UPSC : NCERT Summary: Water Notes | EduRev
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- The major sources of freshwater are rivers, ponds, springs, and glaciers.
- The ocean bodies and the seas contain salty water. The water of the oceans is salty or saline as it contains a large number of dissolved salts. Most of the salt is sodium chloride or the common table salt that you eat.
- Salinity is the amount of salt in grams present in 1000 grams of water. The average salinity of the oceans is 35 parts per thousand.
- The Dead Sea in Israel has a salinity of 340 grams per litre of water. Swimmers can float in it because the increased salt content makes it dense.
- Tsunami is a Japanese word that means “Harbour waves” as the harbours get destroyed whenever there is a tsunami.
- The Indira Point in the Andaman and Nicobar islands got submerged after the tsunami.
- Tsunamis are rare in the Indian Ocean as the seismic activity is less as compared to the Pacific.
- The rhythmic rise and fall of ocean water twice in a day are called a tide.
- It is high tide when water covers much of the shore by rising to its highest level.
- It is low tide when waterfalls to their lowest level and recedes from the shore.
Try yourself:What is the average salinity of the ocean water?
➢ Types of Tides
- During the full moon and new moon days, the sun, the moon, and the earth are in the same line and the tides are highest.
- These tides are called spring tides. But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and moon resulting in low tides. These tides are called neap tides.
➢ High tides
- The water of the earth closer to the moon gets pulled under the influence of the moon’s gravitational force and causes high tide.
- High tides help in navigation. They raise the water level close to the shores. This helps the ships to arrive at the harbour more easily.
- The high tides also help in fishing.
- Much more fish come closer to the shore during the high tide. This enables fishermen to get a plentiful catch.
- The rise and fall of water due to tides is being used to generate electricity in some places.
- Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold.
- Generally, the warm ocean currents originate near the equator and move towards the poles.
- The cold currents carry water from polar or higher latitudes to tropical or lower latitudes.
- The Labrador Ocean current is a cold current while the Gulf Stream is a warm current.
- The ocean current influences the temperature conditions of the area. Warm currents bring about warm temperatures over the land surface.
- The areas where the warm and cold currents meet provide the best fishing grounds in the world.
- Seas around Japan and the eastern coast of North America are such examples.
- The areas where a warm and cold current meets also experience foggy weather making it difficult for navigation.