Ocean Currents

Ocean currents are the continuous, predictable, directional movement of seawater driven by gravity, wind, rotation of the earth (Coriolis Effect), and water density. They are characterised based on their temperature (as cold or warm) and based on their depth (as surface or deep currents). They have numerous effects like regulating the climate, marine life and facilitating ocean travel.They become determinant factors for people's lives and livelihoods in coastal areas.

Oceanic currents describe the horizontal movement of water from one location to another. Currents are generally described by their speed or drift which is measured in meters per second or in knots (1 knot = 1.85 KMPH or 1.15 miles per hour). They are strongest on the surface and slow down closer to the ocean floor. Their average speed is 5knots.

• Based on Temperature: Cold and Warm Ocean Currents.
  • Cold currents: Carry cold water from high latitudes (near the poles) to lower latitudes (near the equator). They are found on the east coast of the continents in Northern Hemisphere e.g. the Labrador Current and the East Greenland Current.
  • Warm currents: Carry warm water from the equator to higher latitudes. Mostly found off the east coasts of continents in the lower and middle latitudes (i.e. closer to the equator). In the Northern Hemisphere, they are found on the west coasts of high latitudes e.g. Alaska Current.
    • E.g. Durban on the eastern coast of South Africa is affected by the warm Mozambique current and has temperatures of 24.4°C compared to Port Nolloth on the west coast along the same latitude which has temperatures of 15.5°C because of the cold Benguela current.
• Based on Depth: Deep and Surface Ocean Currents.
  • Deep ocean currents: Move slowly and deep beneath the surface. They are driven by density differences caused by temperature and salinity. They are the 90% of ocean water slowly moving around ocean basins.
  • Surface ocean currents: Move faster and closer to the surface. They are driven by wind and solar energy. Only around 10% of all water in the ocean is at the top 400m.

Ocean currents offer several advantages, particularly along the coasts of continents, which significantly influence local climates and marine ecosystems:

• Climate Regulation: Along the west coasts of continents in tropical and subtropical latitudes (excluding areas near the equator), cold ocean currents provide a moderating influence on climate. Conversely, in middle and higher latitudes, warm ocean currents along the west coasts create distinct marine climates.
• Moisture and Rainfall: Warm ocean currents flowing parallel to the east coasts of continents in tropical and subtropical latitudes contribute to warm and rainy climates in these regions. This moisture-laden air supports lush vegetation and agricultural activities.
• Ecological Benefits: The mixing of warm and cold ocean currents helps replenish oxygen levels in the water, creating favorable conditions for the growth of plankton, which forms the primary food source for marine ecosystems. This abundance of plankton supports diverse fish populations and contributes to thriving marine ecosystems.
• Fishing Opportunities: Some of the world's best fishing grounds are located in these mixing zones where warm and cold currents converge. The nutrient-rich waters support a wide variety of fish species, attracting commercial fishing activities and providing livelihoods for coastal communities. Examples include Newfoundland which benefits from the convergence of the Labrador and Gulf Stream currents, while Honshu Island in Japan benefits from the Oyashio and Kuroshio currents.
• Navigation: Ocean currents assist ships in navigating the seas. For example, when a vessel needs to journey from Mexico to the Philippines, it can utilize the North Equatorial Current route for a more efficient passage.

