Sulphur and Carbon Isotopes as Tracers of Past Sub-seafloor Microbial Activity

Microbial life below the seafloor has changed over geological time, but these changes are often not obvious, as they are not recorded in the sediment. Sulphur (S) isotope values in pyrite extracted from a Plio- to Holocene sequence of the Peru Margin (Ocean Drilling Program, ODP, Site 1229) show a down-core pattern that correlates with the pattern of carbon (C) isotopes in diagenetic dolomite. Early formation of the pyrite is indicated by the mineralogical composition of iron, showing a high degree of pyritization throughout the sedimentary sequence. Hence, the S-record could not have been substantially overprinted by later pyrite formation. The S- and C-isotope profiles show, thus, evidence for two episodes of enhanced microbial methane production with a very shallow sulphate-methane transition zone. The events of high activity are correlated with zones of elevated organic C content in the stratigraphic sequence. Our results demonstrate how isotopic signatures preserved in diagenetic mineral phases provide information on changes of past biogeochemical activity in a dynamic sub-seafloor biosphere

U-Pb zircon age of volcaniclastic layers in Middle Triassic platform carbonates of the Austroalpine Silvretta nappe (Switzerland)

We present precise U-Pb age determinations from two volcaniclastic layers within Middle Triassic carbonates in the Upper Austroalpine Silvretta nappe near Davos (Switzerland). The two volcaniclastic layers were dated using annealing-leaching techniques and yielded ages of 240.91 ± 0.26Ma (Prosanto Formation) and 239.89 ± 0.21Ma (Altein Formation), respectively. The high resolution ages allow comparison of the Upper Austroalpine record of the Ducan with sections in the Southern Alps. The upper Prosanto Formation is, thus, equivalent to the middle part of the Buchenstein Formation (Middle Pietra Verde, Earliest Ladinian), and the Altein Formation is equivalent to the upper part of the Buchenstein Formation in the section with the Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian (Bagolino, northern Italy). This study demonstrates that we can use precise, accurate and carefully intercalibrated U-Pb zircon ages from volcaniclastic layers to infer the stratigraphic position of their host sediments on zone level. The older volcaniclastic layer (240.91 ± 0.26Ma) allows a precise age determination (earliest Ladinian) for the marine vertebrate beds in the upper Prosanto Formatio

DOLOMITE FORMATION BY NANOCRYSTAL AGGREGATION IN THE DOLOMIA PRINCIPALE OF THE BRENTA DOLOMITES (NORTHERN ITALY)

Upper intra- to supratidal laminites in the Norian Dolomia Principale of the Brenta Dolomites (Northern Italy) commonly consist of aphanitic and partially peloidal dolomite previously interpreted as very early diagenetic or penecontemporaneous. Re-examination of a sample prepared by focused ion beam milling through high-resolution transmission electron microscopy (TEM) revealed that dolomicrite crystals may consist of ca. 5-nm-sized nanocrystals characterized by imperfectly aligned orientation. A similar type of dolomite was found in clay-rich Carnian laminites of the Travenanzes Formation (Venetian Alps, Northern Italy) and was interpreted as indication of primary precipitation. The observation of nanocrystals in both the Dolomia Principale and the Travenanzes Formation allows hypothesizing that dolomite mud formed directly from solution via a non-classical pathway involving nucleation and aggregation of nano-particles. Domains of nanocrystalline dolomite in the Dolomia Principale are embedded within, or cemented by, calcian dolomite showing coherent lattice at the micrometre scale and a modulated structure under the TEM. This new finding provides the first evidence that one of the largest dolomite bodies occurring in the geological record, the Dolomia Principale, commenced with deposition of sediment, consisting of dolomite mud formed from solution via non-classical crystallization, and was partially affected by later pervasive diagenetic dolomitization. Based on these new observations we propose that further nano-scale studies are necessary to substantiate the hypothesis that the formation of large dolomite bodies characterized by abundant dolomicrite may have commenced by non-classical nucleation and growth processes. This approach may provide insight on non-actualistic conditions in ancient environments that may have differed, in their boundary conditions, from their modern analogues

