BP oil spill: 'invisible' pollution spread even further than believed © Getty Images

BP oil spill: ‘invisible’ pollution spread even further than believed

Toxic and invisible oil spread well beyond the known satellite footprint of the April 2010 oil spill.

The Deepwater Horizon oil spill may have been even larger than previously thought, research suggests. Toxic and invisible oil spread well beyond the known satellite footprint of the Deepwater Horizon oil spill, according to a new study.

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Led by scientists at the University of Miami (UM) Rosenstiel school of Marine and Atmospheric Science, researchers combined oil-transport modelling techniques with remote sensing data and in-water sampling to provide a comprehensive look at the oil spill.

They found that a fraction of the spill was invisible to satellites, and yet toxic to marine wildlife.

Lead author Igal Berenshtein said: “We found that there was a substantial fraction of oil invisible to satellites and aerial imaging. The spill was only visible to satellites above a certain oil concentration at the surface leaving a portion unaccounted for.”

Scientists say their findings have important implications for environmental health during future oil spills.

On 20 April 2010, the Deepwater Horizon oil rig exploded, releasing around 795 million litres of crude oil into the Gulf of Mexico for a total of 87 days, making it the largest oil spill in US history. Oil slicks from the disaster covered an estimated area of 149,000 square kilometres.

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The study, published in Science Advances, showed a much wider extent of the spill beyond the satellite footprint, reaching the West Florida shelf, the Texas shores, the Florida Keys and along the Gulf Stream towards the East Florida shelf.

Claire Paris, senior author of the study and professor of ocean sciences the UM Rosenstiel School, said: “Our results change established perceptions about the consequences of oil spills by showing that toxic and invisible oil can extend beyond the satellite footprint at potentially lethal and sub-lethal concentrations to a wide range of wildlife in the Gulf of Mexico.

“This work added a third dimension to what was previously seen as just surface slicks. This additional dimension has been visualised with more realistic and accurate oil spill models developed with a team of chemical engineers and more efficient computing resources.”

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The researchers say the new framework can help emergency managers and decision makers in better managing the impacts of future potential oil spills.

Reader Q&A: What happened to the oil from the Deepwater Horizon spill?

Asked by: Anonymous

The Mississippi Canyon 252 oil well sits at the bottom of the Gulf of Mexico, 1522m below the surface of the ocean. The oil was gushing out of the damaged wellhead at an estimated rate of 2100 litres a minute. That’s more than an Olympic swimming pool every day.

Crude oil is a varied mixture of different hydrocarbons with different viscosities and densities. The lighter fraction floated on the top of the water, where the most volatile compounds simply evaporated. This accounted for 30 per cent of the total volume.

Over the course of a few days or weeks, wave and wind action whipped what remains into a kind of mousse. This was dragged by the main Gulf Loop current up along the east coast of the US towards the Arctic.

But much of the spilled oil seemed to be lurking in a plume around 1000m below the surface. Ocean currents are much weaker there, so the oil tended to collect and without the turbulence at the surface, it doesn’t get broken up, so bacterial digestion happens much more slowly.

Some will clump together as golf balls of tar and sink to the seabed. The rest will eventually wash up on the shores of the Gulf of Mexico. Possibly for decades.

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