A dead Portuguese man-of-war floats on rust-colored oil off the Louisiana coast on Tuesday.

National Geographic on the oil spill in the Gulf of Mexico.

If the oil spill can’t be contained, the Gulf of Mexico could have another “dead zone in the making,” according to Sylvia Earle, a marine biologist and National Geographic explorer-in-residence. (National Geographic News is owned by the National Geographic Society.)

Often caused by algal blooms, dead zones are swaths of ocean devoid of life, save for hardy bacteria. (Related: “Gulf of Mexico ‘Dead Zone’ Is Size of New Jersey.”)

Oil bubbling up from the Gulf of Mexico wellhead, which sits more than 5,000 feet (about 1,500 meters) below the water’s surface, is coming from even deeper inside the Earth.

That means the oil is heavier and thicker than the crude spilled in past, tanker-based disasters, noted Ron Kendall, chair of the Department of Environmental Toxicology at Texas Tech University in Lubbock.

Full article: http://news.nationalgeographic.com/news/2010/05/100504-science-environment-gulf-oil-spill-dead-zone/