Thermohaline circulation powers the “global conveyor belt,” a global-scale current system. The conveyor belt begins near the North Atlantic pole on the ocean’s surface. Arctic temperatures chill the water here. It also becomes saltier as sea ice forms because salt does not freeze and remains in the surrounding water.
Every year, carbon-rich particles transported from the Barents and Kara Seas could bind up to 3.6 million metric tons of CO2 in the Arctic deep sea for millennia. Researchers from the Alfred Wegener Institute and partner institutes report in the current issue of the journal Nature Geoscience that a previously unknown transport route uses the biological carbon pump and ocean currents to absorb atmospheric CO2 on the scale of Iceland’s total annual emissions in this region alone.
The biological productivity of the central Arctic Ocean is limited in comparison to other oceans because sunlight is frequently in short supply (due to the Polar Night or 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 counterparts in other waters. As a result, large quantities of particulate – i.e., carbon stored in plant remains – carbon were discovered in the Nansen Basin of the central Arctic during the ARCTIC2018 expedition in August and September 2018 on board the Russian research vessel Akademik Tryoshnikov.
Subsequent analyses revealed a body of water with large amounts of particulate carbon to depths of up to two kilometres, composed of bottom water from the Barents Sea. The latter is produced when sea ice forms in winter, then cold and heavy water sinks, and subsequently flows from the shallow coastal shelf down the continental slope and into the deep Artic Basin.
Based on our measurements, we calculated that more than 2,000 metric tons of carbon per day flow into the Arctic deep sea via this water-mass transport, the equivalent of 8,500 metric tons of atmospheric CO2. When the total annual amount was extrapolated, it revealed 13.6 million metric tons of CO2, which is on the same scale as Iceland’s total annual emissions.
Dr. Andreas Rogge
“Based on our measurements, we calculated that more than 2,000 metric tons of carbon per day flow into the Arctic deep sea via this water-mass transport, the equivalent of 8,500 metric tons of atmospheric CO2. When the total annual amount was extrapolated, it revealed 13.6 million metric tons of CO2, which is on the same scale as Iceland’s total annual emissions” explains Dr Andreas Rogge, the study’s first author and an oceanographer at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research.
This plume of carbon-rich water extends from the shelf of the Barents and Kara Seas to approximately 1,000 kilometers into the Arctic Basin. In light of this newly discovered mechanism, the Barents Sea, which is already known to be the most productive marginal sea in the Arctic, appears to remove roughly 30% more carbon from the atmosphere than previously thought. Furthermore, model-based simulations revealed that the outflow occurs in seasonal pulses, as phytoplankton absorption in the Arctic’s coastal seas occurs only in the summer.
Understanding the transport and transformation processes within the carbon cycle is critical for developing global carbon dioxide budgets and thus global warming projections. Single-celled algae on the ocean’s surface absorb CO2 from the atmosphere and sink to the deep sea when they die. When carbon bound in this way reaches deep water, it remains there until overturning currents bring the water back to the ocean’s surface, which can take thousands of years in the Arctic.
If the carbon is deposited in deep-sea sediments, it can remain trapped for millions of years because only volcanic activity can release it. This process, also known as the biological carbon pump, can remove carbon from the atmosphere for extended periods of time and is an important sink in the carbon cycle of our planet. The process also provides food for local deep sea fauna such as sea stars, sponges, and worms. Only more research will tell us how much of the carbon is actually absorbed by the ecosystem.
Other largely unexplored regions where bottom water is formed and flows into the deep sea can be found in the polar shelf seas. As a result, it is reasonable to assume that the global impact of this mechanism as a carbon sink is significantly greater. “However, due to ongoing global warming, less ice and thus less bottom water is formed. At the same time, more light and nutrients are available to phytoplankton, allowing more CO2 to be bound. As a result, it is currently impossible to predict how this carbon sink will develop, and identifying potential tipping points necessitates urgent additional research” Andreas Rogge explains.
