Today scientists revealed the results of an investigation into the severity of the Deepwater oil spill. The plume of petroleum hydrocarbon chemicals measures a staggering 22 miles long, and has settled in a deep underwater layer (see photo).

The actual existence of the plume was in some doubt until a team of researchers at Woods Hole Oceanographic Institution provided incontrovertible proof. The researchers managed to catch up with the plume about three miles southwest of the original blowout location, then used a remote-controlled submarine and an underwater spectrometer to figure out its dimensions. They were able to study the plume for ten days in June before Hurricane Alex forced them from the area. It's still not known whether this was the only plume or whether others formed, and the team said at a press conference today that they would be unwilling to commit themselves either way on that point.

Their work took place roughly two months after the initial explosion, and measurements show that it the plume was approximately 1,100 meters deep (as you can see in the top image), over 35 kilometers long, 200 meters high and up to 2 kilometers wide.


Their findings showed conclusively that the hydrocarbons found in this plume could not have come from natural seepage, and that the Deepwater Horizon spill must be the primary culprit for the plume. Beyond its staggering dimensions, there's the question of just how long the plume will take to biodegrade - it's already lasted longer than expected, and microbes don't seem to be doing much to break up the oil. As Woods Hole geochemist Christopher Reddy puts it:

"We don't know how toxic it is and we don't know how it formed, or why. But knowing the size, shape, depth, and heading of this plume will be vital for answering many of these questions."

As big as the plume is - and as oily as the surface water can look - the hydrocarbons in the plume - only exist at 50 micrograms per liter, and the deepest water was clear. Of course, hydrocarbons in the plume make up only about 6 to 7 percent of the total hydrocarbons that leaked from the well. The hydrocarbons found in the plume are known as BTEX hydrocarbons after their first letters - benzene, toluene, ethyl benzene, and xylene.


Those four chemicals make up about 1 percent of the oil in the Gulf of Mexico region, and their particular presence helped confirm that it was the Deepwater spill in particular that had created the plume. As the researchers stressed at today's press conference, there are many other chemicals that make up petroleum, and they're still working on why these ended up in the plume while others didn't.

In a press conference today, Reddy stressed that we still don't know quite how the plume fits into the oil spill as a whole:

All I can tell you is that we found the plume and I can't tell you how much oil was in it because we don't have the values yet. We know there is a plume, we know its links, we know its shape. We know that we collected water samples in it and when we have analyzed those samples, we'll be able to constrain how much – what the inventory of those compounds were in there. And at that point we may be able to see whether it's a penny in a very big checkbook, I mean a checking account or maybe it's bigger. And at that point, you know, the key thing right here in this whole oil spill science is we have to balance patience and urgency. And in some cases I think that patience in a virtue, in other cases we have to balance with urgency and at this point I would say in our case I would comment more when I have more analytical data.

Although it's not oil itself, there's also a massive clump of its constituent chemicals moving slowly underneath (and in the air above) the Gulf of Mexico - so the damage stretches well beyond the visually obvious plume. As the researchers admit, it's going to take months to figure out what all this means for the already damaged marine environment.

[via Science; post updated at 3:30 PST with news from today's press conference.]