Old organic carbon locked in Arctic permafrost can be swept into coastal seas as warming destabilizes frozen ground and erodes shorelines, fueling worries that microbes could turn some of it into additional heat-trapping gases.
However, a new study suggests that much of that carbon may instead be getting buried in the seafloor.
What’s happening?
As a press release on the research laid out, roughly 1.43 trillion tons (1,300 gigatonnes) of organic carbon from ancient plant material are stored in Arctic permafrost ecosystems, and ocean and river-delta sediments contain another 441 billion US tons (400 gigatonnes).
As the Arctic warms faster than the rest of the planet, thawing ground and coastal erosion are moving more of that material into the ocean, the researchers said.
Off Qikiqtaruk, also known as Herschel Island, in Canada, scientists from the Alfred Wegener Institute and MARUM at the University of Bremen studied sediment cores taken from the seafloor. Those samples captured about 50 years of material deposited from the nearby coast.
“Consequently, up to 0.02 gigatonnes are entering the sea each year, and according to forecasts, this outflow could rise by 70% to 150% by 2100,” Dr. Manuel Ruben, lead author of the study, explained in the release.
Their results indicated that microbes converted only about 10% of the organic carbon in the sediments into gases that could move into the water and eventually the atmosphere. The rest largely stayed buried in the seabed.
Why does it matter?
Thawing permafrost has long been seen as a major climate risk. If huge amounts of old carbon are rapidly broken down and released as greenhouse gases, that could create another feedback loop that accelerates warming.
The study suggests the picture may be more complex.
“Carbon isotopes represent our atomic indicators that can identify the food source of the microorganisms,” Gesine Mollenhauer, a geochemist at the Alfred Wegener Institute, explained in the release.
The isotope evidence indicated that microbes tend to favor fresher marine material, including algae, rather than the older organic carbon washed in from thawing permafrost, per the study. If so, less of that permafrost carbon may be turned into climate-damaging gas at the seafloor than scientists once feared.
Material washing off Arctic coasts can both cloud coastal waters with sediment and darken them with dissolved organic matter, leaving less sunlight for algae that support marine food webs. Since those waters also sustain fish, crustaceans, seals, and local communities, the impacts go beyond climate alone.
What’s being done?
Researchers say the findings are an important step, but not the last word, because some old permafrost carbon may already decompose before it ever reaches the seabed. That means scientists still need a clearer picture of pollution from coast to ocean.
The team plans to pursue that work through the 2027 international Arctic Pulse campaign. Using the Polarstern research icebreaker, research aircraft, and land-based fieldwork, scientists will investigate how rapid Arctic change is reshaping ecosystems.
That work could improve climate models and help communities, governments, and industries make better decisions about infrastructure planning, fisheries, and resilience.
“Our study shows, more precisely than ever before, how much carbon is safely stored in the seabed.” Ruben said in the release. “This provides an important foundation for climate models that can predict the consequences of permafrost thawing for the global climate.”
Get TCD’s free newsletters for easy tips, smart advice, and a chance to earn $5,000 toward home upgrades. To see more stories like this one, change your Google preferences here.
