Department of Earth Sciences

The thermodynamic properties of 154 mineral end‐members, 13 silicate liquid end‐members and 22 aqueous fluid species are presented in a revised and updated data set. The use of a temperature‐dependent thermal expansion and bulk modulus, and the use of high‐pressure equations of state for solids and fluids, allows calculation of mineral–fluid equilibria to 100 kbar pressure or higher. A pressure‐dependent Landau model for order–disorder permits extension of disordering transitions to high pressures, and, in particular, allows the alpha–beta quartz transition to be handled more satisfactorily. Several melt end‐members have been included to enable calculation of simple phase equilibria and as a first stage in developing melt mixing models in NCKFMASH. The simple aqueous species density model has been extended to enable speciation calculations and mineral solubility determination involving minerals and aqueous species at high temperatures and pressures. The data set has also been improved by incorporation of many new phase equilibrium constraints, calorimetric studies and new measurements of molar volume, thermal expansion and compressibility. This has led to a significant improvement in the level of agreement with the available experimental phase equilibria, and to greater flexibility in calculation of complex mineral equilibria. It is also shown that there is very good agreement between the data set and the most recent available calorimetric data.

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

Mineral equilibria calculations in the system K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–TiO 2 –Fe 2 O 3 (KFMASHTO) using thermocalc and its internally consistent thermodynamic dataset constrain the effect of TiO 2 and Fe 2 O 3 on greenschist and amphibolite facies mineral equilibria in metapelites. The end‐member data and activity–composition relationships for biotite and chloritoid, calibrated with natural rock data, and activity–composition data for garnet, calibrated using experimental data, provide new constraints on the effects of TiO 2 and Fe 2 O 3 on the stability of these minerals. Thermodynamic models for ilmenite–hematite and magnetite–ulvospinel solid solutions accounting for order–disorder in these phases allow the distribution of TiO 2 and Fe 2 O 3 between oxide minerals and silicate minerals to be calculated. The calculations indicate that small to moderate amounts of TiO 2 and Fe 2 O 3 in typical metapelitic bulk compositions have little effect on silicate mineral equilibria in metapelites at greenschist to amphibolite facies, compared with those calculated in KFMASH. The addition of large amounts of TiO 2 to typical pelitic bulk compositions has little effect on the stability of silicate assemblages; in contrast, rocks rich in Fe 2 O 3 develop a markedly different metamorphic succession from that of common Barrovian sequences. In particular, Fe 2 O 3 ‐rich metapelites show a marked reduction in the stability fields of staurolite and garnet to higher pressures, in comparison to those predicted by KFMASH grids.

The deep-sea sediment oxygen isotopic composition (delta(18)O) record is dominated by a 100,000-year cyclicity that is universally interpreted as the main ice-age rhythm. Here, the ice volume component of this delta(18)O signal was extracted by using the record of delta(18)O in atmospheric oxygen trapped in Antarctic ice at Vostok, precisely orbitally tuned. The benthic marine delta(18)O record is heavily contaminated by the effect of deep-water temperature variability, but by using the Vostok record, the delta(18)O signals of ice volume, deep-water temperature, and additional processes affecting air delta(18)O (that is, a varying Dole effect) were separated. At the 100,000-year period, atmospheric carbon dioxide, Vostok air temperature, and deep-water temperature are in phase with orbital eccentricity, whereas ice volume lags these three variables. Hence, the 100,000-year cycle does not arise from ice sheet dynamics; instead, it is probably the response of the global carbon cycle that generates the eccentricity signal by causing changes in atmospheric carbon dioxide concentration.

