Coccolith

[1] Coccolithophores are an important group of about 200 marine phytoplankton species [2] which cover themselves with a calcium carbonate shell called a "coccosphere".

[10] Their calcareous shell increases the sinking velocity of photosynthetically fixed CO2 into the deep ocean by ballasting organic matter.

[11][12] At the same time, the biogenic precipitation of calcium carbonate during coccolith formation reduces the total alkalinity of seawater and releases CO2.

[20][18] Viral infection is an important cause of phytoplankton death in the oceans,[21] and it has recently been shown that calcification can influence the interaction between a coccolithophore and its virus.

These are estimated to consume about two-thirds of the primary production in the ocean [24] and microzooplankton can exert a strong grazing pressure on coccolithophore populations.

Now, however, it is known through a mix of observations on field samples and laboratory cultures, that the two coccolith types are produced by the same species but at different life cycle phases.

Common shapes include:[34][35] Although coccoliths are remarkably elaborate structures whose formation is a complex product of cellular processes, their function is unclear.

Stable oxygen and carbon isotope data from coccoliths is used to reconstruct estimates of oceanic CO2 concentrations in the geologic past.