The genomes of Australian wild limes.

Australian wild limes occur in highly diverse range of environments and are a unique genetic resource within the genus Citrus. Here we compare the haplotype-resolved genome assemblies of six Australian native limes, including four new assemblies generated using PacBio HiFi and Hi-C sequencing data. The size of the genomes was between 315 and 391 Mb with contig N50s from 29.5 to 35 Mb. Gene completeness of the assemblies was estimated to be from 98.4 to 99.3% and the annotations from 97.7 to 98.9% based upon BUSCO, confirming the high contiguity and completeness of the assembled genomes. High collinearity was observed among the genomes and the two haplotype assemblies for each species. Gene duplication and evolutionary analysis demonstrated that the Australian citrus have undergone only one ancient whole-genome triplication event during evolution. The highest number of species-specific and expanded gene families were found in C. glauca and they were primarily enriched in purine, thiamine metabolism, amino acids and aromatic amino acids metabolism which might help C. glauca to mitigate drought, salinity, and pathogen attacks in the drier environments in which this species is found. Unique genes related to terpene biosynthesis, glutathione metabolism, and toll-like receptors in C. australasica, and starch and sucrose metabolism genes in both C. australis and C. australasica might be important candidate genes for HLB tolerance in these species. Expanded gene families were not lineage specific, however, a greater number of genes related to plant-pathogen interactions, predominantly disease resistant protein, was found in C. australasica and C. australis.

Implementation of major trauma app: usability and data completeness.

BACKGROUND: The current UK standard for major trauma patients is to record notes in a paper trauma booklet. Through an innovative collaboration between a major trauma centre and a digital transformation industry partner, a TraumaApp was developed. Electronic notes have been shown to have fewer errors, granular data collection and enable time stamped contemporaneous record keeping. Implementation of digital clinical records presents a challenge within the context of trauma multidisciplinary trauma resuscitation. Data can be easily accessible and shared for quality improvement, audit and research purposes. This study compared paper and electronic notes for completeness and for acceptability data following the implementation of the TraumaApp. METHODS: Trauma team members who performed scribe function attended training for the newly launched TraumaApp. Two staff members acted as scribe, using either the paper trauma booklet or TraumaApp, and attended major trauma calls. A framework for comparison of paper and electronic notes was created and used for a retrospective review of major trauma patients' notes. Statistical analysis was performed using a two-tailed t-test. Staff using the TraumaApp completed a System Usability Score questionnaire. RESULTS: There was a total of 37 data points for collection per case. The mean numbers collected were paper notes 24.1 of 37 (65.1%) and electronic notes, 25.7 of 37 (69.5%). There was no statistical significance between the completeness of paper and electronic notes. The mean System Usability Score was 68.4. DISCUSSION: Recording accurate patient information during a major trauma call can be challenging and the role of the scribe to accurately record events is critical for immediate and future care. There was no statistically significant difference in completeness of paper and electronic notes, however the mean System Usability Score was 68.4, which is greater than the internationally validated standard of acceptable usability. CONCLUSION: It is feasible to introduce digital data collection tools enabling accurate record keeping during trauma resuscitation and improve information sharing between clinicians.

The influence of candidates' race on examiners' ratings in standardised assessments of clinical practice.

PURPOSE: Delivering fair and reliable summative assessments in medical education assumes examiner decision making is devoid of bias. We investigated whether candidate racial appearances influenced examiner ratings in undergraduate clinical exams. METHODS: We used an internet-based design. Examiners watched a randomised set of six videos of three different white candidates and three different non-white (Asian, black and Chinese) candidates taking a clinical history at either fail, borderline or pass grades. We compared the median and interquartile range (IQR) of the paired difference between scores for the white and non-white candidates at each performance grade and tested for statistical significance. RESULTS: 160 Examiners participated. At the fail grade, the black and Chinese candidates scored lower than the white candidate, with median paired differences of -2.5 and -1 respectively (both p < 0.001). At the borderline grade, the black and Chinese candidates scored higher than the white candidate, with median paired differences of +2 and +3, respectively (both p < 0.001). At the passing grade, the Asian candidate scored lower than the white candidate (median paired difference -1, p < 0.001). CONCLUSION: The racial appearance of candidates appeared to influence the scores awarded by examiners, but not in a uniform manner.

