Responses of Sea-Ice Microalgae to Climatic and Fortnightly Tidal Energy Inputs (Manitounuk Sound, Hudson Bay)

Abstract

Variations of sea-ice microalgae at the ice–water interface (Manitounuk Sound, Hudson Bay, Canada) were studied in relation to various energy inputs (light, tidal mixing, and heat) in April and May 1982. Seasonal photosynthetic activity does not start before the light intensity reaches 7.6 μEinst∙m−2∙s−1. Above this value, the seasonal increase in cell numbers and chlorophyll and in the photoadaptation index (Ik) is related to the increase in underice light intensity. The sea-ice community changes from shade to light adaptation to optimize the use of ambient light energy. Photosynthetic efficiency (αB) is mainly controlled by the fortnightly tidal vertical mixing, which governs the amount of phosphate (or of another nutrient factor) in the upper brackish layer. The ice microflora, which grows at a stable interface, takes advantage of nutrient replenishment during mixed water column conditions. We conclude that production of microalgae depends upon three forms of energy: (1) the flux of solar light, (2) the inputs of auxiliary mechanical energy (here, the fortnightly tides), and (3) the energy exchanges (here, the heat flux) responsible for the maintenance or destruction of energetic interfaces (ergoclines).

Physical control of arctic ice algal production

“…Introductions of fresh water from melting snow and sea ice tend to dilute the available nutrients (Cota et al unpubl. ) and also enhance density stratification, thus impeding both vertical mixing and nutrient fluxes in ice-covered marine ) and estuarine environments (Gosselin et al 1985).…”

“…There is little doubt that light availability has a major influence on ice algal biomass and production in the Arctic, Subarctic and Antarctic (Apollonio 1961, 1965, Clasby et al 1976, Horner & Schrader 1982, Gosselin et al 1985, Horner 1985, Grossi et al 1987, Smith et al 1987, 1988, SooHoo et al 1987, especially during the winter-spring transition when incident irradiance increases dramatically. Growth irradiance (in situ light level) can also be manipulated and maintained fairly easily by stabilizing surface snow cover with a low profile snow fence (Cota 1985).…”

“…Lewis et al 1984). Turbulent mixing has long been known to influence the growth or production of phytoplankton (Grann & Braarud 1935, Sverdrup 1953, Lewis et al 1984), while the potential impact of vertical mixing on populations of sea ice algae has only been considered very recently (Gosselin et al 1985. The interplay between the environmental factors of light and nutrients are markedly different in planktonic (pelagic) versus sea ice (epontic) ecosystems.…”

“…Several independent lines of evidence have led to recent suggestions that inorganic nutrients may limit ice algal production (Grainger 1977, Gosselin et al 1985, McConville et al 1985, Palmisano & Sullivan 1985, Maestrini et al 1986. Cota e t al.…”

“…Specifically, we wished to determine if there was systematic variability in photosynthetic parameters between hght environments (snow depths) and over time. We hypothesized that ice algae display photoadaptative states which are characteristic of their different light regimes (Cota 1985) and that a time series of photosynthetic responses in a population with the same light history would be diagnostic of potential nutrient stress when their nutrient supply may be pulsed at low frequency (Gosselin et al 1985). Most of this study was conducted during May, a period when the physical environment is relatively constant compared to either April when incident Irradiance increases markedly and the bloom progresses from very low biomass to near maximal levels or June when biomass usually declines very rapidly in response to the spring melt.…”