Figure 2. Global oxygen reservoirs, fluxes and turnover times. Major reservoirs are underlined, pool sizes and fluxes are given in 1015 moles O2 and 1015 moles O2 yr-1. Turnover times (reservoir divided by largest flux to or from reservoir ) are in parentheses. To convert moles O2 to Tg O2 , multiply by 3.2 x 1011.

The atmosphere is the largest oxygen reservoir and has the longest turnover time. The atmospheric oxygen reservoir is ~200-fold larger and has a turnover time >106-fold longer than the next largest reservoirs, the ocean dissolved oxygen reservoir and long-lived plants. The major source of oxygen is photosynthesis, but this is almost exactly balanced by respiration. Note that ocean sediments are shown as an oxygen source, because the long-term storage of organic carbon in ocean sediments prevents oxidation and allows accumulation of oxygen in the atmosphere.