Nutrient fluxes during extended blooms of Arctic ice algae

Abstract

Estimates of nutrient demand by dense mats of ice algae in the high Arctic indicate that substantial nutrient fluxes are necessary to satisfy the observed growth over the 2-month bloom. In our study area, Barrow Strait, the quantity of nutrients in the surface-mixed layer is about 3-10 times greater than estimates of total demand during the bloom, and nutrient fluxes in the water column are estimated to be of the same order of magnitude as algal demand. The fluxes in the water column are predicted to vary by more than an order of magnitude over the fortnightly tidal cycle, assuming that fluxes depend upon the strength of tidal currents and the vertical nutrient gradients. In the latter half of the bloom, when biomass levels are high, it appears that established populations of ice algae may experience cyclic conditions of nutrient limitation during neap tides when nutrient fluxes are minimal. Contributions from regeneration and brine exclusion from the ice sheet appear to satisfy only a portion of the bloom's total requirement for nutrients. INTRODUCTIONDense growths of ice algae are a ubiquitous feature beneath annual sea ice in polar regions during the springtime. In the high Arctic these microalgae are largely concentrated at the ice-water interface on or within the skeletal layer of the congelation ice. MacroScopically, they resemble a mottled goldenbrown carpet about 1-2 cm thick. We have found that these algae grow for at least 2 months (April-May) in the central portion of the Northwest Passage. Moreover, the ice alga. e often achieve high levels of biomass (80-100 mg chlorophyll m -e) that are similar to water column values integrated over the depth of the euphotic zone in many planktonic systems.

Physical control of arctic ice algal production

“…There was, on the other hand, a strong relationship between tidal range and nutrient gradients in the pycnocline-nutricline similar to our previous results (see Fig. 9 of Cota et al 1987). where the gradients have units of mm01 m-4, tidal range R is in meters and time t is in days with a 2 d lag.…”

“…2b; also see Fig. 8 of Cota et al 1987). Hence, all observations have been related to tidal data w l c h are generally available and reliable for this region.…”

“…2c) were present even throughout the most intense periods of mixing which coincided with spring tides. Computations of vertical eddy diffusivities K,(t) as a funcbon of time for the surface mixed layer were made with a polynomial expression reported by Cota et al (1987;their Eq. 11) which relates daily mean tidal range (R, in meters) to vertical diffusivity.…”

Mesoscale distribution and functional diversity of picoeukaryotes in the first-year sea ice of the Canadian Arctic

“…A recent ice-ocean regional model predicts spring ice breakup to advance by as much as 2-5 weeks in the Canadian Arctic Archipelago (Sou and Flato, 2009). This may pose a particular threat to the Arctic ecosystem, as the Archipelago is the region where the highest ice-algal biomasses are reported in the Arctic, associated with strong mixing and replenishment of nutrients at the ice-water interface (Cota et al, 1987;Michel et al, 2006). An exhaustive review of dominant physical and biological processes in the Canadian Arctic Archipelago and recent changes in this area can be found in Michel et al (2006).…”

The multiphase physics of sea ice: a review for model developers

“…Convection is either confined in the lowermost, porous sea ice or may develop over the full depth of the ice, with a potential influence on the localization of the communities. Second, dissolved macronutrient concentrations in the ice plotted versus ice salinity lie on a line, in other words, the vertical profiles have the same shape, except when ice microbial communities are active, as indicated by field and laboratory experiments (Clarke and Ackley, 1984;Cota et al, 1987;Meese, 1989;Giannelli et al, 2001;Tison et al, 2008).…”