Distributions of oxygen, argon, nitrogen, and radon in the upper ocean of the subarctic Pacific distinguish the fluxes controlling the oxygen mass balance during the summers of 1987 and 1988. The difference between the net O2 flux (in mmol m−2 d−1) to the atmosphere via gas exchange (32) and the integrated decrease with time (−14) is balanced by biological production (13-17), air injection by bubble entrainment (5), and O2 flux to the thermocline −(0-4). Nitrogen/argon and oxygen/argon ratios reveal that ˜15% of the oxygen supersaturation in summer is produced by air injection and ˜40% by biological production, with the rest induced by surface water warming. Our estimate of biologically induced oxygen production when translated stoichiometrically to nitrogen uptake agrees to within error estimates with both the particulate and dissolved nitrogen mass balances for the upper ocean determined in the SUPER program during the same time period. The oxygen mass balance requires a net carbon production in the euphotic zone of ˜140 mg C m−2 d−1 (PQ=1.5), which is 20–30% of the level of 14C primary production determined by SUPER investigators.