10 Hydrosphere, Tides and Ocean Currents

Class – 9

Geography

Chapter – 10

Hydrosphere, Tides and Ocean Currents

 HIGHLIGHTS– a) Meaning of hydrosphere b) Tides – formation and pattern. c) Ocean Currents – effects of Gulf Stream, North Atlantic Drift, Labrador Current, Kuro Shio and Oya Shio.

HYDROSPHERE –

A hydrosphere in physical geography describes the collective mass of water found on, under, and over the surface of a planet.

Hydrosphere is far more extensive than lithosphere on the surface of the earth. It is calculated that about 71 percent of the earth’s surface is occupied by seas and oceans. An extension of saline water on the earth is called sea. Large sea areas are called oceans.

TIDES –

Tides are the periodical rise and fall of sea level due to changes in the attractive force of the Moon and Sun.

Formation of Tides : Tides are caused by the tidal forces of the Moon, the Sun and rotational of the earth.

Tides are caused mainly by the attraction of the moon and to some extent the sun on the surface of the earth.

The moon being closer to the earth is responsible for tides to a greater extent than the sun.

TYPES OF TIDES –

When the level of the water is the highest, it is called high tide. When the level of water is the lowest, it is called low tide.

Sometimes tides are of a higher magnitude than normal tide. Such tides are called spring tides. They occur when the sun, the moon and the earth are in a straight line.

On the other hand, when the sun, the moon and the earth form right angle, the attractions of the sun and the moon neutralize each other. This happens at the first and the third quarters of the moon. At these times, the tides are weaker and they are called neap tides.

Some coastal areas experience a regular pattern of one high tide and one low tide each day, known as a diurnal tide. For example, Gulf of Mexico and along the coast of Southeast Asia.

In many areas, including the Atlantic Coast of the United States, there is a high tide to low tide sequence repeated twice a day, termed a semidiurnal tide.

The third pattern of tide has two high and two low tides per day, but the tides reach different high and low levels during each daily rhythm called a semidiurnal mixed tide, it results from combining a semidiurnal and diurnal tide.

CURRENTS OF THE ATLANTIC OCEAN –

1. Gulf Stream : This is a warm current and originates in the Gulf of Mexico. Near New found land its water mixes with that of the cold water current of Labrador which results in the formation of dense fog. Here it comes under the influence of the westerly winds and flows north – eastwards as North Atlantic Drift. It’s warm water keeps the Norwegian coast ice free even during winters.

2. Labrador current : It is a cold water current which flows south-wards from the Arctic ocean along the coast of Canada. The current merges with the Gulf Stream near New found land. As the current originates from the Arctic ocean it brings down huge icebergs from the Arctic ocean to the eastern coast of Canada.

3. The Oyo Shio current or the Kurile current : This is a cold current originating in the Arctic ocean. The current has an important impact on the climate of the Russian Far East. The water of the Oyshio current form probably the richest fishery. The current makes the west coast of Japan and the coast of the Asian mainland severely cold in winter.

4. Kurushio Current : It is a warm current in the Pacific. The heat which is carried by the current has an effect on climate of the adjacent land areas. It makes the winter of eastern Japan milder and keeps the coast free from ice. It has a warming effect on the coasts of Alaska and Western Canada.

NORTH ATLANTIC DRIFT

It is a warm ocean current. It prevails under the influence of westerly winds. It is section of the Gulf stream. It is because of this current, Russia is able to move cargo in summers through Arctic ocean (Barents Sea). North Atlantic Drift are responsible for moderating the climate of western Europe, so that winters are less cold than would otherwise be expected at its latitude.

Questions & Answers

Q1. What is Grand Bank?

The Grand Bank near Newfoundland has become one of the leading fishing grounds of the world because of the merger of the Gulf Stream and Labrador currents. The merger of warm and cold currents help in the growth of plankton which is food for fish.

Q2. Describe the effects of North Atlantic Drift.

A2. It is a warm ocean current. It prevails under the influence of westerly winds. It is section of the Gulf stream. It is because of this current, Russia is able to move cargo in summers through Arctic ocean (Barents Sea). North Atlantic Drift are responsible for moderating the climate of Western Europe, so that winters are less cold than would otherwise be expected at its latitude.

 Answer the following questions in brief: 1. What is the cause of the tides? 2. Name the warm ocean currents modifying the climate of USA and Japan. 3. Why the north – eastern coast of Japan is one of the most important fishing grounds of the world? 4. Describe the impact of currents on fishing and navigation. 5. How are tides caused? Why does the magnitude of the tides vary from time to time? 6. Name the major warm and cold currents of the Atlantic ocean and explain their impact on the climatic conditions of the coastal areas. 7. What are spring tides? 8. What are neap tides? 9. What are diurnal tides? 10. What are semidiurnal tides?