Ocean scientists in the Gulf of Mexico have found giant plumes of oil coagulating at up to 1,300 metres below the surface, raising fears that the BP oil spill may be larger than thought – and that it might create huge "dead zones".
Members of the National Institute for Undersea Science and Technology have been traversing the area around the scene of the Deepwater Horizon, the rig that exploded and sank on 20 April.
Using the latest sampling techniques, they have identified plumes up to 20 miles away from the Deepwater Horizon well head that continues to spew oil into the water at a rate of at least 790,000 litres a day. The largest plume found so far was 90 metres thick, three miles wide and 10 miles long.
Samantha Joye, marine science professor at the University of Georgia, who is working on the project, told the Guardian: "The plumes are abundant throughout the region. I would say they've become characteristic of this environment."
BP last night announced the first good news in several days in its efforts to contain the spill, saying it had succeeded in inserting a tube into the riser, the broken pipe from which most of the oil is gushing, allowing oil and gas to be siphoned off into a drill ship at the surface. The procedure, likened to threading a needle, failed early on Sunday morning, but a second attempt succeeded.
Kent Wells, a BP executive, said he had no idea how much oil and gas was now being safely siphoned off. The firm intended slowly to increase the volume until they had reached the maximum possible, he said, though no figures could be put to that either.
Wells added that in the next 10 days BP would try to block off the entire riser using heavy materials which, if successful, would kill the leak for good.
The presence of huge strings of oil deep underwater has puzzled scientists on board the research vessel Pelican, back in dock after almost two weeks at sea. The assumption had been that the oil would rise to the surface, but instead it has formed into multiple layers suspended in varying thicknesses deep in the water.
There is speculation that the plumes, first reported by the New York Times, might be forming as a result of BP's use of dispersants injected close to the source of the spillage at the sea floor.
The technique has never before been used, and scientists are now wondering whether the dispersants are causing the oil to coagulate into relatively large clumps which are then heavier than water and remain suspended below the surface of the sea.
One concern linked to the plumes is that the oil will reduce oxygen levels in the water as micro-organisms work to decompose it. In some parts of the Gulf, oxygen levels are already almost one-third below normal. If they fall below levels needed to support life, dead zones devoid of all marine creatures could be created.
The Pelican scientists, from the University of Mississippi, have been using a range of gadgetry to detect the plumes. They include flourometers that spot oil using colour measurements, a remotely operated vehicle that they submerge to describe oil aggregates at up to 75 metres below the surface, and equipment that records oxygen levels. They have set up a long-term acoustic monitoring device on the sea floor that will pick up marine mammal calls to help track the impact on population sizes over time.
As knowledge grows of the environmental impact, pressure is mounting on both BP and the Obama administration.
The oil giant has been accused of trying to withhold the full scale of the disaster. Some experts who have studied video footage of the oil spewing from the wellhead have estimated the rate of spillage at up to 13m litres a day – 14 times greater than BP's figure.
The US government is also coming under scrutiny for the way it has handled the crisis, and for having had too relaxed an attitude towards offshore drilling before the disaster happened.
One environmental group, the Centre for Biological Diversity, has threatened to sue the administration for having bypassed regulations in approving new drilling sites. The centre says that more than 300 drilling operations have been given the go-ahead since Obama took office in January 2009, without obtaining proper permits relating to protection of whales and other marine mammals.