The various cleaning steps required for preparation of foraminiferal samples for Mg/Ca (and Sr/Ca) analysis are evaluated for their relative importance and effects on measured elemental ratios. It is shown that the removal of silicate contamination is the most important step for the measurement of Mg/Ca ratios. In an example, bulk sample Mg/Ca decreases from 10.5 to 2.5 mmol mol −1 during clay removal. Oxidation of organic material causes a lowering of sample Mg/Ca in the order of 10% or approximately 1°C when converted to temperature. Use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in Mg/Ca. Reductive treatment also causes dissolution of the sample and a decrease in the Mg/Ca ratio of up to 10–15%. Sample preparation for Sr/Ca analysis does not require the same degree of rigor as is necessary for Mg/Ca work. The “within‐run” reproducibility of the method described here for G. ruber in a core‐top sample from the Arabian Sea was ±1.8% (mean sample ratio was 4.72 mmol mol −1 ). When converted to temperature, this becomes 28 ± 0.2°C. The equivalent result for Sr/Ca was ±0.5% (mean ratio = 1.44 mmol mol −1 ).

The Kirkendall effect is a consequence of the different diffusivities of atoms in a diffusion couple causing a supersaturation of lattice vacancies. This supersaturation may lead to a condensation of extra vacancies in the form of so-called "Kirkendall voids" close to the interface. On the macroscopic and micrometer scale these Kirkendall voids are generally considered as a nuisance because they deteriorate the properties of the interface. In contrast, in the nanoworld the Kirkendall effect has been positively used as a new fabrication route to designed hollow nano-objects. In this Review we summarize and discuss the demonstrated examples of hollow nanoparticles and nanotubes induced by the Kirkendall effect. Merits of this route are compared with other general methods for nanotube fabrication. Theories of the kinetics and thermodynamics are also reviewed and evaluated in terms of their relevance to experiments. Moreover, nanotube fabrication by solid-state reactions and non-Kirkendall type diffusion processes are covered.

A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be further improved. The accompanying International Stratigraphic Chart, issued under auspices of the International Commission on Stratigraphy (ICS), shows the current chronostratigraphic scale and ages with estimates of uncertainty for all stage boundaries. Special reference is made to the Precambrian part of the time scale, which is coming of age in terms of detail, and to the Neogene portion, which has attained an ultra-high-precision absolute-age calibration.

Abstract Mixing properties for muscovite–celadonite–ferroceladonite solid solutions are derived from combining available experimental phase equilibrium data with tabulated thermodynamic data for mineral end‐members. When a partially ordered solution model is assumed, the enthalpy of mixing among the end‐members muscovite–celadonite–ferroceladonite is nearly ideal, although the Gibbs energies of muscovite–celadonite and muscovite–ferroceladonite solutions are asymmetric due to an asymmetry in the entropy of mixing. Thermodynamic consistency is achieved for data on phengite compositions inassemblages with (a) pyrope+kyanite+quartz/coesite (b) almandine+kyanite+quartz/coesite (c)talc+kyanite+quartz/coesite and (d) garnet–phengite pairs equilibrated both experimentally at high temperatures and natural pairs from low‐grade schists. The muscovite–paragonite solvus has been reanalysed using the asymmetric van Laar model, and the effects of the phengite substitution into muscovite have been quantitatively addressed in order to complete the simple thermodynamic mixing model for the solid solution among the mica end‐members. Results are applied to a natural pyrope–coesite–phengite–talc rock from the Western Alps, and to investigate the conditions under which biotite‐bearing mica schists transform to whiteschist‐like biotite‐absent assemblages for average pelite bulk compositions.

The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within fine‐grained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a “capillary pressure” in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore‐size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This “freeze‐drying” may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable presence of free gas within the normal zone of hydrate stability.

Piezoelectricity is inherent only in noncentrosymmetric materials, but a piezoelectric response can also be obtained in centrosymmetric crystals if subjected to inhomogeneous deformation. This phenomenon, known as flexoelectricity, can significantly affect the functional properties of insulators, particularly thin films of high permittivity materials. We have measured strain-gradient-induced polarization in single crystals of paraelectric SrTiO3 as a function of temperature and orientation down to and below the 105 K phase transition. Estimates were obtained for all the components of the flexoelectric tensor, and calculations based on these indicate that local polarization around defects in SrTiO3 may exceed the largest ferroelectric polarizations. A sign reversal of the flexoelectric response detected below the phase transition suggests that the ferroelastic domain walls of SrTiO3 may be polar.