Three Ocean Currents Flow through all Oceans:-

• North Equatorial Current (Warm):
  • The North Equatorial Current originates off the western coast of Mexico and flows westward, reaching the Philippines coast after covering approximately 7500 nautical miles.
  • In the Pacific Ocean, it is formed by the Californian current and north-east monsoon winds. As it progresses westward, numerous minor currents contribute to its volume.
  • In the Atlantic Ocean, it is influenced by the cold Canary current, causing it to move westward. Upon encountering the east coast of Brazil, the current splits into two branches: the Antilles current and the Caribbean current.
• South Equatorial Current (Warm):
  • The South Equatorial Current is a significant current in the Atlantic, Pacific, and Indian Oceans, flowing from east to west between the equator and about 20°S.
  • The South Equatorial Current is generated by the influence of southeast trade winds, flowing from east to west. It is stronger than the north equatorial current and gains volume as minor currents join from the left.
  • In the Pacific Ocean, Near New Guinea, it bifurcates into northern and southern branches.
  • In the Atlantic Ocean, it is essentially an extension of the cold Benguela current. Upon encountering the east coast of Brazil, it splits into two branches: one moves northward and merges with the north equatorial current near Trinidad, while the other turns southward, becoming the Brazil warm current along the east coast of South America.
• Counter Equatorial Current (Warm):
  • The Counter Equatorial Current flows eastward between the north and south equatorial currents. It is caused by the immense volume of water accumulating in the western marginal parts of the ocean due to trade winds. This current is particularly well-developed in the Pacific Ocean.
  • It carries relatively warmer water with lower density compared to the equatorial currents.

Pacific Ocean Currents:

• Kuroshio System (Warm): The Kuroshio system, resembling the Gulf Stream system in the Atlantic Ocean, encompasses multiple currents and drifts extending from Taiwan to the Bering Strait. This system includes the Kuroshio Current, Kuroshio Extension, North Pacific Drift, Tsushima Current, and Counter Kuroshio Current.
  • Kuroshio Current: Originating from the deflection of the north equatorial current northward due to the obstruction of the Philippines, the Kuroshio Current flows from Taiwan to the Ryukyu ridge around 30°N latitude. Similar to the North Atlantic's Florida Current, the Kuroshio is a warm current.
  • Kuroshio Extension: Departing from the Japanese coast near 35°N latitude and influenced by the westerlies, the Kuroshio Extension bifurcates into two branches. One branch moves eastward while the other flows northeastward before turning eastward. Ultimately, the northern branch merges with the cold Oyashio current from the north.
  • North Pacific Drift: Under the influence of the westerlies, the Kuroshio Current extends eastward, reaching the western coast of North America. Before reaching 150°W longitude, part of this current turns southward, while the rest continues eastward towards the Hawaiian coast and the western coast of North America.
    • The North Pacific Drift divides into the Aleutian current and the Californian cold current.
    • The Aleutian current further splits into two branches, with one heading towards the Bering Strait and the other towards the Gulf of Alaska.
  • Tsushima Current: A branch separates from the Kuroshio Current at approximately 30°N latitude, entering the Japan Sea as the Tsushima Current. This warm current, characterized by higher temperature and salinity, influences the weather conditions along the western coast of Japan.
  • Counter Kuroshio Current: Forming a gyral system between the Hawaiian islands and the American coast, the Counter Kuroshio Current causes oceanic water to flow westward.
• Oyashio Current (Cold):
  • The Oyashio current, also known as the Kurile or Oya Siwo cold current, flows southward through the Bering Strait, transporting cold water from the Arctic Sea into the Pacific Ocean.
• California Current (Cold):
  • The California current, an example of a cold current, is the eastward extension of the North Pacific drift. It is generated by the movement of oceanic water along the Californian coast, compensating for water loss caused by the north equatorial current. After reaching the Mexican coast, it turns westward and merges with the north equatorial current.
• Peru Current (Cold):
  • The Peru current, also known as the Humboldt Current, flows northward along the western coast of South America. It is referred to as the Peru coastal current near the coast and the Peru oceanic current offshore.
• El Nino or Counter Current (Warm):
  • The El Nino current, a subsurface warm current, flows from north to south along the Peruvian coast. It is caused by the southward shift of the counter equatorial warm current during southern winter. El Nino affects rainfall along the coasts and influences monsoons in the Indian Ocean.
• East Australia Current (Warm):
  • The South Equatorial Current bifurcates near the Australian coast, with the southern branch flowing as the East Australia Current along the eastern coasts of Australia. It is deflected eastward near 40°S latitude and warms the east Australian coast.
• West Wind Drift (Cold):
  • The West Wind Drift is a strong ocean current flowing from west to east between Tasmania and the South American coast. It gains strength due to high-velocity winds called the roaring forties and bifurcates into two branches, one entering the Atlantic Ocean through Cape Horn and the other joining the Peru Current.

