Earth's most severe climate changes occurred during global-scale snowball-Earth glaciations, which profoundly altered Earth's atmosphere, oceans, and biosphere. Extreme rates of glacio-eustatic ...sea-level rise are a fundamental prediction of the snowball Earth hypothesis, but supporting geologic evidence is lacking. We use paleohydraulic analysis of wave ripples and tidal laminae of the Elatina Formation, Australia - deposited following the Marinoan glaciation ca. 635Ma - to show that water depths of 9-16m remained nearly constant for ~100yrs throughout 27m of sediment accumulation. This accumulation rate was too great to have been accommodated by subsidence, and instead indicates an extraordinarily rapid rate of sea-level rise (0.2-0.27m/yr). Our results substantiate a fundamental prediction of snowball Earth models of rapid deglaciation during the early transition to a super-greenhouse climate.
Autoantibodies directed against cytosolic 5'-nucleotidase 1A have been identified in many patients with inclusion body myositis. This retrospective study investigated the association between ...anticytosolic 5'-nucleotidase 1A antibody status and clinical, serological and histopathological features to explore the utility of this antibody to identify inclusion body myositis subgroups and to predict prognosis.
Data from various European inclusion body myositis registries were pooled. Anticytosolic 5'-nucleotidase 1A status was determined by an established ELISA technique. Cases were stratified according to antibody status and comparisons made. Survival and mobility aid requirement analyses were performed using Kaplan-Meier curves and Cox proportional hazards regression.
Data from 311 patients were available for analysis; 102 (33%) had anticytosolic 5'-nucleotidase 1A antibodies. Antibody-positive patients had a higher adjusted mortality risk (HR 1.89, 95% CI 1.11 to 3.21, p=0.019), lower frequency of proximal upper limb weakness at disease onset (8% vs 23%, adjusted OR 0.29, 95% CI 0.12 to 0.68, p=0.005) and an increased prevalence of excess of cytochrome oxidase deficient fibres on muscle biopsy analysis (87% vs 72%, adjusted OR 2.80, 95% CI 1.17 to 6.66, p=0.020), compared with antibody-negative patients.
Differences were observed in clinical and histopathological features between anticytosolic 5'-nucleotidase 1A antibody positive and negative patients with inclusion body myositis, and antibody-positive patients had a higher adjusted mortality risk. Stratification of inclusion body myositis by anticytosolic 5'-nucleotidase 1A antibody status may be useful, potentially highlighting a distinct inclusion body myositis subtype with a more severe phenotype.
Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter— to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science ...Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.
Detailed chemical abundances for five stars in two Galactic globular clusters, NGC 5466 and NGC 5024, are presented from high-resolution optical (from the Hobby-Eberley Telescope) and infrared ...spectra (from the SDSS-III APOGEE survey). We find Fe/H = −1.97 ± 0.13 dex for NGC 5466, and Fe/H = −2.06 ± 0.13 dex for NGC 5024, and the typical abundance pattern for globular clusters for the remaining elements, e.g. both show evidence for mixing in their light element abundance ratios (C, N), and asymptotic giant branch contributions in their heavy element abundances (Y, Ba, and Eu). These clusters were selected to examine chemical trends that may correlate them with the Sgr dwarf galaxy remnant, but at these low metallicities no obvious differences from the Galactic abundance pattern are found. Regardless, we compare our results from the optical and infrared analyses to find that oxygen and silicon abundances determined from the infrared spectral lines are in better agreement with the other α-element ratios and with smaller random errors.
Large ripples with meter‐scale wavelengths are ubiquitous across Mars. Curiosity's traverse of the Bagnold Dune Field revealed a morphologic diversity of large Martian ripples that helps constrain ...their formative mechanism. Large ripples develop in isolated fields and on dunes. They form transversely and obliquely to longitudinally to the net sand‐flux direction in unimodally and bimodally distributed very fine to very coarse sand. They have either straight or sinuous crestlines. Inactive ripples are covered with dust, whereas migrating ripples are dust free. Here we present a unifying view of ripples that form in near‐bed sediment‐transport conditions (encompassing fluid‐drag and coarse‐grained ripples) to explain the range of large‐Martian‐ripple morphologies and expand the use of bedforms as environmental indicators.
