The continental record of Ediacaran volcano‐sedimentary successions in southern Brazil and their global implications

The Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation.     

Composition of hydrated near-Earth object (100085) 1992 UY4

Near-infrared spectra of the near-Earth object (100085) 1992 UY4 are similar to those of P-type asteroids, providing a fitted geometric albedo of 0.052±0.005 and an effective diameter of 1.68±0.08 km. This object, with a likely outer-belt origin, also exhibits a 3-μm absorption feature with a band depth of 3%±1%, corresponding to a regolithic bulk hydrogen-to-silicon ratio of 0.30±0.05. The bulk of this hydrogen seems to be present in H₂O-dominated minerals.     

A synthesis of morphological evolutions and Holocene stratigraphy of a wave-dominated estuary: The Arcachon lagoon,SW France

This work presents the first synthesis of secular to millenary morphological evolutions and stratigraphy of a wave-dominated estuary, the Arcachon lagoon, from a combination of unpublished bathymetric maps (1865 and 2001), core results and high-resolution seismic profiles recorded for the first time in this lagoon. The Arcachon lagoon is located on the Atlantic coast of France, facing the wave-dominated shelf of the Bay of Biscay. It is a mesotidal semi-enclosed environment of about 160 km².The sediment budget of the Arcachon lagoon was computed by subtracting the 1865 bathymetric map from that of 2001. The computed volume difference is low (?9.9±35×10⁶ m³ in 136 yrs) and is the result of the balance between erosion and accretion that occurs within tidal channels and tidal flats, respectively. This morphological evolution pattern is explained by low sediment supply and also by the tidal distortion resulting from the morphology of the lagoon. Deep channels connected to the inlet are dominated by ebb currents inducing erosion. Tidal flats and transverse channels display weak or flood-dominated tidal currents leading to the deposition of silts. The areas of tidal flat siltation locally correlate with the presence of oyster farms, suggesting the influence of Man on the lagoon sediment-fill. Transverse channel-infill is related to weak tidal currents resulting from the hydraulically inefficient orientation of these channels which served as an ancient drainage network.Evidence for tidal channel-infill and channel abandonment are also provided by seismic profiling and cores. The upper stratigraphic succession of the lagoon (about 10 m thick) includes four main stratigraphic units dominated by channel-fills. The two lower units (around 7500–2800 yrs BP) display tabular-shape sandy channels interpreted to be records of the open estuarine phase of the Arcachon lagoon. The two upper units (around 2800 yrs BP to present-day) display U-shaped mixed sand-and-mud channel-fills interpreted to be records of the closure of the lagoon. Given that the basal estuarine units are transgressive and the upper lagoonal units are regressive, the main stratigraphic change at around 2800 yrs BP is interpreted as being the maximum flooding surface (MFS). This late MFS is explained by the low sediment supply. It is proposed that the transition from the estuarine to the lagoonal phase is related to the development of the Cap-Ferret spit in response to an increase in the ratio between wave power to tide power. This change in wave-to-tide ratio may be triggered by wave power increase following the Subboreal/Subatlantic climate instability or a decrease in tide power following a decrease in tidal prism related to the lagoon sediment-fill.Thus, the evolution of the Arcachon lagoon over the last millenaries was mainly controlled by its spit development, leading to a wave-dominated estuary in terms of its geomorphology. Once it was partially closed, extensive mud flats developed in the lagoon which became ebb-dominated.     

Simulations of baryon oscillations

The coupling of photons and baryons by Thomson scattering in the early universe imprints features in both the cosmic microwave background (CMB) and matter power spectra. The former have been used to constrain a host of cosmological parameters, the latter have the potential to strongly constrain the expansion history of the universe and dark energy. Key to this program is the means to localize the primordial features in observations of galaxy spectra which necessarily involve galaxy bias, non-linear evolution and redshift space distortions. We present calculations, based on mock catalogs produced from high-resolution N-body simulations, which show the range of behaviors we might expect of galaxies in the real universe. We investigate physically motivated fitting forms which include the effects of non-linearity, galaxy bias and redshift space distortions and discuss methods for analysis of upcoming data. In agreement with earlier work, we find that a survey of several Gpc³ would constrain the sound horizon at z  1 to about 1%.     

