Enlarge By Gerald Herbert, AP Crewmembers lower a research lander from the Greenpeace ship Artic Sunrise on Oct. 15. NEW ORLEANS  Scientists who were aboard two research vessels studying the Gulf of Mexico oil spill's impact on sea life have found substantial amounts of oil on the seafloor, contradicting statements by federal officials that the oil had largely disappeared. Scientists on the research ship Cape Hatteras found oil in samples dug up from the seafloor in a 140-mile radius around the site of the Macondo well, said Kevin Yeager, a University of Southern Mississippi assistant professor of marine sciences. He was the chief scientist on the research trip, which ended last week. Oil found in samples ranged from light degraded oil to thick raw crude, Yeager said. A research team on a ship called the Arctic Sunrise, sponsored by the environmental activist group Greenpeace, also turned up traces of oil in sediment samples as well as evidence of chemical dispersants in blue crab larvae and long plumes of oxygen-depleted water emanating from the well site 50 miles off Louisiana's coast. FULL COVERAGE: The latest on the oil spill IMAGES: Photos of oil disaster ENGULFED: Your stories from the oil spill Greenpeace was scheduled to announce its findings at a news conference today. Its trip also ended last week. "Clearly, there appears to be vast volumes of oil present on the seafloor," Yeager said. "We saw considerable evidence of it." Yeager said his team still needs to "fingerprint" the samples in labs to determine definitively that the oil came from the runaway well. The sheer abundance of oil and its proximity to the well site, though, makes it "highly likely" that the oil is from the Macondo well, he said. The findings add to an ongoing debate between academic researchers and federal scientists, who have differed on the oil spill's impact on the Gulf. The Deepwater Horizon rig exploded and sank in April, killing 11 crewmembers and releasing more than 100 million gallons of oil before it was sealed Sept. 18. BP leased the rig and is responsible for the spill's cleanup, while the U.S. Coast Guard is overseeing response and cleanup work. Federal officials have said that most of the oil has evaporated or been devoured by oil-eating microbes. Last week, Steve Lehmann, a scientist with the National Oceanic and Atmospheric Administration (NOAA) and a top science adviser to the Coast Guard, told the New Orleans Times-Picayune that his agency has not found any oil on the seafloor. "The concept of a big slick of oil sinking to the bottom is kind of an anathema," he said. "We have not found anything that we would consider actionable at 5,000 feet or 5 feet." Debbie Payton, a NOAA oceanographer leading the agency's subsurface oil monitoring, said NOAA scientists have detected an oily sheen in some of the sediments samples they've taken near the well site, but early results from lab analysis so far have not shown any oil particles. Part of the discrepancy between federal and academic scientists may come from how NOAA scientists lower the multi-ton machinery used to collect the samples, known as a "multiple corer," into the sea, said Samantha Joye, a University of Georgia marine sciences professor who was one of the first to discover oily sediment in the seafloor. Lowering the multiple corer too fast could disrupt the fine sediment on the seafloor and disperse oil particles, she said. "These are really fine layers," Joye said. "If you don't know what you're doing, you're not going to find oil." The three-month Greenpeace research trip aboard the Arctic Sunrise included scientists from Tulane University and Texas A&M University at Galveston, said John Hocevar, Greenpeace's oceans campaign director who participated in the expedition. The Tulane scientists found traces of what appeared to be the dispersant Clorexit, used to break up the gush of oil during the spill, in blue crab larvae, Hocevar said. A third team of scientists took whale recordings in the deep Gulf and will study them to see if the mammal's numbers have dwindled and, if so, what role the oil might have played, he said. Clif Nunnally, a doctoral student and manager of the deep sea biology lab at Texas A&M who was on the Arctic Sunrise, said he gathered sediment samples 6 miles north of the well site that clearly had oil in them. "There's definitely oil there," Nunnally said. "Now it's a matter of getting all the samples up and determining what the impact is on the animals there." Yeager said the next step is to try to determine what lasting effects the oil in the sediment may have on the worms, plankton and other invertebrates burrowed in the seafloor muck and what ripple effects that could trigger up the food chain to humans. "From this point forward, this becomes largely a bottom-up story," he said. "What's troubling to me is we know almost nothing about what's happening on the seafloor in relation to this oil." Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more