To investigate how the unavoidable physical and chemical perturbations associated with Ocean Alkalinity Enhancement (OAE) could influence marine plankton communities and how potential side-effects compare to impacts of climate change, we conducted 19 ship-based experiments in the Equatorial Pacific, examining three prevalent OAE source (NaOH, olivine, and steel slag) and their impacts on natural phytoplankton populations. Our experiments simulated realistic and moderate alkalinity enhancements between 29-16 μmol kg-1. The monitored parameters included total chlorophyll-a concentrations, macro nutrients, trace elements, total alkalinity, Fv/Fm, pH,and flowcytometry.

This dataset contains the input and output data for an extended optimum multiparameter analysis (eOMP). Input data for parameters are given (temperature, salinity, oxygen, nitrate, phosphate and silicate), as obtained from the cited CSIRO open access CTD bottle data for the 2018 SR3 occupation. Output parameters are the proportional contribution of 8 water masses that were defined in the eOMP analysis. The output remineralization estimate, Delta-O, is also given. All data are referenced to depth and geographical position (latitude, longitude) from corresponding CTD bottle data. The eOMP used here was configured following Pardo et al. (2017). Details on the equations, parameterization and end-members that characterize the regional oceanography can also be found in the Supplementary Materials of Traill et al. (2023), including the robustness of the OMP analysis and the uncertainties of both the SWTs’ contributions and the ΔO parameter (Sections S1.2 and S1.3, Table S1, Table S2, Table S3).

To understand the environmental impacts of added alkaline minerals on plankton communities, we enclosed natural coastal plankton communities using 53L microcosms and exposed these communities to ground factory slag (2g/53L) and olivine (100g/53L). The microcosms of seawater were kept at 13.5 °C with circulations. The biochemical changes and responses in microcosms were monitored and measured for 21 days. The measured parameters are pH, total alkalinity, temperature, macro-nutrients concentrations, total chlorophyll-a, flow cytometry data, POC/PON, BSi, Rapid Light Curves, zooplankton abundance, the dissolved trace metal concentrations, and the particulate trace metal concentrations.