The genome of Citrus australasica reveals disease resistance and other species specific genes.

BACKGROUND: The finger lime (Citrus australasica), one of six Australian endemic citrus species shows a high natural phenotypic diversity and novel characteristics. The wide variation and unique horticultural features have made this lime an attractive candidate for domestication. Currently no haplotype resolved genome is available for this species. Here we present a high quality, haplotype-resolved reference genome for this species using PacBio HiFi and Hi-C sequencing. RESULTS: Hifiasm assembly and SALSA scaffolding resulted in a collapsed genome size of 344.2 Mb and 321.1 Mb and 323.2 Mb size for the two haplotypes. The nine pseudochromosomes of the collapsed genome had an N50 of 35.2 Mb, 99.1% genome assembly completeness and 98.9% gene annotation completeness (BUSCO). A total of 41,304 genes were predicted in the nuclear genome. Comparison with C. australis revealed that 13,661 genes in pseudochromosomes were unique in C. australasica. These were mainly involved in plant-pathogen interactions, stress response, cellular metabolic and developmental processes, and signal transduction. The two genomes showed a syntenic arrangement at the chromosome level with large structural rearrangements in some chromosomes. Genetic variation among five C. australasica cultivars was analysed. Genes related to defense, synthesis of volatile compounds and red/yellow coloration were identified in the genome. A major expansion of genes encoding thylakoid curvature proteins was found in the C. australasica genome. CONCLUSIONS: The genome of C. australasica present in this study is of high quality and contiguity. This genome helps deepen our understanding of citrus evolution and reveals disease resistance and quality related genes with potential to accelerate the genetic improvement of citrus.

Intervention to reduce age bias in medical students' decision making for the treatment of older women with breast cancer: A novel approach to bias training.

Objectives: Despite NICE guidelines to 'treat people with invasive breast cancer, irrespective of age, with surgery and appropriate systemic therapy, rather than endocrine therapy alone', older patients receive differential treatment and experience worse outcomes. Research has evidenced the prevalence of ageism and identified the role of implicit bias in reflecting and potentially perpetuating disparities across society, including in healthcare. Yet age bias has rarely been considered as an explanatory factor in poorer outcomes for older breast cancer patients nor, consequentially, has removing age bias been considered as an approach to improving outcomes. Many organizations carry out bias training with the aim of reducing negative impacts from biased decision making, yet the few evaluations of these interventions have mostly seen small or negative effects. This study explores whether a novel intervention to address age bias leads to better quality decision making for the treatment of older women with breast cancer.Methods: An online study compared medical students' treatment recommendations for older breast cancer patients and the reasoning for their decision making before and after a novel bias training intervention. Thirty-one medical students participated in the study.Results: The results show that the bias training intervention led medical students to make better quality decisions for older breast cancer patients. The quality of decision making was measured by decreases in age-based decision making and increased efforts to include patients in decision making. These results suggest there is value in exploring whether if anti-bias training interventions could usefully be applied in other areas of practice where older patients experience poorer outcomes.Conclusions: This study evidences that bias training improves the quality of decision making by medical students in respect of older breast cancer patients. The study findings show promise that this novel approach to bias training might usefully be applied to all medical practitioners making treatment recommendations for older patients.

Pangenome analysis provides insight into the evolution of the orange subfamily and a key gene for citric acid accumulation in citrus fruits.

The orange subfamily (Aurantioideae) contains several Citrus species cultivated worldwide, such as sweet orange and lemon. The origin of Citrus species has long been debated and less is known about the Aurantioideae. Here, we compiled the genome sequences of 314 accessions, de novo assembled the genomes of 12 species and constructed a graph-based pangenome for Aurantioideae. Our analysis indicates that the ancient Indian Plate is the ancestral area for Citrus-related genera and that South Central China is the primary center of origin of the Citrus genus. We found substantial variations in the sequence and expression of the PH4 gene in Citrus relative to Citrus-related genera. Gene editing and biochemical experiments demonstrate a central role for PH4 in the accumulation of citric acid in citrus fruits. This study provides insights into the origin and evolution of the orange subfamily and a regulatory mechanism underpinning the evolution of fruit taste.

