Structural and functional properties of sympagic communities in the annualsea ice at Terra Nova Bay (Ross Sea, Antarctica)

Studies on the chemical and biological properties of annual pack ice at a c oastal station in Terra Nova Bay (74 degrees 41.72'S, 164 degrees 11.63'E) were carried out during austral spring at 3-day intervals from 5 November t o 1 December 1997. Temporal changes of nutrient concentrations, algal bioma sses, taxonomic composition, photosynthetic pigment spectra and P-E relatio nships were studied. Quantity, composition and degradation rates of organic matter in the intact sea ice were also investigated. In addition, microcos m experiments were carried out to evaluate photosynthetic and photo-acclima tion processes of the sympagic flora in relation to different light regimes . High concentrations of ammonia were measured in four ice-cores (weighted mean values of the cores ranged from 4.3 +/- 1.9 mu M to 7.2 +/- 3.4 mu M), whereas nitrate and phosphate displayed high concentrations (up to 35.9 mu M and 7.6 mu M, respectively) only in the bottom layer (135-145 cm depth). Particulate carbohydrate and protein concentrations in the intact sea ice ranged from 0.5 to 2.3 mg l(-1) and 0.2 to 2.0 mg l(-1), respectively, disp laying a notable accumulation of organic matter in the bottom colored layer , where bacterial enzymatic activities also reached the highest values. Ami nopeptidase activity was extremely high (up to 19.7 mu M l(-1) h(-1) +/- 0. 05 in the bottom layer), suggesting a rapid turnover rate of nitrogen-enric hed organic compounds (e.g. proteins). By contrast, bacterial secondary pro duction was low, suggesting that only a very small fraction of mobilized or ganic matter was converted into bacterial biomass (< 0.01 parts per thousan d). The sympagic autotrophic biomass tin terms of chlorophaeopigments) of t he bottom layer was high, increasing during the sampling period from 680 to 2480 mu g l(-1) Analyses of pigments performed by HPLC, as well as microsc ope observations, indicated that diatoms dominated bottom communities. The most important species were Amphiprora sp. and Nitschia cfr. stellata. Bott om sympagic communities showed an average P-max(B) of 0.12 mgC mg Chl(-1) a nd low photoadaptation index (E-k = 18 mu E m(-2) s(-1), E-m = 65 mu E m(-2 ) s(-1)). Results of the microcosm experiment also indicated that communiti es were photo-oxidized when irradiance exceeded 100 mu E m(-2) s(-1). This result suggests that micro-autotrophs inhabiting sea ice might have a minor role in the pelagic algal blooms.