Efficient multiphysics modelling with adaptive grid refinement using a MPFA method

A sequential solution procedure is used to simulate compositional two-phase flow in porous media. We employ a multiphysics concept that adapts the numerical complexity locally according to the underlying processes to increase efficiency. The framework is supplemented by a local refinement of the simulation grid. To calculate the fluxes on such grids, we employ a combination of the standard two-point flux approximation and a multipoint flux approximation where the grid is refined. This is then used to simulate a large-scale example related to underground CO₂ storage.     

Meteoric lithification of catastrophic rockslide deposits: Diagenesis and significance

Deposits of catastrophic rockslides composed of lithologies rich in carbonate minerals may undergo precipitation of cements that can be used to proxy-date the rockslide event and/or subsequent geomorphic changes of the rockslide mass.In the Alps, localized to widespread lithification of post-Glacial rockslide deposits is observed in lithologies ranging from limestones and dolostones to metacarbonates to calcphyllites. Lithification of rockslide deposits to breccias may be localized to meteoric ‘runoff-shadows’ below larger boulders, or may comprise a layer of breccia or may affect a rockslide mass down its base. In addition, precipitation of cements and small stalactites may take place in megapores on boulder undersides. Cements found in rockslide deposits comprise skalenohedral calcite, prismatic calcite, blocky calcite, calcitic micrite and micropeloidal calcitic cement and, rarely, botryoidal aragonite. Initial cement formation probably is driven by meteoric dissolution–re-precipitation of (mini-) micritic abrasive rock powder generated by dynamic disintegration during the rockslide event. Preliminary ²³⁴U/²³⁰Th ages of rockslide cements support a concept that cementation starts immediately or early after a rockslide event. In rockslide deposits of calcphyllite with accessory pyrite, oxidation of pyrite probably also propels the process of carbonate dissolution–re-precipitation. Limestone-precipitating springs emerging from rockslide masses, and well-cemented talus slopes and fluvial conglomerates percolated by rockslide-derived groundwaters, indicate that rockslide deposits remain diagenetically active long after emplacement.     

Fluid-assisted retrogression of garnet and P–T history of metapelites from HP/UHP metamorphic terrane (Pohorje Mountains, Eastern Alps)

Fluid inclusions in garnet combined with element X-ray mapping, phase equilibrium modelling and conventional thermobarometry have been used to constrain the metamorphic evolution of metapelitic gneiss from the HP/UHP metamorphic terrane of Pohorje Mountains in the Eastern Alps, Slovenia. Retrograde P–T trajectory from ~2.75 GPa and 780°C is constrained by the composition of matrix phengite (6.66 apfu Si) coexisting with garnet cores, kyanite and quartz. The intersection of the X _Prp = 0.25 isopleth for the garnet with the upper stability boundary for K-feldspar in the matrix indicates near-isothermal decompression to ~0.9 GPa at 720°C. Temperatures over 650°C during this stage are corroborated by the high degree of ordering of graphite inclusions associated with Zn, Mg-rich staurolite and phlogopite in the Mg-rich (X _Prp = 0.22–0.25) garnet cores. Majority of garnet porphyroblasts are depleted in Mg (down to X _Prp = 0.09) and enriched in Mn (up to X _Sps = 0.12) along cracks and at their margins. The associated retrograde mineral assemblage comprises Zn, Mg-poor staurolite, muscovite, biotite–siderophyllite, sillimanite and quartz. The onset of the retrogression and the compositional modification of the garnet porphyroblasts were accompanied by the addition of fluid-deposited graphite around older graphite inclusions, probably due to removal of water from a graphite-buffered COH fluid by dissolution in partial silicic melt. Instantaneous expulsion of water near the melt solidus (640°C, max. 0.45 GPa) caused dissolution of the graphite at redox conditions corresponding to 0.25–1.25 logfO₂ units below the QFM buffer, giving rise to a H₂O–CO₂–CH₄ fluid trapped in primary inclusions in Mn-rich, Mg-poor, almandine garnet that reprecipitated within the retrogressed domains. The absence of re-equilibration textures and consistent densities of the fluid inclusions reflect a near-isochoric cooling postdating the near-isothermal decompression. Bulk water content in the metapelite attained 2 wt% during this stage. The low-degree partial melting and extensive hydration due to the release of the internally derived, low-pressure aqueous fluids led to the reset of peak-pressure mineral assemblage.     

