| Summary: | Maintenance and Update Frequency: none-planned Statement: Southern Ocean phytoplankton cultures were grown in the artificial seawater medium Aquil enriched with 10 μmol L-1 phosphate, 100 μmol L-1 silicate, 300 μmol L-1 nitrate, and filter-sterilized (0.2 μm Gelman Acrodisc PF) trace metal and vitamin solutions as described in Strzepek et al. (2011). Trace metal concentrations were buffered with the synthetic organic chelator, ethylene-diamine-tetra-acetic acid (EDTA). Iron limiting treatments for Phaeocystis antarctica, and the diatoms Proboscia inermis and Eucampia antarctica employed the siderophore desferrioxamine B (DFB) to control the degree of Fe limitation. Iron replete and iron limiting media for these three species have been described previously (Strzepek et al. 2011). The diatoms Fragilariopsis cylindrus, Chaetoceros neogracilis and Chaetoceros flexuosus were grown in Aquil medium containing 100 μmol L-1 of EDTA. Iron replete medium contained 567 nmol L-1 Fe; iron limiting medium contained 1.5 nmol L-1 Fe for C. neogracilis and C. flexuosus, and 16.7 nmol L-1 Fe for F. cylindrus. Cultures were grown in triplicate, maintained in exponential phase by dilution, and allowed to acclimate to growth conditions for at least two transfers (14–16 cell divisions) before data collection. All cultures were grown at 2.5-3 °C under continuous PAR using cool-white fluorescent bulbs. P. antarctica was grown at 6 PAR levels (10, 20, 30, 60, 100, and 400 μmol quanta m-2 s-1) while the diatoms were grown at 30-35 μmol photons m-2 s-1 . PAR was measured with a 4π quantum meter (model QSL-2101, Biospherical Instruments). In vivo Chl fluorescence (F) of dark-acclimated (30 min) cultures was determined using a Turner Designs model 10-AU fluorometer. To measure cellular Chl concentrations, 25 mL of culture were filtered (< 75 mm Hg) onto glass fibre filters (GF/F; Whatman) immediately following in vivo Chl fluorescence measurements. The filters were extracted in 90% acetone in the dark for 18 h at -20 °C prior to ...
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