OCEAN CURRENTS

OCEAN CURRENTS

Ocean Current is a horizontal movement of seawater that is produced by gravity, wind, and water density.

Classification of Ocean Currents

• Based on depth
  • Surface currents: Constitute about 10% of all the water in the ocean, these waters are the upper 400 m of the ocean.
  • Deep water currents: Make up the other 90% of the ocean water. These waters move around the ocean basins due to variations in density and gravity.
• Based on the temperatures
  • Cold ocean current: They bring cold water into a warm water ocean. They are generally found on the west coast of the continents in the lower (excluding near equators) and middle latitudes in both hemispheres. It is also found on the east coast of the continents in the higher latitudes.
  • Warm Ocean current: It brings warm water into cold water areas and is usually observed on the east coast of continents on the low and middle latitudes in both hemispheres and also found on the west coast of higher latitudes in the northern hemisphere.

Factors responsible for Ocean Currents

• Planetary winds: Planetary winds are permanent winds that blow from one pressure belt to the other. They are probably the dominant influence on the flow of ocean currents.
  • For Example: In the North Indian Ocean there is a change in the direction of ocean currents with a change in direction of the monsoon winds.
• Insolation: Heating by solar energy causes the water to expand. This causes a very slight gradient and water tends to flow down the slope causing ocean current. The flow is normally from east to west.
• Salinity: The density of water also depends on its salinity and the salinity of water varies from place to place. Waters of low salinity flow on the surface of waters of high salinity while waters of high salinity flow at the bottom.
• Earth’s rotation: The earth’s rotation deflects moving objects to the right, and ocean currents are no exception.
• Coriolis force: Under the action of Coriolis force, the movement of ocean currents in the northern hemisphere is in the clockwise direction, and in the southern hemisphere, it is in the anti-clockwise direction. Hence, it can be said that ocean currents obey Ferrel’s law.
• Obstruction due to land: A land mass obstructs the direction of flow of ocean current and divides the ocean current, which in turn flows in a different direction.
  • For Example: The south equatorial current in the Atlantic Ocean is obstructed by the South American continent, and the South equatorial current divides to create the Brazilian current, which flows in the south Atlantic Ocean.
• Other factors: Accumulation of water on east coasts leads to gravity-induced movements down the slope. Wind, coastline and inundation, large river discharge, and the presence of partially enclosed seas also modify ocean currents.

Importance and Significance of Oceanic Currents

1. Geographical and Environmental

• Desert Formation: Cold ocean currents have a direct effect on desert formation in west coast regions of the tropical and subtropical continents.
  • For Example: The Peru Current, also called Humboldt Current, is a cold-water current of the southeast Pacific Ocean and a primary reason for the aridity of the Atacama Desert (driest desert in the world).
  • For Example: The Californian current, which is a cold current, brings a dry and desert type of climate to the region.
• Moderating effect: They are responsible for moderate temperatures at coasts.
  • For Example: The Gulf Stream, which is driven to the western coast of Europe as the North Atlantic Drift, keeps the coasts of the North Sea warm, which is unusual for such high latitudes.
  • Similarly, the warm waters of the Kuroshio current in the North Pacific Ocean are carried as the North Pacific Drift, keeping the ports of the Alaskan coast ice-free in winter.
• Precipitation: Warm ocean currents bring rain to coastal areas and even interiors.
  • For Example: Summer rainfall in the British type of climate.
• Local Climate: Winds blowing over a warm current or cold current become warm and cold respectively, and at the same time, influence the local climate accordingly.

• Tropical cyclones: They pile up warm waters in the tropics, and this warm water is the major force behind tropical cyclones.
• Distribution of nutrients and food: They carry nutrients and food to organisms that live permanently attached in one place and carry reproductive cells and ocean life to new places. Ocean currents are also very important in the dispersal of many life forms.
  • For Example: An example is the life cycle of the European Eel.
• Upwelling: It refers to the rise of ocean bottom water (rich in nutrients) onto the surface. Some of the driest coastal areas on earth are associated with upwelling. It results in desiccation in nearby areas and brings nutrients to the surface, which provides productive fishing grounds.
  • For Example: N-Western Mexico, Northern Chile & Peru (West coast of S. America, N-W & S-W Africa).

