Evidence for massive methane hydrate destabilization during the penultimate interglacial warming

The stability of widespread methane hydrates in shallow subsurface sediments of the marine continental margins is sensitive to temperature increases experienced by upper intermediate waters. Destabilization of methane hydrates and ensuing release of methane would produce climatic feedbacks amplifying and accelerating global warming. Hence, improved assessment of ongoing intermediate water warming is crucially important, especially that resulting from a weakening of Atlantic meridional overturning circulation (AMOC). Our study provides an independent paleoclimatic perspective by reconstructing the thermal structure and imprint of methane oxidation throughout a water column of 1,300 m. We studied a sediment sequence from the eastern equatorial Atlantic (Gulf of Guinea), a region containing abundant shallow subsurface methane hydrates. We focused on the early part of the penultimate interglacial and present a hitherto undocumented and remarkably large intermediate water warming of 6.8 °C in response to a brief episode of meltwater-induced, modest AMOC weakening centered at 126,000 to 125,000 y ago. The warming of intermediate waters to 14 °C significantly exceeds the stability field of methane hydrates. In conjunction with this warming, our study reveals an anomalously low δ¹³C spike throughout the entire water column, recorded as primary signatures in single and pooled shells of multitaxa foraminifers. This extremely negative δ¹³C excursion was almost certainly the result of massive destabilization of methane hydrates. This study documents and connects a sequence of climatic events and climatic feedback processes associated with and triggered by the penultimate climate warming that can serve as a paleoanalog for modern ongoing warming.

Because ocean intermediate waters impinge on marine sediments that often contain potentially unstable shallow subsurface methane hydrates (1–3), better understanding is crucial about the factors that contribute to intermediate water warming and their potential extent, especially in context with ongoing global warming. Simulation studies have suggested warming of intermediate waters has been limited to ∼1.5 °C to 3 °C, and that such warmings were insufficient to significantly affect the stability of shallow subsurface methane hydrates (2–5). However, the magnitude of intermediate water warming can be significantly amplified by meltwater-induced weakening of atmospheric and ocean circulation (6–11), an amplification not considered in the simulations that examined potential gas hydrate destabilization (2–5). A recent simulation study estimates the contribution of weak Atlantic meridional overturning circulation (AMOC) at 0.3 °C to 0.4 °C to the warming of the intermediate waters for a business-as-usual scenario at the end of the 21st century (12), a modest contribution compared to observations in past climate studies (6–11). An accelerated mass loss of the Greenland ice sheet and the associated freshening of subpolar North Atlantic sea surface waters represents a robust proxy of ongoing rapid global warming (13). Causally linked to this freshening is increasing evidence of a steady weakening of the AMOC (14, 15). Warming of the intermediate waters by 3 °C to 5 °C in response to a meltwater-induced AMOC weakening is a robust feature of the last deglacial (6–11). This corresponds to pockmark formations on the ocean floor and extremely negative foraminiferal δ¹³C values in sediment sequences that reflect methane hydrate dissociation in response to intermediate water warming related to meltwater-induced weakening of AMOC and associated changes in atmospheric circulation during the last deglacial (10, 11, 16–18). A sequence of episodic, extremely low foraminiferal δ¹³C values observed in Late Quaternary sediments of Santa Barbara Basin led to the formulation of the “clathrate gun hypothesis” (10, 11). The hypothesis states that episodic warming of intermediate waters during the last glacial and early deglacial led to dissociation of shallow subsurface methane hydrates and release of methane, contributing to the observed increases of atmosphere methane concentrations, further contributing to climatic warming episodes (10, 11). The key findings of our study add to a growing body of observational findings strongly supporting the “clathrate gun hypothesis” (10, 11). The magnitude of intermediate water warming in response to AMOC weakening most likely is critically dependent on the existing mean climatic state. Importantly, the interval we have studied is marked by a mean climate state comparable to future projections of transient global climate warming of 1.3 °C to 3.0 °C (19). Our findings thus provide insights about major meltwater-induced intermediate water warming during warm episodes like the present with the potential to destabilize structural-type methane hydrates.In this study, we focus on the early part of the Eemian interglacial episode (128,000 to 125,000 y before present [ky BP]), the youngest episode when tropical oceans were warmer than the Holocene by up to 2 °C (20–22). We show that the combination of a warm mean climate state and a relatively brief and modest episode of meltwater-induced AMOC weakening produced an exceptionally large intermediate water warming that significantly exceeds the stability field of methane hydrates. Coincident with this warming, we demonstrate that the dissolved inorganic carbon across the entire 1,300-m water column was marked by an anomalously low carbon isotope ratio (¹³C/¹²C) which we interpret to indicate destabilization of shallow subsurface methane hydrates and ensuing methane oxidation.     

