Abundance and photosynthetic activity of ice algae in Resolute Passage in the Canadian high Arctic were measured in relation to in situ irradiance throughout the main growth season in 1985 and 1986. A simple model was used to calculate in situ production rates and the theoretical maximum (light limited) size of crops and production rates. Both the observed and the maximum possible crop sizes and production rates varied directly with irradiance over the natural range of snow cover, and crops attained the theoretical maximum imposed by self-shading (77 to 225 mg m-' chlorophyll a under thin snow cover) in both years. Calculated in situ production of ice algae under thin snow cover (S to 23 gC m-2 yr-l) could equal or exceed typical values for Arctic plankton. Comparison against observed biomass accumulation in the ice indicated that as much as 65 % of the production could be exported from the ice during the growth season. Where light was artificially increased by maintaining snow-free areas, observed crops were much less than the theoretical maximum despite the abscence of photosynthetic photoinhibition. Crops reported from some other arctic sites were also much less than their corresponding theoretical maxima. Low irradiance often limits ice algal growth, but our results suggest that losses associated with excessive irradiance and with grazing by amphipods at near-shore sites are additional factors determining algal abundance and production.

Biochemical composition of the sea ice microbial community was measured in populations of different light histories in the Canadian Arctic (Resolute, N.W.T.). The average composition of the particulate organic matter [soluble and insoluble polysaccharide, particulate protein, intracellular free amino acids (IFAA), lipid, and chlorophyll a] was within the published range for microalgae, but lipid was a relatively large (3 l-59%) and protein a small (20-24%) part of the total. Protein and IFAA pools apparently comprised about 50% of the particulate organic nitrogen, of which 6-10% was in the IFAA pool. Over the cntirc spring growth season, the net synthesis of protein, IFAA, and Chl a (relative to total cell carbon) decreased with increasing light while relative synthesis of lipid and soluble polysaccharide increased, consistent with patterns of short-term photosynthate allocation. In the early growth season patterns of synthesis were relatively insensitive to light, and rates of lipid synthesis were large for all light histories. Photosynthate allocation in 24-h incubations greatly underestimated actual rates of net lipid synthesis and probably overestimated protein synthesis. Microalgae of cold, low-light environments can display rates of lipid synthesis much larger than rates normally encountered in microalgae without displaying a corresponding pattern of shorter term photosynthate allocation.

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The dynamics of bacterial populations in annual sea ice were measured throughout the vernal bloom of ice algae near Resolute in the Canadian Arctic. The maximum concentration of bacteria was 6.0·10(11) cells·m(-2) (about 2.0·10(10) cells·l(-1)) and average cell volume was 0.473 μm(3) in the lower 4 cm of the ice sheet. On average, 37% of the bacteria were epiphytic and were most commonly attached (70%) to the dominant alga,Nitzschia frigida (58% of total algal numbers). Bacterial population dynamics appeared exponential, and specific growth rates were higher in the early season (0.058 day(-1)), when algal biomass was increasing, than in the later season (0.0247 day(-1)), when algal biomass was declining. The proportion of epiphytes and the average number of epiphytes per alga increased significantly (P<0.05) through the course of the algal bloom. The net production of bacteria was 67.1 mgC·m(-2) throughout the algal bloom period, of which 45.5 mgC·m(-2) occurred during the phase of declining algal biomass. Net algal production was 1942 mgC·m(-2). Sea ice bacteria (both arctic and antarctic) are more abundant than expected on the basis of relationships between bacterioplankton and chlorophyll concentrations in temperate waters, but ice bacteria biomass and net production are nonetheless small compared with the ice algal blooms that presumably support them.