Plain Language Summary
Large sand ripples with meter‐scale crest‐to‐crest spacings abound on the Martian surface but are not found in terrestrial sandy deserts. Along its traverse through the Bagnold Dune Field, the Curiosity rover witnessed a rich diversity of such large ripples, both in terms of their shape and of their behavior. Rover observations help understand how these mysterious large Martian ripples form. Here we present a unifying view of ripples that form when grains are mobilized near the sediment bed by various fluids and across planets. Such an understanding of the formation mechanics of similar ripples will enable scientists to use the ripples' imprints on landscapes and in rocks to infer modern and past environmental conditions.
Key Points
Martian ripples are diverse in morphology, dynamics, and activity
Large Martian ripples belong to a family of bedforms that forms when a significant fraction of sediment transport occurs near the bed
Near‐bed‐transport bedforms are found across environments and planets and may prove useful quantitative paleoenvironment indicators
Catastrophic drainage of glacial Lake Missoula through the Columbia River Gorge, USA, produced some of the largest floods ever known. However, erosion of the gorge during flooding has not been ...quantified, hindering discharge reconstructions and our understanding of landscape change by megafloods. Using a neural network and geomorphic observations, we reconstructed the gorge topography and found ∼7.4 km3 of rock was eroded from gorge walls. Accounting for a narrower canyon and matching flood high‐water marks resulted in peak‐flood discharge reconstructions of 6 × 106–7 × 106 m3 s−1, which are 30%–40% lower than prior estimates based on the present‐day topography. Sediment transport modeling indicated that more frequent intermediate‐sized floods transported most of the eroded rock. Thus, similar to alluvial rivers, discharge magnitude‐frequency tradeoffs may also govern canyon formation by repeated megafloods.
Plain Language Summary
Some of the largest floods in Earth's history occurred 20–14 thousand years ago from the catastrophic drainage of glacial Lake Missoula. The floodwaters coalesced near the Columbia Gorge, where the water flowed through a single channel. Prior work focused on the Columbia Gorge to reconstruct the magnitude of these floods. However, these estimates did not account for erosion by the massive floods, which changed the topography. In this study, we used a machine learning computational technique to reconstruct the topography prior to megaflood erosion. Our results show ∼7.4 km3 of rock was eroded from gorge walls. Accounting for a narrower gorge and matching flood high‐water marks resulted in a peak‐flood discharge that is 30%–40% lower than prior estimates, thus downsizing the largest floods in Earth's history. Modeling sediment transport over a series of floods indicated more frequent intermediate‐sized floods transported most of the eroded rock, rather than the largest floods. This finding is similar to observations in rivers with sediment banks where tradeoffs exist between the size and frequency of floods in governing channel shape. Thus, it is possible that the same principles that govern the form of alluvial rivers also govern bedrock canyon formation by repeated megafloods.
Key Points
Geomorphic observations and topographic reconstruction indicate the Missoula floods caused widening of the Columbia Gorge
Peak discharge estimates decline by 30%–40% when accounting for a narrower canyon
Megafloods of moderate frequency and magnitude, rather than the largest flood, transported most of the eroded rock from the Columbia Gorge
Steep mountain streams have channel morphologies that transition from alternate bar to step‐pool to cascade with increasing bed slope, which affect stream habitat, flow resistance, and sediment ...transport. Experimental and theoretical studies suggest that alternate bars form under large channel width‐to‐depth ratios, step‐pools form in near supercritical flow or when channel width is narrow compared to bed grain size, and cascade morphology is related to debris flows. However, the connection between these process variables and bed slope—the apparent dominant variable for natural stream types—is unclear. Combining field data and theory, we find that certain bed slopes have unique channel morphologies because the process variables covary systematically with bed slope. Multiple stable states are predicted for other ranges in bed slope, suggesting that a competition of underlying processes leads to the emergence of the most stable channel form.
Key Points
Channel form in steep rivers systematically changes with bed slope for reasons that remain unclear
Building on previous studies, we identify process variables that control channel form and show how these variables covary with bed slope
The relationship between channel form and bed slope depends on channel width‐to‐depth ratio, grain size‐to‐width ratio, and Froude number
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