Geological respiration of a mountain belt revealed by the trace element rhenium

Oxidation of rock-derived, petrogenic, organic carbon (OCpetro) during weathering of sedimentary rocks is a major source of carbon dioxide (CO2) to the atmosphere. This geological respiration is thought to be enhanced by physical erosion, suggesting that mountain belts could release large amounts of CO2 to counter the CO2 sequestration achieved by the erosion, riverine transfer and oceanic burial of organic carbon from the terrestrial biosphere. However, OCpetro oxidation rates in mountain belts have not been quantified. Here we use rhenium (Re) as a proxy to track OCpetro oxidation in mountain river catchments of Taiwan, where existing measurements of physical erosion rate allow the controls on OCpetro oxidation to be assessed. Re has been shown to be closely associated with OCpetro in rocks and following oxidation during chemical weathering forms a soluble oxyanion (View the MathML source) which contributes to the dissolved load of rivers. Soils on meta-sedimentary rocks in Taiwan show that Re loss is coupled to OCpetro loss during weathering, confirming previous observations from soil profiles on sedimentary rocks elsewhere. In Taiwan rivers, dissolved Re flux increases with the catchment-average sediment yield, suggesting that physical erosion rate is a major control on OCpetro oxidation. Based on our current understanding of Re mobility during weathering, the dissolved Re flux can be used to quantify an upper bound on the OCpetro oxidation rate and the associated CO2 transfer. The estimated CO2 release from this mountain belt by OCpetro oxidation does not negate estimates of CO2 sequestration by burial of biospheric OC offshore. The findings are compared to OC transfers estimated for the Himalaya, where OCpetro oxidation in the mountain belt remains unconstrained. Together, these cases suggest that mountain building in the tropics can result in a net sink of OC which sequesters atmospheric CO2

Dynamic correlations of the Coulomb Luttinger liquid

The dynamic density response function, form-factor, and spectral function of a Luttinger liquid with Coulomb electron-electron interaction are studied with the emphasis on the short-range electron correlations. The Coulomb interaction changes dramatically the density response function as compared to the case of the short-ranged interaction. The form of the density response function is smoothing with time, and the oscillatory structure appears. However, the spectral functions remain qualitatively the same. The dynamic form-factor contains the $\delta$-peak in the long-wave region, corresponding to one-boson excitations. Besides, the multi-boson-excitations band exists in the wave-number region near to $2k_F$. The dynamic form-factor diverges at the edges of this band, while the dielectric function goes to zero there, which indicates the appearance of a soft mode. We develop a method to analyze the asymptotics of the spectral functions near to the edges of the multi-boson-excitations band.Comment: 11 pages, 3 figures, submitted to PR

Experimental application of sum rules for electron energy loss magnetic chiral dichroism

We present a derivation of the orbital and spin sum rules for magnetic circular dichroic spectra measured by electron energy loss spectroscopy in a transmission electron microscope. These sum rules are obtained from the differential cross section calculated for symmetric positions in the diffraction pattern. Orbital and spin magnetic moments are expressed explicitly in terms of experimental spectra and dynamical diffraction coefficients. We estimate the ratio of spin to orbital magnetic moments and discuss first experimental results for the Fe L_{2,3} edge.Comment: 11 pages, 2 figure

Lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion

The erosion of major mountain ranges is thought to be largely cannibalistic, recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift. Despite this recognition, it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean. Here, we have analyzed the Li content and isotope composition (View the MathML source) of suspended sediments sampled along river depth profiles and bed sands in three of the largest Earth's river systems (Amazon, Mackenzie and Ganga–Brahmaputra rivers). The View the MathML source values of river-sediments transported by these rivers range from +5.3 to −3.6‰ and decrease with sediment grain size. We interpret these variations as reflecting a mixture of unweathered rock fragments (preferentially transported at depth in the coarse fraction) and present-day weathering products (preferentially transported at the surface in the finest fraction). Only the finest surface sediments contain the complementary reservoir of Li solubilized by water–rock interactions within the watersheds. Li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks. A mass budget approach, based on Li isotopes, Li/Al and Na/Al ratios, solved by an inverse method allows us to estimate that, for the large rivers analyzed here, the part of solid weathering products formed by present-day weathering reactions and transported to the ocean do not exceed 35%. Li isotopes also show that the sediments transported by the Amazon, Mackenzie and Ganga–Brahmaputra river systems are mostly sourced from sedimentary rocks (>60%) rather than igneous rocks. This study shows that Li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present-day weathering processes. Overall, Li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering

Singular Structure and Enhanced Friedel Oscillations in the Two-Dimensional Electron Gas

We calculate the leading order corrections (in $r_s$) to the static polarization $\Pi^{*}(q,0,)$, with dynamically screened interactions, for the two-dimensional electron gas. The corresponding diagrams all exhibit singular logarithmic behavior in their derivatives at $q=2 k_F$ and provide significant enhancement to the proper polarization particularly at low densities. At a density of $r_s=3$, the contribution from the leading order {\em fluctuational} diagrams exceeds both the zeroth order (Lindhard) response and the self-energy and exchange contributions. We comment on the importance of these diagrams in two-dimensions and make comparisons to an equivalent three-dimensional electron gas; we also consider the impact these finding have on $\Pi^{*}(q,0)$ computed to all orders in perturbation theory

