In McMurdo Sound, Antarctica, an in situ light perturbation study was conducted on 1.5 m thick annual sea ice during the 1981 austral spring ice microalgal bloom. A 100 rn2 quadrat was covered with snow to a depth of 70 cm reducing under ice irradiance by 97 % relative to a control quadrat with 7 cm of natural snow cover. Samples were collected from the ice-seawater interface within each quadrat by SCUBA divers. After the first 3 wk of light perturbation (24 Oct-18 Nov 1981), net ice growth was about 20 cm; there was no significant difference in C : chl a ratios in the 2 quadrats during this period. However, during the following 3 wk when net ice growth was zero (18 Nov-7 Dec 1981), C : chl a ratios dropped to 38 in control while ratios in the light perturbed quadrat remained high (> 200). Photosynthetic rate in the control reached a peak of 0.35 m g C (mg chl a)-' h-' in early December but was not detectable in the light perturbed quadrat. Facultative heterotrophy was found in natural populations of sea ice diatoms at substrate concentrations close to ambient. Respiration and incorporation of 14C-serine into acid-insoluble particles in the 2 1.0 pm size fraction were found in both control and light perturbed quadrats. Variation in uptake among samples was very high, and a light effect was not detected. Microautoradiographs revealed that ice diatoms including Nitzschia sublineata Hasle, a common sea ice alga lacking epiphytic bacteria, were labeled with I4C-serine.
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Palmisano et al. (1985) studied this question.