

All of our planet’s oceans are connected to one another but retain their individual activities and behavior. Because of their connection, they are often referred to as the ‘world ocean’ or ‘global ocean’, the same water is circulated throughout them all.

The various oceans around the world are divided up by their continents and archipelagos.

The major oceans are (in descending order of size) the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean (in the Spring of 2000, the International Hydrographic Organization delimited this new ocean, the Southern Ocean – it surrounds Antarctica and extends to 60 degrees latitude) and the Arctic Ocean (which is sometimes considered a sea of the Atlantic).

Smaller regions of the oceans are called seas, gulfs, bays and other names. These smaller seas are not directly connected to the world’s oceans, but exist between connected countries throughout the world and connect only to the large oceans by small inlets and outlets such as channels, canals, and estuaries. Some have no tides and some are very condensed with salt that they sometimes resemble lakes such as the Mediterranean Sea and the Dead Sea.

The largest seas are the South China Sea, the Caribbean Sea, and the Mediterranean Sea.

Beneath the world’s oceans lie rugged mountains, active volcanoes and bottomless trenches, around bays there are shallower waters which lap sloping areas called ‘continental shelves’. The deepest part of the ocean is called the ‘Abyss’. The Abyss contains plains, long mountains ranges called ‘ocean ridges’, isolated mountains called ‘seamounts’, and ocean trenches which are the deepest parts of the oceans.

Take a dive into the depths of our planet’s amazing but mysterious oceans and seas using the menu on the left.

The Oceans

From the beginning of mankind, the world’s oceans have been an inspiration to many. There tranquility and beauty to their fierce majesty have inspired artists, dancers and the like. They have drawn many a sea explorer into their vastness who delight at the mystery and the unknown secrets of the deep waters and above. The more that is discovered about the oceans and their inhabitants, the more there possible is to discover.

The five oceans combined cover seventy-one percent of the Earth’s surface. The water they contain is ninety-seven percent of the total water on earth. Each of the oceans makes a contribution to the entire global system. Some of these contributions can be wholly unique, based upon the currents, and the position on the globe.

The massive, deep oceans that cover most of the surface of our planet serve many functions. They affect our weather and temperatures as well as being abundant with many forms of sea life, many used as food forms. The moderate the Earth’s temperature by absorbing incoming solar radiation (stored as heat energy). The continuously moving currents of the oceans distribute this heat energy around the globe. This heats up the land and air during winter and cools it during summertime.

Below is a map of the five major oceans on the planet:

The major oceans divide up the earth’s continents. There are five major oceans on our planet, the largest being the Pacific Ocean. Both the Pacific Ocean and the Atlantic Ocean are broken into Northern and Southern hemispheres:

  • North Atlantic divides North America, Europe (including the UK) and North Africa.
  • South Atlantic divides: South America, South Africa, and Antarctica
  • The Indian Ocean falls on the shores of East South Africa, South Asia (India) and West Australia.
  • The North Pacific divides North America, the Arctic, and North Asia.
  • The South Pacific divides East Australia and southwest America.
  • The Southern Ocean falls on the shores of Antarctica.
  • The Arctic Ocean falls on the shores of the Arctic.

In between all of these divisions falls the seas which lay between specific countries.

Below you can click on a particular ocean to find out more about them:

Ocean Area (square miles) Average Depth (feet) Deepest depth (feet)
Pacific Ocean 64,186,000 15,215 Mariana Trench, 36,200 feet deep
Atlantic Ocean 31,800,000 12,881 Puerto Rico Trench, 28,232 feet deep
Indian Ocean 28,400,000 12,760 Diamantina Deep, 26,401feet deep
Southern Ocean 7,848,000 sq. miles (20.327 000 sq km ) 13,100 – 16,400 ft deep (4,000 to 5,000 metres) the southern end of the South Sandwich Trench, 23,736 feet (7,235 m) deep
Arctic Ocean 5,440,000 3,407 Eurasia Basin, 17,881 feet deep

 

Ocean surface waves are surface waves that occur in the upper layer of the ocean. They usually result from wind or geologic effects and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis. There is little actual forward motion of individual water particles in a wave, despite a large amount of energy and momentum it may carry forward.

A tsunami (soo-nah-mee) is a series of waves created when a body of water, such as an ocean, is rapidly displaced on a massive scale. Earthquakes, mass movements above or below water, volcanic eruptions and other underwater explosions, landslides, large meteorite impacts and testing with nuclear weapons at sea all have the potential to generate a tsunami. The effects of a tsunami can range from unnoticeable to devastating. The term was created by fishermen who returned to port to find the area surrounding their harbor devastated, although they had not been aware of any wave in the open water. Tsunami are common throughout Japanese history; approximately 195 events in Japan have been recorded.

A tsunami has a much smaller amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometres long), which is why they generally pass unnoticed at sea, forming only a passing “hump” in the ocean. Tsunami have been historically referred to as tidal waves because as they approach land, they take on the characteristics of a violent onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean (with which people are more familiar). Since they are not actually related to tides the term is considered misleading and its usage is discouraged by oceanographers.

Tsunamis Causes

A tsunami can be generated when the plate boundaries abruptly deform and vertically displace the overlying water. Such large vertical movements of the Earth’s crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunami. Also, one tsunami in the 1940’s in Hilo, Hawaii, was actually caused by an earthquake on one of the Aleutian Islands in Alaska. That earthquake was 7.8 on the Richter Scale.

Tsunami are formed as the displaced water mass moves under the influence of gravity and radiates across the ocean like ripples on a pond.

In the 1950s it was discovered by that larger tsunami than previously believed possible could be caused by landslides, explosive volcanic action, and impact events when they contact water. These phenomena rapidly displace large volumes of water, as energy from falling debris or expansion is transferred to the water into which the debris falls. Tsunami caused by these mechanisms, unlike the ocean-wide tsunami caused by some earthquakes, generally dissipate quickly and rarely affect coastlines distant from the source due to the small area of sea affected. These events can give rise to much larger local shock waves (solitons), such as the landslide at the head of Lituya Bay which produced a water wave estimated at 50 – 150 metres and reached 524 metres up local mountains. However, an extremely large landslide could generate a “megatsunami” that might have ocean-wide impacts.

The geological record tells us that there have been massive tsunami in Earth’s past.

Signs of an approaching tsunami

There is often no advance warning of an approaching tsunami. However, since earthquakes are often a cause of tsunami, an earthquake felt near a body of water may be considered an indication that a tsunami will shortly follow.

When the first part of a tsunami to reach land is a trough rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching crest of the tsunami, although the warning arrives only a very short time before the crest, which typically arrives seconds to minutes later. In the 2004 tsunami that occurred in the Indian Ocean the sea receding was not reported on the African coast or any other western coasts it hit, when the tsunami approached from the east.

Warning Signs of a Tsunamis

One of the early warnings comes from nearby animals. Many animals sense danger and flee to higher ground before the water arrives. The Lisbon quake is the first documented case of such a phenomenon in Europe. The phenomenon was also noted in Sri Lanka in the 2004 Indian Ocean earthquake. Some scientists speculate that animals may have an ability to sense subsonic Rayleigh waves from an earthquake minutes or hours before a tsunami strikes shore. More likely, though, is that the certain large animals (e.g. elephants) heard the sounds of the tsunami as it approached the coast. The elephants reactions were to go in the direction opposite of the noise, and thus go inland. Humans, on the other hand, head down to the shore to investigate.

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