Oceanic Currents

Oceanic currents are propelled into motion by prevailing winds, the trades and the westerlies. These are caused by the interaction of the sun’s energy warming up the earth at different rates from the poles to the equator, and the Coriolis Effect. This effect is induced by the rotation of our planet – anything near the equator moves faster than objects near the poles. Therefore, the winds blowing towards the equator are “left behind” by the rotating earth and bend to the west. The winds blowing away from the equator “outpace” the earth and deflect to the east.

The air at the equator warms up rapidly from the heated surfaces of the continents and oceans. This hot air rises high into the atmosphere creating a zone of low barometric pressure alongside the equator. The low-pressure void is filled with air blowing from the direction of the Tropic of Cancer in the northern hemisphere, causing winds called north-easterly trades, and the Tropic of Capricorn in the southern hemisphere, causing south-easterly trades. These trade winds deflect to the west due to the Coriolis Effect. At high altitudes, the air moves in the direction of the poles, cools down, becomes denser and descends back to the surface of earth, causing a high-pressure zone at around 30° latitude.

On the poles, however, freezing temperatures cause the air to become dense and move downwards, resulting in a high-pressure zone. The air escapes from the poles in the form of polar winds. The Coriolis Effect deflects the polar winds to the west and when they reach 60° latitude, they warm up and start to rise, creating a low-pressure zone.

Between the high-pressure zone at 30° latitude and low-pressure zone at 60° latitude, the air moves towards the poles and is deflected east.

The trade winds and the westerlies cause ocean waters to form five major oceanic gyres. The climate on the Galápagos is determined by four oceanic currents caused by the effects of the South Pacific gyre. The waters of the South Pacific flow from the south to the north alongside the shore of South America. The prevailing trade winds push the surface water away from the continent and it is replaced by the cold water from the depths of the ocean, the Humboldt Current, also known as the Peru Current. This current is the most productive marine ecosystem in the world, supporting an extraordinary abundance of marine life. It is also the prevailing surface current of the Galápagos Islands.

The oceanic currents alongside the equator flow from east to west until they reach a continent. The amount of water accumulating at the shore bulge.
The average difference between the surface on the west and the east side of the ocean is two metres (6.5 feet). This water follows the gravitational pull and flows back, creating the narrow Equatorial Counter Current between the South and North Equatorial Currents. This current is weak, but carries water with the highest surface temperature of all the oceans. When the Pacific Equatorial Counter Current reaches the shores of Central America it diverts south, and washes the Galápagos from the north east in the form of the warm Panama Current, mainly influencing the islands in the north. The islands of Darwin and Wolf are surrounded by water that is several degrees warmer than the rest of the archipelago.

Townsend Cromwell, a prominent oceanographer with the Pacific Oceanic Fishery Investigations in Honolulu, coincidentally discovered, during an expedition in 1952, a fast-flowing current that moved eastwards in the deep surface layers of the Pacific at the equator. This undercurrent flows between 100–200 m (330–660 ft) deep and is only about 100 m (330 ft) thick. The Cromwell Current, as it is called, has a thousand times the volume of the Mississippi river and its speed matches the strongest currents in the world at c.1.5 m/s (3 kn). What causes this massive flow is, as yet, unclear, but some believe that the mechanism may be similar to the Equatorial Counter Current. The Galápagos happens to be situated in the path of the Cromwell Current, causing an upwelling of cold water on its western side around Isabela and Fernandina, although the eddies of the cold undercurrent reach the inner islands too, such as Floreana, Santiago, Española, San Cristóbal, and Santa Cruz.