Each year, the transport of carbon-rich particles from the Barents Sea and the Kara Sea can sequester up to 3.6 million metric tons of CO2 in the arctic depths for millennia. Only in this region, a previously unknown transport route uses a biological carbon pump and ocean currents to absorb atmospheric CO2 on the scale of Iceland’s total annual emissions, researchers from the Alfred Wegener Institute and partner institutes report in the current issue of the journal. Natural science.
Compared to other oceans, the biological productivity of the central Arctic Ocean is limited because sunlight is often scarce—either because of the polar night or because of the sea ice cover—and available sources of nutrients are few. Therefore, microalgae (phytoplankton) in the upper layers of water have less energy than their counterparts in other waters. Therefore, it was a big surprise when during the ARCTIC2018 expedition in August and September 2018, a large amount of particulate matter was detected on board the Russian research vessel Akademik Treshnikov, i.e. of carbon stored in plant remains in the Nansen Basin in the central Arctic. Subsequent analyzes revealed a reservoir with a large amount of solid carbon particles at a depth of up to two kilometers, consisting of the bottom water of the Barents Sea. The latter forms when sea ice forms in winter, then cold, heavy water sinks and then flows from the shallow coastal shelf down the continental slope into the deep Arctic Basin.
“Based on our measurements, we estimate that more than 2,000 metric tons of carbon per day enter the Arctic depths through this water mass transfer, which is equivalent to 8,500 metric tons of atmospheric CO2. Extrapolated to the annual total, as much as 13.6 million metric tons of CO was detected2which is on the same scale as Iceland’s total annual emissions,” explains Dr. Andreas Roghe, first author Natural science and an oceanographer at the Alfred Wegener Institute of the Helmholtz Center for Polar and Marine Research (AWI). This plume of carbon-rich water extends from the Barents Sea shelf and the Kara Sea to approximately 1,000 kilometers into the Arctic Basin. In light of this newly discovered mechanism, the Barents Sea – already known as the most productive marine sea in the Arctic – can effectively remove about 30 percent more carbon from the atmosphere than previously thought. Moreover, model-based simulations have determined that the outflow manifests itself in seasonal pulses, as CO uptake in Arctic coastal seas2 phytoplankton occurs only in summer.
Understanding the transport and transformation processes of the carbon cycle is essential for the creation of global carbon budgets and thus also for global warming projections. On the surface of the ocean, unicellular algae absorb CO2 from the atmosphere and sink into the depths of the sea as they age. Once the carbon bound in this way reaches deep water, it stays there until currents bring the water back to the surface of the ocean, which takes several thousand years in the Arctic. And when carbon is deposited in deep-sea sediments, it can even stay there for millions of years, as only volcanic activity can release it. This process, also known as the biological carbon pump, can remove carbon from the atmosphere over long periods of time and is a vital sink in our planet’s carbon cycle. The process is also a food source for local deep-sea fauna such as starfish, sponges and worms. Only further research can tell us what percentage of carbon is actually absorbed by the ecosystem.
In the polar shelf seas are other largely unexplored regions where bottom water forms and drains into the deep sea. Therefore, it can be assumed that the global impact of this mechanism, as a carbon sink, is actually much larger. “However, due to ongoing global warming, less ice is forming and therefore less bottom water. At the same time, more light and nutrients are available to phytoplankton, allowing more CO2 to be bound. Accordingly, it is currently impossible to predict how this carbon sink will develop, and identifying potential tipping points urgently requires additional research,” says Andreas Roghe.