The Mystery of the Missing Methane

30 January 2011 - Deepwater Horizon aftermath

When a group of US based scientists boarded the vessel Pisces and headed for the Deepwater Horizon disaster site in the Gulf of Mexico on a chemical fact finding mission they fully expected to find large quantities of dissolved methane. The spill after all, had emitted a total of 12,5 billion moles of the gas in addition to the 4.4 million barrels of oil. The concentration of methane in the air had been constantly monitored since the spill started and in one estimation only 0.01% of the gas had as yet surfaced. So the bulk of it had to be still in the water. In a 500 km wide stretch water was sampled on 207 locations up to a depth of 1200 meter (DOI). The researchers were in for a surprise.

Whereas the presence of oil residue was evident from fluorescence measurements, gas chromatography did not signal any methane. On the other hand CTD probing combined with a Winkler dissolved oxygen test did reveal a large oxygen deficit. In one estimate 25 billion moles of O2 was respirated within a 120 day period nicely reflecting the oxygen/methane 2:1 oxidation ratio. The culprits were also found: a DNA survey revealed the presence of host of methane-eating bacteria such as the methylococcaceaeand the methylophaga or at least their DNA remnants. Mystery solved!