Newswise – Each year, the transport of carbon-rich particles from the Barents and Kara Seas could sequester up to 3.6 million tons of CO2 in the Arctic deep sea for thousands of years. In this region alone, a previously unknown transport route uses the biological carbon pump and ocean currents to absorb atmospheric CO2 in the extent of Iceland’s total annual emissions, as researchers from the Alfred Wegener Institute and partner institutes report in the current issue of the journal nature geosciences.
Compared to other oceans, the biological productivity of the central Arctic Ocean is limited because sunlight is often scarce — either through the polar night or through sea ice cover — and available nutrient sources are scarce. As a result, microalgae (phytoplankton) in the upper water layers have less energy available than their conspecifics in other waters. The surprise was correspondingly great when large amounts of particulate carbon – i.e. stored in plant residues – were discovered on board the Russian research vessel Akademik Tryoshnikov in the Nansen Basin of the central Arctic during the ARCTIC2018 expedition in August and September 2018. Subsequent analysis revealed a body of water with large amounts of carbon particles at depths of up to two kilometers consisting of groundwater from the Barents Sea. The latter occurs when sea ice forms in winter, causing cold and heavy water to sink and then flow from the shallow coastal shelf down the continental slope into the deep Arctic Basin.
“Based on our measurements, we calculated that more than 2,000 tons of carbon flow into the Arctic deep sea every day due to this mass transport of water, which corresponds to 8,500 tons of atmospheric CO2. Extrapolated to the total annual amount, the result was even 13.6 million tons of CO2which is roughly the order of magnitude of Iceland’s total annual emissions,” explains Dr. Andreas Rogge, first author of the nature geosciences Studied and oceanographer at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI). This cloud of carbon-rich water extends from the shelves of the Barents and Kara Seas to about 1,000 kilometers into the Arctic Basin. Given this newly discovered mechanism, the Barents Sea — already known as the Arctic’s most productive marginal sea — appears to be effectively removing about 30 percent more carbon from the atmosphere than previously thought. In addition, model-based simulations have determined that runoff manifests itself in seasonal pulses, as Arctic coastal seas absorb CO2 by phytoplankton only takes place in summer.
Understanding transport and transformation processes within the carbon cycle is essential for preparing global carbon dioxide budgets and thus also global warming projections. Single-celled algae absorb CO on the sea surface2 from the atmosphere and sink towards the deep sea with age. If the carbon bound in this way reaches the deep water, it remains there until overturning currents bring the water back to the sea surface, which takes several thousand years in the Arctic. And if the carbon is deposited in deep-sea sediments, it can remain trapped there for millions of years because it can only be released by volcanic activity. Also known as the biological carbon pump, this process can remove carbon from the atmosphere for long periods of time and represents a vital sink in our planet’s carbon cycle. The process also represents a food source for local deep-sea fauna such as starfish, sponges and worms. What percentage of carbon actually absorbed by the ecosystem, only further research can tell us.
The polar shelf seas are home to other largely unexplored regions where groundwater forms and flows into the deep sea. In this respect, it can be assumed that the global influence of this mechanism as a carbon sink is actually much greater. “However, as global warming progresses, less ice is forming and therefore less soil water. At the same time, more light and nutrients are available to the phytoplankton, which means that more CO is released2 to be bound. Accordingly, it is currently not foreseeable how this carbon sink will develop, and the identification of possible tipping points urgently requires further research,” says Andreas Rogge.
Andreas Rogge, Markus Janout, Nadezhda Loginova, Emilia Trudnowska, Cora Hörstmann, Claudia Wekerle, Laurent Oziel, Vibe Shourup-Kristensen, Eugenio Ruiz-Castillo, Kirstin Schulz, Vasily V Povazhnyy, Morten H Iversen, Anya M Waite: Carbon Carbon dioxide sink in the Arctic Ocean from the transverse transport of dense water from the Barents Sea (2022). DOI: https://doi.org/10.1038/s41561-022-01069-z
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