Impact of Ice Algae on Inorganic Nutrients in Seawater and Sea Ice in Barrow Strait, NWT, Canada, During Spring

Abstract

Except in "bottom ice" (lowest few centimetres) and surface waters impacted by autotrophs, the major inorganic nutrients behave conservatively in seawater and sea ice. From mid- to late spring, steep and persistent nutrient gradients were observed in the "well-mixed surface layer" with minima near the ice–water interface. Nitrate, ammonium, and phosphate are highly concentrated in heavily colonized bottom ice relative to seawater and the remainder of the ice sheet; concentrations in darkened, weakly colonized bottom ice are similar to the ice sheet. These nutrients also display strong vertical stratification over millimetre scales. Nitrate and phosphate in the bottom ice layer display strong positive relationships with chlorophyll. The accumulation of these nutrients in bottom ice must be biologically mediated and constitutes a significant sink. In contrast, silicic acid concentrations in bottom ice are close to those expected for sea ice formed from the source seawater, are only weakly related to algal biomass, and vary much less seasonally. Ice algae are apparently shocked osmotically and release their intracellular pools of dissolved nutrients. Intracellular pools of nitrate averaged 1.4–9.5% of total particulate nitrogen. Nitrient stresses, during periods of high biomass and sluggish supply, may be alleviated by pooling.

Role of environmental factors on phytoplankton bloom initiation under landfast sea ice in Resolute Passage, Canada

“…Both explanations fit the under-ice bloom observed in our study. Prior to 6 June, nitrate+nitrite was well correlated with salinity ([nitrate+nitrite] = 8.60 × salinity − 272; r 2 = 0.84, n = 63), similar to that observed by Cota et al (1990) for the same region. By the end of the study period, nitrate+nitrite was depleted over the upper 10 m to less than 0.2 µmol l −1 , whereas silicic acid and phosphate averaged 2.8 and 0.6 µmol l −1 , respectively.…”

“…Prior to 6 June, standardized nitrate+ nitrite, silicic acid, and phosphate concentrations were relatively stable, averaging 7.2, 14.7, and 1.2 µmol l −1 , respectively. These concentrations fall along the lower range previously reported for the region (Cota et al 1990. Following 6 June, standardized nutrient concentrations were drawdown with molar uptake ratios for silicic acid:nitrate+nitrite of 1.7 (r 2 = 0.98, n = 5) and nitrate+ nitrite:phosphate of 10.3 (r 2 = 0.99, n = 5).…”

New estimates of microalgae production based upon nitrate reductions under sea ice in Canadian shelf seas and the Canada Basin of the Arctic Ocean

“…The combined annual production of water column and ice-algae primary production for 60 days was estimated as about 27 g C m -2 year -1 and interannual comparisons of ice-algae production revealed strong year-to-year variability (2-23 g C m -2 year -1 ) (Smith et al 1988). A similar value (27 g C m -2 year -1 ) was estimated from silica depletion over the upper 100 m in Barrow Strait well before the pelagic phytoplankton bloom (Welch and Bergmann 1989;Cota et al 1990;Harrison et al 1990). These values are close to our estimate of 29-30 g C m -2 year -1 in Jones Sound (Meds 1962), and our results (10.7-14.3 g C m -2 year -1 ) for two other data sets (Resolute 1984, CASES) also fall within this range (Table 1).…”

“…The depths of nutrient drawdown as a result of sub-ice and ice primary production and net community production have been previously reported to be about 100 m (Welch and Bergmann 1989;Cota et al 1990) on the Canadian shelf. The data sets herein (Table 1) show drawdown to 50-80 m in Resolute Passage and Barrow Strait, to 80 m in shelf waters of Jones Sound, and to 75 m in the Canada Basin of the Arctic Ocean, well within the depth range of these previous observations.…”

Eukaryotic microbiota in the surface waters and sea ice of the Southern Ocean: aspects of physiology, ecology and biodiversity in a ?two-phase? ecosystem

“…For instance, frazil ice structure may be less porous to nutrient flux than congelation ice and therefore it is more likely that algae within frazil ice will experience nutrient depletion (Dieckmann et al, 1991). The rates of advection and diffusion of nutrients from seawater into the porous bottom layers of sea ice may depend on under-ice current velocities which can vary with diurnal and fortnightly tidal height or atmospheric pressure cycles (Cota et al, 1990). Platelet ice layers containing high algal biomass may reduce the flux of nutrients to algae within the overlying congelation ice (Lizotte and Sullivan, 1992).…”