HYDROSPHERE, OCEANS AND TIDES Revision 10x10learning.com 1
Chapter 12. In the Earth s Atmosphere On surface of the Earth Under the ground Hydrosphere comprises of ALL WATER Water Vapour = 0.001% Is very important for life 2.15% as ice sheets in the North and South Poles; 0.00171% in Rivers and Lakes 97.2% in Oceans Difficult to estimate 10x10learning.com 2
Hydrosphere and Atmosphere Both have a layered structure Both have different dimensions of height and depth The pressure, density and temperature changes at different depths in both structures. Example: At the lowest depths of oceans even at the Equator, is near freezing degrees. However, the chemical content of water does not change due to temperature and pressure. 10x10learning.com 3
Chemical composition of Water Chemical composition of water depends upon whether the water is fresh or salty. Fresh water is needed for living beings, and for agriculture. It is found in lakes, rivers, and under the ground. Brooks, and geysers are natural sources of underground water. Man extracts underground water through wells and pumps. In last 50 years this has resulted in overuse of underground water. 10x10learning.com 4
An Ocean is the great body of water on Earth s surface 71 % is Ocean on Earth 29% is land on Earth 61% is Ocean in Northern Hemisphere 39% is Land In Northern Hemisphere Southern Hemisphere is called Ocean Hemisphere 81% is Ocean in Southern Hemisphere 19 % is land in Southern Hemisphere Northern Hemisphere is called Land Hemisphere 10x10learning.com 5
Ocean floor, and movement such as Ocean currents, Tides, and Waves Ocean along the coasts, slopes gently at 180 meters, to a depth of 100 km almost to the floor of the ocean. In certain places this slope is for a few km only, and remain far from the floor. This slope of land along the coast line, is the submerged extension of the Continent and is, therefore, called the Continental Shelf. The Sonar wave technology is used to measure the depth of the shelf and the floor. 10x10learning.com 6
Continental Shelf Temperature Varies only At the surface 30 to 23 degree C Falls with increasing depth Continental Shelf gently slope at 180 m. To depth of 100 km Depth 4 km to 6 km Mid Ocean ridges 1) Fishing Grounds In Newfoundland And North Sea 2) 25% Off shore petroleum and natural gas - Bombay High and North Sea Near freezing Temperature exists near the ocean floor Ocean Floor with Abyssal plains that are Deep sea plains 10x10learning.com 7
Salinity of Sea water = 35 grams per Kg or 35 per thousand or 35% Evaporation Maximum in the Dead Sea At 240 per thousand Fresh water from rivers Arctic Ocean lowest at 20 per thousand Caspian Sea salt water lake no outflow From rains Arabian Sea 38 per thousand Bay of Bengal- 30 per thousand Gangetic sundarbands - 20 per thousand Oceans have sufficient salt To cover all land with a 100 metre thick layer 10x10learning.com 8
Spring and Neap Tides New and Full Moon Spring tide is higher than normal and occurs on New and Full Moon days Fishermen depend heavily on tides and tidal water is trapped to make salt Neap Tide in 1 st and last quarter when moon is at right angles to the earth - Low tide Tides carry away silt from coastal regions and are now used to general Tidal Energy Spring tides enable large ships to enter a harbour, and Neap tides help them to go out of a harbour Tidal waves break and form a wall of water called Bores. In an estuary Bores can be very dangerous, as in Hoogly River (India) Amazon River and in North China 10x10learning.com 9
Seven Seas, Open and Closed Lakes Arabian Sea Persian Gulf China Sea Red Sea East African Sea Mediter ranean Sea West African Sea 10x10learning.com 10
Ocean Currents regular horizontal or vertical movement of water from one part of the Ocean to another, resulting from action of Density and Winds Currents are streams of water that move on the surface of oceans in a definite direction and have a clear boundary. They may be thousands of kilometres in length and can be up to 200 km wide. Winds help in this movement. Warm Currents originate at Equator and flow towards the Poles Cold Currents flow from the Poles towards the Equator Due to currents and Tides, the Oxygen in the Oceans gets evenly distributed in the Water, otherwise life in depths will not survive as in the Dead Sea Temperatures are higher at the Equator and the imbalance causes the movement due to convection. 10x10learning.com 11
The Coriolis Effect is the deflection of winds and ocean currents due to rotation of the Earth - see diagram on page 59 of the text book. The Coriolis effect is the creation of the Spiral at 900 degrees from the direction of the wind. It has the overall effect of moving a large mass of ocean water, above the depth of frictional resistance. The water is affected by surface winds that drive the sub-surface layers at an angle to the wind. Each layer moves at a slower speed than the layer above it, but the angle against the wind is larger for each layer. 10x10learning.com 12
Important Warm Ocean Currents 1. The Gulf Stream is a warm current, in Atlantic Ocean from Gulf of Mexico, that moves in north-western direction due to Westerly winds, to wash the coasts of England and France. Along the eastern coast of USA, in Newfoundland, the Gulf Stream meets the cold Labrador current, creating dense fogs. The Labrador current from Arctic Ocean is a cold current, that diverts the Gulf Stream towards the coast of Europe. 10x10learning.com 13
Important Warm Ocean Currents 2. The Kuro Shio Current: is a warm current in the Pacific Ocean, that moves as the North Pacific Drift, to keeps the eastern coast of Japan warm and free from ice. Towards north it meets the cold Oya Shio Current. 3. The North Pacific Drift is moved by the Westerly winds towards the western coast of Canada and Alaska. 4. The Oya Shio Current or the Kurile Current in Arctic Ocean flows from Japan and makes the western coast of Japan and coast of Asia, very cold. 5. It is similar to the Labrador Current in the Atlantic Ocean along the north eastern coast of USA. 10x10learning.com 14
Role of Oceans in Earth s Climate Sun s heat causes evaporation of vast quantities of water from the Oceans every day. The water vapour laden air is lighter, and therefore, rises up, to cool down and form clouds. Clouds move with the winds towards land and cause rain. 10x10learning.com 15
Role of Oceans in Earth s Climate In the Oceans, evaporation causes convention current to build up under the surface of water. This causes ocean currents. Ocean currents transfer heat from lower latitudes to higher latitudes. This helps in balancing global temperatures, by absorbing heat in summer and releasing it in winter (?) Oceans have a moderating influence on climate of coastal regions. However, in regions where cold currents merge with warm currents, fog are generated. Many ship wrecks are caused by them. 10x10learning.com 16