Glob. Biogeochem. Cycles http://doi.org/gd3t78 (2018)

Dissolved oxygen (O2) is essential for marine ecosystems, but as the ocean warms levels are expected to decrease because the solubility of gases is reduced. Stratification also increases, reducing mixing and gas exchange from the surface to depth.

Using six CMIP5 Earth system models and an ocean general circulation model (MITgcm), Yohei Takano of the Georgia Institute of Technology, Atlanta, USA (now at the Max Planck Institute for Meteorology, Hamburg, Germany), and colleagues investigate the mechanisms controlling oxygen changes out to 2100 for the Pacific Ocean. Under a high-emissions scenario (RCP8.5), they show that warming is the main cause of deoxygenation in subsurface waters. At mid-to-high latitudes, decreased solubility and reduced ventilation of the subsurface are primarily responsible, with small contributions from wind and precipitation–evaporation changes. For the tropical Pacific, which already has low oxygen levels, smaller changes are projected as warming reduces the demand for oxygen due to organic matter decomposition (in addition to solubility) and circulation changes result in younger waters in this location. This highlights the need to understand regional circulation characteristics when considering future oxygen losses.