Steady state model geochemical system

Fig. 8. Steady-state model for the earth s surface geochemical system. The kiteraction of water with rocks ki the presence of photosynthesized organic matter contkiuously produces reactive material of high surface area. This process provides nutrient supply to the biosphere and, along with biota, forms the array of small particles (sods). Weatheriag imparts solutes to the water, and erosion brings particles kito surface waters and oceans.

The simplest geochemical cycles are based around the concept of maintaining a steady state to satisfy the constraints of mass balance. More complex cycles incorporate the dynamic response of the system to perturbation (Lasaga. Berner, 1998). In this case, the resultant feedback processes are normally quantified using linear models, but, depending on which geochemical cycle is being considered, more complex, nonlinear responses may be more appropriate. 

The key point for an Earth Systems approach to the Earth is that models of geochemical cycles provide the means whereby exchange processes can be quantified. This quantification is element-specific and is a function of the timescale under consideration. It provides the basis for calculating the steady state abundances of particular substances such as oxygen or carbon dioxide in the atmosphere, or sulfate in the ocean. Since these abundances are related to fluxes which relate to biogeo-chemical and physical processes, we can gain an understanding of the controls on key variables in the Earth system. 

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