Ocean chemical composition

Mimura, T., Okabe, M., Satake, M., Nakanishi, T., Inada, A., Fujimoto, Y., Hata, F., Matsumura, Y., and Ikekawa, N., Fatty acids and sterols of the tunicate, Salpa thompsoni, from the Antarctic Ocean chemical composition and hemolytic activity, Chem. Pharm. Bull., 34, 4562, 1986. 

The environmental sampling of waters and wastewaters provides a good illustration of many of the methods used to sample solutions. The chemical composition of surface waters, such as streams, rivers, lakes, estuaries, and oceans, is influenced by flow rate and depth. Rapidly flowing shallow streams and rivers, and shallow (<5 m) lakes are usually well mixed and show little stratification with... 

Ocean sea water is roughly equivalent in strength to a 3 j % w/v solution of sodium chloride, but it has a much more complex composition, embodying a number of major constituents, and traces at least of almost all naturally occurring elements. For convenience, however, the concentration of salts in any sample of sea water is expressed in terms of the chloride content, either as chlorinity or as salinity. Both these units are again subject to arbitrary definition and do not conform simply to the chemical composition. 

Now that we have reviewed some basic aspects of the chemical composition of the ocean we can turn to a more fundamental question. What processes determine the composition of the ocean Current evidence suggests that rivers are the most important contributors of dissolved substances to the ocean. Since there is geologic evidence that the concentration and composition of the ocean has been relatively constant over the last 1.5 billion years, we must conclude that the river input must be balanced by removal. 

MacKenzie and Carrels (1966) approached this problem by constructing a model based on a river balance. They first calculated the mass of ions added to the ocean by rivers over 10 years. This time period was chosen because geologic evidence suggests that the chemical composition of seawater has remained constant over that period. They assumed that the river input is balanced only by sediment removal. The results of this balance are shown in Table 10-13. 

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."... 

McCarthy, M., Pratum, T., Hedges, J. and Bermer, R. (1997). Chemical composition of dissolved organic nitrogen in the ocean. Nature 390,150-154. 

Estuaries exhibit physical and chemical characteristics that are distinct from oceans or lakes. In estuaries, water renewal times are rapid (10 to 10 years compared to 1 to 10 years for lakes and 10 years for oceans), redox and salinity gradients are often transient, and diurnal variations in nutrient concentrations can be significant. The biological productivity of estuaries is high and this, coupled with accumulation of organic debris within estuary boundaries, often produces anoxic conditions at the sediment-water interface. Thus, in contrast to the relatively constant chemical composition of the... 

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. 

Elderfield, H. and Schultz, A. (1996) Midocean ridge hydrothermal fluxes and the chemical composition of the ocean. Anna. Rev. Earth Planet. Sci. Lett., 24, 191-224. 

Edmond, J., Measures, C., McDuff, E. et al. (1979) Ridge crest hydrothermal activity and the balances of major and minor elements in the ocean The Galapagos data. Earth Planet. Sci. Lett., 46, 1-18. Elderfield, H. and Schultz, A. (1996) Midocean ridge hydrothermal fluxes and the chemical composition of the ocean. Annu. Rev. Earth Planet Sci. Lett., 24, 191-224. 

Tab. 6.6 Examples of biological, food, agricultural and related RMs for chemical composition available from, principally, government agency suppliers (Ihnat 1988,1992,1998a International Atomic Energy Agency 1998 Institute for Reference Materials and Measurements 1999 National Oceanic and Atmospheric Administration 1995 Trahey 1998) ...

What chemical composition can we assume for the ocean Unfortunately we have no clear results. Apart from the chemical components, it would be desirable to have information on temperature and pH values. We also do not know whether there was one single primeval ocean, or whether there were several. It is also possible that there were lakes and ponds with differing compositions. We must not forget that huge changes must have taken place on the primeval Earth s surface during the space of a few hundred million years. 

