Phytoplankton Near Coast of Namibia21S 11.7E
A greenish phytoplankton bloom is visible off the coast of Namibia in the lower left hand corner. Such blooms occur frequently in the Atlantic Ocean off southwest Africa, due to cold, nutrient-rich currents that move northward from Antarctica and interact with the coastal shelf.
Simultaneously, the easterly trade winds move surface water away from the coast, permitting water from the ocean’s depths to bring iron and other nutrients to the surface. These nutrients from the currents and upwelling water create a very favorable environment for phytoplankton.
Incredibly, phytoplankton blooms occur so frequently off the Namibian shores that they actually cause a loss of dissolved oxygen in the waters when they die and decompose. After the phytoplankton die, they sink and are consumed by bacteria, which use the dissolved oxygen in the process of breaking down the tiny plants. When dead phytoplankton are overly abudant, the bacteria use all of the available oxygen in the water, creating an area in the ocean where fish cannot live.
In turn, anaerobic bacteria, which do not require oxygen, take over the process of breaking down the phytoplankton, simultaneously releasing sulfur dioxide. The sulfur dioxide then interacts with the ocean water and creates poisonous hydrogen sulfide gas, which may kill fish as it moves to the surface.