Oil-eating bacteria have been working overtime, potentially making them major players in the ultimate fate of the oil spilled into the Gulf's depths.
Oil-eating microbes have been consuming spilled oil at higher-than-expected rates in the deepwater plume.
Since the oil source was stopped, researchers have seen the plume disappear completely.
It remains to be seen whether higher organisms have been affected by exposure to oil.
Oil-degrading microbes in the deep ocean have been munching away on the Gulf of Mexico oil plume at rates faster than expected for the cold temperatures found almost 4,000 feet below the water's surface, according to research published today.
"This paper is great news," said Nancy Kinner, director of the Coastal Response Research Center at the University of New Hampshire in Durham. "I think this paper is another piece in the puzzle showing us that degradation was occurring and was occurring fairly rapidly, even at the cold temperatures."
The results, published today in the journal Science, came from measurements taken between May 25 and June 2. The team has also made follow-up observations since the leak was stopped on July 15. The recent figures indicate that the bacteria -- plus dilution into clean water -- have made quick work of the oil plume.
"Within two weeks we saw the plume entirely disappear," study lead author Terry Hazen of Lawrence Berkeley National Laboratory in Berkeley, Calif., told Discovery News. "We have not been able to detect this plume at all for the last three weeks. They haven't been able to detect oil at the surface. What we do find is that the bacteria are still there."
"Slowly the bacteria will go back to natural levels, assuming that there's no more carbon input," Hazen said.
The team used a long list of methods to compare water inside and out of the plume. They measured levels of oil-related compounds, identified what microbes were present at what quantities, and surveyed which genes were active in the microbes' metabolisms.
Compared to water outside the plume, the oil-laden waters were enriched in microbes known to consume oil at cold temperatures, according to the team's analysis. The researchers also found that many genes responsible for oil degradation were active in these organisms.
The degradation rates estimated by the team were higher than other measurements for the deepwater temperature of 41 degrees Fahrenheit (5 degrees Celsius), but they are not unprecedented, Hazen said.
"This is what we expected because the Gulf of Mexico receives the equivalent of an Exxon Valdez spill every year in seeps of oil," he said. Since the waters continuously receive oil from natural seeps on the sea floor, the Gulf's deep marine microbes have evolved to eat oil.
"This is the only carbon source that they have, so naturally they've become adapted to using this well," Hazen said. The results suggest that these organisms were at the ready when the plume formed.
While the team measured relatively fast degradation rates, they found fairly low overall oil concentrations and little resulting depletion of the oxygen dissolved in the water.
While the study is good news in the context of a disaster, the findings do not mean that everything is back to normal in these waters, Kinner emphasized.
"The book is still open on whether there are impacts on organisms that may have been exposed, or to larvae that may have been exposed," she said. "This shows the power of biodegradation as a mechanism for the weathering of the oil. This does not mean that there are not some organisms that were impacted."