Southern Hemisphere high-resolution palaeoclimate records of the last 2000 years

This study presents a comprehensive assessment of high-resolution Southern Hemisphere (SH) paleoarchives covering the last 2000 years. We identified 174 monthly to annually resolved climate proxy (tree ring, coral, ice core, documentary, speleothem and sedimentary) records from the Hemisphere. We assess the interannual and decadal sensitivity of each proxy record to large-scale circulation indices from the Pacific, Indian and Southern Ocean regions over the twentieth century. We then analyse the potential of this newly expanded palaeoclimate network to collectively represent predictands (sea surface temperature, sea level pressure, surface air temperature and precipitation) commonly used in climate reconstructions. The key dynamical centres-of-action of the equatorial Indo-Pacific are well captured by the palaeoclimate network, indicating that there is considerable reconstruction potential in this region, particularly in the post AD 1600 period when a number of long coral records are available. Current spatiotemporal gaps in data coverage and regions where significant potential for future proxy collection exists are discussed. We then highlight the need for new and extended records from key dynamical regions of the Southern Hemisphere. Although large-scale climate field reconstructions for the SH are in their infancy, we report that excellent progress in the development of regional proxies now makes plausible estimates of continental- to hemispheric-scale climate variations possible.

Untangling a Holocene pollen record with forest model simulations and independent climate data

Adaptation potential of forests to rapid climatic changes can be assessed from vegetation dynamics during past climatic changes as preserved in fossil pollen data. However, pollen data reflect the integrated effects of climate and biotic processes, such as establishment, survival, competition, and migration. To disentangle these processes, we compared an annually laminated late Würm and Holocene pollen record from the Central Swiss Plateau with simulations of a dynamic forest patch model. All input data used in the simulations were largely independent from pollen data; i.e. the presented analysis is non-circular. Temperature and precipitation scenarios were based on reconstructions from pollen-independent sources. The earliest arrival times of the species at the study site after the last glacial were inferred from pollen maps. We ran a series of simulations under different combinations of climate and immigration scenarios. In addition, the sensitivity of the simulated presence/absence of four major species to changes in the climate scenario was examined. The pattern of the pollen record could partly be explained by the used climate scenario, mostly by temperature. However, some features, in particular the absence of most species during the late Würm could only be simulated if the winter temperature anomalies of the used scenario were decreased considerably. Consequently, we had to assume in the simulations, that most species immigrated during or after the Younger Dryas (12 000 years BP), Abies and Fagus even later. Given the timing of tree species immigration, the vegetation was in equilibrium with climate during long periods, but responded with lags at the time-scale of centuries to millennia caused by a secondary succession after rapid climatic changes such as at the end of Younger Dryas, or immigration of dominant taxa. Climate influenced the tree taxa both directly and indirectly by changing inter-specific competition. We concluded, that also during the present fast climatic change, species migration might be an important process, particularly if geographic barriers, such as the Alps are in the migrational path.

Evidence for cooler European summers during periods of changing meltwater flux to the North Atlantic

We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of ≈1°C are inferred at ≈10,700–10,500 and 8,200–7,600 calibrated 14C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1°C in central Europe.

Visualization of cell microtubules in their native state.

BACKGROUND INFORMATION Over the past decades, cryo-electron microscopy of vitrified specimens has yielded a detailed understanding of the tubulin and microtubule structures of samples reassembled in vitro from purified components. However, our knowledge of microtubule structure in vivo remains limited by the chemical treatments commonly used to observe cellular architecture using electron microscopy. RESULTS We used cryo-electron microscopy and cryo-electron tomography of vitreous sections to investigate the ultrastructure of microtubules in their cellular context. Vitreous sections were obtained from organotypic slices of rat hippocampus and from Chinese-hamster ovary cells in culture. Microtubules revealed their protofilament ultrastructure, polarity and, in the most favourable cases, molecular details comparable with those visualized in three-dimensional reconstructions of microtubules reassembled in vitro from purified tubulin. The resolution of the tomograms was estimated to be approx. 4 nm, which enabled the detection of luminal particles of approx. 6 nm in diameter inside microtubules. CONCLUSIONS The present study provides a first step towards a description of microtubules, in addition to other macromolecular assemblies, in an unperturbed cellular context at the molecular level. As the resolution appears to be similar to that obtainable with plunge-frozen samples, it should allow for the in vivo identification of larger macromolecular assemblies in vitreous sections of whole cells and tissues.

