Body temperatures of modern and extinct vertebrates from ^(13)C-^(18)O bond abundances in bioapatite

The stable isotope compositions of biologically precipitated apatite in bone, teeth, and scales are widely used to obtain information on the diet, behavior, and physiology of extinct organisms and to reconstruct past climate. Here we report the application of a new type of geochemical measurement to bioapatite, a “clumped-isotope” paleothermometer, based on the thermodynamically driven preference for ^(13)C and ^(18)O to bond with each other within carbonate ions in the bioapatite crystal lattice. This effect is dependent on temperature but, unlike conventional stable isotope paleothermometers, is independent from the isotopic composition of water from which the mineral formed. We show that the abundance of ^(13)C-^(18)O bonds in the carbonate component of tooth bioapatite from modern specimens decreases with increasing body temperature of the animal, following a relationship between isotope “clumping” and temperature that is statistically indistinguishable from inorganic calcite. This result is in agreement with a theoretical model of isotopic ordering in carbonate ion groups in apatite and calcite. This thermometer constrains body temperatures of bioapatite-producing organisms with an accuracy of 1–2 °C. Analyses of fossilized tooth enamel of both Pleistocene and Miocene age yielded temperatures within error of those derived from similar modern taxa. Clumped-isotope analysis of bioapatite represents a new approach in the study of the thermophysiology of extinct species, allowing the first direct measurement of their body temperatures. It will also open new avenues in the study of paleoclimate, as the measurement of clumped isotopes in phosphorites and fossils has the potential to reconstruct environmental temperatures

Assessing vertical axis rotations in large-magnitude extensional settings: A transect across the Death Valley extended terrane, California

Models for Neogene crustal deformation in the central Death Valley extended terrane, southeastern California, differ markedly in their estimates of upper crustal extension versus shear translations. Documentation of vertical axis rotations of range-scale crustal blocks (or parts thereof) is critical when attempting to reconstruct this highly extended region. To better define the magnitude, aerial extent, and timing of vertical axis rotation that could mark shear translation of the crust in this area, paleomagnetic data were obtained from Tertiary igneous and remagnetized Paleozoic carbonate rocks along a roughly east-west traverse parallel to about 36°N latitude. Sites were established in ∼7 to 5 Ma volcanic sequences (Greenwater Canyon and Brown's Peak) and the ∼10 Ma Chocolate Sundae Mountain granite in the Greenwater Range, ∼8.5 to 7.5 Ma and 5 to 4 Ma basalts on the east flank of the Black Mountains, the 10.6 Ma Little Chief stock and upper Miocene(?) basalts in the eastern Panamint Mountains, and Paleozoic Pogonip Group carbonate strata in the north central Panamint Mountains. At the site level, most materials yield readily interpretable paleomagnetic data. Group mean directions, after appropriate structural corrections, suggest no major vertical axis rotation of the Greenwater Range (e.g., D = 359°, I = 46°, α_(95) = 8.0°, N = 12 (7 normal (N), 5 reversed (R) polarity sites)), little post-5 Ma rotation of the eastern Black Mountains (e.g., D = 006°, I = 61°, α_(95) = 4.0°, N = 9 N, 6 R sites), and no significant post-10 Ma rotation of the Panamint Range (e.g., D = 181°, I = −51°, α_(95) = 6.5°, N = 9 R sites). In situ data from the Greenwater Canyon volcanic rocks, Chocolate Sundae Mountain granite, Funeral Peak basalt rocks, the Little Chief stock, and Paleozoic carbonate rocks (remagnetized) are consistent with moderate south east-side-down tilting of the separate range blocks during northwest directed extension. The paleomagnetic data reported here suggest that the Panamints shared none of the 7 Ma to recent clockwise rotation of the Black Mountains crystalline core, as proposed in recent models for transtensional development of the central Death Valley extended terrane

Extreme enrichment in atmospheric 15N15N.

Molecular nitrogen (N2) comprises three-quarters of Earth's atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets

Stable Te isotope fractionation in tellurium-bearing minerals from precious metal hydrothermal ore deposits

