Chemical weathering atmosphere

Kump LR, Brantley SL, Arthur MA (2000) Chemical weathering, atmospheric COj and climate. Atm Rev Earth Planet Sci 28 611-667... 

Another major process at the Earth s surface not involving rapid exchange is the chemical weathering of rocks and dissolution of exposed minerals. In some instances the key weathering reactant is H30 in rainwater (often associated with the atmospheric sulfur cycle), while in other cases H30" comes from high concentrations of CO2, e.g., in vegetated soils. 

The influence that variations of temperature and levels of atmospheric CO2 and O2 have on chemical weathering are more subtle. Temperature appears to have a direct effect on weathering rate (White and Blum, 1995). The silica concentration of rivers (Meybeck, 1979, 1987) and the alkalinity of ground waters in carbonate terrains (Harmon et al., 1975) are both positively correlated with temperature variations. It is not clear, however, whether temperature-related variations in weathering rates are largely due to variations in vegetational activity that parallel temperature variations. 

Ice ages ended quickly. Processes that promote the increase of carbon dioxide in the atmosphere are positive feedbacks in ending an ice age. Is subglacial chemical weathering a positive or a negative feedback What circumstances would allow one to give the opposite answer (Hint ... 

Drever, J. I. and Hurcomb, D. R. (1986). Neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the North Cascade Mountains. Geology 14,221-224. 

Chemical weathering of crustal material can both add and withdraw carbon from the atmosphere. This has been discussed in Chapter 8. The oxidation of reduced carbon releases CO2 to the atmosphere,... 

Natural mobilization includes chemical, mechanical, and biological weathering and volcanic activity. In chemical weathering, the elements are altered to forms that are more easily transported. For example, when basic rocks are neutralized by acidic fluids (such as rainwater acidified by absorption of CO2), the minerals contained in the rocks can dissolve, releasing metals to aqueous solution. Several examples are listed below of chemical reactions that involve atmospheric gases and that lead to the mobilization of metals ... 

See also Hydrologic cycle chemical weathering in, 26 4-7 coupling of atmosphere, land, and water in, 26 7-12... 

Clay minerals are important to the crustal-ocean-atmosphere fectory, not just for their abundance, but because they participate in several biogeochemical processes. For example, the chemical weathering reactions responsible for their formation are accompanied by the uptake and release of cations and, thus, have a large impact on the chemical composition of river and seawater. This includes acid/base buffering reactions, making clay minerals responsible for the long-term control of the pH of seawater and, hence, of importance in regulating atmospheric CO2 levels. 

On the early Earth, ions were mobilized from volcanic rocks by chemical weathering. Rivers and hydrothermal emissions transported these chemicals into the ocean, making seawater salty. These salts are now recycled within the crustal-ocean-atmosphere fectory via incorporation into sediments followed by deep burial, metamorphosis into sedimentary rock, uplift, and weathering. The last process remobilizes the salts, enabling their redelivery to the ocean via river runoff and aeolian transport. In the case of sodium and chlorine, evaporites are the single most important sedimentary sink. This sedimentary rock is also a significant sink for magnesium, sulfate, potassium, and calcium. 

One of the most notable features of seawater is its high degree of saltiness. In previous chapters, we have discussed various sources of this salt, these being rivers, volcanic gases, and hydrothermal fluids. These elements have ended up in one of four places (1) as dissolved ions in seawater, (2) as sedimentary minerals, (3) as hydrothermal minerals, and (4) as volatiles that reside in the atmosphere. The minerals are recycled via geologic uplift and subduction. Upon return to Earth s surface, these minerals are chemically weathered via acid attack by the atmospheric volatiles remobilizing the salts for return to the ocean in river runoff. 

The sedimentary and metamorphic rocks uplifted onto land have become part of continents or oceanic islands. These rocks are now subject to chemical weathering. The dissolved and particulate weathering products are transported back to the ocean by river runoff. Once in the ocean, the weathering products are available for removal back into a marine sedimentary reservoir. At present, most mass flows on this planet involve transport of the secondary (recycled) materials rather than the chemical reworking of the primary (juvenile) minerals and gases. The natirre of these transport and sediment formation processes has been covered in Chapters 14 through 19 from the perspective of the secondary minerals formed. We now reconsider these processes from the perspective of impacts on elemental segregation between the reservoirs of the crustal-ocean-atmosphere factory and the mantle. 

Inorganic constituents are present in major, minor, and trace concentrations in aquatic environments as a result of weathering, atmospheric, and biogeochemical processes, and also as a consequence of industrial pollution. Inorganic constituents in aquatic ecosystems are a group of chemical species that are characterized by... 

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