Epidemiology of major trauma in older adults within Scotland: A national perspective from the Scottish Trauma Audit Group (STAG).

BACKGROUND: Major trauma in older adults (MTOA) poses distinctive health and social care challenges, further underlined by the unique socioeconomic and geographical environment of Scotland. This study provides epidemiological trends of MTOA, to provide insight into areas where further evaluation and research are required. MATERIALS AND METHODS: Pseudonymised aggregated demographic, injury and outcome data from 2011 to 2020 were obtained from the Scottish Trauma Audit Group (STAG) Database, covering 28 hospitals across Scotland. Only individuals age ≥ 70 with an Injury Severity Score (ISS) > 15 were included. RESULTS: There was an average of 216 annual cases of MTOA, with a 259 % rise in incidence from 2011 to 2020. This was predominantly driven by a rise in low velocity trauma (fall <2 m height; 287 % increase). The proportion of all major trauma attributable to those aged ≥70 rose from 18.5 % in 2011 to 34.6 % in 2020. Death censored median (IQR) acute hospital length of stay was 18 days (9-30). Overall, 30-day survival was 65.3 %, with no improvement seen between 2011 and 2020 (p = 0.50). Independent predictors of improved 30-day survival included Ages 70-79 & 80-89 [compared to reference ≥ 90] (OR 3.12; 95 %CI 2.24,4.31; p < 0.001 and OR 1.66; 95 %CI 1.21,2.29; p = 0.002 respectively), and Extremity injury (OR 1.89; 95 %CI 1.48,2.41; p < 0.001). Head injury (OR 0.72; 95 %CI 0.54,0.96; p = 0.027) and increasing ISS score (OR 0.88, 95 %CI 0.86,0.89; p < 0.001) were associated with lower likelihood of 30-day survival. A further model also including the admission ward (from eSTAG data November 2017 onwards) demonstrated an association with reduced 30-day survival with admission to General Surgery (OR 0.42; 95 %CI 0.19,0.93; p = 0.033), Intensive Care (OR 0.25; 95 %CI 0.10,0.60; p = 0.002) and Medical Specialities (OR 0.33; 95 %CI 0.15,0.73; p = 0.007) compared to the reference (Major Trauma). Exponential Smoothing predictions revealed a further potential 184 % rise in incidence of MTOA from 2021 to 2030 (3657 per 100,000 population at risk to 10,392 per 100,000 population at risk). CONCLUSION: MTOA is likely to be a rising health care burden, requiring larger quantities of health and social care resource. Urgent preventative strategies are required to reduce low velocity trauma (standing height falls), as well as the high mortality and morbidity of MTOA.

Haplotype resolved chromosome level genome assembly of Citrus australis reveals disease resistance and other citrus specific genes.

Recent advances in genome sequencing and assembly techniques have made it possible to achieve chromosome level reference genomes for citrus. Relatively few genomes have been anchored at the chromosome level and/or are haplotype phased, with the available genomes of varying accuracy and completeness. We now report a phased high-quality chromosome level genome assembly for an Australian native citrus species; Citrus australis (round lime) using highly accurate PacBio HiFi long reads, complemented with Hi-C scaffolding. Hifiasm with Hi-C integrated assembly resulted in a 331 Mb genome of C. australis with two haplotypes of nine pseudochromosomes with an N50 of 36.3 Mb and 98.8% genome assembly completeness (BUSCO). Repeat analysis showed that more than 50% of the genome contained interspersed repeats. Among them, LTR elements were the predominant type (21.0%), of which LTR Gypsy (9.8%) and LTR copia (7.7%) elements were the most abundant repeats. A total of 29 464 genes and 32 009 transcripts were identified in the genome. Of these, 28 222 CDS (25 753 genes) had BLAST hits and 21 401 CDS (75.8%) were annotated with at least one GO term. Citrus specific genes for antimicrobial peptides, defense, volatile compounds and acidity regulation were identified. The synteny analysis showed conserved regions between the two haplotypes with some structural variations in Chromosomes 2, 4, 7 and 8. This chromosome scale, and haplotype resolved C. australis genome will facilitate the study of important genes for citrus breeding and will also allow the enhanced definition of the evolutionary relationships between wild and domesticated citrus species.

