Evolution of magma redox state throughout Earth’s history revealed by zircon geochemistry

Metallogeny of the North China Craton: Link with secular changes in the evolving Earth

Considering the history and current state of the problem of the so-called metallogenic specialization of magmatic rocks, the paper places emphasis onto various aspects of the genesis of ore mineralization depending on the redox state of magmas (as a logical continuation of S. Ishihara’s works), fluids, and host rocks. These problems were inadequately poorly explored and discussed by researchers dealing with ore deposits. Various possible variants of ore-forming redox processes for different types of mineral deposits, with ore mineralization affiliated to granites (Ta, Sn, W, Mo, and Be) and mafic magmas (Au, Ag, U, Cu, Zn, Pb, As, Sb, and Hg) and, accordingly, to crustal and mantle origin, are discussed. On the basis of analyzed geological data, including those published over the past three decades, it is shown that the redox state of ore-producing magmas commonly significantly impacted not only the ore potential of magmatic complexes but also the genetic type of the ore mineralization. The redox state of the fluids predetermined the transport and precipitation speciation of metals. Influence mechanisms of hydrocarbons from sedimentary country rocks and gaseous products of their pyrolysis on ore deposition of various metals are considered. Understanding these mechanisms can be helpful for predicting the possible precipitation sites of ore mineralization of noble, radioactive, and chalcophile metals.

Separating effects of changes in atmospheric composition, climate and land-use on carbon sequestration of U.S. Mid-Atlantic temperate forests

Using two-dimensional (2D) thermal structure models and pseudo-2D chemical kinetics models, we explore how atmospheric temperatures and composition change as a function of altitude and longitude within the equatorial regions of close-in transiting Neptune-class exoplanets at different distances from their host stars. Our models predict that the day-night stratospheric temperature contrasts increase with increasing planetary effective temperatures Teff and that the atmospheric composition changes significantly with Teff. We find that horizontal transport-induced quenching is very effective in our simulated exo-Neptune atmospheres, acting to homogenize the vertical profiles of species abundances with longitude at stratospheric pressures where infrared observations are sensitive. Our models have important implications for planetary emission observations as a function of orbital phase with the Ariel mission. Cooler solar-composition exo-Neptunes with Teff = 500–700 K are strongly affected by photochemistry and other disequilibrium chemical processes, but their predicted variations in infrared emission spectra with orbital phase are relatively small, making them less robust phase-curve targets for Ariel observations. Hot solar-composition exo-Neptunes with Teff ≥ 1300 K exhibit strong variations in infrared emission with orbital phase, making them great targets for constraining global temperatures, energy-balance details, atmospheric dynamics, and the presence of certain high-temperature atmospheric constituents. However, such high-temperature exo-Neptunes are arguably less interesting from an atmospheric chemistry standpoint, with spectral signatures being dominated by a small number of species whose abundances are expected to be constant with longitude and consistent with thermochemical equilibrium. Solar-composition exo-Neptunes with Teff = 900–1100 K reside in an interesting intermediate regime, with infrared phase curve variations being affected by both temperature and composition variations, albeit at smaller predicted phase-curve amplitudes than for the hotter planets. This interesting intermediate regime shifts to smaller temperatures as atmospheric metallicity is increased, making cool higher-metallicity Neptune-class planets appropriate targets for Ariel phase-curve observations.

COVID‐19 pandemic responses affected atmospheric composition and climate. These effects depend on the background emissions, climate, and season in which they occur. Although using multiple scenarios is common in explorations of long‐term climate change, they are rarely used to explore atmospheric composition or climate changes in response to transient emission perturbations on the scale of COVID‐19 lockdowns. We used the ModelE Earth system model to evaluate how atmospheric and climate impacts depend on the decade and season in which lockdowns occurred. Global COVID‐19‐related anomalies in aerosols and trace gases differed by up to an order of magnitude or more when comparing lockdowns in 1980, 2008, 2020, and 2051. Regional atmospheric composition anomalies tended to be largest when emissions were near a historical peak: 1980 in Europe and temperate North America, 2008 or 2020 in eastern Asia, and 2051 in south Asia. Regional aerosol direct effect anomalies were almost always less than 0.1 W m−2 during the first pandemic year, but over 0.1 W m−2 in Europe and exceeded 0.2 W m−2 in Europe and temperate North America in 1980, generally changing in tandem with regional emissions. In contrast, direct effect anomalies in Asia were positive in 1980 and negative in 2008, suggesting they may be primarily determined by exogenous emission anomalies. Shifting COVID‐19 onset in 2020 by 3, 6, or 9 months also altered atmospheric composition on the order of 2%–25% globally. In all scenarios, changes in surface temperature or precipitation appeared unrelated to local atmospheric compositional changes.

