| Summary: | Data were obtained from a laboratory growth experiment conducted from April to May 2021 at the Institute for Chemistry and Biology of the Marine Environment (University of Oldenburg). Three Antarctic phytoplankton species (Chaetoceros simplex, Phaeocystis antarctica (single cell culture) and Geminigera cryophila) were grown in monocultures and a mixture of all three species. The phytoplankton strains were previously isolated from the Southern Ocean and maintained at the Alfred-Wegener-Institute in Bremerhaven. Prior to the experiment, semicontinuous stock cultures of the diatom Chaetoceros simplex, the prymnesiophyte Phaeocystis antarctica (single cell culture) and the cryptophyte Geminigera cryophila were grown in exponential phase in 0.2µm filtered natural Antarctic seawater. The natural seawater was enriched with nutrients, trace metals and vitamins according to the F/2 medium (Guillard and Ryther, 1962) but with only 1/6 of the original F/2 iron(Fe)-concentration. The stock cultures were kept at 2°C and an irradiance of 100 µmol m₂ sek⁻¹ with a 16:8 light/dark cycle. We used a factorial design including four different nitrogen/phosphorus (N/P) treatments (control plus three different N/P levels) and 10 different temperatures (-2, -1, 0, 1, 2, 3, 4, 6, 8 and 10°C). Two of the four N/P treatments were applied with an N/P of 12 (control and ambient N/P with higher N and P concentrations), one with a molar N/P ratio of 6 (30 µmol N, 5 µmol P) and one with a molar N/P of 24 (60 µmol N, 2.5 µmol P). The nutrient treatments were generated by adding only 30 µmol L⁻¹ N (N/P 24, +N), 2.5 µmol L⁻¹ P (N/P 6, +P) and both (N/P 12, +N,P) to 0.2 µm filtered Antarctic seawater with an ambient N/P of 12 and an concentration of 30 µmol N and 2.5 µmol P. The ambient control treatment (here N/P 12 control) received no additional N and P. All other nutrients were added according to F/2 with 1/6 of iron to avoid limitation by other elements (Guillard and Ryther, 1962). The experimental temperatures were kept constant. Light was ...
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