The submarine permafrost still wakes up after 12,000 years

New research suggests the slow but substantial release of greenhouse gases from underwater permafrost.

In the far north, the swollen Arctic Ocean has flooded large areas of coastal and steppe tundra ecosystems. Although the ocean water was only a few degrees above freezing, it began to thaw the permafrost beneath it, exposing billions of tons of organic matter to microbial decomposition. Decomposing organic matter has begun to produce CO2 and CH4, two of the most important greenhouse gases.

Although researchers have been studying degrading underwater permafrost for decades, the difficulty of collecting measurements and sharing data between international and disciplinary divisions has prevented a general estimate of carbon footprint and release rate. A new doctoral study. candidate Sara Sayedi and principal investigator Dr. Ben Abbott of Brigham Young University (BYU) published in IOP Publishing Environmental research letters, sheds light on submarine permafrost climate feedback, generating the first estimates of circumarctic carbon stocks, greenhouse gas release and the possible future response of the submarine permafrost area.

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 The researchers combined the results of published and unpublished studies to estimate the size of past and present underwater carbon stocks and the amount of greenhouse gases they could produce over the next three centuries.

Using a methodology called expert assessment, which combines multiple independent plausible values, the researchers estimated that the underwater permafrost region currently captures 60 billion tons of methane and contains 560 billion tons of organic carbon in sediment and soil. As a reference, humans have released into the atmosphere a total of about 500 billion tons of carbon since the Industrial Revolution. This makes the underwater carbon stock permafrost a potential giant ecosystem feedback on climate change.

“Underwater permafrost is truly unique because it continues to respond to a dramatic climate transition of more than ten thousand years ago,” Sayedi said. “In some ways, it can take a look at the possible response of permafrost that is thawing today due to human activity.”

Estimates from Sayedi’s team suggest that submarine permafrost is already releasing substantial amounts of greenhouse gases. However, this version is mainly due to ancient climate change, rather than current human activity. They estimate that underwater permafrost releases about 140 million tons of CO2 and 5.3 million tons of CH4 into the atmosphere each year. This is similar in magnitude to the overall greenhouse gas footprint in Spain.

The researchers found that if man-made climate change continues, the release of CH4 and CO2 from underwater permafrost could increase substantially. However, this response is expected to appear in the next three centuries, rather than abruptly. The researchers estimated that the amount of future greenhouse gas emissions from submarine permafrost depends directly on future human emissions. They found that in a normal scenario, underwater permafrost heating releases four times more CO2 and CH4 compared to when human emissions are reduced to keep heating below 2 ° C.

“These results are important because they indicate substantial but slow climate feedback,” Sayedi explained. “Some coverage of this region has suggested that human emissions could trigger the catastrophic release of methane hydrates, but our study suggests a gradual increase over several decades.”

Although this climate feedback is relatively gradual, the researchers point out that underwater permafrost is not included in current climate agreements or greenhouse gas targets. Sayedi stressed that there is still a great deal of uncertainty about underwater permafrost and that further research is needed.

“Compared to how important underwater permafrost could be for the future climate, we know a shockingly little about this ecosystem,” Sayedi said. “We need more sediment and soil samples, as well as a better monitoring network to detect when the release of greenhouse gases responds to the current warming and how quickly this huge pool of carbon will wake up from its slumber. its frozen ”.

Summary of main scientific points:

• The submarine permafrost has thawed since the end of the last ice age (~ 14,000 years ago), when it began to be flooded by the ocean.
• An international team of 25 permafrost researchers estimates that the submarine permafrost region currently captures 60 billion tonnes of methane and 560 billion tonnes of organic carbon in sediment and soil. However, the exact amount of these carbon stocks remains extremely uncertain.
• This carbon is already released from the submarine permafrost region, although it remains unclear whether this is a natural response to deglaciation or whether anthropogenic warming is accelerating the production and release of greenhouse gases.
• Researchers estimate that the submarine permafrost region currently releases about 140 million tonnes of CO2 and 5.3 million tonnes of CH4 into the atmosphere each year. This accounts for a small share of total anthropogenic greenhouse gas emissions – roughly equal to Spain’s greenhouse gas footprint.
• Experts predict a gradual increase in emissions from underwater permafrost over the next three hundred years, rather than a sudden release.
• The amount of greenhouse gas growth depends on how low human emissions are. Experts estimate that about ¾ of additional underwater emissions can be avoided if people actively reduce their emissions compared to a no-mitigation scenario.
• This climate feedback is still virtually absent from 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 in this study. First, underwater permafrost is probably not a climate clock bomb on a hair trigger. Second, submarine permafrost is a potentially high climate feedback, which must be taken into account 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 in the Nordic countries and research disciplines. “

– Dr. Ben Abbott, Senior Researcher in the Project, Brigham Young University

“This paper demonstrates the power of the synthesis of science and networks by bringing together experts in a wide range of disciplines to assess our state of knowledge based on observations and models currently available. While scientific work will continue to test these ideas, bringing the knowledge together with this assessment by experts provides an important basis for shaping future research on submarine permafrost greenhouse gas emissions. “

– Dr. Ted Schuur, Principal Investigator of the Permafrost Carbon Network, University of Northern Arizona

“This expert assessment is a crucial contribution to the scientific literature in advancing our knowledge of underwater permafrost and potential greenhouse gas emissions from this basin under study so far. Bringing together scientists from several disciplines, institutions and countries has made it possible to move beyond individual data points or studies, providing a much more comprehensive estimate of underwater permafrost. “

– Dr. Christina Schädel, co-investigator of the Permafrost carbon network, University of Northern Arizona

Reference: “Submarine Permafrost Carbon Stocks and Sensitivity to Climate Change Estimated by the 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 BYU Graduate Studies.