The dramatic impacts of global climate change have driven marine carbon dioxide removal (mCDR) innovation, including ocean alkalinity enhancement (OAE), in an attempt to keep global warming under 2 °C. We experimented to assess the impacts of brucite-inspired alkalinity addition (BIAA) as an OAE approach on the carbonate chemistry, biogeochemistry, and composition of the Santa Barbara Channel phytoplankton community sourced from a spring upwelling event. The BIAA treatment used MgCl2 * 6H2O and NaOH to yield a total alkalinity (TA) concentration of 3000 µmol/kg, in contrast with the untreated seawater controls (TA = 2300 µmol/kg).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 Dryad (see Source) by the OA-SICC 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 2026-04-15.