Oceans Submarine Relief and Water Circulation: Spring and Neap Tides, Currents of The Atlantic Ocean

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Spring and Neap Tides

The moon, as it is closer to the earth, exerts twice the gravitational pull of the sun on the earth. When the sun and the moon are in a line as on a new moon or a full moon day, both of them pull together at the same time in the same direction. This combined pull produces an extra-large tide. It is called a spring tide. In its first quarter and the third quarters, the gravitational force of the two heavenly bodies is at right angle. At this time, the two pulls are opposing each other and are not acting in the same direction. It produces a weak tide which is called a neap tide see.

Spring Tides and Neap Tides

Spring Tides and Neap Tides

Spring Tides and Neap Tides

Effect of Tides

Tides act as link between the port and the open sea. Some of the major ports of the world, such as London port on the river Thames and Kolkata port on river Hugli are located on the rivers away from the seacoast. The tidal current clear away the river sediments and slows down the growth of delta. It increases the depth of water which helps the ships to move safely to the ports. It also acts as a source for producing electricity from tidal energy.


The ocean currents are horizontal flow of a mass of waters in a fairly defined direction over great distance. The average speed of current is between 3.2 km to 10 kms per hour. Ocean currents with higher speed are called stream and currents with lower speed are called drift.

Ocean currents can be broadly divided into two types:

  • Warm currents which flow from equatorial regions towards poles have a higher surface temperature.

  • Cold currents which flow from Polar Regions towards equator have a lower surface temperature.

The origin and the nature of circulation of the ocean currents depend on the following factors:

Differences in Density

  • The density of sea water varies from place to place according to its temperature and proportion of salinity. The higher the temperature of water, the lesser will be the density. Hence cold currents always move from the poles to the equator while the warm currents move from equator towards the poles.

  • Currents are also produced by changes in the salinity of ocean waters. If the salinity of the water is more, the density of the water increases and the water sinks. Hence water with lower salinity flows on the surface of the high salinity water while an undercurrent of high salinity flows towards the less dense water.

The Earth’S Rotation

Due to the earth’s rotation air deflects to its right in the northern hemisphere and to its left in the southern hemisphere. In the same way, ocean water is also affected by Coriolis Force and follows the Ferrel’s Law. All the ocean currents follow clockwise direction in the northern hemisphere, and anticlockwise direction in the southern hemisphere.

The Planetary Winds

The planetary winds like the trade winds and westerlies, drive the ocean water in a steady flow in front of them. In low latitudes or in the region of the trade winds the ocean currents change their direction according to the change in the direction of summer and winter monsoon winds.

Currents of the Atlantic Ocean

  • Between the north and south equatorial currents is the Counter Equatorial Current which flows from west to east. This counter current replaces the water removed from the eastern side of the oceans by North and South Equatorial Currents.

  • The South Equatorial Current bifurcates into two branches near the Cape De Sao Roque in Brazil. The southern branch turns south and flows along the eastern coast of South America as Brazil Current. Its northern branch joins the North Equatorial Current. This combined current enters the Caribbean Sea and the Gulf of Mexico, while the remaining current passes along the eastern side of the West Indies as the Antilles Current. The part of the current which enters the Gulf of Mexico, comes out from the Florida strait and joins the Antilles Current, known as Florida Current up to the cape of Hatteras. Beyond the Cape Hatteras, up to the Grand Banks, off Newfoundland, it is known as the Gulf Stream. From the Grand Banks, the Gulf Stream is deflected eastwards under the combined influence of the westerlies and the rotation of the earth and crosses the Atlantic Ocean as North Atlantic Drift.

Surface Currents of the Atlantic Ocean

Surface Currents of the Atlantic Ocean

Surface Currents of the Atlantic Ocean

  • The North Atlantic Drift bifurcates into two branches on reaching the eastern part of the ocean. The northern branch continues as North Atlantic Drift, reaches the British Isles from where it flows along the coast of Norway as the Norwegian Current. The southern branch flows between Spain and Azores Island as the cold Canaries Current. The Canaries Current finally joins the North Equatorial Current and completes the circuit in the North Atlantic Ocean. Within this circuit lies the Sargasso Sea which is full of large quantities of seaweeds called Sargassum, a brown alga.

  • Apart from the clockwise circulation of the currents in the North Atlantic Ocean, there are also two cold currents which flow from the Arctic Ocean into the Atlantic Ocean including the Labrador Current which flows along the eastern coast of Canada and meets the warm Gulf Stream. The confluence of these two currents, one cold and the other hot, produces fog around Newfoundland and makes it the most important fishing ground of the world. The other one is the East Greenland Current which flows between Iceland and Greenland and cools the North Atlantic Drift at the point of their confluence.

  • Near the Cape of Good Hope, the South Atlantic Current is diverted northward as the cold Benguela Current. It finally joins the South Equatorial Currents thus completing the circuit. Another cold current, known as the Falkland Current, flows along the South eastern coast of South America from south to north.

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