Abstract Highly active, stable, and cheap Pt‐free catalysts for the hydrogen evolution reaction (HER) are facing increasing demand as a result of their potential use in future energy‐conversion systems. However, the development of HER electrocatalysts with Pt‐like or even superior activity, in particular ones that can function under alkaline conditions, remains a significant challenge. Here, the synthesis of a novel carbon‐loaded ruthenium nanoparticle electrocatalyst (Ru@CQDs) for the HER, using carbon quantum dots (CQDs), is reported. Electrochemical tests reveal that, even under extremely alkaline conditions (1 m KOH), the as‐formed Ru@CQDs exhibits excellent catalytic behavior with an onset overpotential of 0 mV, a Tafel slope of 47 mV decade −1 , and good durability. Most importantly, it only requires an overpotential of 10 mV to achieve the current density of 10 mA cm −2 . Such catalytic characteristics are superior to the current commercial Pt/C and most noble metals, non‐noble metals, and nonmetallic catalysts under basic conditions. These findings open a new field for the application of CQDs and add to the growing family of metal@CQDs with high HER performance.

Polymer carbon dots (PCDs) are proposed as a new class of room-temperature phosphorescence (RTP) materials. The abundant energy levels in PCDs increase the probability of intersystem crossing (ISC) and their covalently crosslinked framework structures greatly suppress the nonradiative transitions. The efficient methods allow the manufacture of PCDs with unique RTP properties in air without additional metal complexation or complicated matrix composition. They thus provide a route towards the rational design of metal-free RTP materials that may be synthesized easily. Furthermore, we find that RTP is associated with a crosslink-enhanced emission (CEE) effect, which provides further routes to design improved PCDs with diverse RTP performance. Our results show the potential of PCDs as a universal route to achieve effective metal-free RTP.

More than 250 plumes of gas bubbles have been discovered emanating from the seabed of the West Spitsbergen continental margin, in a depth range of 150–400 m, at and above the present upper limit of the gas hydrate stability zone (GHSZ). Some of the plumes extend upward to within 50 m of the sea surface. The gas is predominantly methane. Warming of the northward‐flowing West Spitsbergen current by 1°C over the last thirty years is likely to have increased the release of methane from the seabed by reducing the extent of the GHSZ, causing the liberation of methane from decomposing hydrate. If this process becomes widespread along Arctic continental margins, tens of Teragrams of methane per year could be released into the ocean.

HKT-type transporters appear to play key roles in Na(+) accumulation and salt sensitivity in plants. In Arabidopsis HKT1;1 has been proposed to influx Na(+) into roots, recirculate Na(+) in the phloem and control root : shoot allocation of Na(+). We tested these hypotheses using (22)Na(+) flux measurements and ion accumulation assays in an hkt1;1 mutant and demonstrated that AtHKT1;1 contributes to the control of both root accumulation of Na(+) and retrieval of Na(+) from the xylem, but is not involved in root influx or recirculation in the phloem. Mathematical modelling indicated that the effects of the hkt1;1 mutation on root accumulation and xylem retrieval were independent. Although AtHKT1;1 has been implicated in regulation of K(+) transport and the hkt1;1 mutant showed altered net K(+) accumulation, (86)Rb(+) uptake was unaffected by the hkt1;1 mutation. The hkt1;1 mutation has been shown previously to rescue growth of the sos1 mutant on low K(+); however, HKT1;1 knockout did not alter K(+) or (86)Rb(+) accumulation in sos1.

