Hydrogen Sulphide Eruptions
This image, acquired July 25, 2007 by the MODIS on the Aqua satellite, shows green swirls in the water, off the desert coast of Namibia, Africa. The swirls are actually hydrogen sulphide eruptions.
The conditions off the Namibian coast are prime for this phenomena. Cold waters well up from deep in the ocean, replenishing nutrients at the ocean surface, often resulting in a rapid increase in marine plant life, like phytoplankton. The phytoplankton live just a few days, after which they sink and build up on the ocean floor, where they decompose with the help of bacteria.
One specific kind of bacteria gives off hydrogen sulfide gas which periodically bubbles up to the ocean surface; when it encounters more oxygen-rich water near the surface, a chemical reaction occurs that transforms the gas into pure sulfur. The mixture of the yellow sulfur and blue water make the water look green!