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Ice algae are a case study in photo‐autotrophic growth and metabolism under chronically low temperature and irradiance. We measured the allocation of ¹⁴C‐labelled photosynthate among major classes of intracellular carbon (low molecular weight compounds, or LMW; lipid; protein; and polysaccharide) and found light‐dependent changes in allocation broadly similar to photo‐adaptive responses known in phytoplankton at higher temperatures; average relative allocation to protein varied inversely (10–37%) and allocation to lipids and polysaccharides directly (10–23%, and 16–21%, respectively) with the sub‐inhibiting irradiance levels we employed (3.5–33.0 μE.M⁻². s⁻¹). Unlike many observations at higher temperatures, ours indicated (on average) a large and light‐insensitive allocation to LMW (ca. 40%) and a greater light‐sensitivity in lipid than in polysaccharide allocation. At the higher incubation …