The ocean plays a key role in the current climate change, as it absorbs a considerable part of the atmospheric carbon dioxide emitted by mankind. On the one hand, this slows down the heating of the climate, and on the other hand, the dissolution of CO2 in seawater leads to acidification of the oceans. This has far-reaching consequences for many marine organisms and thus also for the oceanic carbon cycle. One of the most important mechanisms in this cycle, is called the biological carbon pump. Part of the biomass that phytoplankton forms in the surface ocean through photosynthesis sinks to the depths in the form of small carbonaceous particles. As a result, the carbon is stored for a long time in the deep sea. The ocean thus acts as a carbon sink in the climate system. How strongly this biological pump acts varies greatly from region to region and depends on the composition of species in the ecosystem.
The study, which has now been published in the journal Nature Climate Change, is one of the most comprehensive studies so far on the effects of ocean acidification on marine ecosystems. Scientists at the GEOMAR Helmholtz Centre for Ocean Research in Kiel have now been able to show for the first time that ocean acidification influences the carbon content of sinking organic material, and thus the biological pump. Surprisingly, the observed changes were highly variable. The carbon content of sinking particles increased or decreased significantly with increasing CO2, depending on the composition of species and the structure of the food web. Since the underlying data cover a wide range of ocean regions, this seems to be a global phenomenon. These findings allow a completely new assessment of the effects of ocean acidification.