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  • What is the difference between oceans and seas?

    What is the difference between oceans and seas?

    What is the difference between oceans and seas?

    The word 'oceans' implies the large water bodies of the world, namely, the Pacific, Atlantic, Indian, and Arctic, as well as the Antarctic oceans where we find icebergs. Smaller seas are separated from the oceans by island chains or underwater ridges, which are called 'bordering seas'. These include the North Sea, the Baltic Sea, the Mediterranean Sea, and the Caribbean Sea. The bordering seas and the oceans have some common features: both contain salty water and restless seabeds. But there are also differences in the variety of plants and animals living in them and the storm tides-the tides that lash the coast of the North Sea are hardly found along the Pacific coast.


    What does the seabed look like?

    The seabed is that area of the Earth which has been researched the least. However, we know, through sound wave technology, that there are deep valleys, high mountain ranges, steep slopes, and flat regions on the seabed. We also know that the seabed undergoes continuous changes. Underwater volcanic mountain ridges form at place where two tectonic plates move away from each other, and these ridges grow every year by a few centimetres. Generally, the bed of the flat seas, such as the coral reefs (page 78), is densely populated with plants and animals. In contrast, the deeper regions in the seabed are often covered by a layer of sand, dust, and dead organisms from the rivers, which is several hundred metres thick.


    How is salt formed in the sea?

    When rain falls on the ground and seeps below it, it washes away substances from the soil and rocks. It carries these substances into the river and the sea. You can read the names of these substances on the label of a bottle of mineral water. River water contains only a little salt-about 1 g/l, whereas the salt content of the sea is much higher-about 35 g/1, on an average. The reason is that the salt remains in the sea. Although the rivers continue to deposit new salts, the seas do not become over salty' because animals and plants in the sea absorb the salt in their bodies. When they die, they sink to the seabed and decompose into sediments.




  • the deepest point in all the oceans, the Mariana Trench in the Pacific, is just 11 km deep?
  • there is a sea surrounded on all sides by water? The Sargasso Sea to the east of Florida (USA) is separated from the surrounding Atlantic ocean by ocean currents.
  • there are icebergs almost as large in area as the city of Houston in Texas? For example, B15 Antarctic iceberg was the world's largest recorded iceberg.
  • some people are planning to haul icebergs to countries that have water scarcity?
  • researchers can dive up to a depth of 6oo0 m in small, special submarines? The 'black smokers' were discovered in one such dive.

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    Why is the North Sea coast susceptible to storm tides?

    A storm tide is a natural phenomenon, and hence cannot be prevented. It happens when the normal water level rises high along the shore due to strong onshore winds and/or reduced atmospheric pressure (page 37) as in the North Sea. It is not an open ocean, being blocked from the ocean by the British Isles. As a result, the water dams up very quickly. The waves whipped up by the wind destroy or flood the dikes and beach dunes. Parts of the coast are also washed away. The Halligen Islands in Germany, for instance, have emerged as a result of storm tide action. These are small islands on the coast of Schleswig-Holstein, which were earlier connected with the mainland. They are regularly inundated by flood waters.


    How are icebergs made?

    The icebergs in the North Atlantic are large pieces of ice that have broken off from the glaciers of Greenland. Since frozen water is lighter than liquid water, the broken pieces float as icebergs on the sea. They are pointy and often interspersed with debris. In contrast, the icebergs in the South Atlantic are mostly flat. They are broken pieces of the flat sea ice, which surrounds the Antarctic. Icebergs can float for thousands of kilometres before they melt. Only one-ninth of an iceberg stays above the water. If the part above the water is 100 m high, then the part below is 800 m deep.


    How are waves formed?

    Waves are formed as a result of the constant friction between water and wind. If a wind is blowing over the surface,it carries away particles of water with it. The water starts moving in this way. Therefore, the distance between the If a wind is blowing over the water surface, it carries away particles of water with'wave crests' is determined by the wind.

    A constant wind gives rise to long, soft waves, which are also known as 'groundswell'; a high wind, on the other hand,causes small and strong waves, the typical motion of the sea'. Unlike the tsunamis, these waves occur only at the surface of the water. At a depth of a few metres, the waves do not create any disturbance.


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    Iceberg transporter

    You need: An ice-cube tray, 10-12 stones,water, a freezer
    Do as follows: Put a stone in each compartment of the ice-cube tray. Fill the ice-cube tray with water and put it in the freezer. When ice cubes are made place them along the edge of water in the bucket. Observe the movement of ice cubes.