Author: Douglas Fox / Source: Science News for Students
September 8, 2017, was an exciting date for Katey Walter Anthony. On this cool, windless evening she first visited Alaska’s Lake Esieh.
Few people visit this remote stretch of wilderness. It is covered in tundra and scraggly spruce trees. Thousands of lakes dot the region. But Walter Anthony quickly realized that this lake was strange. As her boat glided across it, she came to a place where the water seemed to be boiling.The water wasn’t warm. But it roiled and fizzed. Bubbles of all sizes streamed up, popping at the surface. One bubble, as large as a softball, gave off a loud bloonk as it ruptured. The bubbles covered a swath of the lake larger than a football field. And they rose with such force that they slowly pushed her boat to the side.
Walter Anthony leaned over the edge of the boat and collected some bubbles in a bottle. Then she struck a match and opened the bottle to release the gas she had just collected. The gas caught fire!
The yellow-tipped flame that danced over the bottle confirmed her suspicion. It showed that the lake was gurgling out a flammable gas, called methane. Each molecule (CH4) contains one atom of carbon bonded to four atoms of hydrogen.
As a potent greenhouse gas, methane can absorb radiation from the sun, warming the atmosphere. Methane, along with carbon dioxide, is a major source of global warming. Later calculations would show that this little lake was belching out lots of this gas — some 2,000 kilograms (4,400 pounds) each day.
Walter Anthony works at the University of Alaska in Fairbanks. She’s a limnologist, a scientist who studies lakes. To date, she has studied more than 300 of them in the Arctic. Many give off methane. But Lake Esieh was different. She could hear a deep-throated gurgling as bubbles shoved their way up, violently, through the mud at the bottom of the lake. “The sound was really amazing,” she says. It was coming from deep below her boat. “I’d never heard that before.”
Scientists believe that the Arctic could release large amounts of methane over the next 100 years. The gas is naturally released as frozen soil, called permafrost, warms up and thaws. And some scientists worry that this methane will cause the world to warm more quickly than they had predicted.
Walter Anthony has spent nearly 20 years trying to understand this threat. She is trying to measure how much methane is coming out of warming Arctic lakes. And to her, Lake Esieh could be a warning. If other lakes respond the same way, the Arctic could be poised to burble out far more methane than anyone had expected. “We don’t even know how much gas is down there,” she says. “It’s a wild card.”
For that reason, it’s important to understand what’s happening at Lake Esieh.
Rotting mush
Permafrost covers 22 million square kilometers (8.5 million square miles) of territory across the north of Alaska, Canada, Europe and Asia. That’s an area larger than the United States and Canada combined. This frozen soil is rich in organic matter — the remains of plants that lived hundreds or thousands of years ago.
These dead plants froze before they could fully decay. But as that permafrost now thaws, single-celled microbes have begun dining on those plant remains. They break down the dead stuff into mush, like kitchen scraps in a compost heap. Along the way, the microbes exhale methane and another carbon-based gas, carbon dioxide (CO2).
Scientists have long known that melting permafrost would release these gases. What has not been clear is how much might come out and how quickly. People are especially concerned about methane. Over a period of 100 years, it absorbs more than 20 times as much heat, gram for gram, as carbon dioxide does. Once in the atmosphere, methane slowly turns into carbon dioxide — also a greenhouse gas.
Walter Anthony has been figuring out just how much methane Arctic lakes are spewing. She started in 2002, while she was working toward her PhD at the University of Alaska. Back then, she was spending much of her time in Siberia, in northeast Russia.
Thawing permafrost can make the ground sag. These low spots fill with water — forming what are called “thermokarst” lakes. Walter Anthony saw tiny bubbles of methane bubbling up as she paddled her boat across one of these Siberian lakes, called Shuchi. But she could never anticipate where a bubble would emerge. So she couldn’t catch or measure them.
Starry sky
She got some advice from an ecologist at the Northeast Science Station in Chersky, Russia. This Sergey Zimov suggested that she try a new approach: Wait until winter freezes the lake over. The ice might trap methane bubbles, showing her where the gas was accumulating.
In October 2002, she donned a down jacket and headed out into the cold. She shoveled snow off a strip of lake ice, then poured water onto it. This smoothed the ice so that she could see through it into the lake below.
“It was like looking at a starry night sky,” she says. The white gas bubbles stood out against the dark background of the water below. For the first time, she realized that most of the bubbles were coming up in very specific places — and always the same places. Now she knew where those places were.
She used a crowbar to chip holes in…
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