Abstract Spatial high-resolution estimates of biogenic oxygen were obtained by measuring the concentration of dissolved oxygen, nitrogen and argon during the spring phytoplankton bloom at 21 observation points in the western North Pacific in the area of the Oyashio and Kuroshio Currents off the coast of Hokkaido-Tohoku, Japan. This area extends over approximately 600km. The test region was divided into 6 mesoscale-wide groups (approximately 20–150km wide) of observation stations based on variation in the temperature and salinity of the seawater. As suggested by an analysis of the hydrographic data, the area of which water temperature was lower than around the area was found in the Oyashio–Kuroshio mixing area. In the area, vertical water mixing between the warm mixed layer and cold sub-mixed layer occurred. The biogenic oxygen also varied horizontally at mesoscale intervals. The variation was caused by vertical mixing, because the water masses of the mixed layer and sub-mixed layer had positive and negative biogenic oxygen values, respectively. A spatial high-resolution method for estimating the spatial high-resolution net oxygen production rates (NOP) within the mixed layer using a time-stepped model with biogenic oxygen and the physical data was proposed. The estimated NOP varied widely, even within the same water mass group, and ranged from −23.6±6.0 to 252.7±68.2mmol/m2/day. Therefore, spatial high-resolution NOP estimates are imperative to analyze biological production in areas with complex water mass structures.