MEPS 500:57-65 (2014)  -  DOI: https://doi.org/10.3354/meps10657

ABSTRACT: The response of the coccolithophore calcite and particulate organic carbon (POC) ratio, also known as the rain ratio, to calcite saturation state (Ω_calcite) is increasingly being used as an input parameter for modelling ocean feedbacks to changes in atmospheric pCO₂. Previously, this relationship has only been determined from a small number of studies from a single genus of coccolithophore. However, there is an increasing abundance of literature calcite:POC - Ω_calcite data for several coccolithophore genera. Here, Ω_calcite and calcite:POC data were collated from literature studies of coccolithophore responses to changes in ocean carbonate chemistry. These Ω_calcite data were recalculated using a standardized pH scale and constants. Calcite:POC responses to Ω_calcite were then determined using quantile regression for 2 major orders of coccolithophore: Isochrysidales (Emiliania, Gephyrocapsa) and Coccolithales (Coccolithus, Calcidiscus). These 2 coccolithophore groups display qualitatively and quantitatively different responses to Ω_calcite. A general combined expression was calculated to describe the response of the calcite:POC ratio to Ω_calcite for coccolithophores as a single functional group for use when the relative contributions of each order to the coccolithophore community are unknown.

KEY WORDS: Calcification · Phytoplankton · Carbon cycling · Modelling · Quantile regression · Emiliania