The Arctic experiences some of the most rapid climate changes on the planet, resulting in significant sea-ice melt. This transformation exposed the Arctic Ocean to increasing sunlight, driving a 56% rise in organic matter production through photosynthesis (net primary production) over the past two decades, according to remote-sensing studies. At the same time, permafrost thaw is accelerating due to warming, releasing more nutrients and carbon into the Arctic Ocean, delivered from rivers and coastal erosion. While it might seem logical that these additional nutrients would enhance the ocean’s biological carbon pump, - boosting carbon uptake and long-term storage of carbon - a new study in Nature Climate Change by experts from the Alfred Wegener Institute reveals a surprising outcome. Instead of strengthening, the carbon pump is being weakened. The researchers found that intensified recycling processes and ecosystem impoverishment are undermining the pump’s efficiency, challenging assumptions about the Arctic’s ability to store carbon in a warming world.
For their study, the researchers employed a cutting-edge, high-resolution ocean biogeochemistry model that incorporates carbon and nutrient inputs from both rivers and coastal erosion – an approach that enables groundbreaking future projections. “These terrigenous inputs, and their impacts on biogeochemical cycles, are currently overlooked in the models used by the Intergovernmental Panel on Climate Change”, explains Dr. Laurent Oziel, lead author and modeler at Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “In our study, we focused on the future evolution of the biological carbon pump and the biological processes that transport carbon from the surface ocean to the deep ocean, where it is stored in the long-term.”
Elevator down to the Ocean Floor: the Biological Carbon Pump
The biological carbon pump (BCP) plays a vital role in the global carbon cycle, reducing atmospheric CO2levels by approximately 200 ppm (parts per million) compared to a world without it. By transporting organic carbon from the ocean’s surface to its depth, the biological carbon pump ensures the long-term storage of photosynthetically fixed carbon.
However, the results of the biogeochemistry model simulations were counter-intuitive. While additional nutrients and light boost primary production, they do not enhance the efficiency or magnitude of the biological carbon pump. Instead, the findings reveal that climate change could reduce the carbon pump’s efficiency by 40% by 2100. This was explained by the intensification of recycling processes, enhanced by both ocean warming and increasing terrigenous material transported to the ocean. In addition, increasing terrestrial carbon inputs from permafrost thaw have a direct impact on ocean-atmosphere CO2 fluxes. “This additional carbon from land drives intense coastal CO2 outgassing, reducing the Arctic Ocean's carbon sink by at least 10 percent.” explains Prof. Judith Hauck from the Alfred Wegener Institute. These combined feedbacks lower the Arctic Ocean’s ability to store carbon, reducing its potential to act as a carbon sink by an amount comparable to half of the the emissions of Spain in 2023.
Despite rising net primary production, the future Arctic Ocean appears increasingly unable to transfer this extra organic matter to deeper layers as it once did. Instead, carbon is being recycled more often at the surface. “Our study challenges the assumption that increasing net primary production in the Arctic Ocean will naturally lead to a stronger biological carbon pump”, concludes Laurent Oziel. “We uncover counter-intuitive feedback mechanisms that change our perspective on how the Arctic Ocean’s carbon cycle interacts with climate, with possibly profound implications for the ocean and the benthic ecosystems.”
Original publication
Laurent Oziel et al.: Climate change and terrigenous inputs decrease the efficiency of the future Arctic Ocean’s biological carbon pump, Nature Climate Change (2025). DOI: 10.1038/s41558-024-02233-6