Ladder approximation to spin velocities in quantum wires

The spin sector of charge-spin separated single mode quantum wires is studied, accounting for realistic microscopic electron-electron interactions. We utilize the ladder approximation (LA) to the interaction vertex and exploit thermodynamic relations to obtain spin velocities. Down to not too small carrier densities our results compare well with existing quantum Monte-Carlo (QMC) data. Analyzing second order diagrams we identify logarithmically divergent contributions as crucial which the LA includes but which are missed, for example, by the self-consistent Hartree-Fock approximation. Contrary to other approximations the LA yields a non-trivial spin conductance. Its considerably smaller computational effort compared to numerically exact methods, such as the QMC method, enables us to study overall dependences on interaction parameters. We identify the short distance part of the interaction to govern spin sector properties.Comment: 6 pages, 6 figures, to appear in Physical Review

Ecosystem controlled soil-rock p CO 2 and carbonate weathering – Constraints by temperature and soil water content

Carbonate dissolution in soil-groundwater systems depends dominantly on pH, temperature and the saturation state of the solution with respect to abundant minerals. The pH of the solution is, in general, controlled by partial pressure of CO2 (pCO2) produced by ecosystem respiration, which is controlled by temperature and water availability. In order to better understand the control of land temperature on carbonate weathering, a database of published spring water hydrogeochemistry was built and analysed. Assuming that spring water is in equilibrium with the soil-water-rock-atmosphere, the soil pCO2 can be back-calculated. Based on a database of spring water chemistry, the average soil-rock CO2 was calculated by an inverse model framework and a strong relationship with temperature was observed. The identified relationship suggests a temperature control on carbonate weathering as a result of variations in soil-rock pCO2, which is itself controlled by ecosystem respiration processes. The findings are relevant for global scale analysis of carbonate weathering and carbon fluxes to the ocean, because concentration of weathering products from the soil-rock-system into the river system in humid, high temperature regions, are suggested to be larger than in low temperature regions. Furthermore, results suggest that, in specific spring samples, the hydrochemical evolution of rain water percolating through the soil-rock complex can best be described by an open system with pCO2 controlled by the ecosystem. Abundance of evaporites and pyrite sources influence significantly the chemistry of spring water and corrections must be taken into account in order to implement the inverse model framework presented in this study. Annual surface temperature and soil water content were identified as suitable variables to develop the parameterization of soil-rock pCO2, mechanistically consistent with soil respiration rate findings

On the Ground State of Electron Gases at Negative Compressibility

Two- and three-dimensional electron gases with a uniform neutralizing background are studied at negative compressibility. Parametrized expressions for the dielectric function are used to access this strong-coupling regime, where the screened Coulomb potential becomes overall attractive for like charges. Closely examining these expressions reveals that the ground state with a periodic modulation of the charge density, albeit exponentially damped, replaces the homogeneous one at positive compressibility. The wavevector characterizing the new ground state depends on the density and is complex, having a positive imaginary part, as does the homogeneous ground state, and real part, as does the genuine charge density wave.Comment: 6 double-column pages, 2 figures. 2nd version is an extension of the 1st one, giving more detail

Small-angle X-ray characterization of the nucleoprotein complexes resulting from DNA-induced oligomerization of HIV-1 integrase

HIV-1 integrase (IN) catalyses integration of a DNA copy of the viral genome into the host genome. Specific interactions between retroviral IN and long terminal repeats (LTR) are required for this insertion. To characterize quantitatively the influence of the determinants of DNA substrate specificity on the oligomerization status of IN, we used the small-angle X-ray scattering (SAXS) technique. Under certain conditions in the absence of ODNs IN existed only as monomers. IN preincubation with specific ODNs led mainly to formation of dimers, the relative amount of which correlated well with the increase in the enzyme activity in the 3′-processing reaction. Under these conditions, tetramers were scarce. Non-specific ODNs stimulated formation of catalytically inactive dimers and tetramers. Complexes of monomeric, dimeric and tetrameric forms of IN with specific and non-specific ODNs had varying radii of gyration (R(g)), suggesting that the specific sequence-dependent formation of IN tetramers can probably occur by dimerization of two dimers of different structure. From our data we can conclude that the DNA-induced oligomerization of HIV-1 IN is probably of importance to provide substrate specificity and to increase the enzyme activity

Restricted and unrestricted Hartree-Fock calculations of conductance for a quantum point contact

Very short quantum wires (quantum contacts) exhibit a conductance structure at a value of conductance close to $0.7 \times 2e^2/h$. It is believed that the structure arises due to the electron-electron interaction, and it is also related to electron spin. However details of the mechanism of the structure are not quite clear. Previously we approached the problem within the restricted Hartree-Fock approximation. This calculation demonstrated a structure similar to that observed experimentally. In the present work we perform restricted and unrestricted Hartree-Fock calculations to analyze the validity of the approximations. We also consider dependence of the effect on the electron density in leads. The unrestricted Hartree-Fock method allows us to analyze trapping of the single electron within the contact. Such trapping would result in the Kondo model for the ``0.7 structure''. The present calculation confirms the spin-dependent bound state picture and does not confirm the Kondo model scenario.Comment: 6 pages, 9 figure