Understanding the repeatable nature of the Viking surface pressure curves: Coupling Mars’ CO2 and dust cycles

Viking landers 1 and 2 measured the surface pressure on Mars for multiple annual cycles and found that Mars’ CO2 cycle is highly repeatable [1]. The dust cycle can affect the CO2 cycle by altering the heat balance of the atmosphere and by modifying the emissivity and albedo of the polar caps [2, 3]. One would therefore expect that the highly variable nature of the dust cycle would lead to year-to-year variability in the CO2 cycle. Interestingly, this is not the case. In this study, we utilize a Mars General Circulation Model to investigate interactions between the dust and CO2 cycles. During years of enhanced dust storm activity, one could expect two coupling mechanisms between the dust and CO2 cycles to become important: the radiative and dynamical effects of increasing the atmospheric dust opacity and the albedo changes that will likely result from increased dust sedimentation in the polar regions. As shown below, numerical investigations of these coupling mechanisms suggest that they have opposite effects on the CO2 cycle. Our working hypothesis is that feedbacks between the dust and CO2 cycles could lead to a stable, repeatable annual CO2 cycle.