NEW ORLEANS — Marine scientists discovered a massive new plume of what they believe to be oil deep beneath the Gulf of Mexico, stretching 22 miles from the leaking BP wellhead northeast toward an underwater canyon whose currents feed sea life in the waters off Florida.

The discovery by researchers on the University of South Florida College of Marine Science's Weatherbird II vessel is the second significant undersea plume reported since the Deepwater Horizon exploded April 20.

The cloud was nearing a large underwater canyon whose currents fuel the food chain in Gulf waters off Florida and could potentially wash the tiny plants and animals that feed larger organisms in a stew of toxic chemicals, another researcher said.

Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi, said the DeSoto Canyon off the Florida Panhandle sends nutrient-rich water from the deep sea up to shallower waters.

McKinney said in a best-case scenario, oil riding the current out of the canyon would rise close enough to the surface to be broken down by sunlight. But if the plume remains relatively intact, it could sweep down the west coast of Florida as a toxic soup as far as the Keys.

The thick plume was detected just beneath the surface down to about 3,300 feet and is more than 6 miles wide, said David Hollander, associate professor of chemical oceanography at USF.