Sunday, December 13, 2009

"Bubbles of warming, beneath the ice"

From the LAtimes:

Bering Land Bridge National Preserve, Alaska - Four miles south of the Arctic Circle, the morning sky is streaked with apricot. Frozen rivers split the tundra of the Seward Peninsula, coiling into vast lakes. And on a silent, wind-whipped pond, a lone figure, sweating and panting, shovels snow off the ice.

The young woman with curly reddish hair stops, scribbles data, snaps a photo, grabs a heavy metal pick and stabs at white orbs in the thick black ice.

"Every time I see bubbles, I have the same feeling," says Katey Walter, a University of Alaska researcher. "They are amazing and beautiful."

Beautiful, yes. But ominous. When her pick breaks through the surface, the orbs burst with a low gurgle, spewing methane, a potent greenhouse gas that could accelerate the pace of climate change across the globe.

International experts are alarmed. "Methane release due to thawing permafrost in the Arctic is a global warming wild card," warned a report by the United Nations Environment Programme last year. Large amounts entering the atmosphere, it concluded, could lead to "abrupt changes in the climate that would likely be irreversible."

Methane (CH4) has at least 20 times the heat-trapping effect of an equivalent amount of carbon dioxide (CO2). As warmer air thaws Arctic soils, as much as 55 billion metric tons of methane could be released from beneath Siberian lakes alone, according to Walter’s research. That would amount to 10 times the amount currently in the atmosphere.

At 32, Walter, an aquatic ecologist, is a rising star among the thousands of scientists who are struggling to map, measure and predict climate change. Parts of her doctoral dissertation on Siberian lakes were published in three prestigious journals in 2007: Science, Nature and Philosophical Transactions of the Royal Society.

According to one of her studies, methane emissions from Arctic lakes were a major contributor to a period of global warming more than 11,000 years ago.

"It happened on a large scale in the past, and it could happen on a large scale in the future," says Walter, who refers to potential methane emissions as "a time bomb."

Methane levels in the atmosphere have tripled since preindustrial times. Human activities, including rice cultivation, cattle raising, and coal mining, account for about 70% of releases, according to recent studies. Natural sources, from tropical wetlands to termites, make up the rest. But those estimates had not incorporated the bubbles Walter was probing on an autumn morning on the Seward Peninsula.

That gurgling gas could change the entire model for predicting global warming. And lakes are not the only methane source: Newly discovered seeps -- places where methane leaks to the surface -- from the shallow waters of Siberia's vast continental shelf are also likely to upset previous assumptions....

Walter's work is crucial, according to Romanovsky and others, because global warming hinges partly on the ratio of how much carbon is released as CO2 vs. how much as methane, a molecule that contains both carbon and hydrogen. Methane, although a far more potent greenhouse gas than carbon dioxide, breaks down more quickly. But when it does, it oxidizes into a carbon dioxide molecule, which can last more than a century in the atmosphere.

Out on the lake, Walter explains: When organic matter (dead plants and animals) rots in the ground, it gives off carbon dioxide. Much of the organic material of thawed permafrost is expected to release carbon dioxide.

But as ice inside permafrost melts, small sinkholes open in the ground and fill with water, joining together to form millions of ponds and lakes. Organic matter slips from eroding shorelines to lake bottoms, where microbes feed on it. Because lake bottoms are oxygen-free, the microbes generate methane in addition to carbon dioxide -- as in the burping La Brea tar pits.

"These lakes are getting bigger -- in some places by a meter a year," Walter says, scooping out slush from the hole she has punched through 6 inches of ice. Into the seep, she inserts a plastic umbrellalike contraption fitted with a bottle to collect gas and a suspended brick to hold it straight...

Elsewhere, scientists cast a wary eye toward clouds of methane bubbles roiling the waters of the Siberian continental shelf. Those emissions, possibly from sub-surface permafrost, are even harder to measure than lake emissions.

Meanwhile, researchers are debating the possibility of eventual seeps from methane hydrates -- icy formations beneath the continental shelves and the ocean bottom, and far below land-based permafrost...

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