Potential significance of sulfide mineral oxidation for the Cenozoic carbon cycle
Potential significance of sulfide mineral oxidation for the Cenozoic carbon cycle (in Goldschmidt abstracts 2013, Anonymous)
Mineralogical Magazine (2013) 77 (5): 2347
A climatic control on the rate of CO (sub 2) consumption by silicate weathering is thought to stabilize Earth's climate over geologic timescales. At the same time, the observation that tectonic uplift accelerates weathering rates suggests that mountain building can profoundly affect the carbon cycle and global climate. Extensive uplift of mountain ranges during the Cenozoic is thought to have increased silicate weathering rates as evidenced by the marine isotopic records of Sr, Os, and Li, which all show dramatic changes from approximately 40 Ma to present. Without a corresponding input of CO (sub 2) , increased silicate weathering fluxes would deplete the atmosphere of all CO (sub 2) within a few million years, a clearly unreasonable scenario. While a variety of hypotheses have been put forward in order to balance the Cenozoic C cycle, none of them appear to adequately describe the observations. As such, reconciling this "Cenozoic carbon-weathering paradox" has been a major and as yet unresolved challenge in geochemistry and Earth history. We hypothesize that Cenozoic uplift, in addition to increasing rates of CO (sub 2) drawdown by silicate weathering, increased rates of sulfide oxidation coupled to carbonate dissolution. This provided a transient source of CO (sub 2) that contributed, at least in part, to the relative stability of Cenozoic atmospheric pCO (sub 2) . The feasibility of this hypothesis is tested in two ways: (1) a simplified mass balance model that constrains the duration of transient CO (sub 2) release in response to increased rates of sulfide oxidation and (2) an inverse isotope mass balance model that uses the Cenozoic isotope records of Sr and Os to reconstruct changes in silicate weathering and sulfide oxidation rates. Together, these models show that the contrasting residence times of DIC and SO (sub 4) (super 2-) is sufficient to allow for CO (sub 2) release over 40 Myr timescales and that modeled rates of silicate weathering and sulfide oxidation are consistent with independent proxy records of paleo-pCO (sub 2) .