It's over four years since Deepwater Horizon went belly up—but the whereabouts of two million barrels of oil that burst out from the bottom of the Gulf of Mexico has remained a mystery. Now, a team of scientists believe they've found it.

Researchers from the University of California, Santa Barbara and the University of California, Irvine, have been able to trace the path of the oil that leaked from the well while the spill was being capped (and, err, recapped). In fact, the oil that issued forth now appears to lie in a thin layer at the bottom of the ocean, within 25 miles of the original well.


To figure out how it got there, the team took 3,000 samples from the Gulf of Mexico at 534 different locations, over the course of 12 different expeditions. Those samples covered a footprint of 1,250 square miles, and reveal that up to 16 percent of the oil that poured out of Deepwater Horizon's Macondo well drilling point during the catastrophe still sit on the ocean floor. The findings are published in the journal Proceedings of the National Academy of Sciences.

The majority of the oil sits in a patchy layer, around a half inch thick, on the upper surface of the sea floor. David Valentine, the lead researcher on the project, explains how it got there:

"Based on the evidence, our findings suggest that these deposits are from Macondo oil that was first suspended in the deep ocean, then settled to the sea floor without ever reaching the ocean surface. The pattern is like a shadow of the tiny oil droplets that were initially trapped at ocean depths around 3,500 feet and pushed around by the deep currents. Some combination of chemistry, biology and physics ultimately caused those droplets to rain down another 1,000 feet to rest on the sea floor."


Really very unpleasant rain. Now that we know where so much of the oil went, we can use it to work out the true extent of the damage caused by the Deepwater Horizon spill—and deal with the contamination. Perhaps most importantly, though, we'll be able to use the insight to work out how we should deal with future spills. Let's just hope they're never as bad as this one was. [PNAS via NSF]