Coccolithophore Dynamics in Marine Carbon Cycling

Coccolithophores are unicellular, calcifying phytoplankton that synthesise minute plates of calcium carbonate, or coccoliths, contributing substantially to the ocean’s particulate inorganic carbon pool. Their dual role in organic carbon fixation and inorganic calcification places them at the nexus of the marine carbon cycle. Through photosynthesis, coccolithophores draw down atmospheric CO₂, while their calcification process releases CO₂ locally, generating a complex interplay between the organic and carbonate pumps. The fate of coccolith-derived calcium carbonate—whether it dissolves in the upper ocean or sinks to depth—governs long-term carbon sequestration and influences the alkalinity and buffering capacity of seawater. Environmental drivers such as temperature, nutrient availability, light and ocean acidity modulate coccolithophore growth, bloom dynamics and the efficiency of carbon export. Zooplankton grazing, microbial remineralisation and physical aggregation further determine the sinking flux of coccoliths. Understanding these processes is critical for predicting how coccolithophore populations will respond to climate change and for quantifying their impact on the ocean’s role in regulating atmospheric CO₂.

Research from Nature Portfolio

Recent quantification of pelagic calcium carbonate production in the North Pacific reveals that coccolithophores account for approximately 90 per cent of living CaCO₃ standing stock, with production rates exceeding the sinking flux at shallow depths. This finding emphasises extensive dissolution within the photic zone and highlights the sensitivity of the surface carbonate cycle to warming and acidification. Experimental work on copepod grazing demonstrates that calcite dissolution within zooplankton guts can reach up to 38 per cent of ingested coccoliths under starved conditions, altering faecal pellet density and doubling sinking rates during sustained feeding. These results confirm that biological microenvironments significantly affect calcite turnover above the lysocline and modulate carbon export efficiency. Earth system model simulations further quantify a CO₂–calcification feedback, showing that reduced calcification under lower saturation states could increase oceanic CO₂ uptake by tens to hundreds of petagrams of carbon over millennial timescales, thereby mitigating atmospheric CO₂ rise and alkalinity decline.

Coccolithophore Dynamics in Marine Carbon Cycling publication trend

The graph below shows the total number of articles in coccolithophore dynamics in marine carbon cycling across all publications each year (not limited to Nature Index journals).

Technical terms

Particulate inorganic carbon (PIC): The component of marine particulate matter composed of calcium carbonate, predominantly produced by calcifying organisms such as coccolithophores.

Carbonate pump: The process by which calcifying plankton produce CaCO₃, releasing CO₂ locally in surface waters and influencing the vertical flux of inorganic carbon to the deep ocean.

Ballast effect: The phenomenon whereby dense mineral particles (e.g. coccoliths) increase the sinking rate of organic aggregates, enhancing the export efficiency of organic carbon.

Euphotic zone: The upper layer of the ocean penetrated by sufficient sunlight for photosynthesis, typically extending to depths of 50–200 metres depending on water clarity.

References

1. Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean. Nature Communications (2023).
2. Quantitative and mechanistic understanding of the open ocean carbonate pump - perspectives for remote sensing and autonomous in situ observation. Earth-Science Reviews (2023).
3. A global compilation of coccolithophore calcification rates. Earth System Science Data (2018).
4. Detection of Coccolithophore Blooms With BioGeoChemical‐Argo Floats. Geophysical Research Letters (2020).
5. Simulated effect of calcification feedback on atmospheric CO2 and ocean acidification. Scientific Reports (2016).
6. Coccolith dissolution within copepod guts affects fecal pellet density and sinking rate. Scientific Reports (2018).