Electron cryomicroscopy of E. coli reveals filament bundles involved in plasmid DNA segregation.

Bipolar elongation of filaments of the bacterial actin homolog ParM drives movement of newly replicated plasmid DNA to opposite poles of a bacterial cell. We used a combination of vitreous sectioning and electron cryotomography to study this DNA partitioning system directly in native, frozen cells. The diffraction patterns from overexpressed ParM bundles in electron cryotomographic reconstructions were used to unambiguously identify ParM filaments in Escherichia coli cells. Using a low-copy number plasmid encoding components required for partitioning, we observed small bundles of three to five intracellular ParM filaments that were situated close to the edge of the nucleoid. We propose that this may indicate the capture of plasmid DNA within the periphery of this loosely defined, chromosome-containing region.

Prediction of Trabecular Bone Anisotropy from Quantitative Computed Tomography using Supervised Learning and a Novel Morphometric Feature Descriptor

Patient-specific biomechanical models including local bone mineral density and anisotropy have gained importance for assessing musculoskeletal disorders. However the trabecular bone anisotropy captured by high-resolution imaging is only available at the peripheral skeleton in clinical practice. In this work, we propose a supervised learning approach to predict trabecular bone anisotropy that builds on a novel set of pose invariant feature descriptors. The statistical relationship between trabecular bone anisotropy and feature descriptors were learned from a database of pairs of high resolution QCT and clinical QCT reconstructions. On a set of leave-one-out experiments, we compared the accuracy of the proposed approach to previous ones, and report a mean prediction error of 6% for the tensor norm, 6% for the degree of anisotropy and 19◦ for the principal tensor direction. These findings show the potential of the proposed approach to predict trabecular bone anisotropy from clinically available QCT images.

Primary prevention of peri-implantitis: managing peri-implant mucositis

AIMS Over the past decades, the placement of dental implants has become a routine procedure in the oral rehabilitation of fully and partially edentulous patients. However, the number of patients/implants affected by peri-implant diseases is increasing. As there are--in contrast to periodontitis--at present no established and predictable concepts for the treatment of peri-implantitis, primary prevention is of key importance. The management of peri-implant mucositis is considered as a preventive measure for the onset of peri-implantitis. Therefore, the remit of this working group was to assess the prevalence of peri-implant diseases, as well as risks for peri-implant mucositis and to evaluate measures for the management of peri-implant mucositis. METHODS Discussions were informed by four systematic reviews on the current epidemiology of peri-implant diseases, on potential risks contributing to the development of peri-implant mucositis, and on the effect of patient and of professionally administered measures to manage peri-implant mucositis. This consensus report is based on the outcomes of these systematic reviews and on the expert opinion of the participants. RESULTS Key findings included: (i) meta-analysis estimated a weighted mean prevalence for peri-implant mucositis of 43% (CI: 32-54%) and for peri-implantitis of 22% (CI: 14-30%); (ii) bleeding on probing is considered as key clinical measure to distinguish between peri-implant health and disease; (iii) lack of regular supportive therapy in patients with peri-implant mucositis was associated with increased risk for onset of peri-implantitis; (iv) whereas plaque accumulation has been established as aetiological factor, smoking was identified as modifiable patient-related and excess cement as local risk indicator for the development of peri-implant mucositis; (v) patient-administered mechanical plaque control (with manual or powered toothbrushes) has been shown to be an effective preventive measure; (vi) professional intervention comprising oral hygiene instructions and mechanical debridement revealed a reduction in clinical signs of inflammation; (vii) adjunctive measures (antiseptics, local and systemic antibiotics, air-abrasive devices) were not found to improve the efficacy of professionally administered plaque removal in reducing clinical signs of inflammation. CONCLUSIONS Consensus was reached on recommendations for patients with dental implants and oral health care professionals with regard to the efficacy of measures to manage peri-implant mucositis. It was particularly emphasized that implant placement and prosthetic reconstructions need to allow proper personal cleaning, diagnosis by probing and professional plaque removal.

