Permafrost Carbon Takes A Trip to Davy Jones’ Locker

Mackenzie River delta. Photo: NASA Visible Earth; Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC Satellite: Terra Sensor: MODIS Image Date: 08-29-2001
Mackenzie River delta. Photo: NASA Visible Earth; Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC Satellite: Terra Sensor: MODIS Image Date: 08-29-2001

It’s been widely accepted in the science community that melting permafrost means more carbon in the atmosphere. But a new study has identified a quirk in that process.

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Permafrost is a layer of subsurface soil that stays frozen year-round. And it’s generally understood that melting permafrost in the north means more methane and carbon dioxide in the atmosphere — bad for global warming.

But a new study published in Nature suggests that some of the carbon stored in permafrost meets its bitter end like Bootstrap Bill Turner in “Pirates of the Caribbean” — Davy Jones’ Locker.

In other words, it gets buried at the bottom of the ocean.

Dr. Valier Galy of the Woods Hole Oceanographic Institution is one of the study’s authors.

“The burial of permafrost carbon in marine sediments offshore of the river is something that matters in terms of fluxes when it’s taken for several thousands of years,” he says.

Down in Davy Jones’ Locker, that carbon is sequestered; It becomes a carbon sink as opposed to a carbon source. And it’s in a format that won’t contribute to climate change or ocean acidification.

“That’s correct… as long as permafrost carbon reaches marine sediments and is being buried in marine sediments. It is then stable for really long periods of times,” Dr. Galy says. “We can be talking hundreds of thousands of years. Millions of years.”

High-latitude rivers are the engines at work here. Dr. Galy and his colleagues did their study on the Mackenzie River in Canada:

“So what we did is, we took samples from different places of the river system… and we took samples offshore — sediment core — and then we looked at the organic carbon concentrations, but also its composition using geochemical tools. And what this shows is that a lot of these carbons are pretty old and come from the permafrost.”

Finding those permafrost carbons offshore was somewhat of a surprise.

It was previously understood that these carbons made their way back into the atmosphere when permafrost melted — and that’s still the fate of the majority of the carbon stored in permafrost. Year to year, what’s buried at sea is fairly insignificant, but it adds up over thousands of years.

The Mackenzie is a massive river (the second largest on North America behind the Mississippi) — and the study estimates it buries more than 2 million metric tons of permafrost carbon per year. The power of the Mackenzie is what makes the river so good at burying permafrost carbon.

The Mackenzie has very high physical erosion rates, and that’s what makes it very efficient at burying permafrost carbon at sea.”

Dr. Galy says some version of this carbon burial process likely happens in most watersheds at high-latitudes. More so with big rivers, including Alaska’s Yukon:

“In the Yukon the physical erosion rates are also very high. And so it’s pretty likely that we’ll find the same things that we’ve been finding in the Mackenzie system.”

Even though some permafrost carbon is being cycled to the bottom of the ocean, it’s a process that takes thousands of years — much slower than the rate at which greenhouse gases are being emitted.