Weathering model for the quantification of atmospheric oxygen evolution during the Paleoproterozoic

Estimates of atmospheric CO2 in the Neoarchean–Paleoproterozoic from paleosols

“…The lower constraints reveal that all the paleosols should have been weathered at >0°C local temperature, which is consistent with significant weathering indicated by depletion of cations from the profiles (e.g., Murakami et al, 2011a;Yokota et al, 2013). On the other hand, the Mt.…”

“…The Si depth profiles of the above five paleosols do not show strong depletion of Si in the weathering profiles (Murakami et al, 2011a) and are not substantially different from those in modern weathering, either (e.g., White et al, 2001). Consequently, none of the five paleosols appears to have formed during very hot periods which generate intense weathering, for instance, just after glaciation; instead, they formed under rather moderate conditions (Yokota et al, 2013). Therefore, we can assume the upper constraint of local temperature as 30°C (Holland, 1978) for the five paleosols.…”

“…Roe (1), Mt. Roe (2), Bird, Cooper Lake and Pronto/NAN paleosols) and less so (<$10 À5 mol L À1 ) at <$2.2 Ga (i.e., for the Gaborone, Drakenstein and Flin Flon paleosols), resulting from slower and faster rates of Fe 2+ oxidation, respectively, which is greatly affected by P O 2 levels (Murakami et al, 2011a;Yokota et al, 2013).…”

“…Using this method, Sheldon's group estimated 7-70 PAL of P CO 2 at 2.2 Ga (Sheldon, 2006) and 10-50 PAL at 2.69 Ga (Driese et al, 2011). Importantly, P CO 2 levels have also been used either directly or indirectly as a parameter for the estimation of P O 2 levels from paleosols (Holland, 1984;Murakami et al, 2011a;Yokota et al, 2013). Therefore, the estimated P CO 2 levels need to be sufficiently precise to understand the atmospheric oxygen evolution in the Neoarchean-Paleoproterozoic.…”

Estimates of atmospheric O2 in the Paleoproterozoic from paleosols

“…Murakami et al (2011) have introduced Fe(II) oxidation kinetics for quantitative estimation of P O 2 levels, applying it to the Fe(II) and Fe(III) distributions recorded in paleosols in the Paleoproterozoic, and have suggested that atmospheric oxygen increased gradually during the GOE. Recently, Yokota et al (2013) have developed a model by which Fe redistributions during weathering can be predicted as a function of P O 2 . Yokota et al (2013) have applied their model to the Fe records in paleosols in the Paleoproterozoic and demonstrated that the estimation of P O 2 can be made without constraints from the other geological records.…”