Evolution of the Martian climate: effects of the ice sheets

Abstract

The present climate of Mars is extremely cold and dry and is characterized by an extremely thin CO₂ atmosphere. However, geological evidence suggests that the Martian climate in the past might have been warm and wet. If this were the case, the atmospheric CO₂ pressure would have been several bars higher. Our numerical study suggests that permanent CO₂ ice caps (CO₂ ice sheets) would have played an important role in the evolution of Mars from having a warm climate with a dense CO₂ atmosphere to the present cold climate. Owing to the instability of the CO₂ system, which was triggered by impact erosion and/or sputtering of the atmosphere, the dense CO₂ atmosphere should have collapsed to form large polar caps. The collapse corresponds to a runaway condensation of the atmospheric CO₂ into large CO₂ ice caps (climate jump). Our investigation of the CO₂ ice caps by using an ice sheet model suggests that the temperature at the bottom of the CO₂ ice cap would exceed the melting point of CO₂ due to the geothermal heat flux prevalent in Mars. In that case, gaseous or liquid CO₂ produced by basal melting might have permeated and diffused into the subsurface through the pores of the Martian crust. It is possible that the CO₂ removed from the surface presently exists in the Martian subsurface as clathrate, carbonate, and/or liquid and gaseous phases.