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Dec. 22 (UPI) -- Scientists have come up with an estimate for the first time for the amount of carbon and methane that remains trapped in underwater permafrost. During the last glacial period, some 14,000 of years ago, rising seas swept across coastal tundra and steppe ecosystems, thawing permafrost and triggering microbial breakdown of organic matter.
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Today, the subsea permafrost continues to degrade at the bottom of the Atlantic Ocean, slowly releasing carbon and methane into the water column.
"Subsea permafrost is really unique because it is still responding to a dramatic climate transition from more than ten thousand years ago," Sara Sayedi, doctoral candidate at Brigham Young University and lead author of a new paper on the phenomenon, said in a news release.
"In some ways, it can give us a peek into the possible response of permafrost that is thawing today because of human activity."
For the study, published Tuesday in the journal Environmental Research Letters, researchers used what's called expert assessment to estimate the past and present size of subsea permafrost carbon stocks.
Researchers mined dozens of published and unpublished studies on subsea permafrost and subsea permafrost degradation, gathering best guesses for the size of the carbon and methane stocks that ended up underwater the end fo the last ice age, as well as estimates for how rapidly those stocks have been degrading for the last 14,000 years.
After amalgamating and analyzing the assessments of experts, researchers devised their own best guess. They believe 60 billion tons of methane and 560 billion tons of organic carbon remains trapped in sediment and soil within subsea permafrost regions.
The paper's authors acknowledged that the total amount of carbon and methane stocks in subsea permafrost regions remains uncertain.
Based on the expert assessments, researchers estimated 140 million tons of CO2 and 5.3 million tons of methane gas, CH4, from degraded permafrost stocks are released into the atmosphere each year.
"These results are important because they indicate a substantial, but slow, climate feedback," Sayedi said. "Some coverage of this region has suggested that human emissions could trigger catastrophic release of methane hydrates, but our study suggests a gradual increase over many decades."
While the degradation of permafrost submerged under the Atlantic Ocean was originally triggered by natural climate change some 14,000 years ago, scientists warn that human-caused climate change could accelerate the release of these submerged carbon and methane stocks.
Thought the release of carbon and methane from subsea permafrost is a gradual process, the phenomenon is currently not being accounted for in global climate models. Scientists hope their expert assessment will encourage climate modelers to pay close attention to this climate feedback loop.
"I think there are three important messages from this study," said Ben Abbott, a BYU professor and senior researcher on the project.
"First, subsea permafrost is probably not a climate time bomb on a hair trigger. Second, subsea permafrost is a potentially large climate feedback that needs to be considered in climate negotiations," Abbott said.
"Third, there is still a huge amount that we don't know about this system. We really need additional research, including international collaboration across northern countries and research disciplines."
