Algal species from the ice, the water directly below the ice (the sub-ice area), and the water column from 21 stations in the Arctic Ocean were examined using epifluorescence and inverted light microscopy. Biomass of autotrophic dinoflagellates and other miscellaneous autotrophic flagellates was determined for the first time in the central Arctic basins. Together these two groups dominated phytoplankton biomass in 74% of samples from the central Arctic, with diatom biomass predominant in the remainder. Picophytoplankton at selected stations in the Canada and Makarov Basins contributed 93% to autotroph cell numbers and 36% to autotroph biomass. Diatom species achieved high biomass in ice and sub-ice samples. The centric diatom Melosira arctica dominated the sub-ice area, while pennate diatoms were major contributors to the ice samples. Despite ample silicate concentrations in the water, diatom frustules were often lightly silicified.