The BP oil spill that followed the explosion of the Deepwater Horizon oil rig in 2010 was one of the defining environmental moments of the past decade. It showed the world that things will sometimes go terribly wrong, which is why we shouldn't take stupid risks (can you imagine if that rig had been in the Arctic ocean? How easy would it have been to go up there to plug the leak and rescue people..).
It's now been almost 5 years since over 200 million U.S. gallons of oil were spilled over an area of around 68,000 square miles, and we're still picking up the pieces.
The latest mystery that was finally solved involves about 10 million gallons of crude oil that government officials and BP cleanup crews couldn't account for until now...
It was known that a portion of the oil from the spill had settled on the Gulf of Mexico sea floor, but only a small fraction had been found so far, with 70% of the oil remaining "missing". But a new study published in the journal Environmental Science & Technology found up to 10 million gallons of crude that settled at the bottom of the Gulf.
The researchers took 62 sediment cores from an area encompassing 9,266 square miles (24,000 square kilometers) around the site of the Deepwater Horizon spill. Unlike other sediment on the ocean floor, oil does not contain any carbon-14, a radioactive isotope. Therefore, sediment samples without carbon-14 indicate that oil is present, Chanton said. [...]
After studying the samples, the researchers made a map of the areas affected by the spill. About 3,243 square miles (8,400 square km) are covered with oil from the Deepwater Horizon spill, they found. (source)
Because oil floats on salt water, it is not entirely clear how so much oil sank to the bottom, but there are a few theories on how it could have happened, from zooplankton eating the oil and discarding it in "fecal pellets" that sank to the fires that were used on certain patches of oil making part of it dense enough to sink.
Because there's little oxygen on the sea floor, the oil might stick around for a very long time, potentially causing all kinds of problems to the Gulf ecosystems.
“This is going to affect the Gulf for years to come,” Florida State University Professor of Oceanography Jeff Chanton said. “Fish will likely ingest contaminants because worms ingest the sediment, and fish eat the worms. It’s a conduit for contamination into the food web.”