Dataset S1 - Noelaerhabdaceae organic carbon isotope culture data compilation

The carbon isotope fractionation in algal organic matter (Ep), including the long-chain alkenones produced by the coccolithophorid family Noelaerhabdaceae, is used to reconstruct past atmospheric CO2 levels. The conventional proxy linearly relates Ep to changes in cellular carbon demand relative to diffusive CO2 supply, with larger Ep values occurring at lower carbon demand relative to supply (i.e. abundant CO2).  However, the response of Gephyrocapsa oceanica, one of the dominant alkenone producers of the last few million years, has not been studied closely. Here we subject G. oceanica to various CO2 levels by increasing pCO2 in the culture headspace, as opposed to increasing dissolved inorganic carbon (DIC) and alkalinity concentrations at constant pH. We note no substantial change in physiology, but observe an increase in Ep as carbon demand relative to supply decreases, consistent with DIC manipulations. We compile existing Noelaerhabdaceae Ep data and show that the diffusive model ...