Calcifying plankton: From biomineralization to global change

The cycling of calcium carbonate (CaCO₃) in the ocean is closely linked to seawater alkalinity and the regulation of atmospheric CO₂. In the modern pelagic ocean, almost all CaCO₃ is produced by three groups of calcifying planktonic organisms: coccolithophores, foraminifers, and shelled pteropods. In this Review, we examine the differences in functional traits that define each group's distinctive role in the global carbon cycle and their sensitivity to climate change and ocean acidification. This synthesis reveals that a single representation of CaCO₃ in climate models is unlikely to accurately reflect system dynamics or their impacts on biogeochemical cycling under climate change. We argue that understanding past and future CaCO₃ cycle requires a better delineation of the traits that make up the diversity of calcifying plankton groups.