Pulling the Clathrate Trigger

The seafloor off Santa Barbara just burped up a huge eruption of methane – and scientists caught it on video. Now, at about 5,000 cubic feet at the surface, this methane cloud was huge by people-watching-with-videocameras standards. That’s not to say massive by vast-limitless-ocean standards. But still, it gave the scientists a chance to do some number-crunching on an imaginary massive eruption of methane.

And why are the scientists stretching their imaginations in this way, you might ask? Well, it turns out that there are actually massive (not just huge) deposits of methane on the ocean floor (and in Arctic permafrost, too, but that’s another story). The ocean deposits are quiescent at the moment, frozen into sort of waterlogged crystals called methane hydrates, a.k.a. clathrates (here’s a bit more blogging on clathrates). But it takes a lot of cold combined with a lot of pressure to persuade methane gas to lead a quiet life as a crystal.

At a glance, ocean bottoms are great places for cold and pressure. Except in a warming world. There’s evidence from studies of the last 100,000 years or more that methane has fizzed en masse into the atmosphere at the same time that the Earth’s temperature has warmed dramatically.

As you might expect for people peering back through the millennia at an invisible gas, scientists have had a hard time deciding whether methane surfaced because the world heated up (melting the crystals) or whether the world heated up because great clouds of methane surfaced. But methane is a powerful greenhouse gas. Although it doesn’t persist in the atmosphere as long as carbon dioxide, it traps much more heat (some 20 times more, by some measures) while it’s there.

We can do the math ourselves: If ocean temperatures warm enough to melt the methane clathrates, great quantities of methane could fizz up into the atmosphere, where they would add to our already pressing greenhouse gas woes. We might get a firsthand look at what happened in previous periods of warming: something happened to destabilize the clathrates (ocean warming? a drop in sea level? submarine landslides?), discharging gobs of methane into the atmosphere which then kick the climate into an even more strenuous cycle of warming. That, in a nutshell, is what they call the Clathrate Gun Hypothesis, as proposed by James Kennett of UC Santa Barbara.

What’s really intriguing about the new video and analysis of the (merely huge) burp is that scientists haven’t been content with such an armwavey doomsday scenario. In time-honored science tradition, they looked at a new hypothesis and immediately started trying to poke holes in it. Wouldn’t methane bubbles dissolve back into the water – or react with it – before they ever reached the air and started trapping heat? Experiments with methane seeping slowly into water suggested that small bubbles did indeed re-dissolve.

But the careful measurements coming from the video suggest that very large emissions isolate most of the methane from the water and carry much of the gas (i.e., 90 percent of it from 250 meters depth) to the surface undisturbed. Call it what you want – I think of it as a fizzing gun – the sobering part is that our own CO2 emissions, copious as they are, may just wind up pulling the trigger on the clathrate gun.

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