Distribution of Subsurface Carbon Dioxide Ice at Different Obliquities

We present initial results from the UK version of the LMD Mars Global Circulation Model using a newly developed subsurface model showing the distribution of subsurface carbon dioxide (CO2) at four different obliquities (15°, 25°, 35° and 45°). These results use an initial condition of subsurface CO2 ice at latitudes >50° N/S and are an initial study that will inform future investigations because the amount and distribution of subsurface CO2 ice in the present day is unknown. Studies of subsurface ice on Mars focused mostly on the distribution of water ice, because subsurface CO2 ice is unstable outside of the polar regions. However, subsurface CO2 ice is more likely to be stable at the higher pressures expected for Early Mars [e.g. 1]. Studies [e.g. 2, 3] have also shown that water ice becomes more widespread across the surface at high obliquities due to sublimation of the polar caps and the equatorward transport of water [e.g. 3, 4]. However, since it has been assumed that CO2 ice can only occur within the polar regions, any changes in subsurface CO2 ice distribution with obliquity are unknown. We have included CO2 ice physics in the subsurface to account for potential subsurface CO2 ice outside of the polar regions. [1] Kahn R. (1985) Icarus, 62, 175-190 [2] Mellon M.T., Jakosky B.M. (1995) JGR:Planets, 100, 6, 2156-2202 [3] Head J.W. et al. (2003) Nature, 426, 6968, 797-802 [4] Pollack J.B., Toon O.B. (1982), Icarus, 50, 2, 259-287