Younger Dryas and Allerød summer temperatures at Gerzensee (Switzerland) inferred from fossil pollen and cladoceran assemblages

Linear- and unimodal-based inference models for mean summer temperatures (partial least squares, weighted averaging, and weighted averaging partial least squares models) were applied to a high-resolution pollen and cladoceran stratigraphy from Gerzensee, Switzerland. The time-window of investigation included the Allerød, the Younger Dryas, and the Preboreal. Characteristic major and minor oscillations in the oxygen-isotope stratigraphy, such as the Gerzensee oscillation, the onset and end of the Younger Dryas stadial, and the Preboreal oscillation, were identified by isotope analysis of bulk-sediment carbonates of the same core and were used as independent indicators for hemispheric or global scale climatic change. In general, the pollen-inferred mean summer temperature reconstruction using all three inference models follows the oxygen-isotope curve more closely than the cladoceran curve. The cladoceran-inferred reconstruction suggests generally warmer summers than the pollen-based reconstructions, which may be an effect of terrestrial vegetation not being in equilibrium with climate due to migrational lags during the Late Glacial and early Holocene. Allerød summer temperatures range between 11 and 12°C based on pollen, whereas the cladoceran-inferred temperatures lie between 11 and 13°C. Pollen and cladocera-inferred reconstructions both suggest a drop to 9–10°C at the beginning of the Younger Dryas. Although the Allerød–Younger Dryas transition lasted 150–160 years in the oxygen-isotope stratigraphy, the pollen-inferred cooling took 180–190 years and the cladoceran-inferred cooling lasted 250–260 years. The pollen-inferred summer temperature rise to 11.5–12°C at the transition from the Younger Dryas to the Preboreal preceded the oxygen-isotope signal by several decades, whereas the cladoceran-inferred warming lagged. Major discrepancies between the pollen- and cladoceran-inference models are observed for the Preboreal, where the cladoceran-inference model suggests mean summer temperatures of up to 14–15°C. Both pollen- and cladoceran-inferred reconstructions suggest a cooling that may be related to the Gerzensee oscillation, but there is no evidence for a cooling synchronous with the Preboreal oscillation as recorded in the oxygen-isotope record. For the Gerzensee oscillation the inferred cooling was ca. 1 and 0.5°C based on pollen and cladocera, respectively, which lies well within the inherent prediction errors of the inference models.

European summer temperatures since Roman times

The spatial context is critical when assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatio-temporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June–August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951–2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986–2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850–2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.

Impact of Hybrid Iterative Reconstruction on Agatston Coronary Artery Calcium Scores in Comparison to Filtered Back Projection in Native Cardiac CT

PURPOSE To investigate whether the effects of hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) measurements using the Agatston score lead to changes in assignment of patients to cardiovascular risk groups compared to filtered back projection (FBP). MATERIALS AND METHODS 68 patients (mean age 61.5 years; 48 male; 20 female) underwent prospectively ECG-gated, non-enhanced, cardiac 256-MSCT for coronary calcium scoring. Scanning parameters were as follows: Tube voltage, 120 kV; Mean tube current time-product 63.67 mAs (50 - 150 mAs); collimation, 2 × 128 × 0.625 mm. Images were reconstructed with FBP and with HIR at all levels (L1 to L7). Two independent readers measured Agatston scores of all reconstructions and assigned patients to cardiovascular risk groups. Scores of HIR and FBP reconstructions were correlated (Spearman). Interobserver agreement and variability was assessed with ĸ-statistics and Bland-Altmann-Plots. RESULTS Agatston scores of HIR reconstructions were closely correlated with FBP reconstructions (L1, R = 0.9996; L2, R = 0.9995; L3, R = 0.9991; L4, R = 0.986; L5, R = 0.9986; L6, R = 0.9987; and L7, R = 0.9986). In comparison to FBP, HIR led to reduced Agatston scores between 97 % (L1) and 87.4 % (L7) of the FBP values. Using HIR iterations L1 - L3, all patients were assigned to identical risk groups as after FPB reconstruction. In 5.4 % of patients the risk group after HIR with the maximum iteration level was different from the group after FBP reconstruction. CONCLUSION There was an excellent correlation of Agatston scores after HIR and FBP with identical risk group assignment at levels 1 - 3 for all patients. Hence it appears that the application of HIR in routine calcium scoring does not entail any disadvantages. Thus, future studies are needed to demonstrate whether HIR is a reliable method for reducing radiation dose in coronary calcium scoring.

