Subduction flux modulates the geomagnetic polarity reversal rate

© 2018 The Authors Ascertaining the cause of variations in the frequency of geomagnetic polarity reversals through the Phanerozoic has remained a primary research question straddling paleomagnetism and geodynamics for decades. Numerical models suggest the primary control on geomagnetic reversal rates on 10 to 100 Ma timescales is the changing heat flux across the core-mantle boundary and that this is itself expected to be strongly influenced by variations in the flux of lithosphere subducted into the mantle. A positive relationship between the time-dependent global subduction flux and magnetic reversal rate is expected, with a time delay to transmit the thermal imprint into the lowermost mantle. We perform the first test of this hypothesis using subduction flux estimates and geomagnetic reversal rate data back to the early Paleozoic. Subduction area flux estimates are derived from global, full-plate tectonic models, and are evaluated against independent subduction flux proxies based on the global age distribution of detrital zircons and strontium isotopes. A continuous Phanerozoic reversal rate model is built from pre-existing compilations back to ~320 Ma plus a new reversal rate model in the data-sparse mid-to-early Paleozoic. Cross-correlation of the time-dependent subduction flux and geomagnetic reversal rate series reveals a significant correlation with a time delay of ~120 Ma (with reversals trailing the subduction flux). This time delay represents a value intermediate between the seismologically constrained time expected for a subducted slab to transit from the surface to the core-mantle boundary (~150–300 Ma), and the much shorter lag time predicted by some numerical models of mantle flow (~30–60 Ma). While the reason for this large discrepancy remains unclear, it is encouraging that our novel estimate of lag time represents a compromise between them. Although important uncertainties in our proposed relationship remain, these results cast new light on the dynamic connections between the surface and deep Earth, and will help to constrain new models linking mantle convection, the thermal evolution of the lowermost mantle and the geodynamo

Reprogramming of Escherichia coli K-12 Metabolism during the Initial Phase of Transition from an Anaerobic to a Micro-Aerobic Environment

Background: Many bacteria undergo transitions between environments with differing O2 availabilities as part of their natural lifestyles and during biotechnological processes. However, the dynamics of adaptation when bacteria experience changes in O2 availability are understudied. The model bacterium and facultative anaerobe Escherichia coli K-12 provides an ideal system for exploring this process. Methods and Findings: Time-resolved transcript profiles of E. coli K-12 during the initial phase of transition from anaerobic to micro-aerobic conditions revealed a reprogramming of gene expression consistent with a switch from fermentative to respiratory metabolism. The changes in transcript abundance were matched by changes in the abundances of selected central metabolic proteins. A probabilistic state space model was used to infer the activities of two key regulators, FNR (O2 sensing) and PdhR (pyruvate sensing). The model implied that both regulators were rapidly inactivated during the transition from an anaerobic to a micro-aerobic environment. Analysis of the external metabolome and protein levels suggested that the cultures transit through different physiological states during the process of adaptation, characterized by the rapid inactivation of pyruvate formate-lyase (PFL), a slower induction of pyruvate dehydrogenase complex (PDHC) activity and transient excretion of pyruvate, consistent with the predicted inactivation of PdhR and FNR. Conclusion: Perturbation of anaerobic steady-state cultures by introduction of a limited supply of O2 combined with time-resolved transcript, protein and metabolite profiling, and probabilistic modeling has revealed that pyruvate (sensed by PdhR) is a key metabolic signal in coordinating the reprogramming of E. coli K-12 gene expression by working alongside the O2 sensor FNR during transition from anaerobic to micro-aerobic conditions

Two-site recognition of Staphylococcus aureus peptidoglycan by lysostaphin SH3b

Lysostaphin is a bacteriolytic enzyme targeting peptidoglycan, the essential component of the bacterial cell envelope. It displays a very potent and specific activity toward staphylococci, including methicillin-resistant Staphylococcus aureus. Lysostaphin causes rapid cell lysis and disrupts biofilms, and is therefore a therapeutic agent of choice to eradicate staphylococcal infections. The C-terminal SH3b domain of lysostaphin recognizes peptidoglycans containing a pentaglycine crossbridge and has been proposed to drive the preferential digestion of staphylococcal cell walls. Here we elucidate the molecular mechanism underpinning recognition of staphylococcal peptidoglycan by the lysostaphin SH3b domain. We show that the pentaglycine crossbridge and the peptide stem are recognized by two independent binding sites located on opposite sides of the SH3b domain, thereby inducing a clustering of SH3b domains. We propose that this unusual binding mechanism allows synergistic and structurally dynamic recognition of S. aureus peptidoglycan and underpins the potent bacteriolytic activity of this enzyme

The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation

Background Archosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the archosaur radiation began in the Early Triassic (252.3–247.2 Ma). Understanding of this radiation is currently limited by the poor early fossil record of the group in terms of skeletal remains. Methodology/Principal Findings We redescribe the anatomy and stratigraphic position of the type specimen of Ctenosauriscus koeneni (Huene), a sail-backed reptile from the Early Triassic (late Olenekian) Solling Formation of northern Germany that potentially represents the oldest known archosaur. We critically discuss previous biomechanical work on the ‘sail’ of Ctenosauriscus, which is formed by a series of elongated neural spines. In addition, we describe Ctenosauriscus-like postcranial material from the earliest Middle Triassic (early Anisian) Röt Formation of Waldhaus, southwestern Germany. Finally, we review the spatial and temporal distribution of the earliest archosaur fossils and their implications for understanding the dynamics of the archosaur radiation. Conclusions/Significance Comprehensive numerical phylogenetic analyses demonstrate that both Ctenosauriscus and the Waldhaus taxon are members of a monophyletic grouping of poposauroid archosaurs, Ctenosauriscidae, characterised by greatly elongated neural spines in the posterior cervical to anterior caudal vertebrae. The earliest archosaurs, including Ctenosauriscus, appear in the body fossil record just prior to the Olenekian/Anisian boundary (c. 248 Ma), less than 5 million years after the Permian–Triassic mass extinction. These earliest archosaur assemblages are dominated by ctenosauriscids, which were broadly distributed across northern Pangea and which appear to have been the first global radiation of archosaurs

