Permafrost erosion reduces carbon sequestration in the oceans

A German study shows how permafrost erosion on the coast of the Arctic Ocean leads to an almost 15 per cent decrease in the seawater’s ability to store CO2

by Matteo Cavallito

 

Erosion of Arctic permafrost in coastal areas impacts the ocean’s ability to capture CO2, ultimately affecting climate. This is the hypothesis put forward by a group of scientists in a study by the University of Hamburg‘s Cluster of Excellence published in the journal Nature Climate Change. Due to the low water temperature, the authors point out, the Arctic Ocean absorbs a particularly high amount of carbon relative to its size. Due to climate change and other factors, however, this effect will be less pronounced in the future.

“More than 90% of the ocean uptake of atmospheric CO2 occurs in polar and subpolar regions,” the research states.”Over the Arctic shelves, CO2 uptake is estimated at ~70 TgC yr−1 (70 million tonnes per year, ed.), among the largest per unit area in the globe. However, the sensitivity of the ocean CO2 uptake to coastal permafrost erosion is uncertain, especially as climate change progresses into the future.”

The impact of climate on permafrost

The ‘permafrost’ is the particular type of perennially frozen (but not necessarily ice-covered) soil found in some cold regions. Rising temperatures linked to climate change, however, favour the thawing of these soils, particularly in coastal areas. ‘When stretches of coastland that have been frozen for millennia thaw and crumble, massive amounts of soil and sediment are released into the ocean,’ says a statement released by the same German university.

“How these particles react to the seawater depends on their composition, but in all cases their organic components increase the water’s carbon content, reducing its ability to absorb CO2 from the air.”

The study, the researchers explain, would demonstrate and quantify for the first time the impact of this phenomenon on the oceans, which, to date, mitigate climate change by absorbing about 30% of anthropogenic greenhouse gases from the atmosphere. An estimate of how much permafrost erosion on Arctic Ocean coasts reduces seawater sequestration capacity, in other words, should be included in future climate models.

CO2 absorption capacity may drop by 14 per cent

According to the authors, the rate of erosion of coastal permafrost could double or even triple between now and the end of the century. In this context, the authors developed some simulations taking into account the different properties of organic matter in the soil.

“We find that coastal erosion reduces the Arctic Ocean CO2 uptake from the atmosphere in all simulations: by 4.6–13.2 TgC yr−1 by 2100, which is ~7–14% of the Inner Arctic Ocean uptake,” the scientists explain.

Moreover, “We show that coastal permafrost erosion exerts a positive biogeochemical feedback on climate, increasing atmospheric CO2 by 1–2 TgC yr−1 per °C of increase in global surface air temperature,” compared to previous assumptions. This is, for comparison, an amount equivalent to one-tenth of the emissions produced annually by road traffic in Europe.

New climate models

‘Our work will allow coastal permafrost erosion to be considered in future climate change assessments,’ the scientists conclude, underlining the importance of taking this particular factor into account.

“We should be grateful that our oceans absorb a major percentage of our greenhouse gases,” explains David Nielsen, professor at the University of Hamburg and co-author of the study. “But this ecosystem service might not always continue to be as strong as it has been in the past. To determine whether or not we can keep counting on this effect in the future, we need to first understand the mechanisms of CO2 absorption in more detail”.