Estimation of physiological factors controlling carbon isotope fractionation in coccolithophores in photic zone and core-top samples

Photic zone and core-top (p) show strong latitudinal gradients, which have been interpreted as an effect of growth rate. The factor b, used in previous studies to account for the changes in growth rate, shows high dependence on [CO2](aq) in culture experiments, making difficult the deconvolution of nutrients versus other effects in the field.

We combine coccolithophore growth rate output from a global model, limited by sea surface temperature (SST) and [PO43-] with a statistical model that include [CO2](aq), cell size and light to predict (p), and examine the influence of different environmental and physiological variables on the observed expression of (p) in field samples. Back calculations of the growth rate necessary to match the observed (p) in photic zone and core-top samples using the statistical model show high correlation with modeled growth rates using [PO43-] and SST in temperate regions.