Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth
23 Apr 2013-Proceedings of the National Academy of Sciences of the United States of America (National Academy of Sciences)-Vol. 110, Iss: 17, pp 6646-6650
TL;DR: It is found that MgCO3 (magnesite)—insoluble in water under ambient conditions—becomes at least slightly soluble at the bottom of the upper mantle, suggesting that water may transport significant quantities of oxidized carbon and the Earth’s deep carbon could possibly be recycled through aqueous transport through subduction zones.
Abstract: Water is a major component of fluids in the Earth’s mantle, where its properties are substantially different from those at ambient conditions. At the pressures and temperatures of the mantle, experiments on aqueous fluids are challenging, and several fundamental properties of water are poorly known; e.g., its dielectric constant has not been measured. This lack of knowledge of water dielectric properties greatly limits our ability to model water–rock interactions and, in general, our understanding of aqueous fluids below the Earth’s crust. Using ab initio molecular dynamics, we computed the dielectric constant of water under the conditions of the Earth’s upper mantle, and we predicted the solubility products of carbonate minerals. We found that MgCO3 (magnesite)—insoluble in water under ambient conditions—becomes at least slightly soluble at the bottom of the upper mantle, suggesting that water may transport significant quantities of oxidized carbon. Our results suggest that aqueous carbonates could leave the subducting lithosphere during dehydration reactions and could be injected into the overlying lithosphere. The Earth’s deep carbon could possibly be recycled through aqueous transport on a large scale through subduction zones.
Citations
More filters
TL;DR: In this paper, the balance between carbonate subduction into the deep Earth and CO2 release through degassing at volcanoes is critical for the carbon cycle, and fluid-mediated reactions could liberate significant amounts of carbon from the subducting slab for later release at arc volcanoes.
Abstract: The balance between carbonate subduction into the deep Earth and CO2 release through degassing at volcanoes is critical for the carbon cycle. Geochemical analyses of an exhumed subduction zone complex in Greece show that fluid-mediated reactions could liberate significant amounts of carbon from the subducting slab for later release at arc volcanoes.
268 citations
TL;DR: In this paper, the applicability of the revised Helgeson-Kirkham-Flowers (HKF) equations of state for aqueous species was extended to 60kb by developing estimates of ( e H 2 O ).
226 citations
Cites background or result from "Dielectric properties of water unde..."
...4 represent results from Pan et al. (2013)....
[...]
...The resulting dielectric constants were tested at 727 C and 58 kb by comparison with the results of ab initio molecular dynamics calculations (Pan et al., 2013)....
[...]
...Most recently, ab initio molecular dynamics (AIMD) calculations have resulted in the prediction of (eH2O) at 727 and 1727 C and three discrete pressures at 10, 58, 114 kb (Pan et al., 2013)....
[...]
...Comparison with ab initio molecular dynamics results Recent ab initio molecular dynamics calculations have presented predictions of the dielectric constant at elevated temperatures and pressures as indicated above (Pan et al., 2013)....
[...]
...The intermediate temperature of 727 C was included because recent AIMD calculations were carried out at that temperature (Pan et al., 2013)....
[...]
TL;DR: In this article, a large-scale mantle low δ26Mg anomaly in eastern China has been delineated, suggesting the contribution of sedimentary carbonates recycled into the upper mantle, but limited into the lower mantle.
Abstract: Although deep carbon recycling plays an important role in the atmospheric CO2 budget and climate changes through geological time, the precise mechanisms remain poorly understood. Since recycled sedimentary carbonate through plate subduction is the main light-δ26Mg reservoir within deep-Earth, Mg isotope variation in mantle-derived melts provides a novel perspective when investigating deep carbon cycling. Here, we show that the Late Cretaceous and Cenozoic continental basalts from 13 regions covering the whole of eastern China have low δ26Mg isotopic compositions, while the Early Cretaceous basalts from the same area and the island arc basalts from circum-Pacific subduction zones have mantle-like or heavy Mg isotopic characteristics. Thus, a large-scale mantle low δ26Mg anomaly in eastern China has been delineated, suggesting the contribution of sedimentary carbonates recycled into the upper mantle, but limited into the lower mantle. This large-scale spatial and temporal variation of Mg isotopes in the mantle places severe constraints on deep carbon recycling via oceanic subduction.
220 citations
TL;DR: Compared with the other terrestrial planets, Earth's atmosphere is nitrogen-rich as discussed by the authors, which suggests that nitrogen is readily degassed from oxidized mantle beneath Earth's subduction zones.
Abstract: Compared with the other terrestrial planets, Earth's atmosphere is nitrogen-rich. Thermodynamic calculations suggest that nitrogen is readily degassed from oxidized mantle beneath Earth's subduction zones.
146 citations
TL;DR: Theoretical calculations suggest that large amounts of carbon are returned to Earth’s surface as organic and inorganic carbon ions dissolved in subduction-zone fluids as discussed by the authors, and the deep carbon cycle is poorly constrained.
Abstract: Earth’s deep carbon cycle is poorly constrained. Theoretical calculations suggest that large amounts of carbon are returned to Earth’s surface as organic and inorganic carbon ions dissolved in subduction-zone fluids.
