Methane Deposits in Antarctica

By Christopher Desousa

 

University of Bristol glaciologist Jemma Wadham and her colleagues presented evidence in a 2012 article in Nature that a large deposit of atmospheric methane may linger beneath the Antarctic Ice Sheet. The 2012 Nature article suggests that if the ice sheet melts, methane may seep into the atmosphere and inflate global temperatures.

Thirty-five million years ago, Earth experienced a rapid shift in climate. Large ice sheets formed in Antarctica for the first time. Ice accumulated over millions of years and buried vegetation and forests. Antarctica now holds carbon-rich material suitable for methane production under its ice sheets.

The Antarctic Ice Sheet (AIS), the largest ice sheet on Earth, covers 98% of Antarctica. The AIS divides into the West Antarctic Ice Sheet (WAIS) and the East Antarctic Ice Sheet (EAIS).

Wadham and her colleagues calculate that 50% of the WAIS and 25% of the EAIS covers an Antarctic Sedimentary Basin. Sedimentary basins accumulate a plethora of sediments such as boulders, pebbles, silt, sand and organic matter over long periods of time. The Antarctic Sedimentary Basin holds twenty-one billion metric tones of organic carbon compounds.

Sedimentary basins situated beneath the AIS hold organic carbon accessible to methanogenesis. Methanogenesis generates methane from methanogens. Methanogens are microorganisms that live in oxygen-deprived conditions. Methanogens decompose carbon-rich organic materials and generate methane as a by-product of their metabolism (release of energy).

Wadham used methane hydrate samples to simulate the accumulation of methane in Antarctic Sedimentary Basins. Methane hydrate forms when methane gas gets trapped inside a body of water and freezes into ice. Methane hydrate forms under ice in high pressure and low temperature conditions.

Scientists sawed 0.03 cubic meter blocks of methane hydrate off the edges of an Antarctic glacier. Methane hydrate fills with sediments picked up by glaciers as they float across ocean waters. They identified organic carbon and methane-generating microorganisms living in the sediments after melting the ice blocks.

Wadham conducted further testing on the Antarctic sediment inside methane hydrate samples. She and her team incubated methane hydrate melts in an oxygen-deprived environment for two years. After two years, the scientists documented high rates of methanogenesis. The study calculates an estimate of 400 billion tones of methane beneath the AIS.

The AIS represents a large reservoir of methane hydrate.During episodes of ice sheet retreat — the melting of ice sheets — methane hydrates may deteriorate and release methane gas into the atmosphere.

“Our study highlights the need for continued scientific exploration of remote sub-ice environments in Antarctica,” a glaciologist at the Univeristy of California, Slawek Tulaczyk said, “because they may have far greater impact on Earth’s climate system than we have appreciated in the past.”

Methane Gas in Antarctica

This feedback loop illustrates how the melting of
methane hydrate causes continuous atmospheric heating.
Source: Andrew Melo, 2012.

“Our study highlights the need for continued scientific exploration of remote sub-ice environments in Antarctica,” a glaciologist at the Univeristy of California, Slawek Tulaczyk said, “because they may have far greater impact on Earth’s climate system than we have appreciated in the past.”

 

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