Here we examined the growth, calcification response, and morphology of these two key "endmember" species of coccolithophore (Gephyrocapsa huxleyi and Coccolithus braarudii) to ocean alkalinity enhancement using in vitro laboratory culture experiments. We also compared how the addition of the monovalent cation Na+ and divalent cation Ca2+ to raise total alkalinity affected growth and calcification responses.This dataset is included in the OA-ICC data compilation maintained in the framework of the IAEA Ocean Acidification International Coordination Centre (see https://oa-icc.ipsl.fr). Original data were downloaded from Zenodo (see Source) by the OA-ICC data curator. In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2024) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation by seacarb is 2026-04-30.