2. Economic

• Fishing: The mixing of warm and cold currents helps to replenish the oxygen and favor the growth of planktons, the primary food for fish populations.
  • For Example: Grand Banks around Newfoundland, Canada, and the North-Eastern Coast of Japan.
• Navigation: The atmospheric circulation of the winds and the oceanic circulation of the currents are almost coincidental, and together they aid in the navigation of ships. Ocean currents flow for great distances, and together with the winds, create a conveyor belt system for ship navigation.
  • For Example: If a ship wants to travel from Mexico to the Philippines, it can use the route along the North Equatorial Drift, which flows from east to west.
  • When traveling from the Philippines to Mexico, ships can follow the route along the doldrums when there is a counter equatorial current flowing from west to east.
• Power generation: Ocean currents can also be used for marine power generation, with areas off of Japan, Florida, and Hawaii being considered for test projects.
• Agriculture: Ocean currents influence, in many cases, well beyond the coast. Such influence, characterized mostly by temperature, precipitation, and cloud cover, determines the length of the growing season, and hence many other economic activities of the region.
  • For Example: Indian Kharif season.

Impact of Climate Change on Ocean Currents

• Balance of Oceanic movement: There is an elegant balance to the complex movements of ocean currents, mediated by multiple factors, yet maintaining consistent temperature gradients that make most latitudes hospitable to life.

• Slow down effect: As ocean water warms to greater depths, and temperatures climb in the polar regions, major ocean currents may slow down or even stop.
  • For Example: Scientists are already observing a slowdown in a powerful Northern hemisphere ocean current system known as the Atlantic Meridional Overturning Circulation (AMOC), which helps moderate temperatures on the European continent.
• Shift in temperature: This could lead to dramatic shifts in temperature everywhere—higher latitudes may be plunged into Ice-Age-like conditions, while heat waves might render equatorial regions virtually uninhabitable.

Solution:

• Reduce Carbon emission: Worst-case scenarios can still likely be avoided if strong action is taken to reduce carbon emissions globally.
• Reduce oceanic waste dumping: Increasing pollution in the ocean is another major reason for the effect on ocean currents.

A failure to take those actions will lead us into uncharted territory, and if that causes ocean currents to slow or shut down, it could set off a chain reaction of climate change that will turn hundreds of millions of people (at least) into refugees, fleeing their homes in a desperate search for more habitable regions.

EL-NINO AND LA-NINA

El-Nino

• Meaning: It is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean.
• Effects:

• Impact on Ocean: El Nino also impacts ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America and beyond.
• Increased Rainfall: Convection above warmer surface waters brings increased precipitation. Rainfall increases drastically in South America, contributing to coastal flooding and erosion.
• Increased Droughts: Due to the weakening of Leeuwin warm current, there is a pile-up of cold water on the West coast of Australia, which creates drought-like conditions.
• Forest Fire: Due to a deficiency in rainfall in Southeast Asia, the Savanna forest of Indonesia catches fire due to high temperatures.
• Diseases caused by Floods and Droughts: Diseases thrive in communities devastated by natural hazards such as floods or drought.
• Decrease Fishing: Due to low pressure in the Eastern Pacific, there is a deficiency in upwelling of nutritious water, which makes fishing difficult.
• Effect on Indian monsoon: Statistically, it is found that El-Nino has a negative correlation with the summer monsoon in India. Due to high pressure conditions in the western Pacific or Indian Ocean, there is a weakness in wind flow which affects the monsoon.

La-Nina

• Meaning: La Nina events represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific.
• Effects:

• Europe: La Nina tends to lead to milder winters in Northern Europe (especially UK) and colder winters in southern/western Europe leading to snow in the Mediterranean region.
• North America: In continental North America, most of these conditions are felt. The wider effects include:
  • Stronger winds along the equatorial region, especially in the Pacific.
  • Favorable conditions for hurricanes in the Caribbean and central Atlantic area.
  • Greater instances of tornados in various states of the US.
• South America: La Nina causes drought in the South American countries of Peru and Ecuador.
  • It usually has a positive impact on the fishing industry of western South America.
• Western Pacific: In the western Pacific, La Nina increases the potential for landfall in those areas most vulnerable to its effects, and especially into continental Asia and China.
  • It also leads to heavy floods in Australia.
  • There are increased temperatures in the Western Pacific, Indian Ocean, and off the Somalian coast.
• India: Statistically, La-Nina is seen to have a positive correlation with summer monsoon rain in India.

From helping to keep our planet warm, to influencing precipitation patterns around the world, to playing a critical role in the global carbon cycle—ocean currents are one of the major determinants of weather and climatological conditions.