Uncovering the Ediacaran phosphorus cycle.

Phosphorus is a limiting nutrient that is thought to control oceanic oxygen levels to a large extent1-3. A possible increase in marine phosphorus concentrations during the Ediacaran Period (about 635-539 million years ago) has been proposed as a driver for increasing oxygen levels4-6. However, little is known about the nature and evolution of phosphorus cycling during this time4. Here we use carbonate-associated phosphate (CAP) from six globally distributed sections to reconstruct oceanic phosphorus concentrations during a large negative carbon-isotope excursion-the Shuram excursion (SE)-which co-occurred with global oceanic oxygenation7-9. Our data suggest pulsed increases in oceanic phosphorus concentrations during the falling and rising limbs of the SE. Using a quantitative biogeochemical model, we propose that this observation could be explained by carbon dioxide and phosphorus release from marine organic-matter oxidation primarily by sulfate, with further phosphorus release from carbon-dioxide-driven weathering on land. Collectively, this may have resulted in elevated organic-pyrite burial and ocean oxygenation. Our CAP data also seem to suggest equivalent oceanic phosphorus concentrations under maximum and minimum extents of ocean anoxia across the SE. This observation may reflect decoupled phosphorus and ocean anoxia cycles, as opposed to their coupled nature in the modern ocean. Our findings point to external stimuli such as sulfate weathering rather than internal oceanic phosphorus-oxygen cycling alone as a possible control on oceanic oxygenation in the Ediacaran. In turn, this may help explain the prolonged rise of atmospheric oxygen levels.

A critical role for long-term potentiation mechanisms in the maintenance of object recognition memory in perirhinal cortex revealed by the infusion of zeta inhibitory pseudosubstrate.

Object recognition, the ability to discriminate between a novel and a familiar stimulus, is critically dependent upon the perirhinal cortex. Neural response reductions upon repetition of a stimulus, have been hypothesized to be the mechanism within perirhinal cortex that supports recognition memory function. Thus, investigations into the mechanisms of long-term depression (LTD) in perirhinal cortex has provided insight into the mechanism of object recognition memory formation, but the contribution of long-term potentiation (LTP) to object recognition memory formation has been less studied. Inhibition of atypical PKC activity by Zeta Inhibitory Pseudosubstrate (ZIP) impairs the maintenance of LTP but not LTD, thus here infusion of ZIP into the perirhinal cortex allowed us to investigate the contribution of LTP-like mechanisms to object recognition memory maintenance. Infusion of ZIP into the perirhinal cortex of rats 24 h after the sample phase impaired performance in an object recognition but not an object location task, in contrast infusion of ZIP into the hippocampus impaired performance in an object location but not an object recognition task. The impairment in object recognition by ZIP was prevented by administration of the peptide GluA23y, which blocks the endocytosis of GluA2 containing AMPA receptors. Finally, performance in a perceptual oddity task, which requires perirhinal cortex function, was not disrupted by ZIP. Together these results demonstrate the importance of LTP-like mechanisms to the maintenance of object recognition memory in the perirhinal cortex.

Chiral 480 nm absorption in the hemoglycin space polymer: a possible link to replication.

A 1494 Dalton hemoglycin space polymer of Glycine18 Hydroxy-glycine4 Fe2O4 termed the "core unit" is part of a polymer of Glycine, Si, Fe and O that forms tubes, vesicles and a lattice structure. It has been isolated from four different CV3 meteorites and characterized by mass spectrometry, FIB/SIMS and X-ray analysis. In quantum calculations (HF and DF wB97X-D 6-31G) the polymer has an absorption at 480 nm that is dependent on rectus "R" (= dextro D) chirality in a hydroxy glycine residue whose C-terminus is bonded to an iron atom. The absorption originates in the Fe II state as a consequence of chiral symmetry breaking. In confirmation of theory, measurements at Diamond Light Source UK, on crystals of hemoglycin derived from Acfer-086 and Sutter's Mill meteorites have shown a strong 483 ± 3 nm absorption that confirms the proposed location of hydroxy glycine residues within the polymer. A high 483 nm to 580 nm absorption ratio points to an "R" chirality excess in hemoglycin, suggesting that 480 nm photons could have provided the energy for its replication in the protoplanetary disc.

