Figure 2.
Factors governing oxygen supply to animals. (a) Average annual partial pressure of O2 (pO2) in the global ocean at surface. (b) Average annual solubility of O2 (αO2) in the global ocean at surface. Values increase with latitude owing to the thermal effects on Henry's solubility coefficient. (c) Average annual diffusivity of O2 (DO2) in the global ocean at surface. (d) Average annual bioavailability of O2 in the global ocean at surface, expressed using the oxygen supply index (OSI) [39]. Despite the increased solubility of O2 in cold water, the kinematic viscosity also increases substantially, reducing the diffusivity of O2 at a rate greater than the offsetting effect on solubility. As a result, the supply of O2 to respiratory surfaces actually decreases approximately linearly as water becomes colder.