Photosynthetic carbon assimilation into protein, low-molecular-weight metabolites, polysaccharides, total lipids and into 3 lipid classes (neutral lipids, glycolipids and phospholipids) was determined in batch-culture experiments with natural assemblages of Arctic-ice algae under simulated in situ irradiance. A dramatic increase of lipids was measured under nutrient depletion, which was the result of glycolipid production. Excess light energy during stationary algal growth is dissipated in the form of glycolipids and/or neutral lipids.