The datasets present new data from microscopic counts and selected nutrient and physical data assembled from the following cruises. Aboard the CCGS Amundsen: ArcticNet Expeditions 2006, 2008, 2009, 2010; International Polar Year (IPY) Circumpolar Flaw Lead Study 2008 and MALINA Project 2009 (French IPY project headed by Dr. M. Babin). Aboard the CCGS Louis St-Laurent: IPY Canada's Three Oceans 2007. Temporal coverage is Feb.-Nov., but varies by year, with the greatest sampling effort in July-Oct. Cryothecomonas abundance was measured by cell-counts using fluorescent in situ hybridization with a taxon-specific probe. Biomass of phototrophic and heterotrophic organisms, of different size classes, was obtained by counts of DAPI-stained cells under epifluorescence microscopy. Samples for total chlorophyll a (chl a) were filtered onto GF/F filters, extracted in either ethanol or acetone and analysed by spectrofluorometry. Chl a was also measured for the < 3 µm size fraction. CCGS Amundsen data: Temperature, salinity, oxygen, and photosynthetically active radiation were provided by Dr. Y. Gratton (Institut National de la Recherche Scientifique, Québec). Nitrate and Phosphate concentrations were provided by Dr. J.-É. Tremblay (Université Laval, Québec). CCGS Louis St-Laurent data were supplied by Drs. EC Carmack and John Nelson (Institute of Ocean Sciences, Sidney, B.C.). Distance to ice edge was obtained from the Canadian Ice Services ( http://ice-glaces.ec.gc.ca).