Sulfur dioxide inhibits calcium carbonate precipitation: Implications for early Mars and Earth

Abstract

[1] Recent studies have suggested a role for sulfur dioxide (SO 2 ) in maintaining relatively warm surface temperatures on early Mars. Here we show experimentally, that SO 2 concentrations orders of magnitude lower than those required for it to have been of climatic importance strongly affect the aqueous chemistry and the precipitated mineral assemblage. At near-neutral pH, part-per-billion concentrations of SO 2 prevent the formation of calcium carbonate in favor of hannebachite, a hydrated calcium sulfite. In the presence of iron, possible precursors to phyllosilicate minerals and iron carbonate co-precipitate with hannebachite. This provides an explanation for the existence of early Noachian phyllosilicates in the apparent dearth of outcrop-scale calcium carbonates. Oxidation of this precipitated assemblage produces sulfates, iron oxides and acidity, consistent with evidence for late Noachian -early Hesperian acid-sulfate dominated environments. For early Earth, the results allow placing an upper limit on atmospheric SO 2 concentrations for any period in which carbonates exist in the geologic record.

Sulfur-bearing phases detected by evolved gas analysis of the Rocknest aeolian deposit, Gale Crater, Mars

“…In the presence of iron, however, siderite (and also secondary silicates such as phyllosilicates) can be expected to precipitate together with the Ca sulfite [ Halevy and Schrag , ; Halevy et al ., ]. Later interactions with water and a more oxidizing Martian atmosphere could allow some oxidation of these sulfites to sulfates [ Halevy and Schrag , ; Halevy et al ., ; Marion et al ., ]. These studies suggest that any Ca sulfite in Rocknest materials could have precipitated together with an iron carbonate and could have been partially oxidized to form some of the Ca sulfates found in Rocknest materials by CheMin.…”

Molecular interactions of SO2 with carbonate minerals under co-sequestration conditions: A combined experimental and theoretical study

“…No crystalline Mg and S bearing phases were found. Occurrence of both sulfite and sulfate minerals in reaction products is possible under certain environmental conditions (Valimbe et al, 1995;Halevy et al, 2007;Halevy and Schrag, 2009). If oxidized, sulfite minerals will alter to sulfate, which is one way of producing the mixture of compounds identified by XRD (Halevy and Schrag, 2009).…”

“…Occurrence of both sulfite and sulfate minerals in reaction products is possible under certain environmental conditions (Valimbe et al, 1995;Halevy et al, 2007;Halevy and Schrag, 2009). If oxidized, sulfite minerals will alter to sulfate, which is one way of producing the mixture of compounds identified by XRD (Halevy and Schrag, 2009). Although we cannot rule out the possibility that sulfate minerals formed after depressurization and exposure of the samples to the atmosphere, spontaneous oxidation of hannebachite at room temperature with little or no water present seems highly unlikely.…”

Effect of Mars Atmospheric Loss on Snow Melt Potential in a 3.5 Gyr Mars Climate Evolution Model

“…Additionally, the amount of greenhouse gases released by volcanism on Mars is less than on Earth because the mantle is more reducing (Stanley et al, 2011), and by 3.5 Gya the rate of volcanic degassing had slowed down significantly (Kite et al, 2009). Because orbiters detect only minor post-Noachian carbonate, which may be due to SO 2 or acidity (Bullock & Moore, 2007;Halevy & Schrag, 2009), it is difficult to justify post-Noachian carbonate sequestration of more CO 2 than exists in the present, thin atmosphere (Edwards & Ehlmann, 2015).…”