On the variability of dissolved oxygen and apparent oxygen utilization content for the upper world ocean: 1955 to 1998

We document variability in O2, AOU, and heat content in the top 100 m of the world ocean (70°S–70°N) between 1955 and 1998 using observational data. The lowest O2 (highest AOU) content in the late‐1950s are followed by high content in the mid‐1980s and by low content in the late‐1990s. The O2 and AOU content variability is characterized by relatively small linear trends superimposed on large decadal‐scale fluctuations. The largest O2 content changes occur in the Northern Hemisphere (NH). The NH exhibits a negative linear trend in O2 content of ∼−30 Tmol per decade between 1983 and 1998 and a positive linear trend of ∼6 Tmol per decade between 1955 and 1998 (1 Tmol = 1012 mol). The trends in O2, AOU, and heat content are sensitive to the time frame of the measurements. The results indicate that a constant upper‐ocean O2 content inventory should not be assumed on decadal time‐scales.