Early Mars volcanic sulfur storage in the cryosphere and formation of transient SO2-rich atmospheres during the Hesperian

TL;DR

This study explores how volcanic sulfur was stored in Mars's cryosphere as CO2-SO2 clathrates during the Noachian and Hesperian periods, leading to transient SO2-rich atmospheres that influenced sulfate deposit formation.

Contribution

It clarifies previous models by discussing sulfur particle effects, formation processes of CO2-SO2 clathrates, and the potential for episodic SO2 releases to warm early Mars.

Findings

Massive sulfur storage in cryosphere during Noachian.

Large SO2 releases during Hesperian could have warmed Mars.

Formation of CO2-SO2 clathrates involved gradual enrichment processes.

Abstract

In a previous paper (Chassefi\`ere et al., Icarus 223, 878-891, 2013), we have shown that most volcanic sulfur released to early Mars atmosphere could have been trapped in the cryosphere under the form of CO2-SO2 clathrates. Huge amounts of sulfur, up to the equivalent of a ~1 bar atmosphere of SO2, would have been stored in the Noachian cryosphere, then massively released to the atmosphere during Hesperian due to rapidly decreasing CO2 pressure. It would have resulted in the formation of the large sulfate deposits observed mainly in Hesperian terrains, whereas no or little sulfates are found at the Noachian. In the present paper, we first clarify some aspects of our previous work. We discuss the possibility of a smaller cooling effect of sulfur particles, or even of a net warming effect. We point out the fact that CO2-SO2 clathrates formed through a progressive enrichment of a preexisting reservoir of CO2 clathrates and discuss processes potentially involved in the slow formation of a SO2-rich upper cryosphere. We show that episodes of sudden destabilization at the Hesperian may generate 1000 ppmv of SO2 in the atmosphere and contribute to maintaining the surface temperature above the water freezing point.