The Crustal-Ocean-Atmosphere Factory

THE CRUSTAL-OCEAN-ATMOSPHERE FACTORY AND GLOBAL BIOGEOCHEMICAL CYCLES... 

The crustal-ocean-atmosphere factory. Source-. Stumm, W. and J. J. Morgan QQ6) Aquatic Chemistry, 3rd ed. Wiley-Interscience, p. 874. 

Time- and space-scaies of processes in the crustal-ocean-atmosphere factory. Source-. From Bard, A., et al. (1988). Applied Geochemistry 3, 5. 

Geologists have deemed it necessary to recognize this new epoch because sediments now accumulating on the seafloor are chemically distinct from those whose origins predate human impacts on the crustal-ocean-atmosphere factory. 

General box model summarizing the transport pathways and reservoirs for trace elements in the crustal-ocean-atmosphere factory. 

The chemical composition of seawater is largely regulated by biogeochemical processes that cause dissolved materials to be converted into solid forms. These solids are then deposited on the seafloor, making the sediments a very important reservoir in the crustal-ocean-atmosphere factory. Marine sediments are also important because they contain our only record of past conditions in the ocean. 

Because diatoms play such a large role in the biogeochemistry of silicon, changes in their productivity are thought to have the potential to affect other aspects of the crustal-ocean-atmosphere factory. To consider this future, we first look at the marine silica budget. 

A box model fiar the marine silica cycle is presented in Figure 6.11 with respect to the processes that control DSi and BSi. An oceanic budget is provided in Table 16.3 in which site-specific contributions to oceanic outputs are given. This table illustrates that considerable uncertainty still exists in estimating the burial rate of BSi. Regardless, burial of BSi is responsible for most of the removal of the oceanic inputs of DSi, with the latter being predominantly delivered via river runoff. This demonstrates the importance of the biological silica pump in the crustal-ocean-atmosphere factory. 

Feedbacks in the Crustal-Ocean-Atmosphere Factory for Silica ... 

The chemical reactions that occur in hydrothermal systems are largely the result of interactions between seawater and relatively yoimg ocean crust. During these reactions, some elements are solubilized and released to seawater as ions or gases. Others are precipitated, forming minerals that end up as a component of new oceanic crust or the metalliferous sediments. For some elements, the resulting elemental fluxes rival those associated with river input, making hydrothermal activity a very important process in the crustal-ocean-atmosphere factory. 

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. 

The crust is the largest carbon reservoir in the crustal-ocean-atmosphere factory (8 x 10 Pg C including the sediments). Most of this carbon is in the form of inorganic minerals, predominantly limestone, with the rest being organic matter, predominantly contained in shale and secondarily in fossil fuel deposits (coal, oil, and natural gas). The oceanic reservoir (4 X lO" Pg C) and the terrestrial reservoir (2 to 3 x 10 Pg C) are both far smaller than the crustal reservoir. The smallest reservoir is found in the atmospheric, primarily as CO2 (preindustrial 6 x 10 Pg C, now 8 x 10 Pg C and rising). The flux estimates in Figure 25.1 have been constrained by an assumption that the preindustrial atmospheric and oceanic reservoirs were in steady state over intermediate time scales (millennia). 

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