The smell of rotten eggs could ruin anyone's day at the beach. But residents of coastal towns in Namibia have become used to the disagreeable smells that accompany frequent eruptions of toxic hydrogen sulfide gas in the area. Now research published in the current issue of the journal Nature suggests that these noxious emissions are much more extensive and persistent than previously thought.

Oxygen-starved organic matter decaying on the seafloor in the waters off the coast of southwestern Africa generates the hydrogen sulfide gas. Townspeople know when an eruption has occurred because nearshore fish die and rock lobsters run ashore, fleeing the poisonous water. To get a broader perspective, Scarla Weeks of the University of Cape Town, South Africa and colleagues tracked the gas from afar using satellite imagery. The team observed a region of turquoise-colored, sulfide-infused water that stretched more than 200 kilometers along the coast of the Namib Desert. Moreover, even as the poisonous patch of water moved offshore, a second distinct hydrogen sulfide emission event occurred closer to the coast.

Formerly believed to have only limited local consequences, the bursts of hydrogen sulfide could also have long-term effects, according to the report. Because the gas strips oxygen from the water, subsurface hypoxia might linger longer than the gas itself. If so, the authors note, the marine ecology and valuable coastal fisheries of this region could face considerable problems.