It starts at home? Climate policies targeting household consumption and behavioral decisions are key to low-carbon futures

Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy.     

Reaction rim growth in the system MgO-Al2O3-SiO2 under uniaxial stress

We synthesize reaction rims between thermodynamically incompatible phases in the system MgO-Al₂O₃-SiO₂ applying uniaxial load using a creep apparatus. Synthesis experiments are done in the MgO-SiO₂ and in the MgO-Al₂O₃ subsystems at temperatures ranging from 1150 to 1350 °C imposing vertical stresses of 1.2 to 29 MPa at ambient pressure and under a constant flow of dry argon. Single crystals of synthetic and natural quartz and forsterite, synthetic periclase and synthetic corundum polycrystals are used as starting materials. We produce enstatite rims at forsterite-quartz contacts, enstatite-forsterite double rims at periclase-quartz contacts and spinel rims at periclase-corundum contacts. We find that rim growth under the “dry” conditions of our experiments is sluggish compared to what has been found previously in nominally “dry” piston cylinder experiments. We further observe that the nature of starting material, synthetic or natural, has a major influence on rim growth rates, where natural samples are more reactive than synthetic ones. At a given temperature the effect of stress variation is larger than what is anticipated from the modification of the thermodynamic driving force for reaction due to the storage of elastic strain energy in the reactant phases. We speculate that this may be due to modification of the physical properties of the polycrystals that constitute the reaction rims or by deformation under the imposed load. In our experiments rim growth is very sluggish at forsterite-quartz interfaces. Rim growth is more rapid at periclase-quartz contacts. The spinel rims that are produced at periclase-corundum interfaces show parabolic growth indicating that reaction rim growth is essentially diffusion controlled. From the analysis of time series done in the MgO-Al₂O₃ subsystem we derive effective diffusivities for the Al₂O₃ and the MgO components in a spinel polycrystal as ${\rm D}_{MgO} = 1.4 \pm 0.2 \cdot 10^{-15}$  m²/s and ${\rm D}_{Al_2O_3} = 3.7 \pm 0.6 \cdot 10^{-16}$  m²/s for T?=?1350 °C and a vertical stress of 2.9 MPa.     

Hambergite-rich melt inclusions in morganite crystals from the Muiane pegmatite, Mozambique and some remarks on the paragenesis of hambergite

Raman spectroscopic studies of daughter crystals of hambergite [Be₂BO₃(OH, F)] in primary melt and secondary fluid inclusions in morganite crystals from the Muiane pegmatite, Mozambique, show that the inclusions have extremely high beryllium concentrations, corresponding to as much as 10.6% (g/g) in melt inclusions and 1.25% (g/g) BeO in fluid inclusions. These melt and fluid inclusions were trapped at about 610°C and 277°C, respectively. We propose two possible mechanisms for the formation of the hambergite crystals: (i) direct crystallization from a boron- and beryllium-rich pegmatite-forming melt or (ii) these are daughter crystals produced by the retrograde reaction of the boron-rich inclusion fluid with the beryl host, after release of boric acid from the primary trapped metastable volatile-rich silicate melt during cooling and recrystallization. Although we favor the second option, either case demonstrate the extent to which Be maybe concentrated in a boron-rich fluid at relatively high temperatures, and in which species of Be maybe transported. One important constraint on the stability of the hambergite paragenesis is temperature; at temperatures of ≥650°C (at 2 kbar) hambergite is not stable and converts to bromellite [BeO].     

Shear wave splitting in the Eastern Alps observed at the TRANSALP network

Data from the temporary TRANSALP seismic network were analysed to investigate the seismic anisotropy in the upper mantle beneath the Eastern Alps. We operated mostly short period and some broadband stations in a dense linear array, which transects the Eastern Alps at 12° E longitude. Recorded SKS and SKKS phases with different backazimuths were used simultaneously to calculate the splitting parameters of delay time and fast axis direction for each seismic station. While we found variations in the delay times between 0.8 and 2.0 s, the determined fast axis directions prove to be rather consistent along the profile (60°–70° N). They coincide well with the trend of the Eastern Alps, thus suggesting orogen-parallel flow in the upper mantle. Our findings support the earlier proposed idea that the Adriatic indenter which was forced northwards into the European plate during the late stage of the Alpine orogeny, triggered an escape movement to the less constrained Pannonian basin to the east.     

