Oceans

An Ocean is a is a type of Habitat or Biome composed entirely of water and constitutes a principal part of the Hydrosphere (watery layer of the earth's surface). The Earth's Ocean (World Ocean) is made up of more than 20 Seas and 4 Oceans. The area of the World Ocean is 361×106 km2 (139×106 mi2). Its volume is approximately 1.3 billion cubic kilometres (310 million cu mi). More than half of this area is over 3,000 metres (9,800 ft) deep.  Oceans cover 71% of our Earth's surface. Over 230 countries have coastlines that are washed by the Oceans of the world. By volume, the Ocean makes up 99%  of the Planet's living space- the largest space in our Universe known to be inhabited by living organisms. More than 97% of all Earth's water is contained in the Ocean. 2% is frozen in Ice Caps and Glaciers, less than 0.3 % is carried in the Atmosphere in the form of Clouds, Rain, and Snow. All of Earth's inland Seas, Lakes and Channels combined, add up to only 0.02% of Earth's water. The total length of the World's coastlines is about 315,000 miles which is enough to circle the Equator 12 times. The average temperature of the Oceans is 2ºC, about 39ºF. The average Worldwide Ocean depth is about 12,460 feet (3,798 meters), with the deepest point of 36,198 feet (11,033 meters) which is located in the Mariana Trench in the Pacific Ocean. The floor of the Ocean is called the 'Benthic Habitat' while the water itself is called the 'Pelagic Habitat'. Both support a diversity of Animal life. Coral reefs, which grow in warm tropical and subtropical Seas, are perhaps the richest marine Habitat in terms of the diversity of life they shelter. Smaller regions of the Oceans are called Seas, Gulfs, Bays, Straits and by other names as well.

Types of Oceans

Pacific Ocean - It separates Asia and Australia from the Americas.

Atlantic Ocean - It separates the Americas from Eurasia and Africa.

Indian Ocean - It washes upon southern Asia and separates Africa and Australia.

Southern Ocean - It has has no landmass separating it from other Oceans and is therefore sometimes subsumed as the southern portions of the Pacific, Atlantic, and Indian Oceans, which encircles Antarctica and covers much of the Antarctic.

Arctic Ocean - It is sometimes considered a sea of the Atlantic, which covers much of the Arctic and washes upon northern North America and Eurasia.

The Pacific and Atlantic may be further subdivided by the equator into northern and southern portions.

General Characteristics of an Ocean

• Layered Composition - Scientists have divided the Ocean into 5 main layers. These Layers are also known as Zones which extend from the surface to the most extreme depths where light can no longer penetrate.

i)  Epipelagic Zone  - The surface layer of the Ocean is known as the Epipelagic Zone. It extends from the surface to 200 meters (656 feet). It is also known as the 'Sunlight Zone' because the maximum amount of visible light is available here only. With the light come heat. This heat is responsible for the wide range of temperatures that occur in this zone.

ii)  Mesopelagic Zone - Below the Epipelagic Zone is the Mesopelagic Zone. It extends from 200 meters (656 feet) to 1000 meters (3281 feet). The Mesopelagic Zone is also known as the 'Twilight Zone' because the amount of light here is faint. This Zone is also known as the 'Midwater Zone' because of it's location. This Zone is known for the twinkling lights of bioluminescent (emitting light) organisms. A great diversity of strange and bizarre Fishes can be found here.

iii)  Bathypelagic Zone - Below the Mesopelagic Zone is the Bathypelagic Zone. It is also known as the Midnight Zone or the Dark Zone because of the darkness prevalent in this Zone. This Zone extends from 1000 meters (3281 feet) down to 4000 meters (13,124 feet). The only source of visible light here is the one produced by the Animals residing here. The water pressure at this depth is immense, reaching 5,850 pounds per square inch. In spite of the pressure, a surprisingly large number of Animals can be found here. Sperm Whales can dive down to this level in search of food. Most of the Animals that live at these depths are black or red in colour due to the lack of light.

