A pileup of ancient logs nearly as big as Manhattan is trapping millions of tons of carbon in northern Canada — and much of that stored material could be released into the atmosphere due to climate change, according to a recent study.
The fallen, jumbled-up wood has in some cases been sitting for more than a millennium, protected from decay by the deep freeze and the tight packing of the logs, which are carried northward by the Mackenzie River above the Arctic Circle.
And now, amid warming temperatures and rising seas, the logjam may be at risk of breaking up and decaying more quickly, said Alicia Sendrowski, a researcher at Michigan Technological University who led the study.
Natural carbon sinks, such as forests, peatlands and the ocean,are an important damper on climate change because they trap more carbon than they release into the atmosphere. Carbon sinks on land are estimated to soak up a quarter of the world’s emissions, a powerful but not-always-well-understood factor in slowing warming.
Not all carbon stores are resilient to rising temperatures, though, and some may break down quickly when pushed too hard. Thawing permafrost starts melting slowly, then melts very rapidly, for example, leading to fears of massive releases of carbon into the atmosphere and a problem that builds on itself.
Scientists are racing to map how much carbon is trapped in wood in the Arctic, and how much might be lost to the atmosphere as a result of climate change, as wood that has stayed stable for hundreds or even thousands of years starts to break down from warming temperatures.
“We don’t have a big understanding, systemically, about other large wood deposits,” Sendrowski said.
A 20-square-mile logjam
The massive accumulation of wood that she studied covers a total surface area of 20 square miles, scattered in deposits across the Mackenzie River delta, the endpoint of a powerful river that sweeps across Canada.
The profusion of wood may be storing about 3.4 million tons of carbon, according to Sendrowski’s research work, which was published in the journal Geophysical Research Letters. It sought to map the logjam and estimate its weight and carbon content for the first time, using a mixture of drone and satellite photography and artificial intelligence to estimate the visible amount of wood. That’s equivalent to the emissions of 2.5 million cars for a year, she said.
The oldest wood Sendrowski found was around 1,300 years old, according to radiocarbon dating, she said, although most of it was less than 70 years old.
She still isn’t sure whether the logjam is losing carbon faster than it is accumulating it through new trees being washed into it, but she said the process was likely to start to accelerate.
Live trees that have been rooted in the permafrost may increasingly tumble into rivers as the ground thaws underneath them. And warmer temperatures may accelerate decay as the logs rub against each other and shed more material and float off into the open sea, where they will decay more quickly than if they remain trapped in the logjam, Sendrowski said.
Understanding the world’s carbon sinks
Forests are the crucial carbon sink on land. And research suggests that so far, as carbon emissions have increased, so has their ability to absorb at least part of it. Smithsonian researcher Sean McMahon found that trees he studied near the Chesapeake Bay were growing two to four times faster than he expected. That’s probably because increased levels of carbon dioxide help plants grow faster and because increased temperatures lengthen the growing season and speed other processes required for plant growth.
But other carbon sinks might be found in unusual places — such as in forearcs, the stretch of land between volcanoes and ocean trenches, which researchers believe traps carbon that is bubbling up in gasses from the earth’s core.
Another might be the water flowing through a salty plain of the Taklamakan Desert in Xinjiang province in China, which may pull carbon out of the air as it sinks into the aquifer, according to research by Yan Li, a professor at Zhejiang Agriculture and Forestry University.
Up in Canada, Sendrowski plans to continue researching the logjam, which is one of at least a dozen major log formations in the high north. One question she hopes to answer is the average age of the wood, which would give a more precise sense of the length of time the logjam traps carbon before releasing it. And she wants to quantify the wood she couldn’t see in aerial imagery.
“We don’t have a measurement of what is buried, what is submerged, what is under canopy cover,” she said.
And “the time scale of the decay,” she said, will help “better get at the carbon storage potential of the system.”
Source : Washington Post
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