Ocean Compositions

Observation, 2,15 Ocean, composition of, 440 Ocean water, composition, 439 n-Octadecane, properties, 341 Octahedral complex, 393 Octane, 46, 338 properties, 341 Octanamide, 339 Octanoic acid, 339 1-Octanol, 338 Octaves, Law of, 104 Octyl alcohol, 338 1-Octylamine, 338... 

The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

Table 5.2. Comparison of snowball Earth and hothouse Earth equilibrium oceanic compositions at 1 bar of pressure (assuming the ocean is saturated with dolomite)...

Figure 10.49. Model calculation simulating changes in ocean composition as primary igneous rock minerals react with a solution containing the proportions of "excess volatiles" shown in Table 10.4. Concentrations of dissolved species are shown relative to 1 kilogram of water, and the extent of reaction is measured by the amount of igneous-rock minerals destroyed. Changes in slopes on diagram are due to formation of sedimentary minerals. (After Lafon and Mackenzie, 1974.)...

Obviously the composition of natural waters is markedly influenced by the growth, distribution, and decay of phytoplankton and other organisms. The dominant role of organisms in regulating the oceanic composition and its variation with depth of some of the important sea salt components (i.e., C, N, P, and Si) will be illustrated here by introducing certain aspects of Broecker s kinetic model for the chemical composition of seawater (Broecker and Peng, 1982). We summarize Broecker s line of arguments. 

Grotzinger, j. P. Kasting, J. F. 1993. New constraints on Precambrian ocean composition. Journal of Geology, 101, 235-243. 

The trapping of pore fluids as sediments are buried may potentially preserve fluid from a time when ocean composition differed from the present, such as the last glacial period when salinity should have been greater than at present and the isotopic composition of water should have been heavier. However, pore water is an open system, and diffusion facilitates the re-equilibration between fossil pore water and bottom waters. Consequently, relict signals may be difficult to detect, even in the absence of any influence of diagenetic reactions. 

The statistical collection and representation of the weather conditions for a specified area during a specified time interval, usually decades, together with a description of the state of the external system or boundary conditions. The properties that characterize the climate are thermal (temperatures of the surface air, water, land, and ice), kinetic (wind and ocean currents, together with associated vertical motions and the motions of air masses, aqueous humidity, cloudiness and cloud water content, groundwater, lake lands, and water content of snow on land and sea ice), nd static (pressure and density of the atmosphere and ocean, composition of the dry ir, salinity of the oceans, and the geometric boundaries and physical constants of the system). These properties are interconnected by the various physical processes such as precipitation, evaporation, infrared radiation, convection, advection, and turbulence, climate change... 

Defining a representative composition for the ocean end-member in the models is particularly challenging because nearly every aspect of the physical and chemical state of the coupled ocean/atmosphere system on the early Earth (temperature, pH, elemental composition, salinity, oxidation state, etc.) is poorly understood at present and continues to generate vigoroits debate. We adopt an ocean composition that appears consistent with the cirrrently available corrstraints. The composition of the model late Hadean seawater nsed in this cormnitrrication is given in Table 1. 

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