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CHALKY: Coccolithophore controls on ocean alkalinity

white cliffs next to a beach

Active project

Project start: November 2023  |  Project end: October 2026
Funder: UKRI
Principal Investigator: Dr Glen Tarran

The CHALKY project aims to determine how coccolithophore calcium carbonate production, recycling and export from the surface ocean affects air-sea CO2 fluxes and the ocean's carbon sink, and how this may change in a warming ocean. 

Coccolithophores are unique algae that form calcium carbonate scales that influence ocean alkalinity and the capacity to absorb CO2 when shed. There are gaps in understanding of the balance of coccolithophore growth, grazing, viral lysis, and sinking export processes and how this calcium carbonate cycling impacts ocean carbon uptake. Better quantifying these processes can inform climate modelling and carbon cycle assessments.

The CHALKY project aims to quantify coccolithophore calcium carbonate cycling and examine how associated production, export, and retention processes impact ocean carbon uptake. The project has four main objectives:

  • Measure calcium carbonate production rates at both the community and single cell level across gradients in coccolithophore diversity, growth stages, ecophysiology, and environmental conditions. 
  • Determine loss pathways and rates including viral/microbial lysis, zooplankton grazing, and sinking export fluxes. 
  • Assess community respiration and carbonate chemistry impacts on CO2 fluxes under variable ecology and calcification conditions to elucidate biogeochemical implications.
  • Synthesize measured ecological and biogeochemical rates with bio-optical observations from autonomous platforms and satellites to scale findings. This will improve accounting of variable coccolithophore dynamics in models and carbon cycle assessments.

The combined objectives aim to reduce uncertainties in how coccolithophore calcium carbonate cycling and fate influence ocean carbon uptake and air-sea CO2 exchange.


The project outcomes will provide improved estimates of contemporary and historical air-sea CO2 fluxes, inform model development to better represent calcium carbonate cycling, and develop an ecological understanding to enable better accounting for variable coccolithophore dynamics in carbon budgets and assessments. This will support more accurate climate predictions and carbon management.