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Cromwell Current

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Cromwell Current

The Cromwell Current (also called Pacific Equatorial Undercurrent or just Equatorial Undercurrent) is an eastward-flowing subsurface current that extends the length of the equator in the Pacific Ocean.

The Cromwell Current was discovered in 1952[1][2] by Townsend Cromwell, a researcher with the Honolulu Laboratory. It is 250 miles (400 km) wide and flows to the east. It is hidden 300 feet (100 m) under the surface of the Pacific Ocean at the Equator and is relatively shallow compared to other ocean currents being only 100 feet from top to base. It has 1000 times the volume of Mississippi River and its length is 3500 miles (6000 km).


  • Townsend Cromwell 1
  • Discovery 2
  • Detailed data 3
  • Interaction with El Niño 4
  • Effect on wildlife 5
  • Possible effect on climate 6
  • References 7
  • See also 8

Townsend Cromwell

Townsend Cromwell, a keen surfer, swimmer and oceanographer, discovered the current that now bears his name whilst researching drifting in the equatorial region of the Pacific Ocean. He died in 1958 when his plane crashed en route to an oceanography expedition.


In 1951 researchers on board the U. S. Fish and Wildlife Service research vessel were indulging in a spot of long line fishing. They noticed that the gear deep under water drifted eastwards. This was unusual because the surface currents of the pacific ocean flow westwards on the equator. (They follow the direction of the winds).

The following year Townsend Cromwell led a research party to investigate how the currents of the ocean varied as a function of depth. They discovered a fast flowing current that flowed eastwards in the deep surface layers.

Detailed data

  • Depth: The surface currents flow west. There is reversal point about 40 m down, where the water starts to flow east. The current goes down to about 400 m.
  • Flow rate:The total flow is up to around 30 000 000 cubic meters per second. The top speed is around 1.5 m/s (this is about twice as fast as the westerly surface current)
  • Length:13,000 km

Interaction with El Niño

El Niño is a reversal of the normal situation in the Pacific Ocean. Surface water is blown westwards by the prevailing winds and deeper water is forced upwards to replace it. Every now and then, the surface water sloshes back across the ocean, bringing warm water temperatures along the eastern coasts of the pacific. In non-El Niño years, the Cromwell current is forced to the surface by underwater seamounts near the Galapagos islands (this is called upwelling.) However during El Nino years the current does not upwell in this way. The waters around the islands are therefore considerably warmer during El Niño years than during normal years.

Effect on wildlife

The Cromwell Current is both oxygen- and nutrient-rich. A large number of fish are concentrated in it. Upwelling occurs near the Galapagos islands. This brings food supplies to the surface for Galápagos penguin. Upwelling, however, is a sporadic phenomenon; it fails to occur on a regular basis, and so the food supply comes and goes. The penguins have several adaptations to cope with this, including versatility in their breeding habits.

Possible effect on climate

The effect of this current on world climate is not well understood.


  1. ^ Cromwell, Townsend (1953). "Circulation in a meridional plane in the central equatorial Pacific." Journal of Marine Research 12 196-213.
  2. ^ Cromwell, T., Montgomery, R. B., and Stroup, E. D. (1954). "Equatorial undercurrent in the Pacific Ocean revealed by new methods." Science 119 (3097) 648-649.

See also

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