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The Living Edens
 
The Benguela Current

The Benguela Current is the eastern boundary current of the South Atlantic Ocean. The Benguela, as we know it today, is only about two million years old. It formed to its current state after two geological events -- the closing of the strait that connected the Americas, and formation of the Antarctic ice cap. These developments closed off the Atlantic Ocean, closing off an area for currents to circulate toward the equator.

Ocean currents of South Africa

     

The Benguela Current

The process that contributes most to the Namib's unique ecosystem is the coastal, wind-induced "upwelling" that occurs along the Benguela shelf. The Benguela Current's effect is enhanced by a southwesterly wind, which increases in September and October (early in the southern summer) and blows for approximately 280 days of the year. As this wind strengthens, it drives the surface layers of the Benguela northward, almost parallel with the land. Another wind, the Coriolis Force, deflects this warmer water to the west, causing the colder, deeper layers to surface and replace it. The deeper water rises up from a depth of about 980 feet (300 meters), cooling the surface water on average as much as 41 degrees (5 degrees C) lower than offshore water in the South Atlantic at similar latitudes.

The deeper layers of the Benguela are rich in phosphates and nitrates, a result of the decomposition of animals and plants on the ocean floor. Since there is not enough light below 160 feet (50 meters) underwater to make photosynthesis possible, these nutrients are usually not utilized by phytoplankton.

Water falling down cliffs

However, the upwelling of these nutrients causes dense phytoplankton blooms. Zooplankton then thrive on these abundant phytoplankton blooms, attracting filter-feeding fish such as sardines and anchovies. These filter-feeders are in turn are fed on by larger fish, birds, and mammals such as seals and whales. Because of the effect of the upwelling along the Benguela coast, the Namib supports a biomass that has few rivals in the entire world.

The Benguela Current also helps moderate the climate of the Namib. Factors like solar radiation and dessicating winds are far less extreme than in other deserts that are mid-continental and not coastal. Air temperatures rarely climb to over 104 F (40 C), but can fall to near freezing in the Namib during the winter.


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