The fossil record and models of atmospheric concentrations of O2 and CO2 suggest that past shifts in plant ecological dominance often coincided with dramatic changes in Earth's atmospheric composition. This study tested the effects of past changes in atmospheric composition on the photosynthetic physiology of a limited range of early-diverging angiosperms (eight), gymnosperms (three), and ferns (two). We performed physiological measurements on all species and used the results to parameterize simulations of their photosynthetic paleophysiology using three independent modeling approaches. Unique physiological attributes were identified for the three evolutionary groups: angiosperm taxa displayed significantly higher mesophyll conductance (g m), yet their stomatal conductance (g s) was lower than that of ferns. Gymnosperm taxa displayed low g s and g m, but they partially offset their significant diffusional limitations on photosynthesis through their higher maximum Rubisco carboxylation rate. Despite their high total conductance to CO2, fern taxa lacked an optimized control of g s, which was reflected in their low intrinsic water use efficiency. Simulations of the photosynthetic physiology of ferns, angiosperms, and gymnosperms through Earth's history demonstrated that past fluctuations in O2 and CO2 concentrations may have resulted in significant shifts in the relative competitiveness of the three evolutionary groups. Although preliminary because of limited species sampling, these findings hint at a potential mechanistic basis for the observed broad temporal correlation between atmospheric change and shifts in plant evolutionary group-level richness observed in the fossil record and are presented as a framework to be tested with paleophotosynthetic proxies and through increased species sampling.

Human driven changes in the Earth's atmospheric composition are likely to alter plant disease in the future. We evaluated the effects of elevated carbon dioxide (CO2) and ozone (O3) on three economically important soybean diseases (downy mildew, Septoria brown spot and sudden death syndrome‐SDS) under natural field conditions at the soybean free air concentration enrichment (SoyFACE) facility. Disease incidence and/or severity were quantified from 2005 to 2007 using visual surveys and digital image analysis, and changes were related to microclimatic variability and to structural and chemical changes in soybean host plants. Changes in atmospheric composition altered disease expression, but responses of the three pathosystems varied considerably. Elevated CO2 alone or in combination with O3 significantly reduced downy mildew disease severity (measured as area under the disease progress curve‐AUDPC) by 39–66% across the 3 years of the study. In contrast, elevated CO2 alone or in combination with O3 significantly increased brown spot severity in all 3 years, but the increase was small in magnitude. When brown spot severity was assessed in relation to differences in canopy height induced by the atmospheric treatments, disease severity increased under combined elevated CO2 and O3 treatment in only one of the 3 years. The atmospheric treatments had no effect on the incidence of SDS or brown spot throughout the study. Higher precipitation during the 2006 growing season was associated with increased AUDPC severity across all treatments by 2.7 and 1.4 times for downy mildew and brown spot, respectively, compared with drought conditions in 2005. In the 2 years with similar precipitation, the higher daily temperatures in the late spring of 2007 were associated with increased severity of downy mildew and brown spot. Elevated CO2 and O3 induced changes in the soybean canopy density and leaf age likely contributed to the disease expression modifications.

International concerns about the possibility of detrimental future climate change rest to a significant degree on the documented fact that the atmospheric levels of a number of long-lived greenhouse gases are steadily rising. The underlying causes for the currently observed changes in atmospheric composition involve both natural physical, chemical and biological processes and vital human activities like energy and food production. There is also clear evidence for major changes in atmospheric composition over the last 160,000 years contained in ice cores. The ice core data show us that atmospheric changes can be driven by natural processes alone so the current human processes need to be understood in terms of their perturbations to the natural biogeochemical cycles. Human activity is certainly a major contributor to the positive atmospheric trends of CO2 (0.4% per year), CH4 (1.2 down to 0.3% per year), and N2O (0.25% per year) in recent decades. Humans are in addition the sole contributor to the observed positive CF2Cl2 and CFCl3 trends (4.0% and 3.8% per year respectively in 1978-1988, 2.6% and 3.2% per year respectively in 1989-1991) and probably also for the observed negative trends in stratospheric O3 (0.2% to 3% per year depending on latitude). Tropospheric O3 appears to have increased at least in northern hemisphere midlatitudes over the last century and there are reasons to expect such an increase based on combustion-derived emissions. Similarly, SO2 levels, while controlled in some industrially developed countries, are increasing in several industrially developing regions due particularly to increased coal combustion. All of these trends are important to radiative forcing of climate change: positive trends for CO2, CH4, N2 O, CFCl3, CF2Cl2, and tropospheric ozone produce a positive (warming) force while negative trends for stratospheric ozone and positive trends for SO2 (and thus for the derived reflective sulfate aerosols) produce a negative (cooling) force. Biological processes in terrestrial ecosystems (cultivated or natural) play major roles in the budgets of CO2, CH4 and N2O while marine biology plays a significant role in controlling remote marine atmospheric SO2 levels and the flux of CO2 between atmosphere and ocean. The International Global Atmospheric Chemistry (IGAC) Project of the International Geosphere-Biosphere Program (IGBP) is underway and devoted to understanding the complex coupled atmospheric and biospheric chemistry leading to currently observed changes in atmospheric composition and to improving our capability to predict future changes in atmospheric gaseous and paniculate composition.KeywordsMethane EmissionBiomass BurningStratospheric OzoneCloud Condensation NucleusAtmospheric CompositionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Atmospheric composition changes and the F2-layer seasonal anomaly

