Oceans, compositional changes

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."... 

One major concept applicable to problems dealing with the behavior of carbonic acid and carbonate minerals in seawater is the idea of a "constant ionic media". This concept is based on the general observation that the salt in seawater is close to constant in composition, i.e., the ratios of the major ions are the same from place to place in the ocean. Seawater in evaporative lagoons, pores of marine sediments, and near river mouths can be exceptions to this constancy. Consequently, the major ion composition of seawater can generally be determined from salinity. It has been possible, therefore, to develop equations in which the influences of seawater compositional changes on carbonate equilibria can be... 

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.)...

Material supplied to the ocean originates from tlie atmosphere, rivers, glaciers and hydrothermal waters. The relative importance of these pathways depends upon the component considered and geographic location. River runolf commonly constitutes the most important source. Transported material may be either dissolved or particulate, but discharges are into surface waters and confined to coastal regions. Hydrothermal waters are released from vents on the seafioor. Such hydrothermal waters are formed when seawater circulates into the fissured rock matrix, and under conditions of elevated temperature and pressure, compositional changes in the aqueous phase occur due to seawater - rock interactions. This is an important source of some elements, such as Li, Rb and Mn. The atmosphere supplies particulate material globally to the surface of the ocean. In recent years, this has been the most prominent pathway to the World... 

The 8 Cxco2 varied considerably in geologic history. Generally, three explanations are given for changes of 8 Cxco2 distribution in the ocean (1) changes in the surface-ocean productivity which cause variable fractionation between surface and deep water carbon isotopic composition, (2)... 

Figure 5 Marine Os/ Os record for the past 80 My in all oceans from H202-leached metalliferous and hydrogenetic sediments. Note that the pronounced excursion to low ratios at the K/T boundary (65 My) is explained by a meteorite impact. (Reprinted from Geochi mica et Cosmochimica Acta, 63, Pegram WJ, Turekian KK. The osmium isotopic composition change of Cenozoic sea water as inferred from a deep-sea core corrected for meteoritic contributions, 4053-4088, Copyright (1999), with permission from Elsevier Science.)...

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... 

The mantle composition changes with time as oxidized oceanic crust and organic carbon in sediments subduct into the mantle. Conversely, volcanic rocks erupt from the mantle and gases vent from these rocks. 

It is now widely accepted that the compositions of the atmosphere and world ocean are dynamically controlled. The atmosphere and the ocean are nearly homogeneous with respect to most major chemical constituents. Each can be viewed as a reservoir for which processes add material, remove material, and alter the compositions of substances internally. The history of the relative rates of these processes determines the concentrations of substances within a reservoir and the rate at which concentrations change. Commonly, only a few processes predominate in determining the flux of a substance between reservoirs. In turn, particular features of a predominant process are often critical in controlling the flux of a phase through that process. These are rate-controlling steps. 

Thick sedimentary pile from middle Miocene to late Pliocene is exposed in the Oga Peninsula, northern Honshu, Japan (Fig. 1.153). Age of the sedimentary rocks has been determined by microfossil data. Thus, the sedimentary rocks in the Oga Peninsula where type localities of Miocene sedimentary rocks in northern Japan are well exposed have been studied to elucidate the paleoenvironmental change of the Japan Sea (Watanabe et al., 1994a,b). Kimura (1998) obtained geochemical features of these rocks (isotopic and chemical compositions) and found that regional tectonics (uplift of Himalayan and Tibetan region) affect paleo-oceanic environment (oxidation-reduction condition, biogenic productivity). However, in their studies, no detailed discussions on the causes for the intensity and periodicity of hydrothermal activity, and temporal relationship between hydrothermal activity, volcanism and tectonics in the Japan Sea area were discussed. They considered only the time range from ca. 14 Ma to ca. 5 Ma. 

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