The global oxygen cycle is one of the most important cycles on Earth for all aerobic organisms, and it is a basic constraint sustaining aerobic life. As a major component of the cycle, oceans are now experiencing widespread declines in oxygen concentrations. Here, based on model simulations we found that ocean deoxygenation occurs as a result of oceanic oxygen outgassing, which is tightly related with the marine warming. Although the O2 flux from the ocean to atmosphere is quite small compared with that of oceanic oxygen production, this outgassing accounts for almost all of the decline in marine oxygen and even exceeds the amount of the loss. The model projections indicate accelerated oxygen escape from the ocean under climate change. The oceanic outgassing will…