Who fixes carbon in the dark ocean?
A new study led by Barbara Bayer (CeMESS, University of Vienna) discovered that ammonia-oxidizing microorganisms contribute much less to carbon fixation in the ocean than previously assumed. The study, recently published in Nature Geoscience, was a collaborative effort between researchers from the University of Vienna, the University of California Santa Barbara, and the Woods Hole Oceanographic Institution.
The ocean’s essential role as a carbon sink is regulated by physical and biological processes. In the sunlit surface ocean, photosynthesis is the most important biological process to take up carbon dioxide (CO2) from the atmosphere. In contrast, the deep ocean is home to a plethora of diverse microbes which use chemical energy instead of light to fuel inorganic carbon uptake (= ”dark carbon fixation”). Due to their high abundances in deeper water layers, ammonia-oxidizing microbes were thought to be the main drivers of dark carbon fixation. “In our study, we challenge this current view and experimentally show for the first time that ammonia oxidizers only contribute minimally to this process”, says Bayer. “The deep ocean is one of the least explored ecosystems on our planet – one of the remaining mysteries to solve are the identities of microbes responsible for carbon fixation below the sunlit surface layer.”
