Scientists are questioning the claim by the White House that most of the massive BP oil spill in the Gulf of Mexico has largely dispersed, Channel 4 News’s science correspondent Julian Rush learns.
Two sets of researchers have reported evidence that the spill is persisting deep beneath the sea.
In the journal ‘Science’, one group has revealed the discovery of a long-lasting underwater plume of oil, tens of kilometres long.
The size of the slick will affect the marathon legal battle to come, over who pays whom for what.
US government agencies estimate that some 4.9 million barrels escaped in all – with roughly equal quarters coming ashore, evaporating naturally, skimmed and burnt, and the last quarter dispersing in the ocean itself.
For a time, BP denied that there were underwater plumes of oil – but now scientists have confirmed there was a huge plume: it was tens of kilometres long, a thousand metres below the surface – and it persisted for months.
The scientists found there was a thick layer of oil and dispersant that had settled a few hundred metres above the 1,500 metre deep sea bed.
Some 200 metres thick, they say the plume was remarkably stable, extending to the south-west of the well site for some 35 kilometres or more, and up to 2 kilometres wide in places.
Impact on marine life
The impact on marine life is difficult to assess, but we know extraordinary creatures live at these depths.
They were filmed in the Gulf of Mexico by scientists using the down-time of oil company remote operated vehicles.
Plankton sinks this deep too during the day, rising at night to the surface, potentially carrying oil up and into food chain of fish.
Some of the plume from the well may eventually drift in tiny particles down to the sea bed – where it will be consumed by bacteria and perhaps by creatures adapted to the naturally occurring oil seeps in the Gulf.
But the research team found little evidence of microbial activity in the plume they measured – suggesting it may be many months before it degrades completely.
Where has all the oil gone?
It is likely millions of gallons of oil still remain dispersed in fine droplets in the water column, writes science correspondent Tom Clarke.
Some of these plumes have been detected and low levels of oxygen associated with them suggest bacteria are getting to work on the oil.
But it is not certain how conducive the environment deep in the ocean will be to breaking down the toxic components of crude oil.
"There clearly remain an awful lot of oil products that are unknown at the moment," George Crozier, Director of the Dauphin Island Sea Lab in Alabama, told Channel 4 News.
He worries that the low oxygen levels in the deep waters could mean toxic compounds in the oil will have time to accumulate in the gulf ecosystem – eventually working their way into the food chain.
But Crozier, like many Gulf coast scientists accepts that the Gulf is well suited to dealing with the oil: "This is not the end of the Gulf of Mexico, the Gulf has the capacity to detox this exposure. But the question is, is it going to take days, weeks, months or years," he says.