Revisiting the Uniform Information Density Hypothesis

The uniform information density (UID) hypothesis posits a preference among language users for utterances structured such that information is distributed uniformly across a signal. While its implications on language production have been well explored, the hypothesis potentially makes predictions about language comprehension and linguistic acceptability as well. Further, it is unclear how uniformity in a linguistic signal -- or lack thereof -- should be measured, and over which linguistic unit, e.g., the sentence or language level, this uniformity should hold. Here we investigate these facets of the UID hypothesis using reading time and acceptability data. While our reading time results are generally consistent with previous work, they are also consistent with a weakly super-linear effect of surprisal, which would be compatible with UID's predictions. For acceptability judgments, we find clearer evidence that non-uniformity in information density is predictive of lower acceptability. We then explore multiple operationalizations of UID, motivated by different interpretations of the original hypothesis, and analyze the scope over which the pressure towards uniformity is exerted. The explanatory power of a subset of the proposed operationalizations suggests that the strongest trend may be a regression towards a mean surprisal across the language, rather than the phrase, sentence, or document -- a finding that supports a typical interpretation of UID, namely that it is the byproduct of language users maximizing the use of a (hypothetical) communication channel

Controlled expansion of shell-shaped Bose–Einstein condensates

Motivated by the recent experimental realization of ultracold quantum gases in shell topology, we propose a straightforward implementation of matter-wave lensing techniques for shell-shaped Bose–Einstein condensates. This approach allows to significantly extend the free evolution time of the condensate shell after release from the trap and enables the study of novel quantum many-body effects on curved geometries. With both analytical and numerical methods we derive optimal parameters for realistic schemes to conserve the shell shape of the condensate for times up to hundreds of milliseconds

Polysaccharide Blend Fibres Formed from NaOH, N-Methylmorpholine-N-oxide and 1-Ethyl-3-methylimidazolium acetate

Article disponible sur le site de l'éditeur : http://www.fibtex.lodz.pl/article330.htmlInternational audienceThe aim of the study was to find new structured biopolymer blends bearing adjustable properties able to produce innovative materials. Apart from cellulose and three solvents (NaOH, N-methylmorpholine-N-oxide [NMMO] and 1-ethyl-3-methylimidazolium acetate [EMIMac]), 15 different polysaccharides were chosen to study the interactions ofpolysaccharides or their mixtures in solutions, as well as the solid state after forming. Dissolution screenings yielded promising polysaccharides, which were used for the preparation of cellulose/ polysaccharide solutions and subsequently for the shaping of blends with cellulose. The solubility and miscibility were evaluated by microscopy, DSC, particle analysis and rheology. Polysaccharides with a structure similar to that of cellulose, e.g., xylan, carrageenan or cellulose carbamate were not miscible, showing globular morphologies, whereas high-molar and side chains containing polysaccharides such as xanthan or tragacanth gum form co-continuous morphologies. The forming of blend fibres was nevertheless possible for all three solvents. The textile-physical properties of the blend fibres were slightly decreased compared to those of the unmodified fibre, in which fibres from NMMO and EMIMac had the highest performance. The presence of blended polysaccharides in the fibres produced was verified by residue sugar analysis, in which the highest amounts occurred for EMIMac fibres

Shell-shaped Bose-Einstein condensates realized with dual-species mixtures

Confining Bose-Einstein condensates (BECs) in shell-shaped trapping potentials enables the generation of hollow quasi-2D topologies with superfluid properties. Motivated by recent microgravity experiments, these shell-shaped BECs are nowadays actively studied both theoretically and experimentally, with radio-frequency (rf) dressing being the main trapping mechanism under study. Here we present an alternative approach that utilizes the repulsive interaction in a dual-species mixture to achieve shell-shaped BECs, which could be realized in the future BECCAL mission. In contrast to the rf case, which relies on a dynamical transition from a filled to a hollow condensate, the mixture approach is based on realizing the shell structure as the ground state of the system, where one species is located at the center of the trap surrounded by the other and kept in place by the repulsive inter-species interaction. We compare both approaches by analyzing the initial states, the free expansion dynamics, and the collective excitation spectrum with analytical and numerical methods. In all three categories the mixture performs similar to the rf approach. Moreover, the interaction-driven expansion of the mixture allows to increase the size of the shell during time-of-flight without distorting its shape and therefore magnifying the dynamics within the shell; a mechanism not realizable in the rf case. We conclude by performing a feasibility analysis for both approaches that takes residual gravitational effects and possible trap asymmetries into account, which currently are the main obstacles to experimentally realize shell-shaped BECs