The planets nearest the Sun have a high-temperature surface while those further away have a low temperature. The temperature depends on the closeness to the Sun, but it also depends on the chemical composition and zone structures of the individual planets and their sizes. In this respect Earth is a somewhat peculiar planet, we do not know whether it is unique or not in that its core has remained very hot, mainly due to gravitic compression and radioactive decay of some unstable isotopes, and loss of core heat has been restricted by a poorly conducting mainly oxide mantle. This heat still contributes very considerably to the overall temperature of the Earth s surface. The hot core, some of it solid, is composed of metals, mainly iron, while the mantle is largely of molten oxidic rocks until the thin surface of solid rocks of many different compositions, such as silicates, sulfides and carbonates, occurs. This is usually called the crust, below the oceans, and forms the continents of today. Water and the atmosphere are reached in further outward succession. We shall describe the relevant chemistry in more detail later here, we are concerned first with the temperature gradient from the interior to the surface (Figure 1.2). The Earth s surface, i.e. the crust, the sea and the atmosphere, is of... 

Pollutant Exposure and Chemical Composition of Plants Let us consider the influence of various exposure factors on the chemical composition of plant species in the arctic islands. It seems the most influential factor is the distance from the ocean shore. For example, in arctic willow growing a few meters from the tide line, the content of Zn, Cu, Pb, and Ni was higher than that of the same plant... 

The biodiversity of Mangrove ecosystems is the most profound in the islands and coastline of the Indo-West-Pacific region, where the occurrence of 44 varieties has been reported. On the Atlantic Ocean coast Mangrove ecosystems are especially widespread in the Caribbean region. The chemical composition of plant species and soils of Mangrove ecosystems have been recently discussed (Dobrovolsky, 1994). 

The Piton de la Fournaise volcano (Indian Ocean) erupts basalts with chemical compositions that change with time. The rare-earth elements have been measured on eight dated historic lavas (Table 3.9 and Figure 3.7, Albarede and Tamagnan, 1988), and chondrite-normalized (Ce/Yb)N ratios over the time interval 1948-1985 are given in Table 3.9. Calculate an annual interpolation of these results. 

For the purpose of this report, the committee focused on reference materials for chemical composition measurements used in the ocean sciences. Although a number of these materials are simple mixtures or... 

The ion proportions in most river water is significantly different from that in seawater. As a result, river runoff can have a local impact on the ion ratios of coastal waters. This effect is most pronounced in marginal seas and estuaries where mixing with the open ocean is restricted and river input is relatively large. The variable composition of river water and its impact on the chemical composition of seawater are discussed further in Chapter 21. 

Hydrothermal vents are another source of water entering the ocean. These vents are submarine hot-water geysers that are part of seafloor spreading centers. The hydrothermal fluids contain some major ions, such as magnesium and sulfete, in significantly different ratios than foimd in seawater. The importance of hydrothermal venting in determining the chemical composition of seawater is described in Chapters 19 and 21. 

Trace elements are discharged into the ocean in particulate and dissolved form as a component of river runoff and groundwater seeps. They are introduced into these waters during the chemical and mechanical weathering of crustal rocks. Thus, the chemical composition of river water is dependent on the composition of the rocks in the... 

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. 

The unique chemical composition of cosmogenous debris has provided some insight into why approximately 70% of the species of organisms on Earth were driven extinct over a relatively short time interval approximately 66 million years ago. Evidence for this mass extinction has been observed in marine sediments throughout all the ocean basins. In a contemporaneous layer deposited at the end of the Cretaceous period, the hard parts of many species of marine plankton abruptly vanished from the sedimentary record. This sedimentary layer is also characterized by a large enrichment in the rare element iridium. 

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. 

After delivery to the ocean, clay minerals react with seawater. The processes that alter the chemical composition of the terrigenous clay minerals during the first few months of exposure are termed halmyrolysis. These include (1) cation exchange, (2) fixation of ions into inaccessible sites, and (3) some isomorphic substitutions. Another important transfiarmation is flocculation of very small (colloidal-size) clay particles into larger ones. 

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