Major Oceans

What are Major Oceans in the world? How do temperature of oceans  differs? What is the salinity of oceans? How do horizontal distribution and vertical distribution of salinity differ in the ocean? Read further to know more.

Every living thing on earth depends on water in some way. One of the four spheres that make up the earth is the hydrosphere.

The water on the surface of the world (oceans, rivers, lakes, and glaciers), the water below the surface known as groundwater, and the water in the atmosphere above the surface of the globe are all considered to be part of the hydrosphere.

Large oceans and seas contain about 96.5% salty water. Of the total area of the planet, 70.8% is made up of water and only 29.2% is made up of land. Only 2.5% of it is fresh water. Together, saline lakes and groundwater make up 1% of the total.

Major Oceans

The term ocean is derived from the Greek word “Oceanus” which means enormous river encircling the earth. There are five major oceans in the world- the Pacific Ocean, Atlantic Ocean, Indian Ocean, Arctic Ocean and Southern Ocean.

Pacific Ocean:

• It is the biggest ocean on the planet. It occupies one-third of the earth’s surface and is larger than all the continents combined. Asia and Australia are separated from North and South America by the Pacific Ocean.
• Because he perceived the ocean to be quiet, Portuguese explorer Ferdinand Magellan gave it the name Pacific Ocean, which translates as “peaceful”.
• The Pacific Ocean is where the International Date Line is located. By the Indonesian Seaway, the Pacific Ocean and the Indian Ocean are connected (Torres strait and strait of Malacca).
• The ocean here has an average depth of 4280 metres.
• The world’s deepest oceanic trench is the Mariana trench, which is located in the western Pacific Ocean.

Atlantic Ocean:

• It is the world’s second-largest ocean. 20% of the earth’s surface is covered by it.
• Its name, Atlantis Thalassa, which means Sea of Atlas, comes from Greek mythology.
• Between Africa, Europe, the Arctic Ocean, the Americas, and the Southern Ocean, it is a body of water with an extended S shape. 3,646 metres is about how deep this ocean is on average.
• Puerto Rico Trench is the deepest trench in the Atlantic Ocean (8,376 m).
• In the distant past, when the supercontinent Pangaea broke up, the north Atlantic Ocean was created, and Gondwanaland broke up, the south Atlantic Ocean was created.
• Greenland, the largest island, is found in the Atlantic Ocean.
• The Atlantic Ocean contains the Sargasso Sea, the only sea in the world without a shore.
• The Atlantic and Indian oceans converge in the southeast.

Also read: Bottom topography of Atlantic Ocean

Indian Ocean:

• India, which makes up a large portion of its northern border, inspired the name.
• The eastern hemisphere is where it is located. 19.8% of the surface of the earth’s water is covered by it.
• It is situated between Asia, Australia, the Southern Ocean, and Africa. It is the world’s hottest ocean and is enclosed by land in the northern hemisphere.
• Madagascar is the biggest island in the Indian Ocean (the fourth largest island in the world).
• The deepest trench in the Indian Ocean is called the Sunda/Java Trench and is about 7450 metres deep.
• The Indian Ocean’s marginal seas are crucial for trade because they provide vital marine lanes that link the Middle East, East Asia, Africa, Europe, and the Americas.
• The Indian Ocean’s marginal seas are crucial for trade because they provide vital marine lanes that link the Middle East, East Asia, Africa, Europe, and the Americas. An island, peninsula, or collection of islands that encloses a portion of an ocean is known as a marginal sea (group of islands). They are located close to land and are shallower than the ocean.

Southern Ocean:

• The southernmost parts of the world’s oceans are collectively referred to as the Antarctic Ocean or Austral Ocean.
• It is the second-smallest and fourth-largest ocean in the world, surrounding Antarctica south of 60°S latitude.
• The Atlantic, Indian, and Pacific Oceans round its northernmost (and largest) border. The seas of this ocean are notoriously tumultuous.
• Between Chile’s Cape Horn in South America and Antarctica’s South Shetland Islands is a body of water known as the Drake Passage. It is renowned for having severe storms. It stretches into the Southern Ocean and joins the southwest corner of the Atlantic (Scotia sea) with the southeast corner of the Pacific.

