Researchers from the University of California, Santa Barbara and Texas A & M University report that methane gas concentrations in the Gulf of Mexico have already returned to near normal levels. They called their results “extremely surprising” because it’s only been months since the massive release occurred following the Deepwater Horizon oil rig explosion.
The study was led by oceanographers John Kessler of Texas A&M and David Valentine of UCSB. Their findings show that 200,00 metric tons of dissolved methane were naturally removed from the ocean through the action of bacteria blooms that completely consumed the gas plumes the team identified in June. At that time, the team reported finding methane gas levels 100,000 times above normal. After 120 days from the initial spill, only normal concentrations of methane and evidence of complete methane respiration were found. Their findings were recently published in the journal Science.
“What we observed in June was a horizon of deep water laden with methane and other hydrocarbon gases,” Valentine said. “When we returned in September and October and tracked these waters, we found the gases were gone. In their place were residual methane-eating bacteria, and a 1 million ton deficit in dissolved oxygen that we attribute to respiration of methane by these bacteria.
The research team collected thousands of water samples at 207 locations covering an area of about 36,000 square miles. Their conclusions were based on measurements of dissolved methane concentrations, dissolved oxygen concentrations, methane oxidation rates, and microbial community structure.
“Based on our measurements from earlier in the summer and previous other measurements of methane respiration rates around the world, it appeared that (Deepwater Horizon) methane would be present in the Gulf for years to come,” Kessler added. “Instead, the methane respiration rates increased to levels higher than have ever been recorded, ultimately consuming it and prohibiting its release to the atmosphere.”
“This tragedy enabled an impossible experiment,” Valentine said, “one that allowed us to track the fate of a massive methane release in the deep ocean, as has occurred naturally throughout Earth’s history.”
“We were glad to have the opportunity to lend our expertise to study this oil spil,” Kessler said. “But also we tried to make a little good come from this disaster and use it to learn something about how the planet functions naturally. The seafloor stores large quantities of methane, a potent greenhouse gas, which has been suspected to be released naturally, modulating global climate. What the Deepwater Horizon incident has taught us is hat releases of methane with similar characteristics will not have the capacity to influence climate.”
Copyright © 2011 by Marine Science Today, a publication of OceanLines LLC