The oceans act as significant carbon sinks, absorbing about one-third of the carbon dioxide produced by humans each year. This process occurs via the marine carbon pump, which transports carbon from the surface to the deep sea. Physical processes such as water circulation and biological mechanisms act together and greatly control the carbon pump efficiency. Biological mechanisms include the uptake of carbon dioxide by algae at the water surface and its subsequent transport to deeper layers in the form of biomass. Until now, the exact underlying mechanisms for the interaction between physical and biological processes remained little understood.
The twilight zone extends from a depth of approximately 100 to 1,000 meters and plays a central role in the carbon cycle. In collaboration with the Mediterranean Institute of Oceanography (MIO), IGB researchers analyzed carbon transformations by bacteria under various hydrological conditions in the North-East Atlantic. They found that bacteria play a crucial role in both the decomposition of sinking biomass and the fixation of inorganic carbon.
“The effect of bacteria on the carbon pump is at least as significant as the carbon fluxes through hydrological processes and gravity”, explained Prof. Hans-Peter Grossart from IGB, co-author of the study. “‘In particular, the fixation of inorganic carbon by chemolithotrophic bacteria, and the role these bacteria play in carbon flux, appear to have been greatly underestimated to date. These bacteria can obtain the energy required for carbon fixation independently of light by oxidising chemical compounds such as ammonium.”
The integration of these microbial processes into ocean ecosystem models is essential for enabling more accurate predictions of carbon dioxide storage in the oceans.
