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Sea ice communities were sampled across the Ross Sea in the austral autumn. The biota in first-year pack ice was assessed by measuring chlorophyll a (chl a), phaeopigments, total particu- late carbon and nitrogen (POC and PON, respectively) and collecting samples for identification by microscopy. Physical and chemical parameters were also measured to characterize the environ- ment. Chl a concentrations in ice ranged from 0 to 96.9 µg l -1 in discrete samples and from 0.02 to 20.9 mg m -2 for values integrated throughout floes. Maximum values were similar to those observed in first-year pack ice at other Antarctic locations. Chl a concentrations varied with ice structure and with latitude. POC:chl a and C:N ratios (molar) were high, possibly indicating detritus accumulations. The higher chl a levels north of approximately 72° S were apparently a result of ice forming in the south early in the season with subsequent advection to the north. These dynamics would result in older ice in the mid- or northern pack ice zone that was maintained in a favorable light and temper- ature regime during the seasonal progression of formation and drift. Chlorophyll levels were low in surface-layer communities. High chlorophyll concentrations were associated with internal communi- ties. Bottom-layer algal populations, while present, did not reach the levels of high biomass reported for autumn blooms in some land-fast ice regions. Apparent nutrient and CO2 depletion were corre- lated with biomass parameters but accounted qualitatively for only a fraction of the biomass accumu- lation measured. Overall, autumn ice-associated production in the Ross Sea may be lower than expected because of the ice drift dynamics, apparently low production in the near-surface layers of first year ice flows, and the absence of rich bottom-layer assemblages.

Development of sea ice microbial communities during autumn ice formation in the Ross Sea