36th DPS Meeting, 8-12 November 2004
Session 41 Mars Atmosphere II
Oral, Friday, November 12, 2004, 8:30-10:00am, Lewis

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[41.05] The Effect of Ground Ice on the CO2 Cycle on Mars

R.M. Haberle, F. Montmessin, A. Colaprete (NASA Ames), F. Forget (Laboratoire de Meteorologie Dynamique), J. Schaeffer (QSSS Raytheon)

The Ames general circulation model has been tuned to match the surface pressure observations of the two Viking landers. The tuning involves varying the CO2 polar cap properties (albedos and emissivities) and the total amount of CO2 in the cap-atmosphere system. For reasonable dust loadings, the best-fit values of these parameters are: ~710 Pa in the cap-atmosphere system; a cap albedo of 0.70 in the north and 0.50 in the south; and an emissivity of 0.62 in the south and 0.38 in the north. The best-fit emissivities are very low and suggest that the model is missing a heat source. The most plausible missing heat sources could be the result of enhanced ground conduction due to soil richer in ice than assumed; enhanced downward infrared emission by the polar hood clouds which is not yet included in the model; and stronger poleward heat transport than the model is predicting. Here we explore the consequences of an ice rich soil on the CO2 cycle. The Odyssey observations of ground ice near the surface in both Polar Regions make this a real possibility. Water ice has a high thermal conductivity and when near the surface it will conduct more of the absorbed radiation at the surface deeper into the soil than in the case for pure soil. Consequently, heat conducted down during summer will slowly bleed back out during winter reducing the amount of CO2 that condenses. We have modified the soil model in the GCM to allow for depth dependent variations in soil properties to explore this effect. We find that for plausible ice table depths, the best-fit CO2 cap emissivites can be significantly larger than in our pure soil simulations. Thus, ground ice can have a significant effect on the CO2 cycle.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.