Recovery and curation of the Winchcombe (CM2) meteorite

The Winchcombe meteorite fell on February 28, 2021 and was the first recovered meteorite fall in the UK for 30 years, and the first UK carbonaceous chondrite. The meteorite was widely observed by meteor camera networks, doorbell cameras, and eyewitnesses, and 213.5 g (around 35% of the final recovered mass) was collected quickly—within 12 h—of its fall. It, therefore, represents an opportunity to study very pristine extra-terrestrial material and requires appropriate careful curation. The meteorite fell in a narrow (600 m across) strewn field ~8.5 km long and oriented approximately east–west, with the largest single fragment at the farthest (east) end in the town of Winchcombe, Gloucestershire. Of the total known mass of 602 g, around 525 g is curated at the Natural History Museum, London. A sample analysis plan was devised within a month of the fall to enable scientists in the UK and beyond to quickly access and analyze fresh material. The sample is stored long term in a nitrogen atmosphere glove box. Preliminary macroscopic and electron microscopic examinations show it to be a CM2 chondrite, and despite an early search, no fragile minerals, such as halite, sulfur, etc., were observed.     

Regional projections of the likelihood of very large wildland fires under a changing climate in the contiguous Western United States

Seasonal changes in the climatic potential for very large wildfires (VLWF?≥?50,000 ac?~?20,234 ha) across the western contiguous United States are projected over the 21st century using generalized linear models and downscaled climate projections for two representative concentration pathways (RCPs). Significant (p?≤?0.05) increases in VLWF probability for climate of the mid-21st century (2031–2060) relative to contemporary climate are found, for both RCP 4.5 and 8.5. The largest differences are in the Eastern Great Basin, Northern Rockies, Pacific Northwest, Rocky Mountains, and Southwest. Changes in seasonality and frequency of VLWFs d7epend on changes in the future climate space. For example, flammability-limited areas such as the Pacific Northwest show that (with high model agreement) the frequency of weeks with VLWFs in a given year is 2–2.7 more likely. However, frequency of weeks with at least one VLWF in fuel-limited systems like the Western Great Basin is 1.3 times more likely (with low model agreement). Thus, areas where fire is directly associated with hot and dry climate, as opposed to experiencing lagged effects from previous years, experience more change in the likelihood of VLWF in future projections. The results provide a quantitative foundation for management to mitigate the effects of VLWFs.     

The CLIVAR C20C project: selected twentieth century climate events

We use a simple methodology to test whether a set of atmospheric climate models with prescribed radiative forcings and ocean surface conditions can reproduce twentieth century climate variability. Globally, rapid land surface warming since the 1970s is reproduced by some models but others warm too slowly. In the tropics, air-sea coupling allows models to reproduce the Southern Oscillation but its strength varies between models. We find a strong relationship between the Southern Oscillation in global temperature and the rate of global warming, which could in principle be used to identify models with realistic climate sensitivity. This relationship and a weak response to ENSO suggests weak sensitivity to changes in sea surface temperature in some of the models used here. In the tropics, most models reproduce part of the observed Sahel drought. In the extratropics, models do not reproduce the observed increase in the North Atlantic Oscillation in response to forcings, through internal variability, or as a combination of both.     

Geophysical fingerprints of hyper-extended,exhumed and embryonic oceanic domains: the example from the Iberia–Newfoundland rifted margins

This study investigates the magnetic and gravity signatures and associated seismic character of hyper-extended, exhumed and embryonic oceanic domains along the conjugate Iberia–Newfoundland rifted margins. As these margins have been drilled down to basement along their distal parts, it is possible to explore and test different geophysical techniques and interpretations. The aims of this work are twofold: (1) to investigate the location and nature of the two main marginal boundaries—the necking zone and the J Anomaly, which define the limits of major domains; and (2) to map the lateral variations of gravity and magnetic signatures and their detailed correlation with seismic data, from the proximal margin until the first unequivocal oceanic magnetic anomaly (e.g. C34 Anomaly). The results point out that the J Anomaly corresponds to a first-order tectono-magmatic boundary, with a basement formed by polyphase magmatism. It marks the boundary between the exhumed mantle domain, with little magmatic additions, from a domain oceanwards that reveals comparable trends, frequencies and a general magnetic pattern at both sides of the Atlantic, suggesting a coeval evolution. We propose that the domain between the J and the C34 Anomalies was formed by an embryonic spreading system, with intermittent budgets of magma, similar to those observed at very slow spreading systems. The J Anomaly may thus correspond to the location of lithospheric breakup though its origin and the nature of the domain oceanwards remains to be constrained.     

