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.