Atlantic Ocean Currents:

• Gulf Stream (Warm):
  • The Gulf Stream is a swift system of currents moving northeastward. Originating in the Gulf of Mexico near 20°N latitude, it flows along the eastern coast of North America to approximately 70°N latitude near the western coasts of Europe.
  • The Gulf Stream consists of several currents, including the Florida current, which extends from the Strait of Florida to Cape Hatteras. As it moves northward, it merges with the North Equatorial Current, impacting weather conditions and creating eddies in the Sargasso Sea.
• Canaries Current (Cold):
  • The Canaries Current is a cold current that flows southward along the coasts of Europe and Africa, eventually merging with the North Equatorial Current. It brings cold water from high latitudes to lower latitudes and helps moderate the warm weather conditions of North Africa's western coasts.
• Labrador Current (Cold):
  • The Labrador Current is a cold current flowing southeastward along the eastern coast of Canada, meeting the warm Gulf Stream off Newfoundland. This confluence creates foggy conditions around Newfoundland, making it a prime fishing area.
• Brazil Current (Warm):
  • The Brazil Current is formed by the bifurcation of the South Equatorial Current due to obstruction from the Brazilian coast. The northern branch merges with the north equatorial current, while the southern branch flows southward along the east coast of South America.
• Falkland Current (Cold):
  • The Falkland Current carries cold waters from the Antarctic Sea northward along the eastern coast of South America up to Argentina, bringing icebergs from the Antarctic region.
• South Atlantic Drift (Cold):
  • The South Atlantic Drift, also known as the Westerlies Drift or Antarctic Drift, is the eastward continuation of the Brazil Current. It flows eastward under the influence of westerlies.
• Benguela Current (Cold):
  • The Benguela Current flows northward along the western coast of South Africa, merging with the South Equatorial Current further north.

Indian Ocean:

• North-East Monsoon Current (Warm):
  • During the winter season in the northern hemisphere, the Indian Ocean experiences north-east monsoon winds blowing from the land to the ocean, resulting in westward-flowing north-east monsoon currents. These currents are observed south of the 5°N latitude. Additionally, independent currents originate in the Bay of Bengal and the Arabian Sea, flowing in a south-westerly direction.
• Indian Counter Current (Warm):
  • The Indian counter current emerges during the winter season in the northern hemisphere, flowing eastward between latitudes 2° to 8°S, from Zanzibar to Sumatra.
• South West Monsoon Current (Warm):
  • In the summer season, there is a complete reversal in the direction of monsoon winds. The north-easterly winter monsoon winds shift to south-westerly during the summer season in the northern hemisphere, leading to a reversal in the Indian Ocean currents.
  • The north-east monsoon currents disappear, replaced by south-west monsoon currents. The general direction of these currents is from south-west to north-east, with minor branches emerging in the Bay of Bengal and the Arabian Sea. Consequently, the Indian counter current, developed during the winter season, ceases to exist.
• South Equatorial Current (Indian Equatorial Current) Warm:
  • The Indian Equatorial current is a warm current flowing from east to west between latitudes 10°S to 15°S, extending from the Australian coast to the African coast.
  • After encountering Madagascar, this current divides into multiple branches. One major branch flows southward as the Agulhas current, while another moves northward.
• Mozambique Current (Warm):
  • A branch of the south equatorial current passes through the Mozambique channel, known as the Mozambique current. This current joins the Agulhas current near 30°S latitude, extending to the southern tip of Africa before being redirected eastward.
• The West Wind Drift (Cold):
  • The West Wind Drift current is generated by the eastward-blowing westerlies along the 40°S latitude, also known as the roaring forties. This current splits into two branches near 110°E longitude.
  • One branch turns northward, forming the West Australian cold current along the western coast of Australia, then veering westward and north-westward, eventually merging with the south equatorial current near 100°E longitude. The second branch of the West Wind Drift turns southward.