Marine chemistry Ocean composition

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."... 

Impact of North American Emissions on Wet Deposition to the Western Atlantic Ocean. Wet deposition has been collected by event during WATOX at two sites on Bermuda, one site near Lewes, Delaware, and on board ships. These wet-deposition samples have been analyzed for acidic species, metals, and organic compounds. This section discusses our interpretation of the marine precipitation-chemistry data and the results of our analyses as well as the influence of North American emissions on precipitation composition. 

The marine strontium isotope record is the proxy record most commonly used to constrain the geologic history of chemical weathering. However, in recent years it has been widely criticized as a proxy indicator of past silicate weathering rates. The osmium isotope record is analogous to the strontium record in many respects, and can help to constrain interpretations of the marine strontium isotope record. In this section the geochemical factors that influence the osmium and strontium isotope compositions of seawater are reviewed, and the structure of these two records of Cenozoic ocean chemistry is discussed. 

The chemistry of the carbonic acid system in seawater has been one of the more intensely studied areas of carbonate geochemistry. This is because a very precise and detailed knowledge of this system is necessary to understand carbon dioxide cycling and the deposition of carbonate sediments in the marine environment. A major concept applicable to problems dealing with the behavior of carbonic acid and carbonate minerals in seawater is the idea of a constant ionic medium. This concept is based on the observation that the salt in seawater has almost constant composition, i.e., the ratios of the major ions are the same from place to place in the ocean (Marcet s principle). Possible exceptions can include seawater in evaporative lagoons, pores of marine sediments, and near river mouths. Consequently, the major ion composition of seawater can generally be determined from its salinity. It has been possible, therefore, to develop equations in which the influence of seawater composition on carbonate equilibria is described simply in terms of salinity. 

Wright et al. (1984) determined REE composition of hundreds of individual conodonts and ichthyoliths, and found consistent REE shapes in pre-Carboniferous conodonts, with enrichment of MREE, lesser enrichment of TREE, and no cerium anomaly. This pattern is fundamentally different to the REE pattern found in modem ocean bottom waters, and led Wright et al. (1984) to suggest that the REE chemistry and particularly Ce anomaly in ancient marine apatites could be used to infer widespread anoxia in pre-Carboniferous ocean basins. 

Sources contributing to the composition of inorganic aerosols near the ocearir-atmosphere interface are the oceans themselves, continental dust, volcanic ash, atmospheric production of particulates, and, to lesser extents, human activity and extraterrestrial inputs. Characteristic elements and elemental ratios can be used to determine some of these sources and detect ion fractionation at the sea-air interface. Rain water chemistry is not always simply related to that of the marine aerosol. 

There is only one paper with data on the pore water composition of deep ocean sediments deposited under oxygenated water (Ridout and Pagett 1984). This paper mostly deals with extraction methods and provides poorly documented lanthanide data for a single sample. It is fair to state the lanthanide composition and chemistry of oxic marine sediments is unknown. 

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