The study of calcareous marine biota provides important insight into the climate past, present and future. Biocalcification by marine biota has evolved across many major phyla (e.g. bacteria, eukaryotic algae, protozoans and metazoans) and is a dynamic interface between the biosphere, geosphere and atmosphere. Biocalcification is controlled by both physical and (paleo-)biological processes, which vary considerably on both spatial and temporal scales. A better understanding of these variations and how processes of different scales interact within the global system is critical for more reliable prediction of climate change and its impacts in the future.
Coccolithophores, a group of calcifying unicellular algae, constitute a major fraction of oceanic primary productivity, and generate a continuous rain of calcium carbonate (in the form of coccoliths) to the seafloor. Hence, they play an important role in the global carbon cycle, representing natural feedbacks in the climate system. Coccolithophores are a crucial biological group subjected to present-day climate change and ocean acidification due to oceanic uptake of excess atmospheric CO2. It is not known to what extent the natural populations can acclimatize or adapt to these changes, nor how their natural feedback mechanisms will operate in future. However, we can learn valuable lessons from their past and present-day behavior: Coccolithophore evolutionary rates are fast, with a fossil record dating back to 220 million years. Their global and abundant fossil occurrences in deep-sea sediments provide detailed records of plankton evolution that can be readily compared to proxy records of past ocean environmental parameters. In addition, cultivation of extant species of coccolithophore can inform us how modern calcifiers respond to different experimental physico-chemical conditions, and what factors are pivotal to sustain algal growth and biocalcification. Intriguingly, distinct responses between different modern species could relate to variable evolutionary adaptation strategies of their Cenozoic ancestors.