Climatological annual cycle of upper ocean oxygen content anomaly

The climatological annual cycle of oxygen content anomaly of the 0–100 m depth layer for major ocean basins is described using Fourier analysis of objectively analyzed monthly O 2 anomaly values on a 1° grid (70°S–70°N). The largest seasonal changes in O 2 content anomaly occur in the extra‐tropics in the 30° to 60° latitude belt of each hemisphere. The magnitude of the global cycle is dominated by the Pacific Ocean. The annual and semi‐annual harmonics account for most (>90%) of the annual cycle of the monthly O 2 content anomaly. The magnitude of the annual harmonic is largest in the upper 75 m layer except in the tropics and high latitudes. The annual harmonic accounts for >90% of the variance of the zonally integrated monthly O 2 content anomaly.