Ocean Water and Ocean Currents

The movement of the ocean currents is mostly continuous and the movement can be categorized broadly as:

1. Waves
2. Tides
3. Currents

The ocean currents refer to the streams of water which flow constantly as the ocean surface with definite directions. Ocean currents are one of the important factors which influence the temperature of ocean water.

The distribution of ocean currents is as below:

The oceans absorb most of the solar radiation falling on them, mainly in tropical areas where most of the radiation is received. This heat is transported poleward by ocean currents along the western margins of the oceans. On reaching the higher latitudes, this heat is lost at the surface as latent heat through evaporation, sensible heat flux, and infrared radiations, thus warming the regions near the coast of the eastern margins of the continents.

The North-Atlantic Drift as an extension of the Gulf Stream brings warm water to the North-Western European Coasts, allowing them to remain ice-free even in winter. Quebec, though located at a lower latitude, on the Canadian coast is frozen due to the Cold Labrador Current flowing past it.

To compensate for the water loss in the tropics, cold water from the polar and temperate regions is transported to tropical areas along the eastern margin of the oceans. Hence, the western margins of continents are relatively colder than the western margin along the same latitude. Hence, ocean currents act as a moderating agent along the longitudes and impact the global climatic pattern along the latitudes.

The ocean currents also influence local weather conditions by warming or cooling the lower atmosphere. A warm ocean current warms the air above it, causing upward convection currents in the atmosphere. The upward movement of air results in cloud formation and hence precipitation is caused in the regions near the coast. On the other hand, a cold ocean current cools the air above it, resulting in the sinking of air and hence no cloud formation. This results in cold dry conditions in the coastal regions. This factor, supported by trade winds and the sinking arm of Hadley’s meridional cell has contributed to the formation of subtropical deserts along the western portions of the continents. For example, the Sahara Desert and the Kalahari Desert in Africa, the Great Australian Desert in Australia, the Atacama Desert in South America, and the Great Western Desert in North America.  These desert regions become very hot in the summer and very cold in the winter.

Walker cell is a vertical latitudinal atmospheric circulation produced as a result of rising air over the warm waters of the Eastern Australian Current and sinking air over the cold Humboldt Current along the Peruvian Coast. One arm of vertical rising air over the Eastern Australian Current diverges towards the Indian Ocean, which strengthens the Indian Monsoon. However, at times, due to the weakening of trade winds in the Pacific Ocean, water flows backward from the Warm Water Pool along the Australian North Eastern Corner, thereby replacing the cold Humboldt Current with a warm water current. This causes cloud formations along the Peruvian coast and hence more than normal rainfall in the region. This reverses the direction of Walker Cell and the phenomenon is called El Nino. Now, air sinks above the Eastern Australian Coast, and hence no arm diverges towards the Indian Ocean, thereby weakening the South West Monsoon over the Indian subcontinent. Conversely, when Humboldt Current becomes extremely cold (the phenomena of La Nina), the Indian Ocean arm of the Walker Cell gets strengthened more than usual. This causes excessive rainfall over the Indian subcontinent while causing excessive acidity along the Peruvian coast.

At some land-ocean boundaries, upwelling caused by the offshore winds brings cold water and nutrients brings from below. This moderates the climate in the tropics and lowers the temperature further in temperate regions.

Thermohaline circulation is also believed to impact climate since it transports a large amount of mass and energy. However, it is difficult to quantify its impact.

Ocean currents refer to the horizontal movement of the seawater which is produced with the help of gravity, wind, and water density. Ocean currents play a vital role in the determination of the climates in the coastal areas. Ocean currents move in two directions: horizontally known as currents and vertically which is known as upwellings or downwelling.