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The long term carbon cycle on Mars

Eric Chassefière 1 François Leblanc 2
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : It has been recently shown that several valley networks, like Naktong Vallis [1], have been formed during the Hesperian, 3.6-3.7 Gyr ago. According to the same authors, liquid water could have flowed at the surface of Mars until the early Amazonian, 3.1-3.2 Gyr ago. To explain such a residual hydrological activity, a minimum CO 2 pressure of 0.6 bar seems to be required. At this pressure level, the scattering of infrared radiation by CO 2 clouds could have maintained a global temperature above 0°C [2]. It is generally assumed that a CO 2 pressure of at least 1-2 bar is required to maintain water liquid at the surface of Mars during the formation of valley networks. If 1-2 bar of CO 2 have been present in the Martian atmosphere until the early Amazonian, 3 Gyr ago, where did this CO 2 go? It may not have escaped mainly because during this period non-thermal escape processes were no more efficient [3]. To explain the persistence of a dense CO 2 atmosphere during the whole Noachian, when water was liquid at the surface of Mars and should have formed massive carbonate layers, it has been suggested that carbonates were recycled to the atmosphere due to thermal decomposition of carbonate rocks induced directly and indirectly (through burial) by intense, global scale volcanism [4]. The quantity of CO 2 released by volcanism since the middle-Noachian has been estimated to correspond to a CO 2 global pressure of 400 mbar [5], which one third (150 mbar) would have been emitted during the Amazonian. Whatever is the origin of this CO 2 (crustal carbonates, mantle), it has been necessarily lost to the crust, since escape is unable to have removed more than a few mbar. The recent discovery of methane in the Martian atmosphere [6,7], with a significant estimated release rate, suggests that the carbon inventory of the atmosphere could double in a few tens million years [8]. Thus methane could be an important source of atmospheric CO 2 over time and adding to the amounts thought to have been released by surface volcanism [5]. If this methane is the result of serpentinization in crustal hydrothermal systems, the carbon in the released methane could originate from subsurface carbonates that were decomposed by hydrothermal fluids. We provide an estimate of the integrated flux of methane to the atmosphere since the late Noachian and show that it could be substantial, of the same order as the volcanic flux of carbon (a few hundred millibars). For this purpose, we assume that the hydrothermal activity has remained proportional to the extrusion rate of volcanic lava, estimated from existing geomorphological analysis of the Martian surface [5]. Because CO 2 is more than 100 times less abundant in the present atmosphere than if volcanic and hydrothermal carbon would have accumulated since the late Noachian, we suggest that atmospheric carbon is recycled to the crust through subsurface hydrological activity. In this way, the production of CO 2 through CH 4 release, and the removal of CO 2 from the atmosphere, could have a common origin and be two facets of a currently, although progressively damping with time, active hydrological system. We propose a typical scenario for the CO 2 pressure evolution since the late Noachian (Fig.1)
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  • HAL Id : hal-00610344, version 1


Eric Chassefière, François Leblanc. The long term carbon cycle on Mars. EPSC-DPS Joint Meeting 2011, Oct 2011, Nantes, France. ⟨hal-00610344⟩



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