In the long term, the Arctic Ocean could store significantly more carbon from thawing permafrost than previously thought. This is the conclusion of a study by the Alfred Wegener Institute (AWI) and MARUM – Centre for Marine Environmental Sciences at the University of Bremen. For the first time, the researchers have been able to quantify how much organic carbon is released into the atmosphere from thawing permafrost soils and what proportion is permanently sequestered in the seabed. The findings were published in the journal Nature Geoscience.
The Arctic’s permafrost soils are vast carbon reservoirs. They contain around 1,300 gigatonnes of organic carbon, with further large quantities found in the sediments of river deltas and coastal waters. As the Arctic continues to warm, these soils are thawing at an increasing rate. As a result, more and more organic material is entering the Arctic Ocean via rivers and eroding coastlines. Until now, however, it was unclear how much of this is broken down by microorganisms and released as carbon dioxide.
For their study, the researchers analysed sediment cores taken off the permafrost coast of Qikiqtaruk (Herschel Island) in northern Canada. The deposits from the past 50 years or so show that only around ten per cent of the organic carbon deposited is broken down by microorganisms and converted into carbon dioxide. The vast majority, however, remains stored in the seabed over the long term.
The analysis of carbon isotopes was particularly revealing. It showed that microorganisms clearly prefer fresh organic carbon from marine algae. By contrast, the much older carbon from the permafrost deposits is converted only slowly. This suggests that thawing permafrost may contribute less significantly to the release of additional greenhouse gases than previously assumed. However, the researchers emphasise that some of the carbon could already be broken down during its transport from land to sea.
In addition to its impact on the climate, the input of permafrost material also affects the Arctic’s coastal waters. Turbid water and dissolved organic matter alter light conditions and can thus influence algal production and, ultimately, the entire marine food chain. These relationships are to be investigated in greater detail from 2027 onwards as part of the international research campaign Arctic Pulse.
The study thus provides important new insights into the role of the Arctic Ocean as a carbon sink from thawing permafrost and improves the basis for future climate models.
Heiner Kubny, PolarJournal