Progress towards an improved Precambrian seawater 87Sr/86Sr curve

The secular trend of seawater strontium isotope ratio (87Sr/86Sr) reflects changes in the relative contributions of continental versus mantle reservoirs to ocean composition, and informs global tectonic events, weathering rates and biogeochemical cycling through Earth history. However, the Precambrian seawater 87Sr/86Sr curve is known in far less detail than its Phanerozoic counterpart. For this study, we compiled 2249 strontium isotope ratios of Precambrian marine sedimentary rocks published since 2002, alongside previously compiled older data. Here we evaluate the uncertainty of all published data for constraining coeval seawater 87Sr/86Sr using four criteria (depositional environment, diagenetic alteration, age constraint and dissolution method). The resultant seawater 87Sr/86Sr curve uses mainly ‘high certainty’ data and shows an overall increasing trend from ~0.7005 at c. 3.5 Ga to ≥0.7089 towards the end of the Ediacaran Period. The improved curve shows an earlier deviation of seawater 87Sr/86Sr from the contemporaneous mantle by c. 3.5 Ga, which might reflect the first significant emergence of evolved continental crust related to nascent tectonics. Additionally, the updated curve records two major rises at 2.5-2.2 Ga and 1.9-1.7 Ga in addition to a well-established event at 0.8-0.5 Ga. Despite the relative scarcity of high-certainty data, these two increases are consistent with enhanced continental weathering following the onset of oxidative weathering and assembly of the supercontinent Nuna, respectively. Although confirmation of these two events awaits more high-certainty data, Precambrian seawater 87Sr/86Sr experienced stronger oscillations and better correspondence with supercontinent cycles than previously shown

A new rock-based definition for the Cryogenian Period (circa 720 - 635 Ma)

The Cryogenian Period was first established in 1988 along with other Precambrian eon, era and period-level subdivisions that were defined numerically by Global Standard Stratigraphic Ages (GSSAs). As absolute age constraints have improved, some of these time intervals no longer bracket adequately the geological event(s), for which they were named. For example, the age discrepancy between the basal Cryogenian GSSA at 850 Ma and the onset of widespread glaciation ca. 717 Ma has rendered the 850 Ma boundary obsolete. The International Commission on Stratigraphy has now formally approved the removal of the Cryogenian GSSA from its International Chronostratigraphic Chart and supports its replacement with a rock-based Global Stratotype Section and Point (GSSP). The new Cryogenian GSSP will be placed at a globally correlative level that lies stratigraphically beneath the first appearance of widespread glaciation and is assigned in the interim a 'calibrated age' of circa 720 Ma. This new definition for the Tonian/Cryogenian boundary should be used in future publications until a formal Cryogenian GSSP can be ratified. The change marks progress towards establishment of a 'natural' (rock-based) scale for Precambrian time

A Search for Binary Active Galactic Nuclei: Double-Peaked [OIII] AGN in the Sloan Digital Sky Survey

We present AGN from the Sloan Digital Sky Survey (SDSS) having double-peaked profiles of [OIII] 5007,4959 and other narrow emission-lines, motivated by the prospect of finding candidate binary AGN. These objects were identified by means of a visual examination of 21,592 quasars at z < 0.7 in SDSS Data Release 7 (DR7). Of the spectra with adequate signal-to-noise, 148 spectra exhibit a double-peaked [OIII] profile. Of these, 86 are Type 1 AGN and 62 are Type 2 AGN. Only two give the appearance of possibly being optically resolved double AGN in the SDSS images, but many show close companions or signs of recent interaction. Radio-detected quasars are three times more likely to exhibit a double-peaked [OIII] profile than quasars with no detected radio flux, suggesting a role for jet interactions in producing the double-peaked profiles. Of the 66 broad line (Type 1) AGN that are undetected in the FIRST survey, 0.9% show double peaked [OIII] profiles. We discuss statistical tests of the nature of the double-peaked objects. Further study is needed to determine which of them are binary AGN rather than disturbed narrow line regions, and how many additional binaries may remain undetected because of insufficient line-of-sight velocity splitting. Previous studies indicate that 0.1% of SDSS quasars are spatially resolved binaries, with typical spacings of ~10 to 100 kpc. If a substantial fraction of the double-peaked objects are indeed binaries, then our results imply that binaries occur more frequently at smaller separations (< 10 kpc). This suggests that simultaneous fueling of both black holes is more common as the binary orbit decays through these spacings.Comment: 33 pages, 5 figures, LaTeX. Major revisions. Accepted for publication in ApJ