iv)  Abyssopelagic Zone - Below the Bathypelagic Zone is the Abyssopelagic Zone. It is also known as the Abyssal Zone or simply as the Abyss because it's depth appears to be endless. It extends from 4000 meters (13,124 feet) to 6000 meters (19,686 feet). The water temperature here is near freezing, and there is no light at all. Very few organisms are found at these crushing depths. Most of the organisms here are Invertebrates such as Basket Stars and Tiny Squids. Three-quarters of the Ocean floor lies within this zone.

v)  Hadalpelagic Zone - Below the Abyssopelagic Zone lies the Hadalpelagic Zone. It is also known as the Forbidden Zone as it is very dangerous to dive to such depths. It extends from 6000 meters (19,686 feet) to the bottom of the deepest parts of the Ocean. These areas are mostly found in deep water Trenches and Canyons. The deepest point in the Ocean is located in the Mariana Trench off the coast of Japan at 35,797 feet (10,911 meters). The temperature of the water is just above freezing, and the pressure is an incredible eight tons per square inch. That is approximately the weight of 48 Boeing 747 jets. In spite of the pressure and temperature, life can still be found here. Invertebrates such as Starfish and Tube Worms thrive at these depths.

• Salinity - According to some scientists the Oceans contain as much as 50 quadrillion tons (50 million billion tons=50,000,000,000,000,000) of dissolved solids. If the salt in the Ocean could be removed and spread evenly over the Earth’s land surface it would form a layer more than 500 feet (166 m) thick, about the height of a 40-story office building. The Ocean's principal dissolved solids are sodium salts (sodium chloride or common salt), calcium salts (calcium carbonate or lime, and calcium sulphate), potassium salts (potassium sulphate), and magnesium salts (magnesium chloride, magnesium sulphate, and magnesium bromide). Atlantic Sea water is heavier than Pacific Sea water due to its higher salt content. The freezing point of Sea water depends on its salt content. Typical Ocean water has about 35 grams of salt per litre and freezes at -19°C.

• Variation in Density of Water - The density of Ocean water varies. It becomes more dense as it becomes colder, right down to its freezing point of -1.9°C. (This is unlike fresh water, which is most dense at 4°C, well above its freezing point).

• Water Temperature - Under the enormous pressures of the deep Ocean, Sea water can reach very high temperatures without boiling. A water temperature of 400°C has been measured at one hydrothermal vent. The average temperature of all Ocean water is about 3.5° C. Almost all of the deep Ocean temperatures are only a little warmer than freezing (39°F).

• Occurence of Ice - Antarctica has as much ice as the Atlantic Ocean has water. 10% of the Earth's surface is covered with ice. The Arctic Ocean is the smallest Ocean, holding only 1% of the Earth's Sea water. This is still more than 25 times as much water as all Rivers and fresh water Lakes. The average thickness of the Arctic ice sheet is about 9 to 10 feet, although there are some areas as thick as 65 feet. In the unlikely event that all the polar ice were to melt, the Sea level all over the World would rise 500 to 600 feet. As a result, 85 to 90% of the Earth's surface would be covered with water as compared to the current 71%. The Arctic produces 10,000 to 50,000 icebergs annually. The amount produced in the Antarctic regions is inestimable. Icebergs normally have a four-year life-span; they begin entering shipping lanes after about three years.

• Carbon Dioxide Absorption - Oceans absorb between 30% and 50% of the carbon dioxide produced by burning fossil fuel. Carbon dioxide is transported downwards by Plankton. Any change in the temperature of the Ocean water, influences the ability of Plankton to take up carbon dioxide. This has consequences for the ecosystem, because Plankton form the base of the food web.

• Greatest Variety of Life Forms - Oceans support the greatest variety of life on Earth which ranges from microscopic Plankton to giant Whales. There are more than 21,000 Species of Fish, of which most live in the Oceans. The deepest parts of the Oceans, remain largely unexplored, and new life forms are still being discovered every year. The Oceanic Food Chain begins with microscopic drifting plants called Phytoplankton. Phytoplankton are found close to the surface of the water where there is adequate sunlight for photosynthesis. Phytoplankton are eaten by tiny floating animals known as Zooplankton. Zooplankton include the larvae of Crabs, Jellyfish, Corals and Worms, as well as adult Animals like Tiny Shrimps, Copepods and Euphausiids (krill). Moving up The Food Chain, Zooplankton provide food for Fish. Big Fishes eat small Fishes and at the very top of the Food Chain are large predatory Fish like Sharks, Mammals like Seals, and Sea Birds. The Whale Shark, and the Baleen Whale, feed directly on Zooplankton. Other Ocean Animals include Lobsters, Crabs, Prawns, Starfish, Brittlestars, Featherstars, and many kinds of sea Slugs and Worms. Finally, there are the bottom-feeding Fish such as Rays, Turbots, Halibuts and Gurnards.

