Weathering flux

Tipper ET, Bickle MJ, Galy A, West AJ, PomiFs C, Chapman HJ (2006) The short term climatic sensitivity of carbonate and silicate weathering fluxes insight from seasonal variations in river chemistry. Geochim Cosmochim Acta 70(ll) 2737-2754... 

Usually, for pristine watersheds, biologic and exchange reactions are assumed to be at steady state and the weathering flux is the difference between the watershed output and the precipitation input. In perturbed watersheds, the calculations become more complex due to agricultural inputs or changes in the exchangeable ions due to watershed acidification. 

The alternative approach is to report silicate weathering fluxes on a mineral specific basis. As previously discussed, this requires distributing elemental fluxes among mineral phases using mass balance approaches described in this chapter and elsewhere in this volume (see Chapter 5.04). 

White A. F., Schulz M. J., Davison V., Blum A. E., Stonestrom D. A., and Harden J. W. (2003) Chemical weathering rates of a soil chronosequence on granitic alluvium III. The effects of hydrology, biology, climate on pore water compositions and weathering fluxes. Geochim. Cosmochim. Acta (in press). 

Table 1 Ratio of weathering fluxes from vegetated areas versus unvegetated areas (numbers in parentheses in...

Jacobson A. D., Blum J. D., and Walter L. M. (2002) Reconciling the elemental and Sr isotope composition of Himalayan weathering fluxes insights from the carbonate geochemistry of stream waters. Geochim. Cosmochim. Acta 66, 3417-3429. 

Bestland E. A. (2000) Weathering flux and CO2 consumption determined from paleosol sequences across the Eocene-Oligocene transition. Palaeogeogr. Palaeoclimat. Palaeoe-col. 156, 301-326. 

Lear C. H., Elderfield H., and Wilson P. A. (2003) A Cenozoic seawater Sr/Ca record from benthic foraminiferal calcite and its appheation in determining global weathering fluxes. Earth Planet. Sci. Lett. 208, 69—84. 

This system of equations has four unknowns two burial fluxes and two weathering fluxes. 

If weathering fluxes from eroding sedimentary rocks are independently established, such as through use of mass-dependent weathering fluxes, then all of the weathering fluxes in our system of equations above become effectively known. This leaves only the burial fluxes as unknowns in solving the evolution of the C-S-O system. 

To extrapolate the sea-floor weathering flux Thydro into the past requires a model of the water-rock reaction. There are two important possibilities, depending on whether the reactable cations are more or less abundant than CO2. In equation (11) we implicitly assume that CO2 is quantitatively removed from the sea water. In effect we presume fast reactions with superabundant cations. Walker (1985) and Fran9ois Walker (1992) assumed that CO2 is removed in linear proportion to its concentration. This differs from our picture only in the value of -4hydro in either model it is the delivery of CO2-rich waters to the oceanic crust by hydrothermal circulation that limits uptake, so that CO2 is quantitatively depleted in the circulating sea water until available CaO, MgO and FeO in the rock are exhausted. 

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