A recent Science article by a whole number of people, Kessler et al., from Texas A&M, UC Santa Barbara and UNH provides an interesting answer to the questions of whither dissolving methane clatherates, a major concern with warming oceans, especially the colder, Arctic ones. Nearly all of the methane released in the Deepwater Horizon disaster, and there was a lot of it, was converted into a bacterial bloom by methylotropic bacteria. Pulse releases are fodder for scientists because they clear the chaff associated with steady state measurements, one need not be concerned about balancing the ebb and flow, the flow occurs rapidly and the ebb can be easily, ok, much more easily measured.
Estimates of the methane release from the Deepwater Horizon, range between 0.91 and 1.25 x 1010 moles or 146,000 to 200,000 metric tons methane, or in units to be used later, 109,000 to 150,000 metric tons carbon. It was a big spill, and it happened relatively rapidly. Amazingly (you saw the pictures, less than 0.01% of the methane made it to the surface, the pressure at depth and volume available pushed most of the methane to dissolve in the sea water.
Chemical oxidation would have left elevated dissolved methane in the ocean for years, however from August 17 on (the well was capped August 4, 2010) no methane was detected above that characteristic of the gulf.
The authors looked for, and found a dissolved oxygen anomaly consistent with the methane being food for a bacteria bloom and also found the methylotrophic bacteria who were snacking on the free food. Moreover, as anyone who feeds birds could tell you, the nature of the bacterial colony changed from June, when there were no methylotrophs, to mid August after the food had been laid out. A simple model (from the paper shown to the right) shows how the methylophiles moved in. There are, as usual some complications, but that is the basic picture.
The authors are not stupid. They see the obvious
Previous arguments have been forwarded for the massive release of CH4 from the marine sub-seafloor in the geologic past. An open issue is the fate of released CH4 and whether it enters the atmosphere, is oxidized in the ocean, or some combination of both processes. Our work suggests by analogy that large-scale CH4 release to the deep ocean from gas hydrates or other natural sources may foster a rapid methanotrophic response leading to complete oxidation of CH4 to CO2 within a matter of months. Thus, aerobic methanotrophic bacterial communities may act as a dynamic biofilter that responds rapidly to large-scale CH4 inputs into the deep ocean.The important caveats are that the release happen at depth into a fairly cold region where the methane dissolves rather than bubbling to the surface and that it is not large enough to saturate the solubility.
The value of the environmental services here is perhaps not so large, using a Pigovian tax of ~ $50 per metric ton carbon and a greenhouse gas equivalent of 21-1=20 (for the CO2 they did emit) for methane, only 115 to 158 million US, but the bacteria would appreciate a remittance. Of course the amount of carbon tied up in the clatherates is 500-2500 gigatonnes carbon. It might pay to put something away to pay for the big burp.