New research suggests slow but significant emissions of greenhouse gases from submarine permafrost.
In the far north, the swell-like Arctic Ocean flooded large shards of coastal tundra and steppe ecosystems. Although seawater was only a few degrees above freezing, it began to thaw the permafrost beneath it, exposing billions of tons of organic matter to microbial degradation. The decomposing organic matter began to produce CO2 and CH4, two of the most important greenhouse gases.
Although researchers have studied degrading subsea permafrost for decades, difficulties in collecting measurements and sharing data across international and disciplinary divisions have prevented an overall estimate of the amount of carbon and release rate. A new study led by Ph.D. candidate Sara Sayedi and senior researcher Dr. Ben Abbott of Brigham Young University (BYU) published in the journal IOP Publishing Environmental research letters, sheds light on feedback from the permeafrost climate below sea level and generates initial estimates of carbon stocks in the area, greenhouse gas emissions and possible future response to the subsea permafrost zone.
Sayedi and an international team of 25 permafrost researchers worked under the coordination of the Permafrost Carbon Network (PCN), which is supported by the US National Science Foundation. The researchers combined findings from published and unpublished studies to estimate the size of the former and current underwater carbon stock and how much greenhouse gas it can produce over the next three centuries.
Using a method called expert assessment, which combines several independent probable values, the researchers estimated that the submarine permafrost region currently traps 60 billion tons of methane and contains 560 billion tons of organic carbon in sediment and soil. As a reference, humans have released a total of about 500 billion tons of carbon into the atmosphere since the Industrial Revolution. This makes the subsea permafrost carbon stock a potential giant ecosystem feedback for climate change.
“Permafrost under the sea is truly unique because it is still responding to a dramatic climate change more than ten thousand years ago,” said Sayedi. “In some ways, it can give us a look at the possible response from permafrost that has been thawed today due to human activity.”
Estimates from Sayedi’s team suggest that subsea permafrost is already releasing significant amounts of greenhouse gas. However, this release is mainly due to old climate change rather than the current human activity. They estimate that underwater permafrost releases approximately 140 million tons of CO2 and 5.3 million tons of CH4 into the atmosphere each year. This corresponds in size to the total footprint of the greenhouse gas in Spain.
The researchers found that if man-made climate change continues, the release of CH4 and CO2 from underwater sperm frost can increase significantly. However, this answer is expected to occur over the next three centuries rather than abruptly. Researchers estimated that the amount of future greenhouse gas emissions from submarine permafrost depends directly on future human emissions. They found that heating subsea permafrost under a business-as-usual scenario releases four times more CO2 and CH4 compared to when human emissions are reduced to keep heat less than 2 ° C.
“These results are important because they indicate a significant but slow response from the climate,” Sayedi explained. “Some coverage of this region has suggested that human emissions may trigger catastrophic release of methane hydrates, but our study suggests a gradual increase over many decades.”
Although this feedback from the climate is relatively gradual, the researchers point out that subsea permafrost is not included in any current climate agreements or greenhouse gas targets. Sayedi stressed that there is still great uncertainty about permeafrost below sea level and that further research is needed.
“Compared to how important subsea permafrost may be for future climates, we know shockingly little about this ecosystem,” said Sayedi. “We need more sediment and soil samples as well as a better monitoring network to detect when greenhouse gas emissions respond to current warming and how quickly this huge pool of carbon will wake up from its frozen sleep.”
Summary of key scientific points:
- Permafrost under the sea island has been thawed since the end of the last ice age (~ 14,000 years ago), when it began to be flooded by the sea
- An international team of 25 permafrost researchers estimates that the underwater permafrost region currently traps 60 billion tonnes of methane and 560 billion tonnes of organic carbon in sediment and soil. However, the exact amount of these carbon stocks is still very uncertain.
- This carbon is already released from the subsea permafrost region, although it is still unclear whether this is a natural response to devitrification or if man-made heating accelerates the production and release of greenhouse gases.
- The researchers estimate that the current underwater permafrost region currently releases approx. 140 million tonnes of CO2 and 5.3 million tonnes of CH4 into the atmosphere each year. This represents a small fraction of the total anthropogenic greenhouse gas emissions – roughly equal to Spain’s greenhouse gas footprint.
- Experts predict a gradual increase in emissions from subsea permafrost over the next three hundred years rather than a sudden release.
- The amount of greenhouse gas increase depends on how much human emissions are reduced. Experts estimate that approx. ¾ of the extra subsea emissions can be avoided if humans actively reduce their emissions compared to a scenario without mitigation.
- This climate feedback is still almost non-existent in climate policy discussions, and more field observations are needed to better predict the future of this system.
Quotes from other co-authors:
“I think there are three important messages from this study. First, underwater sperm frost is probably not a climate time bomb on a hair trigger. Second, subsea permafrost is a potentially major climate feedback to be considered in climate negotiations. Thirdly, there is still a huge amount that we do not know about this system. We really need further research, including international collaboration across northern countries and research disciplines. ”
– Dr. Ben Abbott, senior researcher on the project, Brigham Young University
“This work demonstrates the strength of science synthesis and networking by bringing together experts across a range of disciplines to assess our state of knowledge based on currently available observations and models. While scientific work will continue to be conducted to test these ideas, bringing knowledge along with this expert assessment is an important baseline for shaping future research into subsea permafrost greenhouse gas emissions. ”
– Dr. Ted Schuur, senior investigator of the Permafrost Carbon Network, Northern Arizona University
“This expert assessment is a crucial contribution to the scientific literature to advance our knowledge of subsea permafrost and potential greenhouse gas emissions from this hitherto studied pool. Gathering researchers from multiple disciplines, institutions, and countries has made it possible to move beyond individual data points or studies, providing a far more comprehensive estimate of subsea permafrost. ”
– Dr. Christina Schädel, co-researcher of the Permafrost Carbon Network, Northern Arizona University
Reference: “Subsea permafrost carbon stock and climate change sensitivity estimated by expert assessment” by Sayedeh Sara Sayedi, Benjamin W Abbott, Brett F Thornton, Jennifer M Frederick, Jorien E Vonk, Paul Overduin, Christina Schädel, Edward AG Schuur, Annie Bourbonnais, Nikita Demidov, Anatoly Gavrilov, Shengping He, Gustaf Hugelius, Martin Jakobsson, Miriam C Jones, DongJoo Joung, Gleb Kraev, Robie W Macdonald, A David McGuire, Cuicui Mu, Matt O’Regan, Kathryn M Schreiner, Christian Stranne, Elena Pizhankova, Alexander Vasiliev , Sebastian Westermann, Jay P Zarnetske, Tingjun Zhang, Mehran Ghandehari, Sarah Baeumler, Brian C Brown and Rebecca J Frei, 22 December 2020, Environmental research letters.
DOI: 10.1088 / 1748-9326 / abcc29
This research was funded by the US National Science Foundation and by BYU Graduate Studies.