Digital vs. conventional implant prosthetic workflows: a cost/time analysis.

OBJECTIVES The aim of this prospective cohort trial was to perform a cost/time analysis for implant-supported single-unit reconstructions in the digital workflow compared to the conventional pathway. MATERIALS AND METHODS A total of 20 patients were included for rehabilitation with 2 × 20 implant crowns in a crossover study design and treated consecutively each with customized titanium abutments plus CAD/CAM-zirconia-suprastructures (test: digital) and with standardized titanium abutments plus PFM-crowns (control conventional). Starting with prosthetic treatment, analysis was estimated for clinical and laboratory work steps including measure of costs in Swiss Francs (CHF), productivity rates and cost minimization for first-line therapy. Statistical calculations were performed with Wilcoxon signed-rank test. RESULTS Both protocols worked successfully for all test and control reconstructions. Direct treatment costs were significantly lower for the digital workflow 1815.35 CHF compared to the conventional pathway 2119.65 CHF [P = 0.0004]. For subprocess evaluation, total laboratory costs were calculated as 941.95 CHF for the test group and 1245.65 CHF for the control group, respectively [P = 0.003]. The clinical dental productivity rate amounted to 29.64 CHF/min (digital) and 24.37 CHF/min (conventional) [P = 0.002]. Overall, cost minimization analysis exhibited an 18% cost reduction within the digital process. CONCLUSION The digital workflow was more efficient than the established conventional pathway for implant-supported crowns in this investigation.

Influence of Abutment Design on Stiffness, Strength, and Failure of Implant-Supported Monolithic Resin Nano Ceramic (RNC) Crowns

BACKGROUND Recent technical development allows the digital manufacturing of monolithic reconstructions with high-performance materials. For implant-supported crowns, the fixation requires an abutment design onto which the reconstruction can be bonded. PURPOSE The aim of this laboratory investigation was to analyze stiffness, strength, and failure modes of implant-supported, computer-assisted design and computer-aided manufacturing (CAD/CAM)-generated resin nano ceramic (RNC) crowns bonded to three different titanium abutments. MATERIALS AND METHODS Eighteen monolithic RNC crowns were produced and loaded in a universal testing machine under quasi-static condition according to DIN ISO 14801. With regard to the type of titanium abutment, three groups were defined: (1) prefabricated cementable standard; (2) CAD/CAM-constructed individualized; and (3) novel prefabricated bonding base. Stiffness and strength were measured and analyzed statistically with Wilcoxon rank sum test. Sections of the specimens were examined microscopically. RESULTS Stiffness demonstrated high stability for all specimens loaded in the physiological loading range with means and standard deviations of 1,579 ± 120 N/mm (group A), 1,733 ± 89 N/mm (group B), and 1,704 ± 162 N/mm (group C). Mean strength of the novel prefabricated bonding base (group C) was 17% lower than of the two other groups. Plastic deformations were detectable for all implant-abutment crown connections. CONCLUSIONS Monolithic implant crowns made of RNC seem to represent a feasible and stable prosthetic construction under laboratory testing conditions with strength higher than the average occlusal force, independent of the different abutment designs used in this investigation.

Peri-implant bone loss of dental implants with platform-switching design after 5 years of loading: a cross-sectional study

OBJECTIVE The aim of this cross-sectional study was to estimate bone loss of implants with platform-switching design and analyze possible risk indicators after 5 years of loading in a multi-centered private practice network. METHOD AND MATERIALS Peri-implant bone loss was measured radiographically as the distance from the implant shoulder to the mesial and distal alveolar crest, respectively. Risk factor analysis for marginal bone loss included type of implant prosthetic treatment concept and dental status of the opposite arch. RESULTS A total of 316 implants in 98 study patients after 5 years of loading were examined. The overall mean value for radiographic bone loss was 1.02 mm (SD ± 1.25 mm, 95% CI 0.90- 1.14). Correlation analyses indicated a strong association of peri-implant bone loss > 2 mm for removable implant-retained prostheses with an odds ratio of 53.8. CONCLUSION The 5-year-results of the study show clinically acceptable values of mean bone loss after 5 years of loading. Implant-supported removable prostheses seem to be a strong co-factor for extensive bone level changes compared to fixed reconstructions. However, these results have to be considered for evaluation of the included special cohort under private dental office conditions.