Novel antiinflammatory biologics shaped by parasite-host coevolution.

Parasitic helminth infections, while a major cause of neglected tropical disease burden, negatively correlate with the incidence of immune-mediated inflammatory diseases such as inflammatory bowel diseases (IBD). To evade expulsion, helminths have developed sophisticated mechanisms to regulate their host's immune responses. Controlled experimental human helminth infections have been assessed clinically for treating inflammatory conditions; however, such a radical therapeutic modality has challenges. An alternative approach is to harness the immunomodulatory properties within the worm's excretory-secretory (ES) complement, its secretome. Here, we report a biologics discovery and validation pipeline to generate and screen in vivo a recombinant cell-free secretome library of helminth-derived immunomodulatory proteins. We successfully expressed 78 recombinant ES proteins from gastrointestinal hookworms and screened the crude in vitro translation reactions for anti-IBD properties in a mouse model of acute colitis. After statistical filtering and ranking, 20 proteins conferred significant protection against various parameters of colitis. Lead candidates from distinct protein families, including annexins, transthyretins, nematode-specific retinol-binding proteins, and SCP/TAPS were identified. Representative proteins were produced in mammalian cells and further validated, including ex vivo suppression of inflammatory cytokine secretion by T cells from IBD patient colon biopsies. Proteins identified herein offer promise as novel, safe, and mechanistically differentiated biologics for treating the globally increasing burden of inflammatory diseases.

Pathotyping Citrus Ornamental Relatives with Xanthomonas citri pv. citri and X. citri pv. aurantifolii Refines Our Understanding of Their Susceptibility to These Pathogens.

Xanthomonas citri pv. citri (Xcc) and X. citri pv. aurantifolii (Xca) are causal agents of Citrus Bacterial Canker (CBC), a devastating disease that severely affects citrus plants. They are harmful organisms not reported in Europe or the Mediterranean Basin. Host plants are in the Rutaceae family, including the genera Citrus, Poncirus, and Fortunella, and their hybrids. In addition, other genera of ornamental interest are reported as susceptible, but results are not uniform and sometimes incongruent. We evaluated the susceptibility of 32 ornamental accessions of the Rutaceae family belonging to the genera Citrus, Fortunella, Atalantia, Clausena, Eremocitrus, Glycosmis, Microcitrus, Murraya, Casimiroa, Calodendrum, and Aegle, and three hybrids to seven strains of Xcc and Xca. Pathotyping evaluation was assessed by scoring the symptomatic reactions on detached leaves. High variability in symptoms and bacterial population was shown among the different strains in the different hosts, indicative of complex host-pathogen interactions. The results are mostly consistent with past findings, with the few discrepancies probably due to our more complete experimental approach using multiple strains of the pathogen and multiple hosts. Our work supports the need to regulate non-citrus Rutaceae plant introductions into areas, like the EU and Mediterranean, that are currently free of this economically important pathogen.

Bilateral Diffuse Pseudoangiomatous Stromal Hyperplasia Necessitating Mastectomy.

Pseudoangiomatous stromal hyperplasia (PASH) is an uncommon, benign breast lesion often diagnosed incidentally and frequently mistaken for fibroadenoma given similar radiographic appearance. Histopathology classically reveals diffuse, dense fibrous stromal background with a complex network of spindle cells forming slit-like spaces, giving it the appearance of angiomatous proliferation. Surgical excision is generally not necessary. Here we present two unusual cases of PASH: an adolescent patient with bilateral rapid onset of symptoms, and a premenopausal patient with bilateral, diffuse, recurrent PASH. Both required mastectomy. We aim to highlight the variable nature of presentation and briefly review current management options.

Usability of novel major TraumaApp for digital data collection.