Analysis of wave propagation in dry granular soils using DEM simulations

In this paper, a three-dimensional particle-based technique utilizing the discrete element method (DEM) is proposed to study wave propagation in a dry granular soil column. Computational simulations were conducted to investigate the soil response to sinusoidal motions with different amplitudes and frequencies. Three types of soil deposits with different void ratios were employed in these simulations. Different boundary conditions at the base such as rigid bedrock, elastic bedrock, and infinite medium were also considered. Analysis is done in time domain while taking into account the effects of soil nonlinear behavior. The computational approach is able to capture a number of essential characteristics of wave propagation including motion amplification and resonance. Dynamic soil properties were then extracted from conducted simulations and used to predict the response of the soil using the widely used equivalent linear method program SHAKE and compare its predictions to DEM results. Generally, there was a good agreement between SHAKE and DEM results except when the exciting frequency was close to the resonance frequency of the deposit where significant discrepancy in computed shear strains between SHAKE predictions and DEM results was observed.     

Hydroxyl in mantle olivine xenocrysts from the Udachnaya kimberlite pipe

The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to −180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730–3,330 cm⁻¹. Bands at high energies (3,730–3,670 cm⁻¹) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites (3,607 cm⁻¹ E || a, 3,597 E || a, 3,571 cm⁻¹ E || c, 3,567 E || c, and 3,556 E || b), and (b) with vacant M1 sites (most of the bands polarized parallel to a). From the pleochroic behavior and position of the OH bands associated with the vacant M1 sites, we propose two types of hydrogen—one bonded to O1 and another to O2, so that both OH vectors are strongly aligned parallel to a. The O2–H groups may be responsible for the OH bands at higher wavenumbers than those for the O1–H groups. The multiplicity of the corresponding OH bands in the spectra can be explained by different chemical environments and by slightly different distortions of the M1 sites in these high-pressure olivines. Four samples were investigated by SIMS. The calculated integral molar absorption coefficient using the IR and SIMS results of 37,500±5,000 L mol H₂O cm⁻² is within the uncertainties slightly higher than the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003) (28,450±1,830 L mol H₂O cm⁻²). The reason for the difference is the different distributions of the absorption intensity of the spectra of both studies (mean wavenumber 3,548 vs. 3,570 cm⁻¹). Olivine samples with a mean wavenumber of about 3,548 cm⁻¹ should be quantified with the absorption coefficient as determined in this study; those containing more bands at higher wavenumber (mean wavenumber 3,570 cm⁻¹) should be quantified using the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003).

A propensity for n‐ω‐amino acids in thermally altered Antarctic meteorites

Abstract– Asteroids and their fragments have impacted the Earth for the last 4.5 Gyr. Carbonaceous meteorites are known to contain a wealth of indigenous organic molecules, including amino acids, which suggests that these meteorites could have been an important source of prebiotic organic material during the origins of life on Earth and possibly elsewhere. We report the detection of extraterrestrial amino acids in thermally altered type 3 CV and CO carbonaceous chondrites and ureilites recovered from Antarctica. The amino acid concentrations of the thirteen Antarctic meteorites ranged from 300 to 3200 parts‐per‐billion (ppb), generally much less abundant than in amino acid‐rich CI, CM, and CR carbonaceous chondrites that experienced much lower temperature aqueous alteration on their parent bodies. In contrast to low‐temperature aqueously altered meteorites that show complete structural diversity in amino acids formed predominantly by Strecker–cyanohydrin synthesis, the thermally altered meteorites studied here are dominated by small, straight‐chain, amine terminal (n‐ω‐amino) amino acids that are not consistent with Strecker formation. The carbon isotopic ratios of two extraterrestrial n‐ω‐amino acids measured in one of the CV chondrites (δ¹³C approximately ?25‰) are consistent with ¹³C‐depletions observed previously in hydrocarbons produced by Fischer‐Tropsch type reactions. The predominance of n‐ω‐amino acid isomers in thermally altered meteorites hints at cosmochemical mechanisms for the preferential formation and preservation of a small subset of the possible amino acids.     

Crystalline silicates in comets: How did they form?

Two processes have been proposed to explain observations of crystalline silicate minerals in comets and in protostellar sources, both of which rely on the thermal annealing of amorphous grains. First, high temperatures generated by nebular shock processes can rapidly produce crystalline magnesium silicate grains and will simultaneously produce a population of crystalline iron silicates whose average grain size is ∼10-15% that of the magnesium silicate minerals. Second, exposure of amorphous silicate grains to hot nebular environments can produce crystalline magnesium silicates that might then be transported outward to regions of comet formation. At the higher temperatures required for annealing amorphous iron silicates to crystallinity the evaporative lifetime of the grains is much shorter than a single orbital period where such temperatures are found in the nebula. Thermal annealing is therefore unable to produce crystalline iron silicate grains for inclusion into comets unless such grains are very quickly transported away from the hot inner nebula. It follows that observation of pure crystalline magnesium silicate minerals in comets or protostars is a direct measure of the importance of simple thermal annealing of grains in the innermost regions of protostellar nebulae followed by dust and gas transport to the outer nebula. The presence of crystalline iron silicates would signal the action of transient processes such as shock heating that can produce crystalline iron, magnesium and mixed iron-magnesium silicate minerals. These different scenarios result in very different predictions for the organic content of protostellar systems.