Gulf floor fouled by bacterial oil feast
Patchy seafloor deposits are mix of microbial waste, oil and other remnants of clean-up effort

Huge quantities of oil that gushed from BP’s well blowout last spring and summer now taint the Gulf of Mexico’s seafloor, newly released video and chemical sampling data show. Within 40 miles of the damaged wellhead, the oil deposits appear extensive but patchy, and range from little spots of oil on the seafloor to localized blankets of goopy hydrocarbons several inches thick.

New data suggest much of this oil may have rained down from the sea surface, fostered by what scientist Samantha Joye calls “microbial spit.” Joye, an oceanographer and biogeochemist at the University of Georgia in Athens, described her team’s findings on February 19 at the annual meeting of the American Association for the Advancement of Science.

When she and her colleagues extracted cores of sediment from the Gulf’s spill-impacted zones, the top sediment layers often showed signs of what appeared to be the microbial spit. That layer also was devoid of living animals, forming what Joye called an “invertebrate graveyard.”

She often saw dead corals, crabs and sea stars in the affected seafloor areas. Absent were sea cucumbers that are normally abundant in parts of the Gulf where natural petroleum seeps occur. Damage was also evident above the seafloor: Mortality in free-floating jellyfish and sea squirts proved especially high, Joye said. And some worms had become nothing more than hollow tubes filled with the slimy goop that chemical fingerprinting methods would later show had contained BP oil.

But oil wasn’t the only spill-related pollution to be raining down onto the seabed. Joye described data on two chemical indicators of remnants of the burning of oil by spill-cleanup crews. Soot, which is normally not present in ocean sediment, turned up in September water samples. Joye’s team also reports finding an elevated ratio of certain combustion byproducts known as polycyclic aromatic hydrocarbons, or PAHs, in sediments directly under burn sites.

National Oceanic and Atmospheric Administration Administrator Jane Lubchenco acknowledges that extensive sampling by her agency and its university partners “has shown that there is oil — residues or some kind of oil products — on the seafloor.”

Source and more information:
ScienceNews,“Gulf floor fouled by bacterial oil feast“, 20. Februar 2011