BACKGROUND: Delivery of major trauma care is complex and often fast paced. Clear and comprehensive documentation is paramount to support effective communication during complex clinical care episodes, and to allow collection of data for audit, research and continuous improvement. Clinical events are typically recorded on paper-based records that are developed for individual centres or systems. As one of the priorities laid out by the Scottish Trauma Network project was to develop an electronic data collection system, the TraumaApp was created as a data collection tool for major trauma that could be adopted worldwide. METHODS: The study was performed as a service evaluation based at the Queen Elizabeth University Hospital Emergency Department. Fifty staff members were recruited in pairs and listened to five paired major trauma standby and handover recordings. Participants were randomised to input data to the TraumaApp and one into the existing paper proforma. The time taken to input data add into was measured, along with time for clarifications and any errors made. Those using the app completed a System Usability Score. RESULTS: No statistically significant difference was demonstrated between times taken for data entry for the digital and paper documentation, apart from the Case 5 Handover (p < 0.05). Case 1 showed a significantly higher time for clarifications and number of errors with digital data collection (p = 0.01 and p = 1.79E-05 respectively). There were no other differences between data for the app and the proforma. The mean System Usability score for this cohort was 75 out of 100, with a standard deviation of 17 (rounded to nearest integer). CONCLUSION: Digital real-time recording of clinical events using a tool such as the TraumaApp is comparable to completion of paper proforma. The System Usability Score for the TraumaApp was above the internationally validated standard of acceptable usability. There was no evidence of improvement in use over time or familiarity, most likely due to the brevity of the assessments and the refined user interface. This would benefit from further research, exploring data completeness and a potential mixed methods approach to explore training requirements for use of the TraumaApp.

Differences in treatment and survival of older patients with operable breast cancer between the United Kingdom and the Netherlands - A comparison of two national prospective longitudinal multi-centre cohort studies.

BACKGROUND: Previous studies have shown that survival outcomes for older patients with breast cancer vary substantially across Europe, with worse survival reported in the United Kingdom. It has been hypothesised that these differences in survival outcomes could be related to treatment variation. OBJECTIVES: We aimed to compare patient and tumour characteristics, treatment selection and survival outcomes between two large prospective cohorts of older patients with operable breast cancer from the United Kingdom (UK) and The Netherlands. METHODS: Women diagnosed with operable breast cancer aged ≥70 years were included. A baseline comprehensive geriatric assessment was performed in both cohorts, with data collected on age, comorbidities, cognition, nutritional and functional status. Baseline tumour characteristics and treatment type were collected. Univariable and multivariable Cox regression models were used to compare overall survival between the cohorts. RESULTS: 3262 patients from the UK Age Gap cohort and 618 patients from the Dutch Climb cohort were included, with median ages of 77.0 (IQR: 72.0-81.0) and 75.0 (IQR: 72.0-81.0) years, respectively. The cohorts were generally comparable, with slight differences in rates of comorbidity and frailty. Median follow-up for overall survival was 4.1 years (IQR 2.9-5.4) in Age Gap and 4.3 years (IQR 2.9-5.5) in Climb. In Age Gap, both the rates of primary endocrine therapy and adjuvant hormonal therapy after surgery were approximately twice those in Climb (16.6% versus 7.3%, p < 0.001 for primary endocrine therapy, and 62.2% versus 38.8%, p < 0.001 for adjuvant hormonal therapy). There was no evidence of a difference in overall survival between the cohorts (adjusted HR 0.94, 95% CI 0.74-1.17, p = 0.568). CONCLUSIONS: In contrast to previous studies, this comparison of two large national prospective longitudinal multi-centre cohort studies demonstrated comparable survival outcomes between older patients with breast cancer treated in the UK and The Netherlands, despite differences in treatment allocation.

Factors influencing the stewardship activities of Antimicrobial Management Teams: a national cross-sectional survey.

BACKGROUND: The link between inappropriate antibiotic prescribing and the global threat of antimicrobial resistance is well documented. International strategies recommend antimicrobial stewardship (AMS) programmes, with improvement interventions to safeguard antibiotics. AIM: This study sought to systematically evaluate the impact of multi-professional Antimicrobial Management Team (AMT) staff resource availability on stewardship activities. METHODS: We conducted an on-line, cross-sectional survey of AMTs in each regional Health Board and the national specialist hospital in Scotland (N = 15). Responses were analysed descriptively, exploring observed relationships between variables to identify patterns. FINDINGS: Results highlighted apparent variation in the levels of AMT resource availability across Scotland, not directly influenced by Health Board size, with some larger Health Boards having proportionately poorer AMT resource allocation. However, the range and frequency of activities to support AMS was not directly linked to either Health Board size or staff resource allocation, indicating a more complex inter-relationship between factors. CONCLUSIONS: There is apparent inequity in staff resource available for AMTs across Scotland, with significantly lower resource allocation in comparison with recommendations from other international studies. However, considering these survey findings with our earlier qualitative research indicates that leadership style and team member enthusiasm may be as, if not more, influential than resource availability on the scope of AMT activities. These findings have international relevance for hospital service managers considering the recruitment, training and ongoing support of AMTs, in order to maximize impact from a limited resource.

