Tuesday, August 18, 2009

Such a Pretty Picture

Abstract art? Nope. Algae? Nope, though that was the first thing that went through my head when I saw it. Maybe one of those crystal rock gardens that were so popular when I was a kid... but again, nope.

It's a sonar image of methane bubbles rising from newly decomposing methane hydrates on the Arctic Sea floor.
Scientists say they have evidence that the powerful greenhouse gas methane is escaping from the Arctic sea bed.

Researchers say this could be evidence of a predicted positive feedback effect of climate change.

As temperatures rise, the sea bed grows warmer and frozen water crystals in the sediment break down, allowing methane trapped inside them to escape.

The research team found that more than 250 plumes of methane bubbles are rising from the sea bed off Norway.


As temperatures rise, the hydrate breaks down. So this new evidence shows that methane is stable at water depths greater than 400m off Spitsbergen.

However data collected over 30 years shows it was then stable at water depths as shallow as 360m.

These plumes of bubbles were reported a couple of months ago, but the latter revelation, that the decomposition depth has increased by as much as 40 meters (125-130 feet) over the last few decades, is new to me. According to Wikipedia, methane has 72 times the global warming potential (GWP) of CO2:

Carbon dioxide has a variable atmospheric lifetime, and cannot be specified precisely. Recent work indicates that recovery from a large input of atmospheric CO2 from burning fossil fuels will result in an effective lifetime of tens of thousands of years. Carbon dioxide is defined to have a GWP of 1 over all time periods.

Methane has an atmospheric lifetime of 12 ± 3 years and a GWP of 72 over 20 years, 25 over 100 years and 7.6 over 500 years. The decrease in GWP at longer times is because methane is degraded to water and CO2 through chemical reactions in the atmosphere.
So an increasing depth and rate of methane release is kind of scary. On the plus side, the article states that all the observed plumes are dissolving in the water column before they reach the surface. This leaves the possibility that marine bacteria may metabolize most or all of the methane before it reaches the atmosphere. That's a good thing, but will also use up dissolved oxygen, which creates a whole 'nother set of problems.

In short, when I first read about the plumes of bubbles, I sort of figured it might be a steady-state kind of thing- that over the long term, there would be regions where the hydrates were forming, and regions where they were decomposing, with little net gain or loss overall. That appears to be mistaken.

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