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
• 
• 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) 

• 
• 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)
• 
• 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