Modelling the effect of volcanic outgassing of sulphur on early Martian surface temperatures using a 3-D Global Climate Model

Around the time of the transition from the Late Noachian to the Early Hesperianeras (~3.6 Gya), Mars was predicted to have been both volcanically active, andhave sustained a climate warm enough to melt liquid water on its surface episodicallydespite a faint young sun. The effect of volcanic outgassing on the climateof early Mars and its ability to raise temperatures above the melting point of waterhas, however, been disputed, with a major uncertainty being the timescalesover which the greenhouse effect of outgassed sulphur dioxide (SO2) and hydrogensulphide (H2S) can warm the atmosphere of Mars before they react to formH2SO4 and S8 aerosols which act to cool the surface of Mars. We have developedthe first 3-D model of the Martian sulphur cycle from source to sink that includesoutgassing of SO2, H2S and S2 from the surface, the formation of H2SO4 and S8through atmospheric chemistry, and the condensation and deposition of H2SO4and S8 to the surface. We confirm the results of Tian et al. (2010, EPSL 295,412-418) and find that the warming effect of volcanically outgassed SO2 and H2Son the Martian atmosphere is negligibly short, instead resulting in a net coolingof the Martian surface over timescales of 3-4 years near the equator and severaldecades at the poles. Conversely, sufficient outgassing of SO2 can instead result inatmospheric collapse, which may have ended any prior warm period for hundredsof thousands of years.