The Ediacaran ‘Miaohe Member’ of South China: new insights from palaeoredox proxies and stable isotope data

Throughout the Ediacaran Period, variable water-column redox conditions persisted along productive ocean margins due to a complex interplay between nutrient supply and oceanographic restriction. These changing conditions are considered to have influenced early faunal evolution, with marine anoxia potentially inhibiting the development of the ecological niches necessary for aerobic life forms. To understand this link between oxygenation and evolution, the combined geochemical and palaeontological study of marine sediments is preferable. Located in the Yangtze Gorges region of southern China, lagoonal black shales at Miaohe preserve alga and putative metazoans, including Eoandromeda, a candidate total-group ctenophore, thereby providing one example of where integrated study is possible. We present a multi-proxy investigation into water-column redox variability during deposition of these shales (c. 560–551 Ma). For this interval, reactive iron partitioning indicates persistent water-column anoxia, while trace metal enrichments and other geochemical data suggest temporal fluctuations between ferruginous, euxinic and rare suboxic conditions. Although trace metal and total organic carbon values imply extensive basin restriction, sustained trace metal enrichment and δ15Nsed data indicate periodic access to open-ocean inventories across a shallow-marine sill. Lastly, δ13Corg values of between −35‰ and −40‰ allow at least partial correlation of the shales at Miaohe with Member IV of the Doushantuo Formation. This study provides evidence for fluctuating redox conditions in the lagoonal area of the Yangtze platform during late Ediacaran time. If these low-oxygen environments were regionally characteristic, then the restriction of aerobic fauna to isolated environments can be inferred

Family-centred care for hospitalised children aged 0-12 years (Review)

This is an update of the Cochrane systematic review of family-centred care published in 2007 (Shields 2007). Family-centred care (FCC) is a widely used model in paediatrics, is thought to be the best way to provide care to children in hospital and is ubiquitous as a way of delivering care. When a child is admitted, the whole family is affected. In giving care, nurses, doctors and others must consider the impact of the child's admission on all family members. However, the effectiveness of family-centred care as a model of care has not been measured systematically. To assess the effects of family-centred models of care for hospitalised children aged from birth (unlike the previous version of the review, this update excludes premature neonates) to 12 years, when compared to standard models of care, on child, family and health service outcomes. In the original review, we searched up until 2004. For this update, we searched: the Cochrane Central Register of Controlled Trials (CENTRAL,The Cochrane Library, Issue 12 2011); MEDLINE (Ovid SP); EMBASE (Ovid SP); PsycINFO (Ovid SP); CINAHL (EBSCO Host); and Sociological Abstracts (CSA). We did not search three that were included in the original review: Social Work Abstracts, the Australian Medical Index and ERIC. We searched EMBASE in this update only and searched from 2004 onwards. There was no limitation by language.\ua0We performed literature searches in May and June 2009 and updated them again in December 2011. We searched for randomised controlled trials (RCTs) including cluster randomised trials in which family-centred care models are compared with standard models of care for hospitalised children (0 to 12 years, but excluding premature neonates). Studies had to meet criteria for family-centredness. In order to assess the degree of family-centredness, we used a modified rating scale based on a validated instrument, (same instrument used in the initial review), however, we decreased the family-centredness score for inclusion from 80% to 50% in this update. We also changed several other selection criteria in this update: eligible study designs are now limited to randomised controlled trials (RCTs) only; single interventions not reflecting a FCC model of care have been excluded; and the selection criterion whereby studies with inadequate or unclear blinding of outcome assessment were excluded from the review has been removed. Two review authors undertook searches, and four authors independently assessed studies against the review criteria, while two were assigned to extract data. We contacted study authors for additional information. Six studies found since 2004 were originally viewed as possible inclusions, but when the family-centred score assessment was tested, only one met the minimum score of family-centredness and was included in this review. This was an unpublished RCT involving 288 children post-tonsillectomy in a care-by-parent unit (CBPU) compared with standard inpatient care.The study used a range of behavioural, economic and physical measures. It showed that children in the CBPU were significantly less likely to receive inadequate care compared with standard inpatient admission, and there were no significant differences for their behavioural outcomes or other physical outcomes. Parents were significantly more satisfied with CBPU care than standard care, assessed both before discharge and at 7 days after discharge. Costs were lower for CPBU care compared with standard inpatient care. No other outcomes were reported. The study was rated as being at low to unclear risk of bias. This update of a review has found limited, moderate-quality evidence that suggests some benefit of a family-centred care intervention for children's clinical care, parental satisfaction, and costs, but this is based on a small dataset and needs confirmation in larger RCTs. There is no evidence of harms. Overall, there continues to be little high-quality quantitative research available about the effects of family-centred care. Further rigorous research on the use of family-centred care as a model for care delivery to children and families in hospitals is needed. This research should implement well-developed family-centred care interventions, ideally in randomised trials. It should investigate diverse participant groups and clinical settings, and should assess a wide range of outcomes for children, parents, staff and health services

