PHYSIOLOGY OF SEA ICE DIATOMS. I. RESPONSE OF THREE POLAR DIATOMS TO A SIMULATED SUMMER‐WINTER TRANSITION1

Abstract
Three axenic polar sea ice diatom cultures were subjected to a 30 day simulated summer‐winter transition in which light and temperature were decreased and salinity was increased to mimic seasonal changes previously reported for ice‐covered polar seas. The diatoms responded to these changes by a reduction in cellular metabolism as indicated by: 1) A decline in growth rate and photosynthetic rate; 2) a decrease in cellular ATP; and 3) the storage and subsequent utilization of endogenous carbon reserves. In addition, heterotrophic potential of the three clones increased by as much as 60‐fold. In some cases, the decrease in light intensity characteristic of the onset of polar winter was alone sufficient to trigger these physiological changes.