Arctic Ocean:

• In comparison to the other four oceans, the Arctic Ocean is shallower and smaller. The Arctic Circle encompasses the entire area.
• It covers roughly 1.3% of the water surface of the planet.
• Eurasia and North America encircle it. In the winter, ice fully covers it. Of the five great oceans, its salinity is the lowest on average.
• The Greenland Sea, Labrador Sea, and Norwegian Sea connect the Arctic Ocean to the Pacific Ocean while the Bering Strait connects it to the Atlantic Ocean.
• The deepest spot in the Arctic Ocean is the Molloy Deep, or “Molloy Hole,” which is located in the Fram Strait (inside the Greenland Sea).

The temperature of Oceans

• Similar to land, ocean waters also become warmer due to sun radiation. Oceanic water warms and cools more slowly than land-based water.
• Temperature Distribution Influences Ocean water temperature distribution is influenced by several factors, including:
• Latitude: As one moves further away from the poles, the amount of insolation decreases, causing the temperature of surface water to drop.
• Uneven distribution of land and water: The northern hemisphere’s oceans experience greater heat because they are in contact with a larger area of land than the southern hemisphere’s oceans.
• Prevailing wind: The winds blowing from the land towards the oceans drive warm surface water away from the coast resulting in the upwelling of cold water from below. It results in the longitudinal variation in the temperature. Contrary to this, the onshore winds pile up warm water near the coast and this raises the temperature.
• Ocean currents: Warm ocean currents raise the temperature in cold areas while cold currents decrease the temperature in warm ocean areas. The Gulf stream (warm current) raises the temperature near the eastern coast of North America and the West Coast of Europe while the Labrador current (cold current) lowers the temperature near the northeast coast of North America.
• All these factors influence the temperature of the ocean currents locally.
• The enclosed seas in the low latitudes record relatively higher temperatures than the open seas; whereas the enclosed seas in the high latitudes have a lower temperatures than the open seas.

The salinity of Oceans

• Salinity is an important property of seawater. It is defined as the amount of salt (in grams) dissolved per kilogram (1000 g) of seawater. It is usually expressed as parts per thousand, ppt or °/₀₀. For example, 30 ppt means 30g of salt in 1000 g of seawater. A salinity of 24.7 ppt has been considered as the upper limit to demarcate brackish water.
• The composition of seawater varies both spatially (varies from one area to another) and temporally (varies from one-time span to the other time unit- seasonally, yearly).

Horizontal distribution of salinity of oceans

• On average, the salinity decreases from the equator towards the poles. The highest salinity is observed between 20° and 30° N and S latitudes because this zone is characterized by high temperature, high evaporation and less rain than the equatorial region. Subpolar and polar zones record minimum salinity due to less evaporation.
• The North Sea, though in higher latitude, records higher salinity due to more saline water brought by the North Atlantic Drift.
• Baltic Sea records low salinity due to the influx of river waters in large quantities.
• The average salinity of Ithe ndian Ocean is 35°/₀₀..The Bay of Bengal records low salinity due to the influx of river water and the Arabian Sea has higher salinity due to high evaporation and a low influx of fresh water.
• Highest salinity in water bodies – Lake Van in turkey (330 °/₀₀), Dead Sea (238 °/₀₀), Great Salt Lake, Utah USA (220°/₀₀).

Vertical distribution of salinity

• There is a marked difference in the salinity between the surface zones and the deep zones of the oceans. Salinity at the surface increases by the loss of water to ice or evaporation, or it decreases by the input of fresh waters. However, salinity at depth is very much fixed, because there is no way that water is lost or salt is added.
• Although salinity generally increases with depth, there is a distinct zone where the salinity increases sharply called the halocline.
• Highly saline sea water (dense) generally sinks below the lower saline sea water (less dense) which leads to the stratification of seawater.

Density stratification of oceans

1. The surface layer of lowest density – Also called photic zone as this layer is directly penetrated by solar radiation. It has a thickness of 100 m- 200 m. It carries only 2% of the total volume of ocean water.
2. Pycnocline layer of sharp density gradient – (by no means density). This layer is found between 300 m – 1000 m depth of ocean water. It carries about 18% of the total volume of ocean water. Pycnocline (sharp density gradient), thermocline (steep temperature gradient) and halocline (sharp salinity gradient) occupy almost the same depth zones of 300 m – 1000 m.
3. The bottom layer of highest but uniform density- It carries about 80% of the total volume of ocean water.

Article written by Aseem Muhammed