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Summary

Geography Class 32

## Brief Discussion on the Previous Class (5:13 PM)

## Currents of the South Atlantic Ocean (5:22 PM)

- South equatorial current, which moves along Brazil forms the **Brazilian current**. It is a warm current.
- The Brazilian current gets deflected towards the left in the southern hemisphere (Due to Coriolis force) and joins the **West Wind Drift**.
- West Wind Drift is a cold current, which circulates the continent of Antarctica. (It flows under the influence of Westerlies).
- The Brazilian current once when comes under the influence of West wind drift is called **South Atlantic Drift.**
- Near the coast of Africa, it turns upward and is known as **Cold Benguela Current.**
- Benguela current is responsible for the formation of the Namib and Kalahari Deserts.
- Cold Benguela current joins the South Equatorial current.
- Falkland Current flows along the eastern coast of the South American continent.
- Gyre is formed in the South Atlantic Ocean,

## Currents of the Pacific Ocean (5:34 PM)

- North Equatorial current gets divided by the archipelago and turns rightward. This current is known as Warm **Kuroshio Current** (along the coast of Japan).
- It is a warm current moving along the coast of the Philippines and Japan.
- The **North Pacific Current** is an ocean current that flows west-to-east between 30 and 50 degrees north in the Pacific Ocean.
- It gets divided near the North American Continent.
- One branch moves upward and is known as **Warm Alaskan Current**.
- Another branch moves southward and is known as the cold **California Current.**
- Cold California Current joins the North Equatorial Current. therefore a gyre is formed here.
- Near Sakhalin Island, there are two cold currents- **Oyashio Current** and **Okhotsk Current**.

## Southern Pacific Ocean

- The southern equatorial current moves down and is called Warm **East Australian Current.**
- Coming down, it joins West wind drift and is known as Cold **South Pacific Drift.**
- Then it flows along the coast of the South American continent and is known as the cold **Humboldt Current.**
- Then, finally, it joins the South Equatorial current.

## Indian Ocean currents (5:48 PM)

- **Southern Indian Ocean**
- There is a Southern equatorial current.
- It gets divided into two currents by Madagascar: Mozambique current and Madagascar Current
- Mozambique and Madagascar combine to form the Agulhas current.
- It flows along with West Wind Drift and then, moves along the western coast of Australia. It is then known as Western Australian Current.
- Western Australian Current then, merges with the Southern Equatorial current.
- **Northern Indian Ocean**
- **![](https://www.researchgate.net/publication/27668602/figure/fig1/AS:671524163952641@1537115245080/Schematic-of-major-surface-currents-in-the-Indian-Ocean-during-a-the-northeast-monsoon.png)**
- Here, the wind reversal takes place. Also, there is huge dominance of land in the Northern Indian Ocean.
- ==Winters==
- We have North Equatorial Current, South Equatorial current, and Counter equatorial current during the winter.
- North equatorial current flows westward, above the equator.
- Counter equatorial current flows in between the North and South Equatorial Currents.
- The Northeast monsoon drives the water of the Bay of Bengal and Arabian sea to circulate in an anti-clockwise direction as the Northeast monsoon drift.
- ==Summers==
- The entire water of the Northern Indian Ocean comes under the influence of the Southwest Monsoon.
- This produces a clockwise flow of the southwest monsoon drift.
- During this time, there are no north equatorial currents and counter equatorial currents.

