| Wind deflation and deposition are powerful agents of surface change on Mars. Erosion is sensitive to surface pressure, so feedback between orbit variations and pressure can enhance the sensitivity of erosion rates to orbital parameters. We use statistics derived from a 1 Cyr integration of the spin axis of Mars, coupled with 3-D general circulation models (GCMs) at a variety of orbital conditions and pressures, to explore this feedback. We also employ a seasonally resolved 1-D energy balance model to illuminate the characteristics of the long-term atmospheric evolution, wind erosion, and deposition over one billion years, for the current conditions and those of early Mars. We find that seasonal polar cycles have a critical influence on the ability for the regolith to release CO2 at high obliquities, and find that the atmospheric CO2 decreases slightly at high obliquities due to the cooling effect of polar deposits at latitudes where seasonal caps form. At low obliquity, the formation of massive, permanent polar caps depends critically on the values of the frost albedo and frost emissivity. Using our 1-D model matched to the NASA Ames GCM results, we find that permanent caps only form at obliquities <10 degrees. We also find that wind erosion in the GCM is associated with two factors: cap edge winds, and strong cross-equator solstice flows. Both of these processes are influenced by topography, producing an asymmetry in the erosion pattern between the north and the south. Our 1-D erosion model, excluding solstice winds, produces erosion rates of 5 × 10−6 m yr−1 in the north and 6 × 10 −7 m yr−1 in the south, which increase by an order of magnitude in an early 40 mbar atmosphere. The stability of these erosion patterns over geological time indicates that the lowland regions of Mars are continuously eroded, and that wind is capable of eroding substantial sediment deposits that may have otherwise been preserved. Our results suggest that low-lying areas most likely to collect astrobiologically interesting sediments may be the least likely places to preserve them, and our search strategies should be adjusted accordingly. |