Family-centered care for hospitalized children aged 0-12 years: a systematic review of qualitative studies

The foundation for a family-centered approach to pediatric health care is the belief that a child'semotional and developmental needs, and overall family wellbeing are best achieved when the service system supports the ability of the family to meet the needs of their child by involving families in their child’s care. There are a range of potential benefits and difficulties associated with the provision of family centred care, e.g. role negotiation, parental expectations in regard to participation in their child’s care, and issues relating to power and control. Currently, however, there is limited systematic information on how the principles of family-centered care are implemented in the delivery of care to the hospitalized child and their family, and the impact on the family and the health care providers

The case for a neoproterozoic oxygenation event: Geochemical evidence and biological consequences

The Neoproterozoic era marked a turning point in the development of the modern earth system. The irreversible environmental changes of that time were rooted in tectonic upheavals that drove chain reactions between the oceans, atmosphere, climate, and life. Key biological innovations took place amid carbon cycle instability that pushed climate to unprecedented extremes and resulted in the ventilation of the deep ocean. Despite a dearth of supporting evidence, it is commonly presumed that a rise in oxygen triggered the evolution of animals. Although geochemical evidence for oxygenation is now convincing, our understanding of the Neoproterozoic earth system and of early animal evolution has changed apace, revealing an altogether more complicated picture in which the spread of anoxia played an important role. The challenge to future researchers lies in unraveling the complex entanglement of earth system changes during this pivotal episode in Earth’s history

Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this record Animal burrowing and sediment-mixing (bioturbation) began during the run up to the Ediacaran/Cambrian boundary, initiating a transition between the stratified Precambrian and more well-mixed Phanerozoic sedimentary records, against the backdrop of a variable global oxygen reservoir probably smaller in size than present. Phosphorus is the long-term limiting nutrient for oxygen production via burial of organic carbon, and its retention (relative to carbon) within organic matter in marine sediments is enhanced by bioturbation. Here we explore the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model. We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir - the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments. Bioturbation also reduces steady-state marine phosphate levels, but this effect is offset by the decline in iron-adsorbed phosphate burial that results from a decrease in oxygen concentrations. The introduction of oxygen-sensitive bioturbation to dynamical model runs is sufficient to trigger a negative feedback loop: the intensity of bioturbation is limited by the oxygen decrease it initially causes. The onset of this feedback is consistent with redox variations observed during the early Cambrian rise of bioturbation, leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles. © 2014 Macmillan Publishers Limited. All rights reserved.Natural Environment Research Council (NERC)Inge Lehmann ScholarshipVILLUM FoundationNational Basic Research Program of ChinaNational Natural Science Foundation of ChinaDeutsche Forschungsgemeinschaft (DFG