5. Ocean Currents
Complete solutions to the textbook exercise. Maharashtra State Board (Balbharati), Grade Eight Geography.
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Exercise
(a) In which ocean does the Labrador current flow?
- (i) Pacific
- (ii) South Atlantic
- ✓ (iii) North Atlantic
- (iv) Indian
Answer: North Atlantic
(b) Which current out of the following flows in the Indian Ocean?
- (i) East Australian Current
- (ii) Peru current
- (iii) South Polar current
- ✓ (iv) Somali current
Answer: Somali current
(c) Which factor out of the following does not affect the region along the coast?
- (i) Precipitation
- (ii) Temperature
- (iii) Land breezes
- ✓ (iv) Salinity
Answer: Salinity (Note: Salinity is a property of the ocean water itself, whereas temperature and precipitation are climatic factors that directly affect the land regions along the coast.)
(d) Which of the following occurs in the area where the cold and warm currents meet?
- (i) High temperature
- (ii) Snow
- (iii) Low temperature
- ✓ (iv) Thick fog
Answer: Thick fog
(e) Which of these following currents flows from the northern polar region upto Antarctica?
- (i) Warm ocean currents
- (ii) Surface ocean currents
- (iii) Cold ocean currents
- ✓ (iv) Deep ocean currents
Answer: Deep ocean currents
(a) Ocean currents give specific direction and velocity to the water.
Answer: Right
(b) The deep ocean currents flow with high velocity.
Answer: Wrong
Correct Statement: Deep ocean currents flow continuously like rivers below the surface of the sea but at a very slow velocity. The global redistribution of water through these currents takes around 500 years to complete.
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(c) Generally, surface ocean currents are formed in the equatorial regions.
Answer: Wrong
Correct Statement: Surface ocean currents are formed in both equatorial regions as well as polar regions. These currents flow horizontally from the equator to the poles (warm currents) and from the poles to the equator (cold currents).
(d) Ocean currents hold great importance for human life.
Answer: Right
(e) The movement of icebergs is not dangerous for water transport.
Answer: Wrong
Correct Statement: The movement of icebergs carried away from the polar areas by cold currents is highly hazardous and dangerous for ships on marine routes.
(f) Water becomes warm near Brazil due to ocean currents. On the other hand, it becomes cold near African coast.
Answer: Right
(a) Warm ocean currents on climate
Warm ocean currents play a vital role in modifying the climate of coastal regions. When warm ocean currents flow near cold regions, they raise the temperature of the coastal areas, reducing the intensity of the freezing winters and making them warmer. Because of this warming effect, the ports in these areas do not freeze in winters. They also increase the amount of precipitation in those coastal areas.
(b) Cold ocean currents on the movement of icebergs
Because of the continuous flow of cold ocean currents originating from polar regions, massive blocks of ice (icebergs) are broken off and carried away into the open ocean. If these large icebergs drift along major marine trade routes, they become extremely hazardous and dangerous to ships and water transport.
(c) The shape of the coast line on ocean currents
Ocean currents do not flow perfectly straight across the entire globe. As they move across the oceans, they encounter continents. According to the structure and alignment of the coastline of the landmasses, the ocean currents are forced to deflect and change their direction of flow.
(d) Meeting of warm and cold ocean currents
When warm and cold ocean currents meet at a specific location, it creates a unique environment. The mixing of temperatures leads to the formation of dense, thick fog, which creates problems for transportation. However, this same environment promotes the abundant growth of plankton, algae, and vegetation. This attracts fish in massive numbers to feed and breed, leading to the formation of some of the world's most extensive fishing grounds (e.g., Grand Bank, Dogger Bank).
(e) The transportational capacity of ocean currents
Ocean currents transport immense volumes of water across the globe. Because of this massive transportational capacity, objects dropped in the ocean (like the cargo of toys from Hawaii) can be carried across different oceans and continents over years. For human transportation, if ships sail along the natural flow of these ocean currents, their speed increases, which significantly saves time and fuel.
(f) Deep ocean currents
Deep ocean currents (thermohaline circulation) are formed due to differences in temperature and density of water. They flow continuously like slow rivers deep below the ocean surface. Their primary effect is the massive global redistribution of ocean water. Warm surface water is transferred to the deep bottom, while the nutrient-rich cold water from the depths is circulated back up to the surface.
(a) How does the Humboldt current affect the climate of the South American coast?
The Humboldt current (also known as the Peru current) is a cold ocean current flowing along the western coast of South America. Because it is a cold current, it drastically reduces the amount of precipitation in the region. As a result, it creates dry and arid conditions, contributing to the formation of coastal deserts like the Atacama Desert in Peru and Chile.
(b) In which oceans are counter equatorial currents not observed and why?
Counter equatorial currents are strictly observed near the equator. Therefore, they are not observed in the Arctic Ocean (in the extreme north) and the Southern Ocean (in the extreme south) because the equator simply does not pass through these polar oceans.
(c) Which currents are absent in northern part of the Indian Ocean and why?
Cold currents are absent in the northern part of the Indian Ocean. This is because the Indian Ocean is completely land-locked by the continent of Asia in the north. Unlike the Pacific and Atlantic oceans, there is no open connection to the Arctic Ocean, meaning cold polar waters cannot flow down into the northern Indian Ocean.
(d) In which regions do the cold and warm ocean currents meet?
Cold and warm ocean currents generally meet in the mid-latitude zones of the major oceans. Based on the map, prominent meeting regions include:
• Near the Newfoundland island off the North American coast (where the warm Gulf Stream meets the cold Labrador current).
• Near the coast of Japan in the Pacific Ocean (where the warm Kuroshio current meets the cold Oyashio current).
• Near the eastern coast of South America (where the warm Brazil current meets the cold Falkland current).
(a) What are the reasons responsible for the formation of deep ocean currents?
The primary reasons responsible for the formation of deep ocean currents (flowing beyond a depth of 500 meters) are the differences in the temperature and the density of the sea water in different parts of the ocean. Warm water has lower salinity and density, keeping it near the surface. As this surface water moves toward the freezing polar regions (like Greenland), it gets cold, dense, and heavy, causing it to sink to the ocean floor. This continuous sinking and rising creates a global conveyor belt of deep ocean currents known as thermohaline circulation.
(b) What is the reason behind the dynamics of the ocean water?
The dynamics and movements of the ocean water are primarily caused by differences in temperature and water density. In addition to these natural differences, the strong planetary winds give continuous speed and push to the surface ocean waters. Furthermore, the rotation of the Earth and the physical structure (alignment) of the continental coastlines dictate the circular patterns and direction of these dynamic ocean currents.
(c) How do winds give direction to the ocean currents?
Planetary winds continuously blow across the earth's surface and physically push the top layer of the ocean water over long distances. Near the equator, the planetary winds push the ocean currents to flow from east to west. Conversely, in the mid-latitudes, under the strong influence of the Westerlies, the winds push the ocean currents to flow from west to east. This interaction with the winds leads to the formation of massive circular flow patterns (gyres) in the oceans.
(d) Why do the ports in the eastern coast of Canada freeze in winter?
The eastern coast of Canada is directly affected by the Labrador Current, which is a very strong and cold ocean current originating from the freezing Arctic region. This cold current drastically lowers the temperature of the coastal waters and the surrounding climate. Because the water temperature drops below the freezing point due to the chilling effect of the Labrador current, the ports on the eastern coast of Canada freeze solid during the winter months.