Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13c..03h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13C-03
Physics
[1039] Geochemistry / Alteration And Weathering Processes, [1060] Geochemistry / Planetary Geochemistry, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Sulfur dioxide (SO2) is abundant in terrestrial volcanic emissions and was likely at least as abundant in early martian emissions. Recent photochemical studies indicate that during episodes of vigorous volcanic activity, the atmospheric lifetime of SO2 may have been sufficiently long for it to have helped maintain liquid water on the surface of Mars and perhaps to have regulated the climate through a negative feedback between the atmospheric abundance of SO2 and the rate of chemical weathering of silicate minerals. Here we show experimentally, that atmospheric SO2 concentrations three orders of magnitude lower than those required for it to have been of climatic importance would have had a major impact on the aqueous chemistry at the planet's surface and the precipitated mineral assemblage. Specifically, at near-neutral and even mildly alkaline pH, part-per-billion (ppb) concentrations of SO2 prevent the formation of calcium carbonate in favour of hannebachite - a hydrated calcium sulfite. Based on the results of recent photochemical studies, a volcanic outgassing flux ~300 times smaller than the modern terrestrial flux would have been enough to maintain such atmospheric concentrations. This implies that almost any period of active volcanism would have given rise to conditions under which carbonate precipitation is prevented at near-neutral pH. In the presence of ferrous iron, green rust, a possible precursor to phyllosilicate minerals, co-precipitates with hannebachite. This provides a possible explanation for the presence of phyllosilicates on early Noachian surfaces in the apparent absence of outcrop-scale carbonates. Finally, oxidation of the mineral assemblage precipitated in the experiments produces sulfates, iron oxides and acidity, consistent with observed mineral assemblages and with evidence for acid-sulfate dominated environments on late Noachian-early Hesperian surfaces.
Halevy Itay
Schrag Daniel P.
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