Ferrimagnetic Cr and Mn spinels in sediments:Residual magnetic minerals after diagenetic dissolution

Ferrimagnetic Cr-Fe and Mn-Fe spinels are the dominant remanence carrying phases in the late Triassic Lunde Formation. These have largely been identified by magnetic mineral extraction from the sediments, combined with microscopy. The extensive removal of most of the originally deposited magnetic Fe-Ti oxides during diagenesis has left the Cr-Fe and Mn-Fe spinels as a mineral residue which is resistant to dissolution. The rock magnetic signature of these minerals is not sufficiently known, to be able to identify these minerals on the basis of their magnetic properties alone

Magnetostratigraphy of the Sherwood Sandstone Group (Lower and Middle Triassic), south Devon, UK:detailed correlation of the marine and non-marine Anisian

The Sherwood Sandstone Group in south Devon consists of the Budleigh Salterton Pebble Beds and the Otter Sandstone Formation. The Otter Sandstone Formation comprises four lithostratigraphic sub-units, from the base labelled A–D, and contains tetrapods corresponding to the Perovkan land vertebrate faunachron, and is consequently a key European non-marine Anisian succession. A total of 181 palaeomagnetic specimens from 92 horizons were measured to determine the palaeomagnetic signal. The magnetic properties and characteristic remanence is predominantly carried by haematite, most of which probably formed early in the depositional and diagenetic history. The lower part of the Sherwood Sandstone Group (Budleigh Salterton Pebble Beds and Otter Sandstone Formation, unit A, lower part of unit B) has predominantly normal polarity (magnetozones BS1, BS2 and BS3n) with three thin reversed polarity magnetozones. The lower part of unit B to the lower part of unit C of the Otter Sandstone Formation is predominantly reverse polarity (magnetozones BS3r, BS4 and BS5), but includes three short normal polarity intervals. The upper ca. 50 m of unit C shows a mix of normal and reverse polarity (BS6, BS7) with normal dominating. The ca. 15-m-thick unit D is entirely of normal polarity (BS8n). The magnetostratigraphy allows unambiguous comparison with conodont and ammonite calibrated magnetostratigraphies from elsewhere in Europe. These show that the BS2 and BS3n magnetozones of the Otter Sandstone Formation are lower Aegean to middle Pelsonian (lower to middle Anisian). The BS3r to BS5r magnetozone interval, is middle Pelsonian to lower Illyrian (middle to upper Anisian), and the BS6 to BS8n magnetozone interval is middle Illyrian to lower Fassanian. The top of unit D is correlated to an interval in the middle of the Nevadites Zone (close to the Anisian–Ladinian boundary). Consequently, the Otter Sandstone Formation correlates with the Muschelkalk in the Polish Basin, but is equivalent to only part of the Germanic Basin Muschelkalk. The continuous magnetostratigraphy from the Sherwood Sandstone Group, provides additional details of the polarity pattern through the Pelsonian to Illyrian interval, which appears to be lacking in discontinuous marine sections. A synthesis of adjacent European sedimentary basins in combination with the magnetostratigraphy, suggests that the Budleigh Salterton Pebble Beds are probably Late Spathian to lower Aegean

Magnetic properties of charcoal rich deposits associated with a Roman bath-house, Butrint (Southern Albania)

A section adjacent to a building structure at Shën Dëli, Butrint, Southern Albania exposes what is believed to be the remains of a former Roman bath-house. This section shows a transition from the underlying natural marsh clay into an archaeological deposit, which is both the basal remains of a building structure, and what appears to be an ash and charcoal enriched midden. The micro and macrocharcoal, magnetic and physical properties indicate a number of phases in the archaeological deposits, culminating in the micro and macrocharcoal rich and magnetically enhanced midden. The magnetic properties of these deposits are strongly related to the charcoal content that is probably a reflection of the ash content. The midden deposit is strongly enhanced in both superparamagnetic and low coercivity magnetite. The charcoal content and magnetic properties of the midden indicate a high content of wood-ash produced at the bath-house site, which is consistent with the anticipated fuel source for the region in Roman times

Sensitivity and sample shape related measuring effects on the MOLSPIN susceptibility anisotropy meter

The Helmholtz coil system of the MOLSPIN anisotropy delineator is shown to be partly sensitive to the specimen shape, particularly if the sample departs from the optimum shape. The effect is found to be most marked when measuring weakly anisotropic rocks which have an anisotropy below about 13 × 10−12 m3 and susceptibility less than 50 × 10−10 m3. However, comparison of MOLSPIN data to measurements undertaken on low and high field torque magnetometers, suggest the results are not unduly affected by sample shape if the rock anisotropy signal is sufficient to dominate this spurious effect. Some suggestions are also made for minimising noise factors and thus improving instrument sensitivity

Heavy-mineral, mineral-chemical and zircon-age constraints on the provenance of Triassic sandstones from the Devon coast, southern Britain

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