Predicting coccolithophore rain ratio responses to calcite saturation state

The response of the coccolithophore calcite and particulate organic carbon (POC) ratio, also known as the rain ratio, to calcite saturation state (Ωcalcite) 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 – Ωcalcite data for several coccolithophore genera. Here, Ωcalcite and calcite:POC data were collated from literature studies of coccolithophore responses to changes in ocean carbonate chemistry. These Ωcalcite data were recalculated using a standardized pH scale and constants. Calcite:POC responses to Ωcalcite 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 Ωcalcite. A general combined expression was calculated to describe the response of the calcite:POC ratio to Ωcalcite for coccolithophores as a single functional group for use when the relative contributions of each order to the coccolithophore community are unknown.

Fielding S. R., 2014. Predicting coccolithophore rain ratio responses to calcite saturation state. Marine Ecology Progress Series 500:57-65. Article (subscription required).

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