Abstract The geochemical modelling of many small-volume continental magmas shows that their source regions must have been depleted by basalt formation, and later enriched by the addition of a metasomatic melt, formed by melting ∽0·3% of the MORB source. The presence of such magmas throughout western Turkey and the Aegean, where no plume is present, requires such magmas to be formed at temperatures considerably below the dry solidus. Similar magmas elsewhere bring up nodule suites, many of which have the same composition as the source regions of the host magmas. Pressure and temperature estimates from garnetbearing suites, and temperature estimates from those without garnet, show that the nodules last equilibrated at pressures and temperatures close to those of the wet solidus. Magmas from the smaller oceanic islands and from some seamounts closely resemble small-volume continental magmas, and also come from sources that have been metasomaticaUy enriched. However, no data sets from any of the oceanic islands that have yet been modelled require their source regions to have been depleted before being enriched The density of the sources of continental and oceanic basalts can be obtained from their calculated modes. In the garnet peridotite stability field the sources of ocean island basalts have densities that are slightly greater than that of the MORB source, whereas those of most small-volume continental magmas are lighter. Therefore ocean island sources alone are easily entrained into the thermal convection beneath the plates. A numerical experiment shows that material in the hot and cold boundary layers of high Rayleigh number time-dependent convection tends to remain in the boundary layers for several overturns, rather than moving into the interior of the circulation. A simple model that can account for the elemental and isotopic composition of ocean island basalts forms their sources by the addition of metasomatic melt to the undcplcUd MORB source while it forms the lower part of the mechanical boundary layer beneath continents. The isotopic differences between ocean island basalt and MORB are generated before the source becomes entrained in the cold sinking plumes that fall to the base of the convecting layer. At the base the material is heated and rises as part of a hot plume. Because the metasomatic melt contains water and carbonates, the enriched regions start to melt and generate more melt on decompression than does the MORB source. Such regions can therefore generate islands and seamounts. Even when the enriched material moves into the interior of the circulation and acquires the mean potential temperature of the mantle, it will still generate more melt on decompression than will the MORB source, and the isotopic and elemental composition will still be distinctive. The model can therefore account for the observed composition of magmas from seamounts that cannot be produced from either the MORB or the primitive source.

Multicollector ICP-MS has been used for the precise measurement of variations in the isotopic composition of the isotopic standard of magnesium (SRM980) provided by the National Institute of Standards and Technology (Gaithersburg, MD, USA). The SRM980 consists of metal chips weighing between 1 and 50 mg and each unit delivered by the National Institute of Standards and Technology corresponds to a bottle containing about 0.3 g. Height units were analysed. Variations in sample 25Mg/24Mg, and 26Mg/24Mg ratios are expressed as δ25Mg and δ26Mg units, respectively, which are deviations in parts per 103 from the same ratio in a standard solution. The differences in δ25Mg and δ26Mg of the SRM980 are up to 4.20 and 8.19‰, respectively, while the long-term repeatability of δ25Mg and δ26Mg are 0.09 and 0.16‰, respectively, at 95% confidence. However, when plotted in a three-isotope diagram, all the data fall on a single mass fractionation line. Overall limits of error of the SRM980 reported here fall within the previously reported overall limits of error. The isotopic heterogeneity not only corresponds to differences among units but has been found at the chip-size level. This result, due to the precision of the MC-ICP-MS technique, makes the SRM980 inappropriate for the international isotopic standard of magnesium. The SRM980 can still be used to report the excess of 26Mg, which is defined by the deviation from the mass-dependent relationship between 25Mg/24Mg, and 26Mg/24Mg ratios. Two large batches (around 10 g of Mg in each) of pure Mg solutions (in 0.3 M HNO3) have been prepared and characterised. These 2 solutions (DSM3 and Cambridge 1) are suitable reference material because they are immune to heterogeneity. DSM3 and Cambridge 1 are isotopically different (by 1.3‰ per u) and are available upon request from the first author. In addition, DSM3 has an isotopic composition very similar to the Mg-isotopic composition of carbonaceous chondrites (Orgueil and Allende). Because of the lack of heterogeneity and the cosmochemical and geochemical significance of DSM3, we urge the use of DSM3 as the primary isotopic reference material to report Mg-isotopic variations.