Magnetic Doping and Kondo Effect in Bi2Se3 Nanoribbons

A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically-protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surface-to-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically-doped Bi2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than ~ 2%, low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics.Comment: 16 pages, 4 figure

Factors controlling the carbon isotope composition of dissolved inorganic carbon and methane in marine porewater: An evaluation by reaction-transport modelling

Carbon isotope compositions of dissolved inorganic carbon (DIC) and methane (CH4) in porewater of marine sediments at seafloor temperatures show very large variation covering a δ13C range from −100‰ to +35‰. These extreme values are the result of isotope fractionation during microbial carbon metabolism, but the combined effect of all factors controlling the isotope distributions is still not completely understood. We used a model approach to evaluate the effects of reaction and transport on carbon isotope distributions in modern sediment porewater under steady state. Simulated δ13CDIC profiles typically show negative values in the sulphate reduction zone and more positive values in the methanogenic zone. With increasing depth in the methanogenic zone, δ13C values approach a distribution where the offset of δ13CDIC from δ13C of total organic carbon (TOC) to more positive values is similar to the offset of δ13CCH4 to more negative values (δ13CDIC and δ13CCH4 approach a symmetric distribution relative to δ13CTOC). The model never exceeds this symmetry of the DIC-CH4 couple towards more positive values under steady-state conditions in a purely diffusive system. Our model shows that to reach an offset in δ13C between DIC and CH4 in the order of 70‰, as frequently observed in methanogenic zones, a larger fractionation than reported from culture experiments with acetoclastic or autotrophic methanogens would be required. In fact, the observed isotope offset in natural systems would be consistent with the known inorganic equilibrium fractionation factor at in-situ temperature, which may suggest isotope exchange via a microbial pathway, during methanogenesis. Furthermore, the model reproduces strongly negative δ13CCH4 values at the sulphate methane-transition (SMT) as result of a reverse flux of carbon from DIC to CH4 during AOM. Such a reverse AOM has no influence on the δ13CDIC at the SMT as methane is almost completely consumed. Only at high sedimentation rate combined with low porosity, δ13CDIC values significantly more negative than δ13CTOC occur at the SMT

Tubular Compression Fossils from the Ediacaran Nama Group, Namibia

Abundant tubular macrofossils occur in finely laminated siltstones and shales of the 548-542 Ma Schwarzrand Subgroup. Nama Group, Namibia. The Nama tubes occur in both the Vingerbreek and Feldschuhhorn members commonly in dense populations and always in fine-grained, lower shore-face lithologies deposited below fair-weather wave base. The tubes are preserved mostly as compressed casts and molds that range in width from 0.6 to 2.1 mm: apparently incomplete specimens reach lengths up to 10 cm. All specimens show sinuous bending and occasional brittle fracture, indicating an original construction of strong but flexible organic matter. Feldschuhhorn specimens preserve fine longitudinal pleats or folds that record pliant organic walls, but the older Vingerbreek Populations do not. Similarly. some specimens in the Feldschuhhorn Member display branching. while Vingerbreek tubes do not. The abundant Feldschuhhorn tubes are assigned to the widespread Ediacaran problematicum Vendotaertia antiqua: however, the distinctive Vingerbreek population remains in open nomenclature. The most abundant fossils in Nama rocks, these tubes resemble populations in Ediacaran successions front Russia. China. Spain, and elsewhere. Beyond their local importance, then. such tubes may turn Out to be the most abundant record of Ediacaran life.Earth and Planetary SciencesOrganismic and Evolutionary Biolog