• Availability of Oil - Oil is one of the Ocean's greatest resources. Nearly one-third of the World's oil comes from offshore fields in our Oceans. Areas most popular for oil drilling are the Arabian Gulf, the North Sea, and the Gulf of Mexico. Oil was also borne from the sea. Millions of years ago, countless marine microscopic Plants (phytoplankton) and Animals (zooplankton) lived in the ancient Seas as they do today. As they died, the skeletal remains of these tiny organisms settled to the sea floor, mixed with mud and silt, and over millions of years, formed organic-rich sedimentary layers. Other sediments continued to be deposited and further buried the organic-rich sediment layer to depths of thousands of feet, compressing the layers into a rock that would become the source for oil. Over the years, as the depth of the burial increased, pressure increased, along with the temperature. Under such conditions, and over long periods of time, the original skeletal remains of Phytoplankton and Zooplankton changed, breaking down into simpler substances called Hydrocarbons - compounds of hydrogen and carbon. This process still continues, although it will be millions of years before the next batch of oil is done cooking.

• Presence of Gold - The Worlds Oceans contain nearly 20 million tons of gold. If all the gold suspended in the World's Seawater were mined, each person on Earth could have about 9 pounds of gold.

Origin of Oceans

There are several theories about the origin of the Seas. According to a popular theory, the Ocean had its origin from the prolonged escape of water vapour and other gases from the molten igneous rocks of the Earth to the clouds surrounding the cooling Earth. After the Earth's surface had cooled to a temperature below the boiling point of water, rain began to fall and continued to fall for centuries. As the water drained into the great hollows in the Earth's surface, the primeval ocean came into existence. The forces of gravity prevented the water from leaving the Planet. Life began in the Seas 3.1 billion to 3.4 billion years ago. Land dwellers appeared 400 million years ago; a relatively recent point in the geologic time line. Some Scientists believe that the Seas are as much as 500 million years old because Animals that lived then occur as fossils in rocks which once were under ancient Seas.

Importance of Oceans

• Three-quarters of the World's mega-cities are located by the Sea. More than half the World’s population lives within a 100 km or 60 miles distance from the coast. This is more than 2.7 billion people.

• The Ocean determines climate and plays a critical role in Earth's habitability. Most of the solar energy that reaches the Earth is stored in the Ocean and helps power Oceanic and Atmospheric circulation. In this manner, the Ocean plays an important role in influencing the weather and climatic patterns of the Earth. The top 10 feet of the Ocean holds the same amount of thermal energy as it exists in the entire Atmosphere.

• Oceans are an ancient and widely used mode of transportation. Over 90% of trade among countries is carried by ships.

• About half the communications between nations are via underwater cables.

• Fish supply the greatest percentage of the World's protein consumed by humans. The Sea provides the biggest source of wild or domestic protein in the World. Each year some 70 to 75 million tons of Fish are caught in the Ocean. Of this amount around 29 million tons is for human consumption. The global Fish production exceeds that of cattle, sheep, poultry or eggs.

• Oceanography (study of oceans) can enhance the conditions for trade, communications, and defence.

• Sea water can and is being converted into fresh water for human consumption. The Arabian Gulf Reverse Osmosis Plants treat 500,000,000 gallons of Sea water to obtain 100,000,000 gallons of fresh water. Over 500,000,000 gallons of Sea water is heated to extremely high temperatures. Mixed with toxic chemicals the Sea water is injected under high pressure through a series of membrane filters. Only 100,000,000 gallons of fresh water is generated. Though the 5:1 ratio is an inefficient process as but it has led to various research in reducing the wastage and reducing the pollution caused by these Plants.

• The Ocean floor holds 200 million years old geological and biological history of the Earth. By studying the Ocean floor scientists can learn about ancient climate, how it changed and how better to predict our own climate.