Soot in the Sky, Gas in the Water
UCSB Scientist Studies Microbes in the Gulf that Eat Gas and Oil, but Deplete Oxygen
Although, after three long months, it appears BP’s ruptured oil well in the Gulf of Mexico has finally been plugged, there are still many unanswered questions as to what impact the massive spill has had — and continues to have — on delicate aquatic biology.
UCSB scientist Dr. David Valentine — a marine geochemistry expert — returned earlier this month from a 10-day research cruise to the region. He and a team of graduate students studied microorganisms that survive solely on diets of methane and oil. The highly adapted, single-celled bacteria — gobbling up oil and gas that was seeping from the broken drilling pipe — require oxygen to metabolize their unusual food.
It’s Valentine’s goal to better understand how rapidly the compounds are being consumed and how the process is contributing to the significant oxygen loss that’s been observed in the spill site and beyond. “So far, oxygen hasn’t run out for [the organisms],” said Valentine. “The concern is what’s going to happen moving forward. What we observed is that these organisms are definitely consuming the gases. We don’t have the data in yet about how rapidly that’s happening — that’s part of what we’re still working on. But we can say with certainty that there is enough gas present to continue to bring the oxygen down.” Should oxygen levels drop low enough, larger animals will either die or avoid those areas.
His team also took a close look at how the hydrocarbon gases are distributed throughout the ocean — looking mainly at methane, ethane, and propane, which made up about half of the supercritical mass that was shooting out of the seabed — by sending down an instrument that collected water samples at 23 different depths. During these experiments, reported Valentine, the scientists were right in the thick of cleanup and abatement measures, witnessing close-up the massive surface burns and the swaths of oil slicks that dot the Gulf’s surface.
Valentine said he observed a 5-30 percent reduction in oxygen below 2,500 feet, which, although not enough to start killing off marine life outright, is nevertheless something to keep an eye on. And because the gases present around the spill site are around 100,000 times their normal levels, Valentine said the possibility of oxygen levels dropping to zero is not out of the realm of possibility if the bacteria’s reactions go to completion. “Once you get down to 80 percent, then you’re going to start seeing more significant problems,” he said.
Working within seven nautical miles of the spill site — and getting as close as 1,500 feet to ground zero — the vessel’s crew was composed of scientists from UCSB and Texas A&M, including Valentine’s longtime collaborator, earth science professor Dr. Jon Kessler. Named the RV Cape Hatteras, the boat was run by Duke University and the North Carolina Marine Consortium. Funding for Valentine’s group came from the National Science Foundation and the Department of Energy.
While there are thousands of different microbe species floating in the Gulf’s waters, Valentine is concentrating on the select few that are actually involved in taking up the gases and oil. “If you imagine it’s a forest, we’re looking for a few specific trees — the ones that are active, not ones that are just hanging out,” said Valentine.
By using precise targeting techniques — introducing a sample of organisms to ocean water with “labeled” hydrocarbon gases, then centrifuging out the microbes’ DNA after they’ve eaten for a few days — Valentine can determine which microbes, out of the massive community out there, are actually targeting the compounds. “There are thousands of species present,” he said, “but there’s only a few that are going after these specific compounds and are doing the lion share of the oxygen drawdown.”
Specifically, Valentine is looking at methanotrophs, a general term for bacteria that is able to metabolize methane as its only source of energy. As Valentine put it, “That is there life, they are dedicated to it. As a matter of fact,” he went on, “you have to undergo a lot of unusual evolutionary adaptations to become a methanotroph because it’s not a easy lifestyle. Methane is a very difficult molecule for organisms to consume. They end up dedicating much of their internal biological structure to hosting the actual apparatus to consume methane.” Valentine is also studying alcanivorax, a microbe that degrades oil.
Even though his team was only studying microscopic bacteria, researchers also noticed 5- to 6-inch organisms — called pyrosomes, which are mid-water filter feeders that look like sea cucumbers — dying off en masse. The phenomenon was especially unusual, said Valentine, because the creatures floated to the surface instead of sinking. “This could be the canary in the coal mine for the deep waters,” said Valentine, remarking on the delicateness of the Gulf’s food web and how oxygen depletion may be having detrimental effects on bigger animals.
Because Valentine collected mountains of data — only a portion of which could be analyzed shipboard — his UCSB lab is still sifting through the information. Publication is still a ways away, he said.
Speaking about the experience of working so close to the spill site, Valentine described what the slicks look like up close and personal: “There’s places where you can’t really see the water through the slick. It comes in many different forms. There are places where it’s just a light sheen on the water and you get that rainbow hue, then there are places where it’s a thick, orangey mess.”
He also spoke about the surface burns — the igniting of oil that’s been boomed together into a concentrated pile — noting that the spill site when he was there had a cloud of smoke hanging over it at all times; the airborne mass was a combination of surface burn smoke and methane flare-up from the oil capture rig nearby, which burns excess methane it takes up. “The surface burns tend to burn black and they form black clouds over them as they go,” he said. “It’s one thick mass of clouds, and when it rains a lot of junk comes down from the particulate. The burns are black — it looks like a pile of burning tires.”
The research boat received permission from BP to work directly around the spill site for a 24-hour block, said Valentine, but there was very little contact with company officials after that. When asked if BP expressed any interest in the scientists’ work and their collected data, Valentine responded: “In my experience, no. They aren’t interested in seeing results. I think science is not something they’re really keen on, probably because it’s likely to uncover unforeseen issues.”