Physical control of arctic ice algal production

Abstract

Algal colonication of annual sea ice in the high Arctic approximates plate culture, presenting a model system for physiological studies of natural populations of marine microalgae. Time series of observations were made in the Northwest Passage during the latter half of the spring bloom. Although in situ temperature, salinity and irradiance ware nearly constant, the photosynthetic performance of ice algae as indicated by maximum assimulation rates (PmB, mg C mg chl-1 h-1) and photosynthetic efficiencies (.alpha., mg C mg chl-1 h-1) (.mu. E m-2 s-1)-1) displayed large, low-frequency fluctuations. In contrast, the photoadaptive index, Ik (.mu.E m-2 s-1), varied little up until the last few days of our study when snow cover melted and tramsitted light increased rapidly. When compared to cells from other snow covers or light histories, algal populations from a snow-free area exhibited higher assimilation rates and photoadaptive indices but had similar photosynthetic efficiencies and lower standing stocks. Nutrient fluxes in the 'surface mixed layer' also varied by about an order of magnitude over the fornightly tidal cycle. Tidally dominated vertical mixing resulting in a pulsed nutrient regime which is apparently reflected in a modulation of algal photosynthesis and growth.