Mars’ Obliquity-Driven CO2 Exchange between the Atmosphere, Regolith, and Polar Cap

Discerning the total mass of Mars’ exchangeable CO2 inventory has been elusive for decades due to the unknown adsorptive capacity of its regolith. Now, however, the stratigraphy of Mars’ recently discovered South Polar Massive CO2 Ice Deposit (MCID) provides a record of orbit-driven CO2 exchange between its polar cap, atmosphere, and regolith with sufficient constraint to calculate the adsorptive capacity of its regolith and therefore the total mass of its exchangeable CO2 inventory. We use a numerical climate model and Markov Chain Monte Carlo analysis to show that the observed MCID stratigraphic record is most consistent with a total exchangeable CO2 inventory of 〖1.9〗_(-0.5)^(+1.0)×10^17 kg (49_(-12)^(+26) mbar), active regolith thickness of 244_(-92)^(+150) m, and regolith specific surface area of 〖1.0〗_(-0.7)^(+2.6)×10^4 m^2 kg^(-1). The maximum likelihood value for Mars’ adsorbed CO2 inventory is 1.3 ×10^17 kg (35 mbar), with a 68% confidence interval of 8.4 ×10^16 to 2.3 ×10^17 kg (22 to 62 mbar). Our best-fit model yields a peak mean annual surface pressure 30% lower than CO2 exchange models that neglect an adsorbing regolith. We provide machine-readable text files of our results to aid future study of Mars’ climate.