Impacts of rising atmospheric CO2 concentrations and increased daily irradiances from enhanced surface water stratification on phytoplankton physiology in the coastal Southern Ocean remain still unclear. Therefore, in the two Antarctic diatoms Fragilariopsis curta and Odontella weissflogii the effects of moderate and high natural solar radiation combined with either ambient or future pCO2 on cellular particulate organic carbon (POC) contents and photophysiology were investigated. Results showed that increasing CO2 concentrations had greater impacts on diatom physiology than exposure to increasing solar radiation. Irrespective of the applied solar radiation regime, cellular POC quotas increased with future pCO2 in both diatoms. Lowered maximum quantum yields of photochemistry in PSII (Fv/Fm) indicated a higher photosensitivity under these conditions, being counteracted by increased cellular concentrations of functional photosynthetic reaction centers. Overall, our results suggest that both bloom‐forming Antarctic coastal diatoms might increase carbon contents under future pCO2 conditions despite reduced physiological fitness. This indicates a higher potential for primary productivity by the two diatom species with important implications for the CO2 sequestration potential of diatom communities in the future coastal Southern Ocean.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2016) 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 2018-08-03.

Supplement to: Heiden, Jasmin; Thoms, Silke; Bischof, Kai; Trimborn, Scarlett (2018): Ocean acidification stimulates particulate organic carbon accumulation in two Antarctic diatom species under moderate and high natural solar radiation. Journal of Phycology