129 citations
References
More filters
TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
146,533 citations
"Dielectric properties of water unde..." refers methods or result in this paper
...Overall, the comparison between our ab initio results and those of available EOS is satisfactory and we conclude the PBE functional (18) may be used to predict the dielectric constant of water under pressure....
[...]
...However, the difference between DFT-PBE and SPC/E results, including the data in ref....
[...]
...3 shows that Gk at the DFT-PBE level of theory is ∼2.5 at 1,000 K, and it does not substantially vary with increasing pressure along an isotherm....
[...]
...We used the PBE (18) exchange-correlation functional and norm-conserving Fig....
[...]
...As a first step of our investigation, we validated the description of the equation of state of water under pressure provided by density functional theory (DFT) with the Perdew–Burke–Ernzerhof (PBE) exchangecorrelation functional (18)....
[...]
TL;DR: The dynamical steady-state probability density is found in an extended phase space with variables x, p/sub x/, V, epsilon-dot, and zeta, where the x are reduced distances and the two variables epsilus-dot andZeta act as thermodynamic friction coefficients.
Abstract: Nos\'e has modified Newtonian dynamics so as to reproduce both the canonical and the isothermal-isobaric probability densities in the phase space of an N-body system. He did this by scaling time (with s) and distance (with ${V}^{1/D}$ in D dimensions) through Lagrangian equations of motion. The dynamical equations describe the evolution of these two scaling variables and their two conjugate momenta ${p}_{s}$ and ${p}_{v}$. Here we develop a slightly different set of equations, free of time scaling. We find the dynamical steady-state probability density in an extended phase space with variables x, ${p}_{x}$, V, \ensuremath{\epsilon}\ifmmode \dot{}\else \.{}\fi{}, and \ensuremath{\zeta}, where the x are reduced distances and the two variables \ensuremath{\epsilon}\ifmmode \dot{}\else \.{}\fi{} and \ensuremath{\zeta} act as thermodynamic friction coefficients. We find that these friction coefficients have Gaussian distributions. From the distributions the extent of small-system non-Newtonian behavior can be estimated. We illustrate the dynamical equations by considering their application to the simplest possible case, a one-dimensional classical harmonic oscillator.
17,939 citations
"Dielectric properties of water unde..." refers methods in this paper
...A time step of 1 fs was used, and a Nosé-Hoover thermostat (46, 47) was used, with a relaxation time of 1 ps....
[...]
TL;DR: A new implementation of the molecular simulation toolkit GROMACS is presented which now both achieves extremely high performance on single processors from algorithmic optimizations and hand-coded routines and simultaneously scales very well on parallel machines.
Abstract: Molecular simulation is an extremely useful, but computationally very expensive tool for studies of chemical and biomolecular systems Here, we present a new implementation of our molecular simulation toolkit GROMACS which now both achieves extremely high performance on single processors from algorithmic optimizations and hand-coded routines and simultaneously scales very well on parallel machines The code encompasses a minimal-communication domain decomposition algorithm, full dynamic load balancing, a state-of-the-art parallel constraint solver, and efficient virtual site algorithms that allow removal of hydrogen atom degrees of freedom to enable integration time steps up to 5 fs for atomistic simulations also in parallel To improve the scaling properties of the common particle mesh Ewald electrostatics algorithms, we have in addition used a Multiple-Program, Multiple-Data approach, with separate node domains responsible for direct and reciprocal space interactions Not only does this combination of a
14,032 citations
TL;DR: In this paper, the authors present a new molecular dynamics algorithm for sampling the canonical distribution, where the velocities of all the particles are rescaled by a properly chosen random factor.
Abstract: The authors present a new molecular dynamics algorithm for sampling the canonical distribution. In this approach the velocities of all the particles are rescaled by a properly chosen random factor. The algorithm is formally justified and it is shown that, in spite of its stochastic nature, a quantity can still be defined that remains constant during the evolution. In numerical applications this quantity can be used to measure the accuracy of the sampling. The authors illustrate the properties of this new method on Lennard-Jones and TIP4P water models in the solid and liquid phases. Its performance is excellent and largely independent of the thermostat parameter also with regard to the dynamic properties.
11,327 citations
TL;DR: On the other hand, in this paper, a superparamagnetically collapsed Mossbauer spectrum is obtained for carbon with fewer active sites, and these particles sinter and carburize in a manner more similar to that of Fe particles supported on graphite.
Abstract: on carbon. These particles can interact with the active sites of the carbon to form a species a t the metal-carbon interface which is stable against high-temperature reduction. This interaction may occur via oxygen atoms bonding with both the carbon surface and iron atoms contacting the carbon. This oxygen could be provided by dissociation of the C O ligands during decomposition. The remainder of the surface Fe can exist in either a reduced or carburized state, but the small size of these particles results in either case in a superparamagnetically collapsed Mossbauer spectrum. For carbons with fewer active sites, more of the particles are unbound, and these particles sinter and carburize in a manner more similar to that of Fe particles supported on graphite.
11,221 citations
"Dielectric properties of water unde..." refers background in this paper
...Zhang and Duan (26) showed that the simple point charge extended (SPC/E) water model (27) reproduces experimental equation of state (EOS) data with an accuracy of less than 1%, for P up to 5....
[...]