The Early Spörer Minimum – A Period of Extraordinary Climate and Socio-economic Changes in Western and Central Europe

Throughout the last millennium, mankind was affected by prolonged deviations from the climate mean state. While periods like the Maunder Minimum in the 17th century have been assessed in greater detail, earlier cold periods such as the 15th century received much less attention due to the sparse information available. Based on new evidence from different sources ranging from proxy archives to model simulations, it is now possible to provide an end-to-end assessment about the climate state during an exceptionally cold period in the 15th century, the role of internal, unforced climate variability and external forcing in shaping these extreme climatic conditions, and the impacts on and responses of the medieval society in Central Europe. Climate reconstructions from a multitude of natural and human archives indicate that, during winter, the period of the early Spörer Minimum (1431–1440 CE) was the coldest decade in Central Europe in the 15th century. The particularly cold winters and normal but wet summers resulted in a strong seasonal cycle that challenged food production and led to increasing food prices, a subsistence crisis, and a famine in parts of Europe. As a consequence, authorities implemented adaptation measures, such as the installation of grain storage capacities, in order to be prepared for future events. The 15th century is characterised by a grand solar minimum and enhanced volcanic activity, which both imply a reduction of seasonality. Climate model simulations show that periods with cold winters and strong seasonality are associated with internal climate variability rather than external forcing. Accordingly, it is hypothesised that the reconstructed extreme climatic conditions during this decade occurred by chance and in relation to the partly chaotic, internal variability within the climate system.

Tracking eolian dust with helium and thorium: Impacts of grain size and provenance

Reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates. Dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples. More recently, dust fluxes have been estimated from measurements of helium and thorium, as rare isotopes of these elements (He-3 and Th-230) allow estimates of sediment flux, and the dominant isotopes (He-4 and Th-232) are uniquely associated with the lithogenic fraction of marine sediments. In order to improve the fidelity of dust flux reconstructions based on He and Th, we present a survey of He and Th concentrations in sediments from dust source areas in East Asia, Australia and South America. Our data show systematic relationships between He and Th concentrations and grain size, with He concentrations decreasing and Th concentrations increasing with decreasing grain size. We find consistent He and Th concentrations in the fine fraction (<5 μm) of samples from East Asia, Australia and Central South America (Puna-Central West Argentina), with Th concentrations averaging 14 μg/g and He concentrations averaging 2 μcc STP/g. We recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine-grained, and suggest that previous studies may have systematically overestimated Th-based dust fluxes by 30%. Source areas in Patagonia appear to have lower He and Th contents than other regions, as fine fraction concentrations average 0.8 μcc STP/g and 9 μg/g for 4He and 232Th, respectively. The impact of grain size on lithogenic He and Th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably. Our data also have important implications for the hosts of He in long-traveled dust and for the 3He/4He ratio used for terrigenous He in studies of extraterrestrial He in sediments and ice. We also investigate the use of He/Th ratios as a provenance tracer. Our results suggest differences in fine fraction He/Th ratios between East Asia, Australia, central South America and Patagonia, with ratios showing a positive relationship with the geological age of source rocks. He/Th ratios may thus provide useful provenance information, for example allowing separation of Patagonian sources from Puna-Central West Argentina or Australian dust sources. He/Th ratios in open-ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas. He/Th ratios in mid-latitude South Atlantic sediments suggest that dust in this region primarily derives from the Puna-Central West Argentina region (23–32°S) rather than Patagonia (>38°S). In the equatorial Pacific, He/Th ratios are much lower than in extratropical Pacific sediments or potential source areas measured as a part of this study (East Asia, South America, Australia) for reasons that are at present unclear, complicating their use as provenance tracers in this region.