Deep water cuspate stromatolites of the Cryogenian Trezona Formation.

Stromatolites and microbialites contain a rich repository of environmental and biological information. Despite extensive research, questions remain regarding the biological, chemical, and physical processes that control stromatolite macro, meso, and microstructure. We report unusual deep water cuspate stromatolites from the Cryogenian Trezona Formation, South Australia, from a mixed siliciclastic-carbonate open marine ramp setting. Cuspate stromatolite horizons develop near the base of decameter-scale transgression-regression cycles and typically overlie decimeter-scale irregular erosion surfaces. The cuspate structure within the stromatolites form near vertical, stacked cusp structures in cross section. In plan view, the cusps form cm-scale sharp parallel ridges oriented perpendicular to the regional downslope direction and perpendicular to the elongation direction of stromatolites. Stromatolites colonized topographic highs of irregular erosion surfaces (often hardgrounds) and grew in carbonate supersaturated, iron-rich marine waters in low turbidity sediment-starved settings. Cuspate stromatolites are interpreted as forming in deep water environments during maximum transgression as condensed intervals. Their microbial metabolism may require low light and low oxygen. A deep water origin for the Trezona Formation cuspate stromatolites and other Precambrian cuspate stromatolites suggests a link between the cuspate morphology and physical/chemical (carbonate supersaturated, low light, and low oxygen) conditions of Precambrian deep water marine settings.

Neoproterozoic syn-glacial carbonate precipitation and implications for a snowball Earth.

The Neoproterozoic 'snowball Earth' hypothesis suggests that a runaway ice-albedo feedback led to two intense glaciations around 717-635 million years ago, and this global ice cover would have drastically impacted biogeochemical cycles. Testing the predictions of this hypothesis against the rock record is key to understanding Earth's surface evolution in the Neoproterozoic. A central tenet of the snowball Earth hypothesis is that extremely high atmospheric CO2  levels-supplied by volcanic degassing over millions of years-would be required to overcome a strong ice-albedo feedback and trigger deglaciation. This requires severely diminished continental weathering (and associated CO2 drawdown) during glaciation, and implies that carbonate minerals would not precipitate from syn-glacial seawater due to a lack of alkalinity influxes into ice-covered oceans. In this scenario, syn-glacial seawater chemistry should instead be dominated by chemical exchange with the oceanic crust and volcanic systems, developing low pH and low Mg/Ca ratios. However, sedimentary rocks deposited during the Sturtian glaciation from the Adelaide Fold Belt-and contemporaneous successions globally-show evidence for syn-sedimentary dolomite precipitation in glaciomarine environments. The dolomitic composition of these syn-glacial sediments and post-glacial 'cap carbonates' implies that carbonate precipitation and Mg cycling must have remained active during the ~50 million-year Sturtian glaciation. These syn-glacial carbonates highlight a gap in our understanding of continental weathering-and therefore, the carbon cycle-during snowball Earth. In light of these observations, a Precambrian global biogeochemical model (PreCOSCIOUS) was modified to explore scenarios of syn-glacial chemical weathering, ocean chemistry and Sturtian carbonate mineralogy. Modelling results suggest that a small degree of chemical weathering during glaciation would have been capable of maintaining high seawater Mg/Ca ratios and carbonate precipitation throughout the Sturtian glaciation. This is consistent with a severe ice age during the Sturtian, but challenges predictions of biogeochemical cycling during the endmember 'hard snowball' models. A small degree of continental weathering might also help explain the extreme duration of the Sturtian glaciation, which appears to have been the longest ice age in Earth history.