Multi-century simulations with the coupled GISS–HYCOM climate model: control experiments

Multi-century climate simulations obtained with the GISS atmospheric general circulation model coupled to the hybrid-isopycnic ocean model HYCOM are described. Greenhouse gas concentrations are held fixed in these experiments to investigate the coupled model’s ability to reproduce the major features of today’s climate with minimal drift. Emphasis is placed on the realism of the oceanic general circulation and its effect on air–sea exchange processes. Several model runs using different closures for turbulent vertical exchange as well as improvements to reduce vertical numerical diffusion are compared with climate observations. As in previous studies, the Southern Ocean emerges as the Achilles Heel of the ocean model; deficiencies in its physical representation had far-reaching consequences in early experiments with the coupled model and have provided the strongest impetus for model improvement. The overarching goal of this work is to add diversity to the pool of ocean models available for climate prediction and thereby reduce biases that may stand in the way of assessing climate prediction uncertainty.

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Constraints on interpretation of the Eltanin impact from numerical simulations

The results of numerical simulations of the Eltanin impact are combined with the available geological data in order to reconstruct the impact dynamics and to get some constraints on the impact parameters. Numerical simulations show that the Eltanin projectile size should be less than 2 km for a 45° oblique impact and less than 1.5 km for a vertical impact. On the other hand, we demonstrate that the projectile diameter cannot be considerably smaller than 1 km; otherwise, the impact‐induced water flow cannot transport eroded sediments across large distances. The maximum displacement approximately equals the water crater radius and rapidly decreases with increasing distances. Numerical simulations also show that ejecta deposits strongly depend on impact angle and projectile size and, therefore, cannot be used for reliable estimates of the initial projectile mass. The initial amplitudes of tsunami‐like waves are estimated. The presence of clay‐rich sediments, typical for the abyssal basins in cores PS2709 and PS2708 on the Freeden Seamounts (Bellingshausen Sea, Southern Ocean) combined with numerical data allow us to suggest a probable point of impact to the east of the seamounts. The results do not exclude the possibility that a crater in the ocean bottom may exist, but such a structure has not been found yet.     

The Ardón L6 ordinary chondrite: A long‐hidden Spanish meteorite fall

We report and describe an L6 ordinary chondrite fall that occurred in Ardón, León province, Spain (longitude 5.5605°W, latitude 42.4364°N) on July 9th, 1931. The 5.5 g single stone was kept hidden for 83 yr by Rosa González Pérez, at the time an 11 yr old who had observed the fall and had recovered the meteorite. According to various newspaper reports, the event was widely observed in Northern Spain. Ardón is a very well‐preserved, fresh, strongly metamorphosed (petrologic type 6), and weakly shocked (S3) ordinary chondrite with well‐equilibrated and recrystallized minerals. The mineral compositions (olivine Fa_23.7±0.3, low‐Ca pyroxene Fs_20.4±0.2Wo_1.5±0.2, plagioclase An_10.3±0.5Ab_84.3±1.2), magnetic susceptibility (log χ = 4.95 ± 0.05 × 10^?9 m³ kg^?1), bulk density (3.49 ± 0.05 g   cm^?3), grain density (3.58 ± 0.05 g   cm^?3), and porosity (2.5 vol%) are typical for L6 chondrites. Short‐lived radionuclides confirm that the meteorite constitutes a recent fall. The ²¹Ne and ³⁸Ar cosmic ray exposure ages are both about 20–30 Ma, similar to values for many other L chondrites. The cosmogenic ²²Ne/²¹Ne ratio indicates that preatmospheric Ardón was a relatively large body. The fact that the meteorite was hidden in private hands for 83 yr makes one wonder if other meteorite falls may have experienced the same fate, thus possibly explaining the anomalously low number of falls reported in continental Spain in the 20th century.