Résumé
Distribution of pico- and nanophytoplankton in surface waters was investigated in relation to environmental factors at 10 stations in the North Water (NOW), northern Baffin Bay, and at 4 more southerly stations in Baffin Bay in fall 1999. Water temperature (T), salinity (S), dissolved inorganic nitrogen (DIN), phosphate concentrations and pico- and nanophytoplankton abundances were measured in the surface waters in the studied area. A clustering analysis was performed on these data and allows 2 major ecological regions to be distinguished. An eastern region was characterized by warmer, more saline, surface waters (T > -0.04 degree C, 31.1 < S < 32.7) where the picophytoplankton (eukaryotic flagellates, prasinophyte) were more abundant (700 to 4000 cells ml super(-1)). The distribution of picophytoplankton in the NOW was directly correlated with the surface water T and S. Another region, the northwestern, was characterized by colder, less saline, surface waters (T < -1.2 degree C, 29.3 < S < 31.0), can be divided into northern and western sub-regions. Nanophytoplankton (mostly diatoms) were more abundant (> 3000 cells ml super(-1)) in the northern sub-region and their distributions followed the change in DIN concentrations. DIN and phosphate concentrations were higher in the northern sub-region than in the eastern region and the western sub-region, although DIN and phosphate concentrations were low in the NOW, with values ranging from 0.1 to 1.0 and 0.09 to 0.69 mu M, respectively. Based on these ecological results, it is hypothesized that a surface current flows northward along the western coast of Greenland in fall, bringing warm, more saline water to the eastern part of the NOW. In contrast, surface Arctic water (colder, less saline) coming from the Kane Basin flows southward along the western part of the NOW. These 2 distinct water masses, with their different physical and chemical characteristics, govern pico- and nanophytoplankton distributions in the NOW during the fall.