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Following sea‐ice retreat, surface waters of Arctic marginal seas become nutrient‐limited and subsurface chlorophyll maxima (SCM) develop below the pycnocline where nutrients and light conditions are favorable. However, the importance of these “hidden” features for regional productivity is not well constrained. Here, we use a unique combination of high‐resolution biogeochemical and physical observations collected on the Chukchi shelf in 2017 to constrain the fine‐scale structure of nutrients, O₂, particles, SCM, and turbulence. We find large O₂excess at middepth, identified by positive saturation () maxima of 15%–20% that unambiguously indicate significant production occurring in middepth waters. Themaxima coincided with a complete depletion of dissolved inorganic nitrogen (DIN = NO₃⁻ + NO₂⁻ + NH₄⁺). Nitracline depths aligned with SCM depths and the lowest extent ofmaxima, suggesting this horizon represents a compensation point for balanced growth and loss. Furthermore, SCM were also associated with turbulence minima and sat just above a high turbidity bottom layer where light attenuation increased significantly. Spatially, the largestmaxima were associated with high nutrient winter‐origin water masses (14.8% ± 2.4%), under a shallower pycnocline associated with seasonal melt while lower values were associated with summer‐origin water masses (7.4% ± 3.9%). Integrated O₂excesses of 800–1,200 mmol m⁻²in regions overlying winter water are consistent with primary production rates that are 12%–40% of previously reported regional primary production. These data implicate short‐term and long‐term control of SCM and associated productivity by stratification, turbulence, light, and seasonal water mass formation, with corresponding potential for climate‐related sensitivities.