Carbon system, modeling

Changes. Marine Silica Cycle. Ocean Carbon System, Modeling of. Radioactive Wastes. Stable Carbon Isotope Variations in the Ocean. Tritium-Helium Dating. 

Carbon Dioxide (CO2) Cycle. Cenozoic Climate -Oxygen Isotope Evidence. Cenozoic Oceans -Carbon Cycle Models. Ocean Carbon System, Modeling of. Pore Water Chemistry. 

Rosholt NJ (1967) Open system model for uranium-series dating of Pleistocene samples. In Radioactive Dating and Methods of low-level Counting. 1. A. E. A. Proc Ser Publ, SM-87/50, p 299-311 Rosholt JN, Antal PS (1962) Evaluation of the Pa /U-Th °/U method for dating Pleistocene carbonate rocks. US Geol Survey Prof Paper 450-E 108-lll... 

The interaction of carbon disulfide as a substrate in carbonic anhydrase model systems has been studied using density functional theory methods. A higher activation energy of CS2 compared to C02 in the reaction with [L3ZnOH]+ was due to the reduced electrophilicity of CS2. The reversibility of the reaction on the basis of these calculations is questionable with [L3ZnSC(0)SH]+ as intermediate.572... 

Mackay D, Yeun ATK (1983) Mass transfer coefficients correlations for volatilisation of organic solutes from water. Environ Sci Technol 17 211-233 Maier-Reimer E, Kriest I, Segschneider J, Wetzel P (2005) The UAMburg Ocean Carbon Cycle Model HAMOCC5.1 - Technical Description Release 1.1 -. MPI Reports on Earth System Science No. 14 1-57... 

The elucidation of actinide chemistry in solution is important for understanding actinide separation and for predicting actinide transport in the environment, particularly with respect to the safety of nuclear waste disposal.72,73 The uranyl CO + ion, for example, has received considerable interest because of its importance for environmental issues and its role as a computational benchmark system for higher actinides. Direct structural information on the coordination of uranyl in aqueous solution has been obtained mainly by extended X-ray absorption fine structure (EXAFS) measurements,74-76 whereas X-ray scattering studies of uranium and actinide solutions are more rare.77 Various ab initio studies of uranyl and related molecules, with a polarizable continuum model to mimic the solvent environment and/or a number of explicit water molecules, have been performed.78-82 We have performed a structural investigation of the carbonate system of dioxouranyl (VI) and (V), [U02(C03)3]4- and [U02(C03)3]5- in water.83 This study showed that only minor geometrical rearrangements occur upon the one-electron reduction of [U02(C03)3]4- to [U02(C03)3]5-, which supports the reversibility of this reduction. 

Another source of divergence is the use of different models for the aqueous carbonate systems. Precipitation and dissolution experiments can be carried out in closed or open systems and various ways of pH-adjustments (see 8.2). 

Equipment cost for industrial activated carbon systems were provided in undated vendor material. The Model 4 system contains two 4-ft-diameter adsorbers and contains 2000 lb of granular activated carbon. The Model 8 system has two 8-ft-diameter adsorbers and contains 6000 to 10,000 lb of granular activated carbon. The Model 10 system has two 10-ft-diameter adsorbers, and the Model 12 system contains two 12-ft-diameter adsorbers. Both units contain 20,000 lb of granular activated carbon (D15749X, pp. 19-22). Estimated capital costs for the systems are given in Table 1. 

By comparing the actual composition of sea water (sediments + sea -f- air) with a model in which the pertinent components (minerals, volatiles) with which water has come into contact are allowed to reach true equilibrium, Sillen in 1959 epitomized the application of equilibrium models for portraying the prominent features of the chemical composition of this system. His analysis, for example, has indicated that contrary to the traditional view, the pH of the ocean is not buffered primarily by the carbonate system his results suggest that heterogeneous-equilibria of silicate minerals comprise the principal pH buffer systems in oceanic waters. This approach and its expansion have provided a more quantitative basis for Forchbammer s suggestion of 100 years ago that the quantity of the different elements in sea water is not proportional to the quantity of elements which river water pours into the sea but is inversely proportional to the facility with which the elements in sea water are made insoluble by general chemical actions in the sea. 

Each GCC model differs in the set of assumptions made and therefore concentrates on different effects. For instance, a simple numerical model of the gas exchange at the ocean-atmosphere boundary in the case of wind-driven roughness of the sea at wind speeds of 7 m s 1 makes it possible to formulate, in the global model, a unit to calculate the persistent C02 flux between the water surface and the atmosphere. This can be exemplified by models of the ocean carbonate system described by many authors. Also, there are other models of the C02 cycle in natural systems (Riedo et al., 2000 Zonneveld, 1998). 

On the whole, when synthesizing a global model of the C02 biogeochemical cycle, the unit to simulate that part of the cycle spent in the ocean must describe how the ocean carbonate system works. Alekseev et al. (1992), analyzing the system C02 IICO, COj and the distribution of pH values in ocean waters, discovered that more than 80% of dissolved carbon dioxide is in the form of hydrocarbonate ion of HC03. This means that when synthesizing a model of the ocean carbonate system only the first stage of the dissociation of carbonic acid can be reliably considered. As a result, the flux of C02 dissolved in the upper layer of the ocean can be calculated by the formula... 

Several reaction pathways are built into the FREZCHEM model including (1) temperature change, (2) evaporation, (3) pressure change, (4) equilibrium or fractional crystallization and, for gas hydrates, (5) open or closed carbon systems, and (6) pure or mixed gas hydrates. Under the temperature change option, the user can specify the upper and lower temperature range and a decremental temperature interval (AT) at which equilibrium at a fixed pressure is calculated (e.g., 298.15 to 253.15K with AT = 5 would result in... 

Only a few of the reactions summarized in Table 3.3 are actually based on data at subzero temperatures. In most cases, the lower temperature for data is 0°C. This could potentially be a serious limitation for the FREZCHEM model. For example, quantifying carbonate chemistry requires specification of Ah,co2 -ftcb - 2 and Kw all of these reactions are only quantified for temperatures > 0 °C (Table 3.3). Figure 3.9 demonstrates how six of the most important relationships of Table 3.3 extrapolate to subzero temperatures. We were able, based on these extrapolations, to quantify the solubility product of nahcolite (NaHCOa) and natron (Na2CO3 10H2O) to temperatures as low as — 22°C (251 K) (Marion 2001). Even for highly soluble bicarbonate and carbonate minerals such as nahcolite and natron, their solubilities decrease rapidly with temperature (Marion 2001). For example, for a hypothetical saline, alkaline brine that initially was 4.5 m alkalinity at 25 °C, the final alkalinity at the eutectic at —23.6°C was 0.3m (Marion 2001). At least for carbonate systems it is not necessary to extrapolate much beyond about —25 °C to quantify this chemistry, which we believe can reasonably be done using existing equation extrapolations (Fig. 3.9). 

The solubility of TB 1 in supercritic carbon dioxide over the pressure range from 8 to 19 MPa and from 308 to 328 K has been measured using a flow system. Models based on chemical association, which did not require the critical parameters of the solute, were used to correlate the experimental data (00JCED464). Addition of methanol dramatically enhances the solubility (00MI823). 

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