The Effect of Ground Ice Redistribution on the Martian Paleo- CO 2 ${\text{CO}}_{2}$ Cycle

Abstract

${CO}_2$ is the primary component of the martian atmosphere and its seasonal surface-atmosphere exchange is responsible for many of the climate phenomena on the planet. Near-surface ground water ice (’GI’) has been found to inhibit seasonal ${\text{CO}}_2$ ice accumulations. Previous studies concerning the response of the ${\text{CO}}_2$ cycle to orbital variations did not take into account the redistribution of GI arising from the same orbital variations. This work aims to analyze the effect of GI redistribution on the ${\text{CO}}_2$ cycle in past climates. We use the LMD Planetary Climate Model to simulate the full ${\text{CO}}_2$ cycle at different orbital configurations and compare simulations with reference modern GI as observed by the Mars Odyssey Neutron Spectrometer (“MONS GI” scenario) to simulations with equilibrium GI produced by the Mars Subsurface Ice Model (“Eq. GI” scenario). In the Eq. GI scenario, equilibrium GI underlies 0.8–0.9 of the seasonal caps area at high obliquity periods, whereas in the reference MONS GI scenario, the overlap between GI and the seasonal cap is reduced, reaching less than 0.3 by obliquity $45°$. The mass and duration of seasonal ${\text{CO}}_2$ ice are significantly reduced relative to the reference scenario, especially in the mid-latitudes, and the expected increase of seasonal pressure amplitude with obliquity is attenuated (by a factor of $\sim$2 at obliquity $45°$). Interpolating the seasonal variations and mean annual pressure over the past 20,000 kyr, we highlight the influence of GI migration in attenuating both seasonal pressure variations and long-term oscillations of the martian atmospheric pressure.