Carbon acquisition and growth of Antarctic sea ice diatoms in closed bottle incubations

Mixed cultures of 4 polar diatoms regularly found in Antarctic pack ice were grown over 20 d In closed bottles at high light (200 to 250 pm01 photons m-' S-') and at 0C in order to investigate growth physiology and biomass production under conditions simulating the sea ice habitat during summer. Species tested were: Chaetoceros cf. neogracile, Fragilariopsis c~~lindrus. Thalassiodra antarctica and Porosira pseudodenticulata. Initially, all species grew exponentially, but exponential growth ceased for P pseudodenticulata and 7 antarctica after 6 d, for F. cylindrus after 8 d, and for C. cf. neogracile after 10 d. Slight increases in cell number were observed for all species 2 d later. Peak biomass amounted to 140 pg chl a (850 pm01 particulate organic carbon, POC) 1.' At the same time. concentrations of dissolved inorganic carbon (DIC) were reduced by 1000 PM, oxygen concentrations increased to 1400 pM, and pH Increased to 10.5. At this stage, a substantial decline in plasma-containing cells was recorded for E cylindrus. C. cf. neogracile accounted for 80",<,, and C. cf. neogracile and F cyl~ndrus accounted for >95'.'b of total carbon biomass The carbon isotope composition of POC