Oceans kinetic models

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."... 

In addition to the thermodynamic and kinetic models shown above, which use parameters such as temperature, pressure, and carbon content, three initial detection tools enable initial estimates of hydrates in an ocean geologic setting ... 

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. 

Figure 15.16. Broecker s (1974) idealized kinetic model for the marine cycles of biologically fixed elements. volume of river water entering the ocean per year expressed as volume per unit sea area (m m yr or m yr ) = 0.1 m yr Chv, concentration of an element in average river water (mol m ) x Cnv, input flux (mol yr ) Fmix. volume of water sinking into deep water box = volume of water rising to surface water box (volume m yr ) = 2(X) m yr Q...

The conditions on Titan, both in the atmosphere and in the oceans, can be investigated using the kinetics and thermodynamics introduced in the modelling of the ISM and the prebiotic Earth, now tuned to the surface temperature and atmospheric temperature conditions on Titan. We have seen previously what happens to reaction rates in the ISM and the atmosphere using the Arrhenius equation but we have not yet extended the concepts of AG and thermodynamics to low temperatures. 

The kinetic interpretation of the chemistry of oceanic waters (kinetics of inputs of primary constituents interactions between biologic and mixing cycles) leads to the development of steady state models, in which the relatively constant chemistry of seawater in the recent past (i.e., Phanerozoic cf. Rubey, 1951) represents a condition of kinetic equilibrium among the dominant processes. In a system at... 

Morse J.W. and Berner R.A. (1979) The chemistry of calcium carbonate in the deep oceans. In Chemical Modelling—Speciation, Sorption, Solubility, and Kinetics in Aqueous Systems (ed. E. Jenne), pp. 499-535. Amer. Chem. Soc., Washington, D.C. 

In such models the OH concentration field is computed using measured or estimated concentration fields of the precursor molecules and photon flux data. The resulting OH field is then tuned such that it correctly predicts the lifetime of methyl chloroform (CH3CCI3) with respect to OH radical attack. From measurements of the atmospheric turnover time of CH3CCI3 (4.8 years) [20], its lifetime with respect to loss in the stratosphere (45 years), and its lifetime with respect to loss in the oceans (85 years) the tropospheric lifetime of CH3CCI3 with respect to OH radical attack has been inferred to be 5.7 years [17,21], Methyl chloroform is the calibration molecule of choice because it has a long history of precise atmospheric measurements, it has no natural sources, its industrial production is well documented, and because the kinetics of reaction Eq. 20 are well established, feo = 1.8 x 10-12 exp(- 1500/T) cm3 molecule-1 s-1 [22]. 

The accumulation of calcium carbonate in deep ocean sediments is a complex process. It is primarily governed by the interplay between biological production of calcium carbonate in the nearsurface ocean and the chemistry of deep ocean waters. After over 100 years of study, the major problem of determining the saturation state of deep ocean water remains largely unresolved. It is currently possible, using recent laboratory measurements, to arrive at saturation states that differ by as much as a factor of 2. Both laboratory and water column experiments indicate that calcium carbonate dissolution kinetics are not simply related to saturation state. It is our opinion that the saturation state problem must be resolved and considerably more detail added to our present knowledge of calcium carbonate dissolution kinetics and accumulation patterns before attempts to model the accumulation of calcium carbonate in deep ocean sediments can be truly successful. 

The main conclusions from the early model studies on iodine chemistry remain valid there is a significant lack of information on the kinetics of reactive iodine (especially lO and OIO reactions paths to stable particulate iodine) and on fluxes of alkyl iodides from the oceans. Nevertheless, important progress has recently been made and work is currently ongoing in several laboratories worldwide. This is an important area of atmospheric research in need of more attention. 

The physical-chemical controls on seawater can be attributed to the effect of composition of the major components on the thermodynamic and kinetics of processes in the oceans. In this chapter I will review the experimental and modeling work that has been done on how the composition of the major components of seawater (Na, Mg... 

Much of the chemistry of the oceans and of freshwater systems depends on the kinetics of various physical and chemical processes and on biochemical reactions rather than on equilibrium conditions. The simplest model describing systems open to their environment is the time-invariant steady-state model. Because the sea has remained constant for the recent geological past, it may be well justified to interpret the ocean in terms of a steady-state model. 

We hope to reinforce his ideas by showing for the I -I03 couple that a combination of one- or two-electron stepwise redox processes is not adequate for equilibrium modeling of iodine in oceanic waters and that the kinetics of redox processes governs oceanic iodine chemistry. In fact, a rich chemistry relating to carbon dynamics is the result. 

Polzin et al. (1995) were able to find a scaling of the dissipation rate of turbulent kinetic energy in terms of the frequency distribution of energy within the deep-ocean internal wave field for wave fields that differed from the Garret-Munk model. 

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