Figure 4 Econ Geol 96
Figure 4 pH-pE(Eh) diagram for Mn species in seawater (1 atm, 25 °C, 35 ppt. salinity, total dissolved sulfur species: 28 mM (activity coefficient, 0.12; Garrels and Christ, 1965, p.l03). (after Quinby-Hunt and Wilde, 1994). The area of interest is within the stability field of water-- below the oxidation of H2O to O2, and above reduction of H2O to H2.
Shaded areas show mineral phase stable at designated concentrations of dissolved Mn.
Lightly shaded areas indicate region in which mineral dissolves until concentrations observed under some anoxic conditions are reached.
Reduction of SO42- to H2S and HS- (concentration independent) is shown by the long dashes; reduction of NO3 to N2 is indicated by the line of short dashes (concentration independent ).
Solubility of Mn species is calculated at approximate oxic (10- 3 M; Martin and Knauer, 1984) and anoxic (10-5M; Jacobs and Emerson, 1982; Jacobs et al., 1987) concentrations. Rhodochrosite "fence": Modern Ocean: Total dissolved carbonate species, 2.2 mM (Skirrow,1975) with an activity coefficient of 0.47 (Garrels and Christ, 1965, p.93). Late Cambrian: Total dissolved carbonate species, concentration 18 X present (Berner, 1990).


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