The redox geodynamics linking basalts and their mantle sources through space and time

Abstract. It has long been assumed that Rayleigh lidar can be used to measure atmospheric temperature profiles up to about 90 or 100 km and that above this region the technique becomes invalid due to changes in atmospheric composition which affect basic assumptions on which Rayleigh lidar is based. Modern powerful Rayleigh lidars are able to measure backscatter from well above 100 km requiring a closer examination of the effects of the changing atmospheric composition on derived Rayleigh lidar temperature profiles. The NRLMSISE-00 model has been used to simulate lidar signal (photon-count) profiles, taking into account the effects of changing atmospheric composition, enabling a quantitative analysis of the biases and errors associated with extending Rayleigh lidar temperature measurements above 100 km. The biases associated with applying a nominal correction for the change in atmospheric composition with altitude has also been investigated. The simulations reported here show that in practice the upper altitude limit for Rayleigh lidar is imposed more by the accuracy of the temperature or pressure used to seed the temperature retrieval algorithm than by accurate knowledge of the atmospheric composition as has long been assumed.

Stellar flares present challenges to the potential habitability of terrestrial planets orbiting M dwarf stars through inducing changes in the atmospheric composition and irradiating the planet’s surface in large amounts of ultraviolet light. To examine their impact, we have coupled a general circulation model with a photochemical kinetics scheme to examine the response and changes of an Earth-like atmosphere to stellar flares and coronal mass ejections. We find that stellar flares increase the amount of ozone in the atmosphere by a factor of 20 compared to a quiescent star. We find that coronal mass ejections abiotically generate significant levels of potential bio-signatures such as N2O. The changes in atmospheric composition cause a moderate decrease in the amount of ultraviolet light that reaches the planets surface, suggesting that while flares are potentially harmful to life, the changes in the atmosphere due to a stellar flare act to reduce the impact of the next stellar flare.

There is large uncertainty about the magnitude of warming and how rainfall patterns will change in response to any given scenario of future changes in atmospheric composition and land use. The models used for future climate projections were developed and calibrated using climate observations from the past 40 years. The geologic record of environmental responses to climate changes provides a unique opportunity to test model performance outside this limited climate range. Evaluation of model simulations against palaeodata shows that models reproduce the direction and large-scale patterns of past changes in climate, but tend to underestimate the magnitude of regional changes. As part of the effort to reduce model-related uncertainty and produce more reliable estimates of twenty-first century climate, the Palaeoclimate Modelling Intercomparison Project is systematically applying palaeoevaluation techniques to simulations of the past run with the models used to make future projections. This evaluation will provide assessments of model performance, including whether a model is sufficiently sensitive to changes in atmospheric composition, as well as providing estimates of the strength of biosphere and other feedbacks that could amplify the model response to these changes and modify the characteristics of climate variability.

Abstract. Advances in trace gas analysis allow localised, non-atmospheric features to be resolved in ice cores, superimposed on the coherent atmospheric signal. These high-frequency signals could not have survived the low-pass filter effect that gas diffusion in the firn exerts on the atmospheric history and therefore do not result from changes in the atmospheric composition at the ice sheet surface. Using continuous methane (CH4) records obtained from five polar ice cores, we characterise these non-atmospheric signals and explore their origin. Isolated samples, enriched in CH4 in the Tunu13 (Greenland) record are linked to the presence of melt layers. Melting can enrich the methane concentration due to a solubility effect, but we find that an additional in situ process is required to generate the full magnitude of these anomalies. Furthermore, in all the ice cores studied there is evidence of reproducible, decimetre-scale CH4 variability. Through a series of tests, we demonstrate that this is an artifact of layered bubble trapping in a heterogeneous-density firn column; we use the term “trapping signal” for this phenomenon. The peak-to-peak amplitude of the trapping signal is typically 5 ppb, but may exceed 40 ppb. Signal magnitude increases with atmospheric CH4 growth rate and seasonal density contrast, and decreases with accumulation rate. Significant annual periodicity is present in the CH4 variability of two Greenland ice cores, suggesting that layered gas trapping at these sites is controlled by regular, seasonal variations in the physical properties of the firn. Future analytical campaigns should anticipate high-frequency artifacts at high-melt ice core sites or during time periods with high atmospheric CH4 growth rate in order to avoid misinterpretation of such features as past changes in atmospheric composition.

Water movement, oxygen supply and biological processes on the aggregate scale