CHALKY: Coccolithophore controls on ocean alkalinity

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.