A milky green cloud of water off the Namib Desert coast of Namibia in southern Africa is a tell-tale sign of sulfur rising to the surface. The yellowish clouds of sulfur come from hydrogen sulfide gas produced by anaerobic bacteria (bacteria that can live without oxygen) at the ocean floor. In this region, strong currents bring abundant food from the bottom of the ocean to nurture large plant and animal populations. As the surface life dies, it sinks to the bottom of the ocean, where it becomes food for anaerobic bacteria.. The bacteria release hydrogen sulfide gas, which produces pure sulfur when it reacts with oxygen near the surface. In the first stages of the reaction, the sulfur appears white, and in this image creates a milky-green green tinge to the water. When the transformation is more complete, the yellowish sulfur and the blue water will combine to make the plume appear very green.
The hydrogen sulfide gas is highly toxic to fish. Periodic die-offs of whole populations of fish and other commercial seafood are ongoing concerns for the regional fishing industry. This true-color Moderate Resolution Imaging Spectroradiometer (MODIS) image was acquired by the Terra satellite on March 5, 2004. The diagonal stripes that run across the image mark the beginning and end of the rotation of MODIS’ double-sided scan mirror. The scan lines are caused by small differences between the two sides of the scan mirror.
The high-resolution image provided above is at MODIS’ maximum resolution of 250 meters per pixel. The image is available in additional resolutions.
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.