(CN) – The loss of Arctic permafrost deposits by coastal erosion could amplify climate warming via the greenhouse effect, according to a study published Monday in the journal Nature Communications.
Researchers from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, studied sediment samples from the Sea of Okhotsk on the eastern coast of Russia. They found the loss of Arctic permafrost at the end of the last glacial period – 20,000 years ago – led to repeated sudden increases in the carbon dioxide concentration in the atmosphere.
The findings reveal a process that could again become reality in the future, they say.
“Our findings show that this coastal erosion is an important process, but to date it has not been sufficiently considered in climate models. Such effects need to be included in future models.” Gesine Mollenhauer, one of the lead researchers, said.
Researchers believe this is the first direct evidence for the release of ancient carbon from degrading permafrost in East Asia in the last 17,000 years, and proof it’s happening again today as the Arctic continues to warm and could yield similar increases in carbon dioxide as a result.
Rapid warming in the Arctic is causing severe coastal erosion, with some areas receding at a rate of 65 feet per year. While the exact magnitude of the future increase in greenhouse gas concentrations remains unknown as carbon dioxide is also produced by humans burning fossil fuels, the release of ever increasing amounts of carbon dioxide from natural environmental warming processes is an added threat.
Permafrost is ground that remains frozen year-round down to depths of more than 2,000 feet. Like a giant freezer, permafrost soils preserve huge quantities of dead biomass, mainly plant remains. When the permafrost thaws, bacteria start degrading the ancient biomass, and their metabolisms release carbon dioxide and methane – both greenhouse gases.
Wegener Institute scientists along with colleagues from Copenhagen and Zurich have now found evidence of this phenomenon for the Arctic permafrost regions. Their investigations show that several thousand years ago, large quantities of carbon dioxide were released from Arctic permafrost due to a rapid rise of sea level.
About 11,500, 14,600 and 16,500 years ago, significant and sudden rises in the carbon dioxide level in the atmosphere occurred. The reasons for these three rapid fluctuations remain poorly understood, scientists say.
“Originally we assumed that at the time, the vast Amur River carried tremendous quantities of plant material from the hinterland, which microorganisms in the water then broke down into carbon dioxide. So we collected sediment samples from the sea floor, which we then analyzed,” Mollenhauer said.
The team was surprised to find evidence of plant remains that had been deposited on the sea floor deep in the sediment that were several thousand years older than the surrounding deposits. This made it clear that they must have originated in extremely old permafrost that for some reason had suddenly thawed.
Mollenhauer and her team found particularly large amounts of these plant remains were washed into the sea after especially intense melting of the ice sheets known as meltwater pulses.
“We assume that this resulted in severe erosion of the permafrost coast in the Sea of Okhotsk and the North Pacific – a phenomenon that we can observe in the Arctic today,” Mollenhauer said.
To determine whether such permafrost erosion could indeed have been a key factor in increases in the global carbon dioxide concentration, Dr. Peter Köhler used a computer model to simulate the global carbon cycle. By estimating the area of permafrost lost to the sea at the time, he obtained data on the likely amount of carbon dioxide released.
The results are eye-opening, according to Kohler. Erosion of Arctic permafrost around 11,500 and 14,600 years ago likely contributed to about 50 percent of the carbon dioxide increase, and 16,500 years ago to about a quarter, according to the data modeling.
Rates and pathways of carbon release from permafrost are highly uncertain but crucial to understand how strongly, and over which timescales, these feedbacks may affect climate.
Until now, assessments of the susceptibility of permafrost to degradation and assessments of future and past feedbacks were based only on indirect estimates of the age of permafrost-derived old carbon.