IMPACT OF FRESH-WATER ON A SUB-ARCTIC COASTAL ECOSYSTEM UNDER SEASONAL SEA-ICE (SOUTHEASTERN HUDSON-BAY, CANADA) .1. INTERANNUAL VARIABILITY AND PREDICTED GLOBAL WARMING INFLUENCE ON RIVER PLUME DYNAMICS AND SEA-ICE

Analysis of sea ice cover, runoff and air temperature observations in Hudson Bay shows marked interannual variability. This variability is t hought to play a major role in determining overall productivity of the coastal ecosystem by changes to river plume extent, under-ice light c onditions and nutrient levels during spring. Extensive field work off the Great Whale River in southeastern Hudson Bay has shown the importa nce of freshwater discharge, sea ice cover and meteorological forcing on the production of under-ice microalgae and the success of first fee ding in fish larvae. Recent global climate model (GCM) results for a d oubling of present atmospheric carbon dioxide indicate increases of bo th air temperature and precipitation in the Hudson Bay area. Predictio ns based on GCM results are used to estimate future changes to the sea ice and runoff regime. Sea ice breakup in the offshore is predicted t o occur about one month earlier than presently. Estimates of the sprin g freshet in the Great Whale River indicate it will also advance by ap proximately one month. Onset of the spring freshet will occur about on e month before Hudson Bay ice breakup, similar to present. A predicted reduction of about 35% in maximum sea ice thickness will lead to an i ncrease in the ice-ocean interface irradiance and a decrease in melt w ater input to the Hudson Bay surface waters. These results are used in a discussion of potential effects of global climate change on norther n coastal marine environments.