## Significance of Ocean Currents (6:25 PM)

- (a) The continuous movement of water from east to west in the tropical region causes cold water upwelling, along the eastern parts of oceans.
- This causes a drop in the temperature
- (b) Accumulation of warm waters along the western parts of the ocean in tropical regions, leads to a rise in water temperature.
- (c) The western parts of the Ocean within the tropical regions, experience favourable conditions for the formation of cyclones.
- (d) The cold ocean currents along the western coast in sub-tropical regions, suppress precipitation through the desiccation effect.
- It contributes to the formation of deserts. For example, the Kalahari desert and Namib desert due to the Benguela current, the Atacama desert due to the Humboldt current, etc.
- (e) Warm and Cold ocean currents merge near the temperate regions to create favourable conditions for the development of large-scale fishing banks.
- For Example Grand Bank (near Newfoundland Island due to the merging of labrador current with the gulf stream)
- (f) The off-shore winds along the western margins of the continent, in tropical and sub-tropical regions push the surface water away.
- This causes the cold water from the bottom to rise upwards to the surface.
- This brings cold and nutrient-rich water to the surface through upwelling.
- The reasons for upwelling support large-scale fishing growth. For example, the Humboldt current along the coast of Peru and chile.
- (g) Ocean Currents help in the global distribution of temperature and salinity.
- (h) the warm ocean currents in the temperate region along the western coast of continents, result in mild winters and keep the port ice-free.
- For example, North Atlantic Drift along Britain.
- (i) Ocean currents can be used in navigation, to find directions in the open oceans.
- (j) The merging of Warm and Cold Ocean currents results in fog formation, which may obstruct ocean navigation.

## Upwelling and downwelling (7:17 PM)

- ==Downwelling==
- The on-shore winds pile up the water near the coast, causing the sinking of water below the surface layer.
- Downwelling is more active where warm and cold ocean currents meet.
- ==Upwelling==
- The off-shore winds push the surface water away and cause the cold water from the bottom to rise from the surface.
- Upwelling is more active in the regions of cold ocean currents.
- In Polar regions, ice formation leaves the water saltier and denser causing it to sink.

## Thermohaline Circulation (7:21 PM)

- ![](https://www.e-education.psu.edu/earth103/sites/www.e-education.psu.edu.earth103/files/module06/02_02_04_a.gif)
- The deep ocean currents are driven by differences in the water density, which is controlled by the temperature and salinity and is called thermohaline circulation.
- The circulation begins near polar regions, of the downwelling where ice formation leaves the water saltier and denser leading to the sinking.
- This underwater current moves in a single and continuous belt across the different oceans.
- They are connected to surface water currents in the regions of upwelling.
- They are also called **Great Ocean Conveyor belts.**

## Atlantic Meridional Overturning Circulation (7:46 PM)

- AMOC is a part of the thermohaline circulation, in the Atlantic ocean.
- The recent report of the IPCC, talks about the weakening of AMOC, due to global warming.
- ==Factors responsible for the weakening==
- (a) The temperature difference between the tropical and polar regions is decreasing due to the warming of the arctic region.
- This weakens the north Atlantic drift.
- (b) The excessive addition of freshwater due to increased melting of ice in polar regions.
- This reduces downwelling as the freshwater is less dense.
- ==Impacts==
- (a) Western European countries will experience harsh winters and frozen ports.
- (b) Western parts of Oceans in the tropical regions, will experience a rise in sea levels.
- (c) Increased occurrence of cyclones in tropical waters.
- (d) Disturbance of fishing zones.
- (e) Disturbance of marine ecosystem.
- **==Water Mass==(7:53 PM)**
- **![](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Antarctic_bottom_water.svg/1200px-Antarctic_bottom_water.svg.png)**
- It is a body of water with uniform characteristics of temperature and salinity.
- ==They are three types:==
- (a) ==surface water mass==- For example, Antarctic Surface Water mass
- (b) ==Intermediate water mass==: For example Sub tropical Intermediate water mass of the Atlantic Ocean.
- (c) ==Deepwater mass:== For example, North Atlantic Deep Water Mass
- water mass helps in the generation and maintenance of thermohaline circulation.
- they result in upwelling and downwelling.
- The movement of water mass helps distribute temperature, salinity, and oxygen.
- The uniformity of conditions, within water mass, supports plankton and coral growth.

## The Topic for the next Class: El Nino and the related phenomena