Source: Journal of Geophysical Research: Biogeosciences
Coccolithophores are a type of algae that are ecologically and biogeochemically important, playing significant roles in the marine biological pump and the carbon cycle. Coccolithophores are enveloped by calcium carbonate plates called coccoliths that together form a shell called a coccosphere. As photosynthetic organisms, coccolithophores take up CO2 and transform it into organic matter. On the other hand, calcification and coccosphere formation in these algae release inorganic CO2 back into seawater.
The balance of photosynthesis and calcification can be measured as the ratio of inorganic to organic carbon within the algal cell (PIC:POC) and can be used to determine whether coccolithophore growth is a net CO2 source or sink. Further, coccolithophores are well preserved in the fossil record and the shape, size, and geometry of their coccosphere and coccoliths can be used to investigate changes in past climate.
Jin and Liu  use microscopy to measure thickness, length, and volume of coccospheres and individual coccoliths from the South China Sea to develop an equation that links geometry of the coccosphere to the PIC:POC ratio. The results suggest coccolithophore growth is not a net source of CO2. The final equation developed by the authors will also be useful to reconstruct past ocean environments including their calcium concentration as well as to investigate future changes that can occur with climate change and ocean acidification.
Citation: Jin, X., & Liu, C. (2023). Estimating coccolithophore PIC:POC based on coccosphere and coccolith geometry. Journal of Geophysical Research: Biogeosciences, 128, e2022JG007355. https://doi.org/10.1029/2022JG007355
—Marguerite A. Xenopoulos, Editor in Chief, JGR: Biogeosciences