Fig. 9. Carbon dioxide lost by a Magellanic penguin over the course of a surface pause lasting 22 s after having completed a dive of 74 s. Conditions are as in Fig. 8 and total CO₂ in the body at the onset of the pause is taken to be 220x0.78=172 ml (derived from a respiratory quotient RQ in penguins of 0.78; see text). (A) The rate of CO₂ transfer is taken to be directly proportional to the difference in CO₂ partial pressure between total body stores and air in the respiratory system, with the rate constant k2 nominally taken to be 0.04. (B) The rate of CO₂ transfer is initially taken to be constant (with a rate constant of 0.005) until tidal volume reaches a minimum (at 10.6 s into the surface pause), whereupon the rate constant is then taken to be directly proportional to the oxygen levels in the body (cf. Fig. 8A) with k2 set at 0.0005.