Evaluating the role of climate and tectonics during non-steady incision of the Yellow River: evidence from a 1.24 Ma terrace record near Lanzhou,China

The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision.     

A georeferenced agent-based model to analyze the climate change impacts on ski tourism at a regional scale

One main argument for modeling socio-ecological systems is to advance the understanding of dynamic correlations between various human and environmental factors, including impacts and responses to environmental change. We explore the shift in skier distribution among ski resorts taking into account the behavioral adaptation of individuals due to the impact of climate change on snow conditions. This analysis is performed at a regional scale by means of a coupled gravity and georeferenced agent-based model. Four different scenarios are considered. Two scenarios assume an increase of winter mean temperature of +2°C and +4°C, respectively, taking into account only natural snow conditions. Two additional scenarios add the effect of snowmaking to enhance the natural snow depth and extend the skiing season in the +2°C and +4°C base scenarios. Results show differing vulnerability levels, allowing the classification of ski resorts into three distinct groups: (1) highly vulnerable ski resorts with a strong reduction in visitors attendance for all climate change scenarios, characterized by unfavorable geographical and attractiveness conditions, making it difficult to ensure snow availability in the future; (2) low vulnerability ski resorts, with moderate reduction in season length during a high climate change scenario but no reduction (or even an increase) in a low one, characterized by ski resorts with a medium capacity and attractiveness to ensure enough snow conditions and capture skiers from other ski resorts; and (3) resilient ski resorts, with good conditions to ensure future snow-reliable seasons and outstanding attractiveness, allowing them to offer longer ski seasons than their competitors and potentially attracting skiers from other closed or marginal resorts. Ski resorts included in this last group increase their skier attendance in all climate change scenarios. Although similar studies in the literature foretell a significant reduction of the ski market in the near future, another probable effect outlined in this study is a redefinition of this market due to a redistribution of skiers, from vulnerable ski resorts to more resilient ones.     

Laboratory plasma dynamos, astrophysical dynamos and magnetic helicity evolution

The term 'dynamo' means different things to the laboratory fusion plasma and astrophysical plasma communities. To alleviate the resulting confusion and to facilitate interdisciplinary progress, we pinpoint conceptual differences and similarities between laboratory plasma dynamos and astrophysical dynamos. We can divide dynamos into three types: 1. magnetically dominated helical dynamos which sustain a large-scale magnetic field against resistive decay and drive the magnetic geometry towards the lowest energy state, 2. flow-driven helical dynamos which amplify or sustain large-scale magnetic fields in an otherwise turbulent flow and 3. flow-driven non-helical dynamos which amplify fields on scales at or below the driving turbulence. We discuss how all three types occur in astrophysics whereas plasma confinement device dynamos are of the first type. Type 3 dynamos require no magnetic or kinetic helicity of any kind. Focusing on Types 1 and 2 dynamos, we show how different limits of a unified set of equations for magnetic helicity evolution reveal both types. We explicitly describe a steady-state example of a Type 1 dynamo, and three examples of Type 2 dynamos: (i) closed volume and time dependent; (ii) steady state with open boundaries; (iii) time dependent with open boundaries.     

Infrared imaging spectroscopy with micron resolution of Sutter's Mill meteorite grains

Synchrotron‐based Fourier transform infrared spectroscopy and Raman spectroscopy are applied with submicrometer spatial resolution to multiple grains of Sutter's Mill meteorite, a regolith breccia with CM1 and CM2 lithologies. The Raman and infrared active functional groups reveal the nature and distribution of organic and mineral components and confirm that SM12 reached higher metamorphism temperatures than SM2. The spatial distributions of carbonates and organic matter are negatively correlated. The spatial distributions of aliphatic organic matter and OH relative to the distributions of silicates in SM2 differ from those in SM12, supporting a hypothesis that the parent body of Sutter's Mill is a combination of multiple bodies with different origins. The high aliphatic CH₂/CH₃ ratios determined from band intensities for SM2 and SM12 grains are similar to those of IDPs and less altered carbonaceous chondrites, and they are significantly higher than those in other CM chondrites and diffuse ISM objects.