Though these aquamarine clouds in the waters off the coast of northern Namibia
may look like algae blooms, they are in fact clouds of sulfur produced by
anaerobic bacteria on the ocean’s floor. This image of the sulfur-filled water
was taken on April 24, 2002, by the Sea-viewing Wide Field-of-View Sensor
(SeaWiFS), flying aboard the Orbview-2 satellite.
The anaerobic bacteria (bacteria that can live without oxygen) feed upon
algae carcasses that exist in abundance on the ocean’s floor off of Namibia. As
the bacteria ingest the algae husks, they produce hydrogen sulfide, which slowly
builds up in the sea-floor sediments. Eventually, the hydrogen sulfide reaches
the point where the sediment can no longer contain it, and it bubbles forth.
When this poisonous chemical reaches the surface, it combines with the oxygen in
the upper layers of the ocean to create clouds of pure sulfur. The sulfur
causes the Namibian coast to smell like rotten eggs, and the hydrogen sulfide
will often kill fish and drive lobsters away.
People living along Namibia’s desert coast have long been familiar with the rotten-egg smell that periodically emanates from the Atlantic Ocean. With an economy that is largely based on fishing, the locals are also used to seeing millions of fish die whenever the unpleasant scent fills the air. The smell and the fish die-off are caused by hydrogen sulfide erupting from decaying plants on the sea floor. On May 12, 2004, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image of a hydrogen sulfide eruption in progress.