The tellurium isotope compositions of naturally-occurring tellurides, native tellurium, and tellurites were measured by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) and compared to theoretical values for equilibrium mass-dependent isotopic fractionation of representative Te-bearing species estimated with first-principles thermodynamic calculations. Calculated fractionation models suggest that 130/125 Te fractionations as large as 4 ‰ occur at 100° C between coexisting Te(IV) and Te(II) or Te(0) compounds, and smaller, typically \u3c 1 ‰ fractionations occur between coexisting Te(-I) or Te(-II) (Au,Ag)Te2 minerals (i.e., calaverite, krennerite) and (Au,Ag)2Te minerals (i.e., petzite, hessite). In general, heavyTe/light Te is predicted to be higher for more oxidized species, and lower for reduced species. Tellurides in the system Au-Ag-Te and native tellurium analyzed in this study have values of δ130/125Te = -1.54 to 0.44 ‰ and δ130/125 Te = -0.74 to 0.16 ‰, respectively, whereas those for tellurites (tellurite, paratellurite, emmonsite and poughite) range from δ130/125 Te = -1.58 to 0.59 ‰. Thus, the isotopic composition for both oxidized and reduced species are broadly coincident. Calculations of per mil isotopic variation per amu for each sample suggest that mass-dependent processes are responsible for fractionation. In one sample of coexisting primary native tellurium and secondary emmonsite, δ130/125 Te compositions were identical. The coincidence of δ130/125 Te between all oxidized and reduced species in this study and the apparent lack of isotopic fractionation between native tellurium and emmonsite in one sample suggest that oxidation processes cause little to no fractionation. Because Te is predominantly transported as an oxidized aqueous phase or as a reduced vapor phase under hydrothermal conditions, either a reduction of oxidized Te in hydrothermal liquids or deposition of Te from a reduced vapor to a solid is necessary to form the common tellurides and native tellurium in ore-forming systems. Our data suggest that these sorts of reactions during mineralization may account for a ~3 ‰ range of δ130/125 Te values. Based on the data ranges for Te minerals from various ore deposits, the underpinning geologic processes responsible for mineralization seem to have primary control on the magnitude of fractionation, with tellurides in epithermal gold deposits showing a narrower range of isotope values than those in orogenic gold and volcanogenic massive sulfide deposits

Theoretical constraints on the effects of pH, salinity, and temperature on clumped isotope signatures of dissolved inorganic carbon species and precipitating carbonate minerals

The use of carbonate 'clumped isotope' thermometry as a geochemical technique to determine temperature of formation of a carbonate mineral is predicated on the assumption that the mineral has attained an internal thermodynamic equilibrium. If true, then the clumped isotope signature is dependent solely upon the temperature of formation of the mineral without the need to know the isotopic or elemental composition of coeval fluids. However, anomalous signatures can arise under disequilibrium conditions that can make the estimation of temperatures uncertain by several degrees Celsius. Here we use ab initio calculations to examine the potential disequilibrium mineral signatures that may arise from the incorporation of dissolved inorganic carbon (DIC) species (predominantly aqueous carbonate and bicarbonate ions) into growing crystals without full equilibration with the crystal lattice.We explore theoretically the nature of clumping in the individual DIC species and the composite DIC pool under varying pH, salinity, temperature, and isotopic composition, and speculate about their effects upon the resultant disequilibrium clumping of the precipitates. We also calculate equilibrium clumped signatures for the carbonate minerals calcite, aragonite, and witherite. Our models indicate that each DIC species has a distinct equilibrium clumped isotope signature such that, δ47(H2CO3)>δ47HCO3->δ47(equilibrium calcite)>δ47CO32-, and predict a difference between δ47HCO3-andδ47CO32->0.033‰ at 25°C, and that δ47 (aragonite)>δ47 (calcite)>δ47 (witherite). We define the calcite clumped crossover pH as the pH at which the composite δ47 (DIC pool)=δ47 (equilibrium calcite). If disequilibrium δ47 (calcite) is misinterpreted as equilibrium δ47 (calcite), it is possible to overestimate or underestimate the growth temperature by small but significant amounts. Increases in salinity lower the clumped crossover pH and may cause larger effects. Extreme effects of pH, salinity, and temperature, such as between cold freshwater lakes at high latitudes to hot hypersaline environments, are predicted to have sizeable effects on the clumped isotope composition of aqueous DIC pools.In order to determine the most reliable and efficient modeling methods to represent aqueous dissolved inorganic carbon (DIC) species and carbonate minerals, we performed convergence and sensitivity testing on several different levels of theory. We used 4 different techniques for modeling the hydration of DIC: gas phase, implicit solvation (PCM and SMD), explicit solvation (ion with 3 water molecules) and supermolecular clusters (ion plus 21 to 32 water molecules with geometries generated by molecular dynamics). For each solvation technique, we performed sensitivity testing by combining different levels of theory (up to 8 ab initio/hybrid methods, each with up to 5 different sizes of basis sets) to understand the limits of each technique. We looked at the degree of convergence with the most complex (and accurate) models in order to select the most reliable and efficient modeling methods. The B3LYP method combined with the 6-311++G(2d,2p) basis set with supermolecular clusters worked well. © 2013 Elsevier Ltd

