Physical control of the horizontal patchiness of sea-ice microalgae

Abstract

Factors controlling the horizontal distribution of sea-ice microalgae were studied in Southeastern Hudson Bay and adjacent Manitounuk Sound (Canadian Arctic). Both large (-30 km) and small (0.3 to 500m) scales of variability were investigated. Results showed that salinity was the most important factor controlling large scale distribution of the ice-microalgal biomass, through its effect on the structure of the ice (surface available for colonization). Variation in the thickness of the snow-ice cover, which determines irradiance at the bottom of the ice, was the factor controlling distribution of the algal biomass at smaller scale (diameter of patches of microalgal biomass ranging between 20 and 90 m). The relation between ice-algal abundance and snow-ice thickness changed however over the season. At the beginning of the growing season (in April when the bottom-ice irradiance was higher than a minimum critical irradiance), maximum algal biomass was observed under areas covered by the smallest snow depths. Towards the end of the season, when light transmitted through the snow-lce cover increased, maximum algal biomass was observed under areas covered by the deepest snow. This suggests that ice algae have both minimum and maximum critical light levels. The minimum level is the irradiance below which there is no photosynthetic activity (Imi, -7.6 CL Einst m-2 S-') and the maximum level corresponds to the inhibiting light intensity, which may vary during the growth season. The horizontal heterogeneity of the snow-ice cover, whlch is influenced by wind at the air-ice interface, thus provides diversified bottom-ice habitats where irradiance is compatible or not with the physiological limits of the ice microalgals cells. This results in a strong patchiness in distribution of ice-bottom microalgae.

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

“…Other investigators have shown that photosynthetic microbes can inhabit the interior, upper surface, and lower surface of ice, and tend to be most concentrated on the bottom surface (Welch et al, 1988;Cota et al, 1991;Frenette et al, 2008;Boetius et al, 2013). Traditionally, investigators have argued that ice-associated communities are most prevalent in ice formed from seawater; as salinity increases, the volume of unfrozen brines within the ice that the microbes can inhabit increases, and the bottom surface of the ice becomes more uneven, increasing bottom algal settlement efficiency (Legendre et al, 1981;Gosselin et al, 1986). However, more recently, investigators have also found algae growing within and on the bottom of freshwater ice in lakes and rivers, including locations in Canada such as the Great Lakes and the St. Lawrence River (Bondarenko et al, 2006;Frenette et al, 2008;Twiss et al, 2012;D'souza et al, 2013).…”

Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

“…9) is very large compared to that of other flux methods (Berg et al, 2007) and is expected to integrate most variability commonly observed at the ice-water interface (McMinn and Ashworth, 1998; Rysgaard et al, 2001). It has been suggested that to include all horizontal variations in light, algal biomass and algal activity it is necessary to measure across distances of 20 to 100 m as dictated by variations in light availability below melting ponds and snow drifts (Gosselin et al, 1986;Rysgaard et al, 2001;Søgaard et al, 2010). Figure 9 shows the size of the footprint to be over 60 m long, and therefore it integrates over most of this variability.…”

“…The techniques presently used to study sea-ice primary production sample at either one point on the ice surface or within an ice core, though algal patchiness and activity have been reported to vary across a much wider range (Gosselin et al, 1986;Rysgaard et al, 2001). This may lead to misrepresentation of the actual sea-ice environment and requires that many replicates are taken over a large area.…”

Characterizing Spatial Variability of Ice Algal Chlorophyll a and Net Primary Production between Sea Ice Habitats Using Horizontal Profiling Platforms

“…This relationship explains the similar patch sizes observed for snow and sea ice algae biomass on the same study sites. Between study sites, however, patch sizes had a large range between 5 and 90 m, which was the result of differences in the snow distribution and drifting patterns over relatively level FYI (Gosselin et al, 1986;Rysgaard et al, 2001;Granskog et al, 2005;Søgaard et al, 2010). In contrast, the undulating surface topography of MYI plays an important role in the distribution of snow, which has been linked to the presence of high ice algal chl a biomass at the bottom of thick MYI hummocks with little or no snow cover .…”

“…It is within this spatial range that many sea ice and snow properties (such as thickness, porosity, temperature) can vary, which can have a large influence on light availability, ice melt and growth, nutrient availability, and therefore, the spatial distribution of ice algae. Typical patch sizes of snow have been reported in the range 20-25 m (Gosselin et al, 1986;Steffens et al, 2006). Surface properties such as albedo have patch sizes of ∼10 m (Perovich et al, 1998;Katlein et al, 2015a) and sea ice draft can vary at scales of around 15 m (Katlein et al, 2015a).…”