Oceans mass balance

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."... 

The surface-ocean mass balance equation (Eq. 9.1) can be rewritten as... 

Oceanic Mass Balance of Elements Interactive with Ca, Mg, and C... 

Levasseur S., Birck J. L., and AUegre C. J. (1999) The osmium riverine flux and the oceanic mass balance of osmium. Earth... 

A schematic representation of the two-layer ocean model including the equations for the surface and deep-ocean mass balance of dissolved constituent C (mol m ). j, particle flux (mol y ) Vo> deep ocean volume (1.35 X IO m ) Vs. surface... 

The flow of hydrothermal solutions iato the oceans from hydrothermal vents, ie, springs coming from the sea floor ia areas of active volcanism, and the chemical reactions occurring there by high temperature alteration of basalts ate of significance ia the mass balance of and. Eurthermore,... 

MacKenzie and Carrels chemical mass balance between rivers and oceans... 

Table 10-13 Mass balance calculation for removal of river-derived constituents from the ocean (all units in lO mmol)...

Fitzgerald WF, Mason RP. 1996. The global mercury cycle oceanic and anthropogenic aspects. In Baeyens W, Ebinghaus R, Vasihev O, editors. Global and regional mercury cycles sources, fluxes and mass balances, Dordrecht, the Netherlands Kluwer Academic Publishers, p. 85-108. 

Bulk rock chemistry of hydrothermally altered midoceanic ridge basalt has been well studied and used to estimate the geochemical mass balances of oceans today (Wolery and Sleep, 1976 Humphris and Thompson, 1978 Mottl, 1983). In contrast, very few analytical data on hydrothermally altered volcanic rocks that recently erupted at back-arc basins are available. However, a large number of analytical data have been accumulated on the hydrothermally altered Miocene volcanic rocks from the Green tuff region in the Japanese Islands which are inferred to have erupted in a back-arc tectonic setting (section 1.5.3). 

An important aspect in the preceding discussion is the need to separate the fluid and sediment components spatially and (as we will see) also temporally. Quantitative mass balance estimates (e g., McCulloch and Gamble 1991 Stolper and Newman 1994 Ayers 1998) often conclude that there is as much, or even more, Th and U in the bulk slab componenf (i.e., sediment plus fluid from the altered oceanic crust). However, if the sediment component added is in U-Th isotope equilibrium (or returns to this state prior to fluid addition see Section 5.3), then addition of only 0.02 ppm U in the fluid will result in significant U-excesss in the composite source (e.g., Condomines and Sigmarsson 1993 Turner et al. 1997). 

The short4ived particle reactive radionuclides of the U/Th series also have enormous potential for tracking particle source and transport in ocean margins. Mass balances comparing inventories in sediments with supply can be used to determine import or export of particles to an area. Such approaches are increasingly important in understanding the fates of particle-reactive contaminants whose sources are often enhanced in the coastal ocean. Studies of especially when supplemented by other... 

Bowers and Taylor (1985) were the first to incorporate isotope fractionation into a reaction model. They used a modified version of EQ3/EQ6 (Wolery, 1979) to study the convection of hydrothermal fluids through the oceanic crust, along midocean ridges. Their calculation method is based on evaluating mass balance equations, as described in this chapter. 

Sirbescu ML, and Nabelek PI (2003) Crustal melts below 400°C. Geology 31 685-688 Stoffyn-Egli P, Mackenzie FT (1984) Mass balance of dissolved lithiimi in the oceans. Geochim Cosmochim Acta 48 859-872... 

Figure 6. Summary of existing Mo isotope data from natural samples. Isotopic composition of ocean source is based on mass balance (see text). Data are presented as 5 Mo and S Mo relative to the Rochester JMC standard (5 Mo 2/3 x 5 Mo). References ( ) McManus et al. 2002 (t) Siebert et al. 2003 ( ) Barling et ah 2001 ( ) Arnold et al. 2004. Molybdenite values of Wieser and DeLaeter (2003) are omitted because of standard normalization problems (see text). Data obtained by different research groups using different standards are cross-calibrated by comparing seawater 5 values.

From the perspective of the surface box, the biolimiting elements are supplied via river runoff and from upweUing. The elements are removed via the sinking of biogenic particles and downwelling. Since this model considers only the transport of materials into and out of the ocean and between the two reservoirs, details as to what happens to the elements while they reside in the boxes are not needed other than that they are present in a steady state. In such a case, the input rate of a biolimiting element will equal its output rate. For the surface-water reservoir, the mass balance that describes this steady state is given by... 

Table 21.11 Mass Balance Calculation for the Removal of River-Derived Constituents from the Ocean. ... 

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