A new study by a team from the University of California-Santa Barbara, University of California-Irvine, and the Woods Hole Oceanographic Institute has found that there are still two million barrels-worth of oil from BP’s 2010 Deepwater Horizon disaster sitting on the floor of the Gulf of Mexico. The study, published October 27, 2014 in the Proceedings of the National Academy of Sciences describes a “bathtub ring” of oil droplets covering an area of the seabed larger than Rhode Island.
To find the missing oil, the researchers tested more than 3,000 samples from 534 locations for evidence of the crude oil that leaked from the Macondo Well. What they found were two distinct patterns of deposited oil, a “bathtub ring’ formed from an oil-rich layer of water” at a depth of around half a mile, and a “‘fallout plume’ where suspended oil particles sank to underlying sediment,” at a depth of a mile.
The droplets of oil are about the size of “marbles, peas and BBs,” and are reportedly having a noticeable effect on marine live on the floor of the Gulf of Mexico. According to US News and World Report, the droplets are found in high concentration on deep sea coral. Lead author David Valentine explained the importance of the oils impact on these corals: “These are communities that lived for hundreds of years in the deep oceans – home for ecosystems. These are corals that are fixed to rocks on the seafloor and eat things that happen by… It’s rich in life, and the oil has the impact to affect that life, and in this case it did.”
The spread of the oil on the seabed is huge, some 1,235 square miles, but the report believes that the oil reaches even further, stating “We also suggest that a significant quantity of oil was deposited on the ocean floor outside this area but so far has evaded detection because of its heterogeneous spatial distribution.”
In total, some five million barrels of oil spewed from BP’s rig at the stricken Macondo Well, and much of that oil formed slicks on the water’s surface and washed up ashore. While the new discovery answers questions as to where the remaining oil went, it also raises questions as to why some oil, fresh from the well, sank to the seabed rather than floating to the surface—in short, the droplets ought not have been dense enough to sink in water.
Which brings us back to those controversial dispersants, used by BP to “break up” the oil. Speaking to US News, Valentine explained that while dispersant contributed to the presence of oil droplets on the seabed, there is still more to the story, and much more still to be found out: “The dispersant certainly contributed to the oil that got stuck in the water of the deep ocean. But dispersant is not going to make something sink to the seafloor, nor is it going to make it rise. Something acted on that oil that made at least some of it sink to the seafloor below.”