Scale dependent forcing on ice algae dynamics: Observations and modelling

Sea ice algae play a critical role as the first available food source in ice-covered polar oceans. Changes in the thermal, physical and optical properties of the snow-sea ice system and feedbacks between various temporal and spatial scales affect accumulation of algae at the sea ice bottom and are the focus of this dissertation. The principle objective is to determine the importance of various characteristics and scales of physical processes on the accumulation and loss of bottom ice algae during the spring season. Field data used in the dissertation come from two spring field seasons undertaken in 2002 and 2003 near Resolute Bay, Nunavut, on landfast first-year sea ice. Results show that transmitted light, ice temperature and bottom ice structure are largely dependent on the spatial distribution and highly variable depth history of the overlying snow cover, which induces variability on ice algae biomass. Furthermore, the physical processes controlling the magnitude of biomass can differ based on snow depth from a thermal melt-off effect under thin snow to light limitation and thermal insulation under thick. It is also noted that destructive point sampling of the sea ice for algal biomass estimation limits a direct analysis of the principle objective. Therefore, algae optical absorption properties are used to develop methods for remote estimation of ice algal biomass. A coupled ice algae growth model is also employed to further examine the principle objective. Improvements were made to the model using detailed measurements of snow, sea ice and ice algae thermal and optical properties. The results supported the conclusions drawn from observations; however, simulations also demonstrated that the thermal and optical factors are not exclusive in their effects on algal accumulation and loss based on snow depth. The model was also found to be very sensitive to variability in light attenuation and the ice warming rate. This dissertation highlights the importance of snow cover history and distribution on the sea ice system operating below. Furthermore, results emphasize the sensitivity of the bottom ice algae ecosystem to Arctic climate change through potential shifts in snow depth distribution and thermophysical changes induced by atmospheric or oceanic changes in temperature.