Patterns of deoxygenation - natural and anthropogenic driver

Analyses of historical data sets reveal more and more robust patterns of oxygen changes during the past 50 years, showing declining trends in the tropical oceans where the major open-ocean oxygen deficient regions are located. Results of numerical models, however, often show little agreement with observed patterns of deoxygenation, and it has remained unclear to what extent out-of-phase natural variability, errors in the models' mean state or unresolved anthropogenic impacts are responsible for the model-data mismatch. Here we report results of a detailed investigation of CMIP5 model results, complemented with own sensitivity studies revealing the importance of equatorial dynamics, local and remote wind changes, and model parameterizations of anthropogenic nitrogen emissions and fishery effects. Our results reveal some unexpected impacts of previously neglected changes in environmental forcing and provide a better understanding of the mechanisms of decadal to multi-decadal oxygen changes on regional to global ocean scales