It just sank to the bottom of the ocean. (facepalm)
http://www.npr.org/...
Scientists on a research vessel in the Gulf of Mexico are finding a substantial layer of oily sediment stretching for dozens of miles in all directions. Their discovery suggests that a lot of oil from the Deepwater Horizon didn't simply evaporate or dissipate into the water — it has settled to the seafloor.
The Research Vessel Oceanus sailed on Aug. 21 on a mission to figure out what happened to the more than 4 million barrels of oil that gushed into the water. Onboard, Samantha Joye, a professor in the Department of Marine Sciences at the University of Georgia, says she suddenly has a pretty good idea about where a lot of it ended up. It's showing up in samples of the seafloor, between the well site and the coast.
Joye describes seeing layers of oily material — in some places more than 2 inches thick — covering the bottom of the seafloor.
"It's very fluffy and porous. And there are little tar balls in there you can see that look like microscopic cauliflower heads," she says.
It's very clearly a fresh layer. Right below it she finds much more typical seafloor mud. And in that layer, she finds recently dead shrimp, worms and other invertebrates.
(heavysigh) So basically the dirt on the ocean floor is soaking up the oil as it settles. Oh well, I suppose the hungryhungry Microbes dream was nice while it lasted. I'm glad at least that scientists are finding out just what happened. Hopefully some bright engineers will be able to come up with half-decent ways of getting more of it cleaned up. On BP's dime, of course.
SMALL UPDATE:
Rei has some helpful and illuminating comments below. I recommend you check them out. Here's one:
http://www.dailykos.com/...
This exactly how oil breaks down.
The lighter fragments are either eaten by microbes or evaporate. The heavier fragments steadily agglomerate and eventually sink to the sea floor. The more of the light materials they lose, the harder and less toxic they become, until they're basically a rock. The sediments are slowly buried and eventually recycled into the crust.
This happens naturally at low levels all over the gulf, and at high levels around "asphalt volcanoes". Tar-rich layers are all over gulf sediment cores. Our planet developed a method to recycle oil billions of years ago, once enough had accumulated from marine plankton sediments that the first oil seeps opened up. We just forced it into overdrive by creating the sort of disastrous event that occurs naturally only once in tens of thousands of years. Most of the time, the rate of seepage is much lower.