This study was conducted in autumn/winter 2021/2022 at the laboratory of the Alfred-Wegener-Institute Bremerhaven. To assess temperature response patterns of various functional traits in Arctic phytoplankton species, we cultivated Thalassiosira hyalina, Phaeocystis pouchetii, Micromonas pusilla and Nitzschia frigida at a temperature gradient of 0°C to 14°C under saturating light of 100 µmol photons m-2 s-1 (T. hyalina, P. pouchetii, M. pusilla) or 30 µmol photons m-2 s-1 (N. frigida) and replete nutrient conditions (micronutrients following F/2; 100 µmol L-1 nitrate, 100 µmol L-1 silicate, 6 µmol L-1 phosphate) in dilute batch cultures. Culture bottles were aerated with air containing a pCO2 of 400 µatm ensure a stabilized carbonate chemistry and to avoid sedimentation. After an acclimation period of >7 generation or >10 days, respectively, various functional traits were obtained: specific growth rate, quotas of particulate organic carbon (POC) and nitrogen (PON) as well as chlorophyll a (Chl a), photo-physiology using fast repetition rate fluorometry. Furthermore, the following parameters were calculated from the obtained data: POC:PON, Chl a:POC, POC production rate, photosystem II quantum yield, absolute electron transport rates at in-situ irradiance and maximal irradiance, light use efficiency, light acclimation indices, lifetime of PSII reopening and absorption cross section.

Thalassiosira hylina strain KB3SS5, isolated 2020 in Kongsjford (Svalbard)Phaeocystis pouchetii strain PS78, isolated 2012 in the Fram straitMicromonas pusilla strain CLP1, isolated 2014 in Kongsfjord (Svalbard)Nitzschia frigida strain UIO-542, isolated in 2019 in the Fram strait