The Engineer

Drop in methane levels reported in Gulf oil spill region

News

Researchers from the University of California, Santa Barbara (UCSB) and Texas A&M University report that methane gas concentrations in the Gulf of Mexico have returned to near normal levels only months after a massive release occurred following the Deepwater Horizon oil rig explosion.

The study into the methane concentrations was led by oceanographers John Kessler of Texas A&M and David Valentine of UCSB. The findings show that more than 200,000 metric tons of dissolved methane were removed through the action of bacteria blooms that completely consumed the immense gas plumes the team had identified in mid-June.

At that time, the team reported finding methane gas in amounts 100,000 times above normal levels. But, about 120 days after the initial spill, they could only find normal concentrations of methane.

’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 one million ton deficit in dissolved oxygen that we attribute to respiration of methane by these bacteria.’

Kessler added: ’Based on our measurements from earlier in the summer and previous measurements of methane respiration rates around the world, it appeared that [Deepwater Horizon] methane would be present in the Gulf for years to come. Instead, the methane respiration rates increased to levels higher than have ever been recorded, ultimately consuming it and prohibiting its release to the atmosphere.’

The research team collected thousands of water samples at 207 locations covering an area of about 36,000 square miles. It based its conclusions on measurements of dissolved methane concentrations, dissolved oxygen concentrations, methane oxidation rates and microbial community structure.

The Deepwater Horizon offshore drilling platform exploded on 20 April 2010, about 40 miles off the Louisiana coast. The blast killed 11 workers and injured 17 others. Oil was gushing from the site at the rate of 62,000 barrels per day, eventually spilling an estimated 170 million gallons of oil into the Gulf. The leak was capped on 15 July 2010 and the well was permanently sealed on 19 September.