I. Predicting Equilibrium Stable Isotope Fractionations of Iron, Chlorine, and Chromium. II. Oxygen-Isotope Investigation of Mesozoic and Cenozoic Granitoids of the Northeastern Great Basin, Nevada and Utah

Theoretical studies of the stable isotope geochemistry of iron, chlorine, and chromium are presented, with the goal of providing a framework to aid interpretations of new measurements and to identify promising areas for future study. In addition, new oxygen-isotope measurements of Mesozoic and Cenozoic granitoids from the northeastern Great Basin are used to constrain the temporal evolution of magmatic sources in the region. The stable isotope compositions of elements heavier than sulfur (atomic no. 16) are generating great geochemical interest, now that new mass-spectrometry techniques make it possible to measure their isotopic abundances with high precision. Theoretical calculations for three of these elements (iron, chlorine, and chromium) are made using published infrared, Raman, and inelastic neutron scattering measurements of vibrational frequencies, in combination with empirical and ab initio force-field estimates of unknown frequencies. The calculations suggest that a number of natural processes can drive significant stable isotope fractionations of heavy elements, including oxidation/reduction during the precipitation or dissolution of dissolved metals (inorganically or organically), and bond-partner exchange during hydrothermal alteration, or degradation of Cl-bearing organic compounds. At equilibrium and 25°C, ^(56)Fe/^(54)Fe will be ~5‰ higher in [Fe(H_2O)_6]^(3+) than in coexisting [Fe(H_2O)_6]^(2+), ^(53)Cr/^(52)Cr will be ~6-7‰ higher in [CrO_4]^(2-) than in coexisting [Cr(H_2O)_6]^(3+) or Cr_2O_3, and aqueous Cl- will be ~2-3‰ lighter than coexisting alteration minerals like mica and amphibole. Oxygen isotope measurements of whole-rock samples from granitoid plutons in the northeastern Great Basin suggest that two or three different types of source rocks were melted in varying proportions during the three stages of magmatism in this region in the Late Jurassic, Late Cretaceous, and mid-Cenozoic. Radiogenic-isotope measurements were previously made on the same samples. Late Cretaceous (90-70 Ma) granites have high δ^(18)O (+9.3 to + 12.1) and ^(87)Sr/^(86)Sr_i (0.711 to 0.734), and low εNd (-13 to -23) indicating that their source was dominated by evolved crustal sediments and basement. However, late Jurassic plutons in this region span a larger range of δ^(18)O values (+7.2 to + 13.2), despite having Sr and Nd isotopic compositions that are much less suggestive of an ancient crustal component (^(87)Sr/^(86)Sr_i = 0.705 to 0.711, εNd = -2.5 to -6.5) than the Late Cretaceous plutons, suggesting moderate to extensive mixing or assimilation of high-δ^(18)O sedimentary rocks into a more mafic parent melt. The 40-25 Ma Cenozoic plutons (δ^(18)O = +7.0 to + 9.7, ^(87)Sr/^(86)Sr_i = 0.707 to 0.717, εNd= -13.2 to -26.3) probably have a source dominated by continental basement. The Cenozoic plutons can be subdivided into a higher δ^(18)O (+8.6 to + 9.7) southern group and a lower δ^(18)O (+7.0 to + 8.2) northern group across a Crustal Age Boundary (CAB) at roughly 40° 40' N; this CAB coincides with a radiogenic isotope boundary defined with the same samples, as well as with the approximate southern limit of exposure of Archean basement. The low δ^(18)O values and depleted lead isotope compositions of the Lower Array (northern) samples indicate that Archean age basement is present beneath a large area of the most northeasterly part of the Great Basin. A further, speculative conclusion is that δ^(18)O of the (meta)sedimentary source region may have dropped by 2-3‰ as a result of fluid-rock interaction sometime between the Jurassic and Late Cretaceous magmatic episodes.</p

^(18)O^(13)C^(16)O in Earth’s atmosphere

The chemistry and budgets of atmospheric gases are constrained by their bulk stable isotope compositions (e.g., δ^(13)C values), which are based on mixing ratios of isotopologues containing one rare isotope (e.g., 16O13C16O). Atmospheric gases also have isotopologues containing two or more rare isotopes (e.g., ^(18)O^(13)C^(16)O). These species have unique physical and chemical properties and could help constrain origins of atmospheric gases and expand the scope of stable isotope geochemistry generally. We present the first measurements of the abundance of ^(18)O^(13)C^(16)O from natural and synthetic sources, discuss the factors influencing its natural distribution and, as an example of its applied use, demonstrate how its abundance constrains the sources of CO_2 in the Los Angeles basin. The concentration of ^(18_O^(13)C^(16)O in air can be explained as a combination of ca. 1‰ enrichment (relative to the abundance expected if C and O isotopes are randomly distributed among all possible isotopologues) due to enhanced thermodynamic stability of this isotopologue during isotopic exchange with leaf and surface waters, ca. 0.1‰ depletion due to diffusion through leaf stomata, and subtle (ca. 0.05‰) dilution by ^(18)O^(13)C^(16)O-poor anthropogenic CO_2. Some air samples are slightly (ca. 0.05‰) lower in ^(18)O^(13)C^(16)O than can be explained by these factors alone. Our results suggest that ^(18)O^(13)C^(16)O abundances should vary by up to ca. 0.2‰ with latitude and season, and might have measurable sensitivities to stomatal conductances of land plants. We suggest the greatest use of Δ_(47) measurements will be to “leverage” interpretation of the δ^(18)O of atmospheric CO_2

