Diatoms are the most important producers of plant biomass in the ocean and help to transport carbon dioxide (CO₂) from the atmosphere into the deep ocean and thus regulate climate. Because diatoms rely on silica rather than calcium carbonate to build their shells, they were previously thought to benefit from ocean acidification — a chemical change in seawater triggered by the increasing uptake of CO₂ that makes calcification more difficult. Scientists now show that diatoms, which are a type of plankton, are also affected. Analyses of data from field experiments and model simulations suggest that ocean acidification could drastically reduce diatom populations.

While calcifying organisms like oysters and corals have difficulty forming their shells and skeletons in more acidic seawater, diatoms have been considered less susceptible to the effects of ocean acidification. The globally widespread tiny diatoms use silica, a compound of silicon, oxygen and hydrogen, as a building material for their shells. That diatoms are nevertheless under threat has now been demonstrated for the first time by researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel, the Institute of Geological and Nuclear Sciences Limited New Zealand and the University of Tasmania in a study published in Nature. For the study, researchers linked an overarching analysis of various data sources with Earth system modelling. The findings provide a new assessment of the global impact of ocean acidification.

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