Hi All

The main argument against ancient Martian oceans is the lack of carbonates - but what if the primordial ocean couldn't make carbonates because it was too acidic???

Here's an MSNBC news story on the latest theory...

Acid Ocean

...ok so a pH of 6.2 is not super-acidic but it's nasty enough for most life-froms, yet there are many that live quite happily in such conditions if not worse. One important point in the Nature study the article is based on is the need for other greenhouse gases such as methane. Something had to release or make methane to keep the oceans from freezing over.

Nature 431, 423 - 426 (23 September 2004); doi:10.1038/nature02911

Inhibition of carbonate synthesis in acidic oceans on early Mars

ALBERTO G. FAIRÉN1, DAVID FERNÁNDEZ-REMOLAR2, JAMES M. DOHM3, VICTOR R. BAKER3,4 & RICARDO AMILS1,2

Correspondence and requests for materials should be addressed to A.G.F. (agfairen@cbm.uam.es).

Several lines of evidence have recently reinforced the hypothesis that an ocean existed on early Mars. Carbonates are accordingly expected to have formed from oceanic sedimentation of carbon dioxide from the ancient martian atmosphere. But spectral imaging of the martian surface has revealed the presence of only a small amount of carbonate, widely distributed in the martian dust. Here we examine the feasibility of carbonate synthesis in ancient martian oceans using aqueous equilibrium calculations. We show that partial pressures of atmospheric carbon dioxide in the range 0.8–4 bar, in the presence of up to 13.5 mM sulphate and 0.8 mM iron in sea water, result in an acidic oceanic environment with a pH of less than 6.2. This precludes the formation of siderite, usually expected to be the first major carbonate mineral to precipitate. We conclude that extensive interaction between an atmosphere dominated by carbon dioxide and a lasting sulphate- and iron-enriched acidic ocean on early Mars is a plausible explanation for the observed absence of carbonates.
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© 2004 Nature Publishing Group
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There's a new geophysical theory in which methane can be made deep down in the interface between the crust and mantle, so perhaps the enhanced vulcanism of early Mars is the source, but the current methane/water link in the ESA orbiter data might indicate the other methane machine - Life!