Equilibrium Fractionation of Non-traditional Isotopes: a Molecular Modeling Perspective

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^(13)C^(18)O^(16)O in air

The atmospheric budget of CO_2 is constrained by its concentration, δ^(13)C and δ^(18)O. However, these are insufficient to resolve source and sink processes, which vary complexly in flux and/or isotope signature. There are twelve stable isotopologues of CO_2, each of which has unique thermodynamic and kinetic properties and could offer unique constraints on the budget. However, only three are commonly measured (^(12)C^(16)O^(16)O, ^(13)C^(16)O^(16)O, and ^(12)C^(18)O^(16)O); most of the rest have not been previously analyzed in natural materials

Preferential formation of ^(13)C–^(18)O bonds in carbonate minerals, estimated using first-principles lattice dynamics

Equilibrium constants for internal isotopic exchange reactions of the type: Ca^(12)C^(18)O^(16)O_2+Ca^(13)C^(16)O_3 ↔ Ca^(13)C^(18)O^(16)O_2+Ca^(12)C^(16)O_3 for individual CO_3^(2−) groups in the carbonate minerals calcite (CaCO_3), aragonite (CaCO_3), dolomite (CaMg(CO_3)_2), magnesite (MgCO_3), witherite (BaCO_3), and nahcolite (NaHCO_3) are calculated using first-principles lattice dynamics. Calculations rely on density functional perturbation theory (DFPT) with norm-conserving planewave pseudopotentials to determine the vibrational frequencies of isotopically substituted crystals. Our results predict an ∼0.4‰ excess of ^(13)C^(18)O^(16)O_2^(2-) groups in all studied carbonate minerals at room-temperature equilibrium, relative to what would be expected in a stochastic mixture of carbonate isotopologues with the same bulk ^(13)C/^(12)C, ^(18)O/^(16)O, and ^(17)O/^(16)O ratios. The amount of excess ^(13)C^(18)O^(16)O^(2-)_2 decreases with increasing temperature of equilibration, from 0.5‰ at 0 °C to <0.1‰ at 300 °C, suggesting that measurements of multiply substituted isotopologues of carbonate could be used to infer temperatures of ancient carbonate mineral precipitation and alteration events, even where the δ^(18)O of coexisting fluids is uncertain. The predicted temperature sensitivity of the equilibrium constant is ∼0.003‰/°C at 25 °C. Estimated equilibrium constants for the formation of ^(13)C^(18)O^(16)O^(2-)_2 are remarkably uniform for the variety of minerals studied, suggesting that temperature calibrations will also be applicable to carbonate minerals not studied here without greatly compromising accuracy. A related equilibrium constant for the reaction: Ca^(12)C^(18)O^(16)O_2+Ca^(12)C^(17)O^(16)O_2 ↔ Ca^(12)C^(18)O^(17)O^(16)O+Ca^(12)C^(16)O_3 in calcite indicates formation of 0.1‰ excess ^(12)C^(18)O^(17)O^(16^O^(2−) at 25 °C. In a conventional phosphoric acid reaction of carbonate to form CO_2 for mass-spectrometric analysis, molecules derived from ^(13)C^(18)O^(16)O_2^(2-) dominate (∼96%) the mass 47 signal, and ^(12)C^(18)O^(17)O^(16)O^(2−) contributes most of the remainder (3%). This suggests that carbonate internal equilibration temperatures can be recovered from acid-generated CO_2 if abundances of isotopologues with mass 44–47 can be measured to sufficient precision. We have also calculated ^(18)O/^(16)O and ^(13)C/^(12)C reduced partition function ratios for carbonate minerals, and find them to be in good agreement with experiments and empirical calibrations. Carbon and oxygen isotope fractionation factors in hypothetical ^(40)Mg—magnesite and ^(40)Ba—witherite indicate that M^(2+)-cation mass does not contribute significantly to equilibrium isotopic fractionations between carbonate minerals