We conducted a full-factorial lab experiment to study the individual and combined effects of temperature (18°C and 21°C), pCO2 (400 and 1000 ppm), and dissolved N:P ratio (16 and 25 molar) on the antioxidant capacity and carbon metabolism of the phytoplankton Phaeodactylum tricornutum (strain CCAP 1052/1A). The antioxidant response was assessed based on different biomarkers, including the contents of protective carotenoids (ß-Carotene, diadinoxanthin and violaxanthin), and by determination of antioxidant enzyme activities, and Malondialdehyde (MDA) as a biomarker for oxidative stress. We quantified the activity of Managanese Superoxide Dismutase (SOD-Mn), Glutathione S-transferase (GST), Catalase (CAT), Glutathione Peroxidase (GPx). As possible consequence of oxidative stress on metabolic pathways of carbon, we also quantified carbon fluxes by measuring rates of growth, respiration, dissolved organic carbon (DOC) exudation, and cellular organic carbon content and particulate phosphorus (PP). We also quantified the concentration of photosynthetic pigments chlorophyll a (Chl-a) and fucoxanthin. We used least-squares fitting on the obtained data to derive physiological photosynthesis parameters, such as compensation point, as well as photochemical efficiency (α), light acclimation index (Ik) and maximum net photosynthesis rate (Vmax).

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 2024-03-20.