Abstract Perovskite nickelates (RNiO3, where R is rare earth or a heavy metal such as Tl or Bi) display sharp metal–insulator transitions, unusual magnetic order, charge order and, perhaps, orbital order. Furthermore, there are strong reasons to believe that some of them may be magnetoelectric multiferroics. In this article the author reviews recent research perovskite nickelates, highlighting the important role that thin film research has contributed to our understanding of their properties. A special emphasis is placed on open questions and highly topical issues such as whether or not nickelates have orbital order, and whether or not (and why) some of them may be multiferroic. Keywords: nickelateNdNiO3 magnetoelectricmultiferroicthin filmstrainmetal insulator transition

Heinrich events are well documented for the last glaciation, but little is known about their occurrence in older glacial periods of the Pleistocene. Here we report scanning XRF and bulk carbonate δ 18 O results from Integrated Ocean Drilling Program Site U1308 (reoccupation of Deep Sea Drilling Project Site 609) that are used to develop proxy records of ice‐rafted detritus (IRD) for the last ∼1.4 Ma. Ca/Sr is used as an indicator of IRD layers that are rich in detrital carbonate (i.e., Heinrich layers), whereas Si/Sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals. A pronounced change occurred in the composition and frequency of IRD at ∼640 ka during marine isotope stage (MIS) 16, coinciding with the end of the middle Pleistocene transition. At this time, “Hudson Strait” Heinrich layers suddenly appeared in the sedimentary record of Site U1308, and the dominant period of the Si/Sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward. The onset of Heinrich layers during MIS 16 represents either the initiation of surging of the Laurentide Ice Sheet (LIS) off Hudson Strait or the first time icebergs produced by this process survived the transport to Site U1308. We speculate that ice volume (i.e., thickness) and duration surpassed a critical threshold during MIS 16 and activated the dynamical processes responsible for LIS instability in the region of Hudson Strait. We also observe a strong coupling between IRD proxies and benthic δ 13 C variation at Site U1308 throughout the Pleistocene, supporting a link between iceberg discharge and weakening of thermohaline circulation in the North Atlantic.

Little is known about the signalling processes involved in the response of roots to abiotic stresses. The Arabidopsis root is a model system of root anatomy with a simple architecture and is amenable to genetic manipulation. Although it is known that the root responds to cold, drought and salt stress with increases in cytoplasmic free calcium, there is currently no information about the role(s) of the functionally diverse cell types that comprise the root. Transgenic Arabidopsis with enhancer-trapped GAL4 expression in specific cell types was used to target the calcium reporting protein, aequorin, fused to a modified yellow fluorescent protein (YFP). The luminescence output of targeted aequorin enabled in vivo measurement of changes in cytosolic free calcium concentrations ([Ca2+]cyt) in specific cell types during acute cold, osmotic and salt stresses. In response to an acute cold stress, all cell types tested as well as plants constitutively expressing aequorin displayed rapid [Ca2+]cyt peaks. However, there were significant quantitative differences between different cell types in terms of their response to cold stress, osmotic stress (440 mM mannitol) and salt stress (220 mM NaCl), implying specific roles for certain cell types in the detection and/or response to these stimuli. In response to osmotic and salt stress, the endodermis and pericycle displayed prolonged oscillations in cytosolic calcium that were distinct from the responses of the other cell types tested. Targeted expression of aequorin circumvented the technical difficulties involved in fluorescent dye injection as well as the lack of cell specificity of constitutively expressed aequorin, and revealed a new level of complexity in root calcium signalling.

Journal Article Editorial: Constructing an evolutionary economic geography Get access Ron Boschma, Ron Boschma Department of Economic Geography,Faculty of Geosciences,Utrecht University,NL-3508 TC, Netherlands.email <r.boschma@geo.uu.nl>Department of Geography,University of Cambridge,Cambridge CB2 3EN,UK.email <rlm1@cam.ac.uk> Search for other works by this author on: Oxford Academic Google Scholar Ron Martin Ron Martin Department of Economic Geography,Faculty of Geosciences,Utrecht University,NL-3508 TC, Netherlands.email <r.boschma@geo.uu.nl>Department of Geography,University of Cambridge,Cambridge CB2 3EN,UK.email <rlm1@cam.ac.uk> Search for other works by this author on: Oxford Academic Google Scholar Journal of Economic Geography, Volume 7, Issue 5, September 2007, Pages 537–548, https://doi.org/10.1093/jeg/lbm021 Published: 18 June 2007