Modifying Factors for the generation of Ocean Currents

There are certain other factors which do not help the generation of ocean currents, but they bring about important changes in the direction, velocity and extent of already generated ocean currents.

1. Nature of sea coast

2. Seasonal changes

3. Bottom topography of oceans.

1. Nature of sea coast:

The shape and direction of sea coasts modify the ocean currents. When ocean currents approach a coast, they start flowing in accordance with the alignment of the coast.

The South Equatorial Current reaching the coast of South America is split into two branches by the topographic interference of the eastern extension of Brazil, Cape San Rogue.

One branch of the South Equatorial Current enters into the Caribbean Sea moving along the northeastern coast of South America. The other branch moves off along the Brazilian coast towards the south.

It is called the Brazil Current. Similarly in the Pacific Ocean also different islands exercise dominant control on the movement and direction of ocean currents by the nature of their coasts.

Another most glaring example of the modifying effect of the nature of coasts is found in the Indian Ocean where ocean currents induced by the monsoon are influenced by the shape of the coastline of the Indian Peninsula.

So is the case with Gulf Stream, whose direction of flow clearly demonstrates the effect of the eastern coast of the United States of America.

2. Seasonal Changes:

In certain regions the direction of ocean currents undergoes a change along with the changes in the seasons. Ocean currents in the north Indian Ocean change their direction with the seasonal reversal of winds, the monsoons.

During the winter monsoon (the northeast monsoon) the surface current moves south along the coast of Indian Peninsula and turns west at about 10°N latitude.

During the southwest monsoon the North Equatorial Current disappears, and a part of the South Equatorial Current starts flowing north along the Somali coast as the Somali Current.

Seasonal changes cause displacement of the pressure as well as the wind belts. Therefore the ocean currents, particularly the North Equatorial and the South Equatorial currents in the Atlantic and the Pacific oceans are also affected by the seasonal changes.

3. Bottom topography:

Ocean currents are also subject to modification by the bottom relief of the oceans. Any type of physical barriers presents on the bottom of oceans influence the flow of currents to a large extent.

Currents of the mid-latitudes as well as the Polar Regions in particular are all the more affected by the bottom relief of the oceans. Whenever there are physical barriers obstructing the path of deeper currents, they tend to deflect to the right of their path in the northern hemisphere and to the left of their path in the southern hemisphere.

Even the surface currents are also affected by the presence of such physical obstructions. For example, due to the presence of the Mid-Atlantic Ridge almost all the currents of the North Atlantic Ocean are affected to a certain extent.

When the Gulf Stream crosses the Wyville Thompson Ridge, various changes occur in it. The maximum effect of the bottom relief on ocean currents is visible in those parts of the oceans where there are many islands or where the water is shallow because of the presence of continental shelf.

The bottom relief of the oceans controls the details of the deep oceanic circulation. The Arctic Sea waters, for example, are not allowed to move southward at depth due to the obstruction caused by the submarine ridges north of Iceland and across the Bering Sea.

Similarly, the submarine ridges present at the entrance to the Arctic Basin prevent any bottom waters formed in the Arctic Sea from coming into the open ocean of the Atlantic.

The Bering Strait is very narrow (58 km) and very shallow (58 m). So there is a very small exchange of water through it between the Pacific and Arctic Oceans.

Water of the Atlantic origin enters the Arctic Basin mainly through the deep channel between Greenland and Spitzbergen and spreads towards the east, along the margin of the continental shelf of Eurasia, and towards the North Pole.

In addition to the above-mentioned factors, the earth’s rotation on its axis plays very important role in modifying the direction of the path of motion of the ocean currents.

As stated earlier, the Coriolis force produced due to the rotation of the earth tends to deflect all the currents of the northern hemisphere to the right of their path and those of the southern hemisphere to their left.