Diatoms build silica shells and produce organic carbon at the ocean surface. Today, much of the silica dissolves relatively quickly as the particles consisting of dead diatoms sink (e.g. after blooms). The resulting dissolved silicon is returned to the surface by upwelling waters, where it supports the growth of more diatoms. Under ocean acidification, the silica in sinking particles will dissolve slower, thereby reducing the return flux of dissolved silicon to the ocean surface as much of the marine silicon budget will become trapped in deep water. The result is a substantial global decrease in diatom biomass.
Appendicularia population dynamics display typical boom-and-bust characteristics, i.e. high grazing rates in combination with a short generation time and life cycle, allowing them to develop intense blooms. The most prominent feature of appendicularians is their mucous feeding-structure (“house”), which is produced and discarded several times per day. These sinking houses can contribute substantially to carbon export. Low pH conditions as expected for future ocean acidification extreme events resulted had beneficial effects on physiology (digestion, assimilation efficiency) and fecundity (egg production) of O. dioica, thereby enhanced its population growth and contribution to carbon fluxes
A common assumption in marine biogeochemisty is that changes in C:N (and biogeochemistry, in general) are mainly driven by phytoplankton. In a series of in situ mesocosm experiments in different biomes (left), Taucher et al., (2020) found distinct impacts of ocean acidification on the C:N ratio of sinking organic matter (middle). By linking these observations to analysis of plankton community composition, the authors found a key role of heterotrophic processes in controlling the response of C:N to OA, particularly by altering the quality and carbon content of sinking organic matter within the biological pump
