Stocks of vulnerable carbon twice as high where permafrost subsidence is factored in

June 17, 2020

New research from a team at Northern Arizona University suggests that subsidence, gradually sinking terrain caused by the loss of ice and soil mass in permafrost, is causing deeper thaw than previously thought and making vulnerable twice as much carbon as estimates that don't account for this shifting ground. These findings, published this week in the Journal of Geophysical Research: Biogeosciences, suggest traditional methods of permafrost thaw measurement underestimate the amount of previously-frozen carbon unlocked from warming permafrost by over 100 percent.

"Though we've known for a long time that subsidence happens across the permafrost zone, this phenomenon hasn't been systematically accounted for when we talk about thaw and carbon vulnerability," said Heidi Rodenhizer, a researcher at the Center for Ecosystem Science and Society at Northern Arizona University and lead author of the study, which was co-authored by a team from NAU, Woods Hole Research Center, Instituto de Ciencias Agrarias, and Yale University. "We saw that in both warming and control environments, slight temperature increases drove significant thaw and unlocked more carbon than we saw when we weren't looking at subsidence."

Traditionally, permafrost thaw has been calculated by measuring active layer thickness. To do that, scientists insert a metal rod into the ground until it hits permafrost, and measure from that depth to the soil surface. However, subsidence can mask actual thaw by lowering the soil surface and changing the frame of reference; for instance, some long-term experiments that rely on measuring active layer thickness have not recorded significant changes in thaw depth from year to year, despite rapid temperature warming.

So Rodenhizer and her team combined subsidence with active layer measurements to discover how much the ground was sinking, and how much unlocked carbon was being missed. At their warming site near Healy, Alaska, the team used high-accuracy GPS to measure the elevation of experimental plots at six time points over nine years. At each plot, Rodenhizer and her team found that permafrost thawed deeper than the active layer thickness indicated: 19 percent in the control plots, and 49 percent in the warming plots. The amount of newly-thawed carbon within the active layer was between 37 percent and 113 percent greater.

As the Arctic warms twice as fast as the rest of the planet, these findings have potentially vast implications for global carbon fluxes. Due to the widespread nature of subsidence--about 20 percent of the permafrost zone is visibly subsided, and contains approximately 50 percent of all carbon stored in permafrost--failing to account for subsidence could lead to significant underestimates of future carbon release in global climate change projections. Rodenhizer's team hopes that this study will convince more Arctic researchers across the permafrost monitoring network to apply this method and help change that.

"We know that these vast carbon stores in permafrost are at risk, and we have the tools to account for subsidence and track where the carbon is going," said permafrost researcher and senior author Ted Schuur. "We should be using everything in our toolbox to make the most accurate estimates, because so much depends on what happens to Arctic carbon."
-end-


Northern Arizona University

Related Permafrost Articles from Brightsurf:

Coastal permafrost more susceptible to climate change than previously thought
Research led by Micaela Pedrazas, who earned her masters at The University of Texas at Austin Jackson School of Geosciences working with Professor Bayani Cardenas, has found permafrost to be mostly absent throughout the shallow seafloor along a coastal field site in northeastern Alaska.

Arctic Ocean sediments reveal permafrost thawing during past climate warming
Sea floor sediments of the Arctic Ocean can reveal how permafrost responds to climate warming.

Thawing permafrost releases organic compounds into the air
When permafrost thaws due to global warming, not only the greenhouse gases known to all, but also organic compounds are released from the soil.

Siberia's permafrost erosion has been worsening for years
The Arctic is warming faster than any other region on the planet.

Alaska is getting wetter. That's bad news for permafrost and the climate.
Alaska is getting wetter. A new study spells out what that means for the permafrost that underlies about 85% of the state, and the consequences for Earth's global climate.

Plant roots increase carbon emission from permafrost soils
A key uncertainty in climate projections is the amount of carbon emitted by thawing permafrost in the Arctic.

Stocks of vulnerable carbon twice as high where permafrost subsidence is factored in
Twice as much carbon in permafrost is vulnerable to microbial respiration when researchers from Northern Arizona University accounted for subsidence, the gradual sinking of terrain caused by loss of ice and soil mass.

Carbon emission from permafrost soils underestimated by 14%
Picture 500 million cars stacked in rows. That's how much carbon -- about 1,000 petagrams, or one billion metric tons - -is locked away in Arctic permafrost.

Nitrogen in permafrost soils may exert great feedbacks on climate change
A new Sino-German scientific collaboration investigating nitrogen in the soils of China's melting permafrost aims to get to the bottom of why emissions of nitrous oxide -- an often overlooked greenhouse gas -- are greater than they are supposed to be.

Patterns in permafrost soils could help climate change models
A team of scientists spent the past four summers measuring permafrost soils across a 5,000 square-mile swath of Alaska's North Slope.

Read More: Permafrost News and Permafrost Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.