Thawing Arctic hills release a significant amount of organic carbon that has been locked up in frozen soil for thousands of years but may now contribute to an already warming climate, according to new research.
The finding comes from the study of slopes in a far northern region of Russia, where the researchers also found a significant and rapid increase in collapsed slopes. The collapses feature landslides that gradually expose more of the permafrost for thawing — and more carbon for release.
Global climate models do not account for the once-frozen carbon released by these collapsing hills. That has to change, the researchers believe.
The findings were published on July 15 in The cryosphere, a journal of the European Geosciences Union. They are the first to rely on the use of satellite imagery to estimate carbon emissions from collapsing Arctic hills.
“Permafrost landscapes are expected to change dramatically in the coming decades,” said Simon Zwieback, an assistant professor at the University of Alaska’s Fairbanks Geophysical Institute and one of the authors of the research paper. “One of the many consequences of this is the release of greenhouse gases such as carbon dioxide, which can exacerbate climate change.”
Similar thaw drops are also widespread on Russia’s Yamal Peninsula in Siberia, northwestern Canada, and Canada’s Arctic archipelago.
PhD student Philipp Bernhard from the Swiss Federal Institute of Technology in Zurich and Irena Hajnsek from the Institute in Zurich and the German Aerospace Center also contributed to the research. Zwieback and Hajnsek were Bernhard’s Ph.D. advisors.
The work focused on 10,500 square miles on the northern Taymyr Peninsula in Russia’s Siberia, an area bordered by the Byrranga Mountains to the south and the Kara Sea to the north.
The researchers compared satellite images from two time periods — 2010-2017 and 2018-2021 — to note changes in elevation and movement of debris and of the exposed leading edge of the slump. They then recorded an organic carbon map in the soil and made assumptions about the soil ice content and carbon stocks to calculate the amount of organic carbon released.
An ice sheet covered the entire study area about 130,000 years ago, with subsequent periods of ice retreat and advance covering an increasingly smaller area. The most recent retreat occurred at the end of the last ice age and was largely completed 12,000 years ago.
Satellite images revealed the spread of thaw drops in areas with remnants of that long-ago ice sheet.
A receding layer usually leaves significant amounts of ice, covered with clay, sand, gravel and rocks, especially along the edges of the ice sheet. The receding layer that once covered the present-day Taymyr area created several of these ice-rich zones, called ice margin zones. Two of those zones are in the researchers’ study area.
Images of the study area showed an increase in declines from 82 in the 2010-2017 study period to 1404 in the 2018-2021 period, with nearly all of that increase occurring during the region’s extremely warm 2020.
The images also showed that the annual volume of the affected material increased by about 43 times from the first to the second period.
“The extreme heat was exacerbated by the fact that there was a lot of ground ice close to the surface,” Zwieback said. “This is due to the long-term legacy of past ice ages, but also to the fact that so much of this ancient ice is still there because summers are usually cool and there are no fires.
“And the ice isn’t well protected by insulating organic layers because there isn’t much life in the harsh climate,” he said.
Alaska has thaw drops, but not nearly as many as those in Canada and Russia. Alaska also has other slope deformations caused by thawing permafrost, and these may contribute to climate change, Zwieback said.
There is little research on such a large geographic scale as that in the Taymyr Peninsula on thaw drops. The work of Zwieback, Bernhard and Hajnsek shows that carbon release from thawing Arctic slopes must be taken into account when assessing the Arctic’s carbon cycle. Researchers also need to quantify how much of it is converted to greenhouse gases such as carbon dioxide.
“The big challenge is to quantify and predict where, when and how much carbon dioxide is released,” Zwieback said.