RSV Replication,Transmission, and Disease Are Influenced by the RSV G Protein

It is important to understand the features affecting virus replication, fitness, and transmissibility as they contribute to the outcome of infection and affect disease intervention approaches. Respiratory syncytial virus (RSV) is a major contributor to respiratory disease, particularly in the infant and elderly populations. Although first described over 60 years ago, there are no approved vaccines and there are limited specific antiviral treatments due in part to our incomplete understanding of the features affecting RSV replication, immunity, and disease. RSV studies have typically focused on using continuous cell lines and conventional RSV strains to establish vaccine development and various antiviral countermeasures. This review outlines how the RSV G protein influences viral features, including replication, transmission, and disease, and how understanding the role of the G protein can improve the understanding of preclinical studies.     

Nanomechanical and Vibrational Signature of Chikungunya Viral Particles

Chikungunya virus (CHIKV) belongs to the genus Alphaviridae, with a single-stranded positive-sense RNA genome of 11.8 kbp encoding a polyprotein that generates both non-structural proteins and structural proteins. The virus is transmitted by the Aedes aegypti and A. albopictus mosquitoes, depending on the location. CHIKV infection leads to dengue-like musculoskeletal symptoms and has been responsible for several outbreaks worldwide since its discovery in 1952. Patients often experience fever, headache, muscle pain, joint swelling, and skin rashes. However, the ultrastructural and mechanical properties of CHIKV have not been fully characterized. Thus, this study aims to apply a physical approach to investigate CHIKV′s ultrastructural morphology and mechanical properties, using atomic force microscopy and Raman spectroscopy as the main tools. Using nanomechanical assays of AFM and a gold nanoparticles substrate for Raman signal enhancement, we explored the conformational plasticity, morphology, vibrational signature, and nanomechanical properties of the chikungunya virus, providing new information on its ultrastructure at the nanoscale and offering a novel understanding of the virus’ behavior upon mechanical disruptions besides its molecular composition.     

Systematic evaluation of machine learning algorithms for neuroanatomically‐based age prediction in youth

Application of machine learning (ML) algorithms to structural magnetic resonance imaging (sMRI) data has yielded behaviorally meaningful estimates of the biological age of the brain (brain‐age). The choice of the ML approach in estimating brain‐age in youth is important because age‐related brain changes in this age‐group are dynamic. However, the comparative performance of the available ML algorithms has not been systematically appraised. To address this gap, the present study evaluated the accuracy (mean absolute error [MAE]) and computational efficiency of 21 machine learning algorithms using sMRI data from 2105 typically developing individuals aged 5–22 years from five cohorts. The trained models were then tested in two independent holdout datasets, one comprising 4078 individuals aged 9–10 years and another comprising 594 individuals aged 5–21 years. The algorithms encompassed parametric and nonparametric, Bayesian, linear and nonlinear, tree‐based, and kernel‐based models. Sensitivity analyses were performed for parcellation scheme, number of neuroimaging input features, number of cross‐validation folds, number of extreme outliers, and sample size. Tree‐based models and algorithms with a nonlinear kernel performed comparably well, with the latter being especially computationally efficient. Extreme Gradient Boosting (MAE of 1.49 years), Random Forest Regression (MAE of 1.58 years), and Support Vector Regression (SVR) with Radial Basis Function (RBF) Kernel (MAE of 1.64 years) emerged as the three most accurate models. Linear algorithms, with the exception of Elastic Net Regression, performed poorly. Findings of the present study could be used as a guide for optimizing methodology when quantifying brain‐age in youth.     

Carbon Dioxide Absorption from An?sthetic Atmospheres : (Section of An?sthetics)

A safe and practical technique for the application of carbon dioxide absorption from anæsthetic atmospheres is described. It has been found satisfactory in over 20,000 administrations over a period of fifteen years. High-grade soda lime is utilized as the chemical absorbent. Granules are placed in a canister between face mask, and breathing bag. The canister is carefully checked for efficiency by both chemical analyses and physical experiments. Its size, shape and arrangement is shown to be important for safety and maximum efficiency. Detailed techniques are described for the use of various agents. Advantages of carbon dioxide absorption are set forth. The “Apnœa” suggested by Guedel is described under the term “Controlled Respiration” and attention is called to certain of its advantages.