The ecological effects of the 2010 Deepwater Horizon oil spill are still largely unknown. Josh Fischman, a senior writer at The Chronicle, is on the research vessel Endeavor in the Gulf of Mexico with a team of university scientists seeking answers. He is filing reports from the ship.
This oil slick was spotted from the deck of the Endeavor this weekend. (Courtesy of Kai Ziervogel)
About one mile from Deepwater Horizon’s former site—Gallons and gallons of chemicals called dispersants get poured onto oil spills, including the one that started here. It’s tempting to view dispersants as chemicals added to chemicals. But they really may be aids to biology, working hand in glove with microbes to break apart slicks. An experiment now running aboard the Endeavor is starting to show how this happens.
An oil slick is a film floating on the water, a really big film. Bacteria that normally pull oil’s carbon molecules apart can’t handle the size. It’s more than a mouthful, if bacteria had mouths. The dispersants break up the film into small dots, and the reduced size lets bacteria grab on and cut them up into even smaller pieces, which can be gnawed on by still other bacteria. By making things easier for the microorganisms, the dispersants accelerate a natural process of destruction. At least that’s the theory.
To see if theory fits facts, at one of the natural seeps that the ship has visited—sites where hydrocarbons like oil and gases bubble from the sea floor—Kai Ziervogel, a research scientist from the University of North Carolina, collected bacteria from the sea surface. He and Julia Sweet, a lab manager from the University of California at Santa Barbara, put some in tanks with the dispersant used after the spill, others in tanks with oil, and still others in tanks with both oil and dispersant. The idea was to see if some situations led to more active bacteria, doing more carbon-munching.
And in a clever move, the researchers began to roll them around. In a metal box the size of a footlocker, Ziervogel attached the tanks to motors that slowly spin them, simulating the turbulence that normally mixes things up near the surface. “The rolling tanks are nice,” says Ziervogel. “Most incubation experiments use bottles, and what’s in them simply sits there. But where in the ocean are things not moving? Even at the bottom, where things are very still, there are currents.”
Kai Ziervogel, a biologist, pulls bacteria from seawater in the ship’s lab.
Ziervogel and Sweet opened their roller tanks this weekend, after three days of turbulence, and found that one situation—one alone—indeed stimulated bacterial activity. It wasn’t with the oil by itself, indicating the film is indeed too much to handle. But oil and dispersant together changed things. The scientists could detect elevated levels of enzymes that bacteria use when they feed on oil components, such as fats and sugars. “They are the enzymes that you typically see when bacteria become more active,” Ziervogel says.
The news may not be all good, however. Sweet and Uta Passow, the biological oceanographer she works with back in Santa Barbara, plan to look at phytoplankton in the samples, rather than bacteria. “There’s a hunch that dispersant could harm the plankton under certain conditions,” Sweet says. She did lots of preparations with various dispersant concentrations. It is possible that the chemical could help bacteria while hurting another vital part of the microscopic community. Or it could be totally safe. It’s one of the many unknowns about the ecosystem.
The other issue is that while dispersants may speed up bacterial attacks on the oil, the breakup of the film still may put some of the oil out of their reach. “One of my concerns is that a lot of oil has clumped up and sunk to the bottom,” says Samantha Joye, a biogeochemist at the University of Georgia who is not on the ship, but helped design the overall ECOGIG ecology research project.
“It’s worrisome because the degradation processes in the deep sea, under very cold temperatures and high pressure, are much, much slower than in coastal waters,” says Ziervogel. “It’s like the surface of the moon down there. There is practically nothing. And anything that moves is moving very slowly, conserving energy,” says the biologist, who has seen the bottom of the Gulf through the window of a research submarine.
To figure out whether bacteria in the bottom sediments are energetic enough to deal with oil remnants, the Georgia team sends down a heavy device called a multi-corer, which hits the sea floor hard enough to drive eight tubes deep into the muck. Then it comes back up, bringing cylindrical cores of mud.
On ship, the cores are sliced into thin discs, squeezed to extract water, and everything is analyzed for signs of bacterial activity, like the rates at which nutrients are broken down. “In 2010, when we first came out here, the top layer had very little going on,” says Melitza Crespo-Medina, a microbiologist and postdoctoral fellow at Georgia. “Beneath that, things looked more normal.”
It’s another instance of the complexity of this situation: What helps on the surface may cause deeper problems.
