Environmental Services
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.
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10 comments:
I would feel much better about this if:
1. Atmospheric methane wasn't rising steadily for the last 3 years+, with a poor understanding of where it's coming from, and
2. We didn't have observational data piling up of methane releases from off the coast of Siberian plus permafrost.
Well yes, but the permafrost is not the ocean, and we really don't know what is coming out of things like coal mines.
The ESS clathrates are quite shallow and methane bubbling to the surface has already been observed there. Enough methane is present to do some serious damage.
IIRC some evidence has been found of possible bulk methane relases (maybe associated with the PETM) on the deepish seafloor off Norway. Something like that seems likely to allow much of the methane to reach the surface and thus the atmosphere.
Aside from the ESS, the big danger does seem to be permsfrost, although isn't it the case that there's a permafrost cap over the ESS clathrates (which during the Pleistocene glaciations were above sea level)?
On the whole, the fate of the Gulf methane seems less like good news than an absence of bad news. But we take what we can get.
Not that I know what I'm talking about (should be an acronym for that), but I wonder if the location of the DH spill, in an area with lots of natural seeps, meant the biota was ready to take on the challenge we offered. Somewhere else, and they might fail the quest.
@Brian Schmidt
Indeed, there must be a vast army of hydrocarbon-loving microbes in the North Gulf. There are many miles of beaches on the Louisiana Gulf Coast near the Texas border that are persistently fouled with seeping oil, and must have been for tens of thousands of years.
> we really don't know what is coming out of things like coal mines.
http://www.methanegasdetectors.com/info/coal-mining-and-the-risk-of-methane-gas-explosions/
"Well yes, but the permafrost is not the ocean, and we really don't know what is coming out of things like coal mines."
You mean off the open cuts, not the mines, surely.
No, when coal is mined today it is ground at the mine face into fairly small chunks which are moved on conveyors. In doing this a fair amount of VOCs are released, less for anthracite, more for lower grades. That, among other things is the reason why ventilation is so huge in mines.
The other point is that this report is going to lead to surveys of the clathrate areas in the Arctic to look for the methylophiles, and maybe even suggestions to plant a few.
Is the DO anomaly in the graph plotted as a negative?
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