Phytoplankton and nutrient dynamics were investigated during the 2007 and 2008 summers in the euphotic zone of five broad domains across Subarctic and Arctic Seas: the Eastern Subarctic North Pacific Ocean, ESNP; Bering and Chukchi Seas, BE-CH; Beaufort Sea and Canada Basin, BS-CB; Canadian Arctic Archipelago, CAA; and Baffin Bay and Labrador Sea, BB-LS. Average concentrations of nutrients (NO3−, NH4+, Si(OH)4, and PO43−) decreased markedly from west to east, with minima in NO3− and NH4+ in surface BS-CB waters, but relatively invariant urea-N concentrations across the entire region. In the BS-CB domain, low uptake rates of nitrate (ρNO3−) and ammonium (ρNH4+) were exceeded by uptake of urea (ρUrea-N). Whereas average ρNO3− was highest in the BE-CH domain, ρUrea-N was maximal in BB-LS. Average depth-integrated f-ratios ranged from 0.27 in the BS-CB domain to 0.57 in BE-CH, while chlorophyll a (chl a) and primary productivity (ρC) were highest in BE-CH and BB-LS, and consistently low in the BS-CB domain. The >5 µm phytoplankton fraction dominated ρC and ρNO3− in the BE-CH and CAA domains, whereas ESNP and BS-CB were dominated by the <5 µm fraction. In the BB-LS domain, the larger cells were responsible for ∼50% of ρC, ρNO3−, and ρUrea-N. This study highlights the contrast in ice-corrected average new production between the BE-CH (396 mg C m−2 d−1) and BS-CB (5.50 mg C m−2 d−1) domains in summer, and the larger contribution of urea-N uptake to total N uptake in central and eastern regions where NO3− concentrations were lower.