Full-depth englacial vertical ice-sheet velocities measured using phase-sensitive radar

We describe a geophysical technique to measure englacial vertical velocities through to the beds of ice sheets without the need for borehole drilling. Using a ground-based phase-sensitive radio-echo sounder (pRES) during seven Antarctic field seasons, we measure the temporal changes in the position of englacial reflectors within ice divides up to 900 m thick on Berkner Island, Roosevelt Island, Fletcher Promontory and Adelaide Island. Recorded changes in reflector positions yield 'full-depth' profiles of vertical ice velocity that we use to examine spatial variations in ice flow near the divides. We interpret these variations by comparing them to the results of a full-Stokes simulation of ice-divide flow, qualitatively validating the model and demonstrating that we are directly detecting an ice-dynamical phenomenon called the Raymond Effect. Using pRES, englacial vertical ice velocities can be measured in higher spatial resolution than is possible using instruments installed within the ice. We discuss how these measurements could be used with inverse methods to measure ice rheology, and to improve ice-core dating by incorporating pRES-measured vertical velocities into age modelling

Decreased sAβPPβ, Aβ38, and Aβ40 Cerebrospinal Fluid Levels in Frontotemporal Dementia.

International audienceTo improve the etiological diagnosis of neurodegenerative dementias like Alzheimer's disease (AD) or frontotemporal dementia (FTD), we evaluated the value of individual and combined measurements of the following relevant cerebrospinal fluid (CSF) biomarkers: Tau, 181p-Tau, Aβ38, Aβ40, Aβ42, sAβPPα, and sAβPPβ. This study conducted in two centers included patients with FTD (n = 34), AD (n = 52), as well as a control group of persons without dementia (CTRL, n = 42). Identical clinical criteria and pre-analytical conditions were used while CSF biomarkers were measured using commercial single and multiplex quantitative immunoassays. Thorough statistical analyses, including ROC curves, logistic regressions, and decision trees, were performed. We validated in AD the specific increase of p-Tau levels and the decrease of Aβ42 levels, two biological hallmarks of this disease. Tau concentrations were highest in AD and intermediate in FTD when compared to CTRL. The most interesting results were obtained by focusing on amyloid biomarkers as we found out in FTD a significant decrease of sAβPPβ, Aβ38, and Aβ40 levels. Aβ38 in particular was the most useful biomarker to differentiate FTD subjects from the CTRL population. Combining p-Tau and Aβ38 led us to correctly classifying FTD patients with sensitivity at 85% and specificity at 82%. Significant changes in amyloid biomarkers, particularly for Aβ38, are therefore seen in FTD. This could be quite useful for diagnosis purposes and it might provide additional evidence on the interrelationship between Tau and AβPP biology which understanding is essential to progress towards optimal therapeutic and diagnostic approaches of dementia

Brief communication: Candidate sites of 1.5 Myr old ice 37 km southwest of the Dome C summit, East Antarctica

The search for ice as old as 1.5 Myr requires the identification of places that maximize our chances to retrieve old, well-resolved, undisturbed and datable ice. One of these locations is very likely southwest of the Dome C summit, where elevated bedrock makes the ice thin enough to limit basal melting. A 3-D ice flow simulation is used to calculate five selection criteria, which together delineate the areas with the most appropriate glaciological properties. These selected areas (a few square kilometers) lie on the flanks of a bedrock high, where a balance is found between risks of basal melting, stratigraphic disturbances and sufficient age resolution. Within these areas, several sites of potential 1.5 Myr old ice are proposed, situated on local bedrock summits or ridges. The trajectories of the ice particles towards these locations are short, and the ice flows over a smoothly undulating bedrock. These sites will help to choose where new high-resolution ground radar surveys should be conducted in upcoming field seasons

Fully-coupled 3D modelling of Halvfarryggen Ice Rise, Dronning Maud Land, East Antarctica

Antarctica is fringed by floating ice shelves through which more than 80% of the overall ice is discharged. These ice shelves provide the main interface between the Antarctic Ice Sheet and the surrounding ocean. Virtually all ice shelves are either laterally constrained by embayments or locally reground on topographic highs causing the formation of ice rises. In both cases the locally enhanced friction is transmitted upstream, resulting in a restraining force that decelerates ice discharge and controls rates of sea-level rise. As ice rises are typically on the order of ten sof kilometers in diameter, they are usually not resolved, both in the observations and the physical approximations,in large-scale ice-sheet models. In addition to their stabilising influence, ice rises also provide a proxy for stable ice-sheet condition in the past as they archive their own evolution in their stratigraphy, providing the opportunity to derive a Pan-Antarctic archive for the deglaciation history. To adequately simulate ice rise evolution, the full stress balance needs to be considered including the full coupling of ice sheet, ice shelf, and ice rise. Here, we use the Full-Stokes ice-sheet model Elmer/Ice for the Ekström Ice Shelf embayment in Dronning Maud Land, East Antarctica, to study the effect of ice rises on the overall stability of the ice sheet. We initialise the model for prognostic simulations using today’s surface velocity to invert for basal drag and ice-shelf rigidity in full Stokes. To account for inconsistencies in the input data we relax the initial geometry over 10 years resulting in a quasi-steady state which stays close to today’s observations. As a first application of this 3D model including the fully coupled system with a dynamic grounding line, we derive erosion rates for the outlet glaciers of the Ekström Ice Shelf embayment, revealing moderate rates of up to∼0.75 mm/yr, using published sliding-erosion ratios from others areas. This will be compared to sedimentary structures derived from seismic measurements. Our perturbation experiments of the Ekström Ice Shelf embayment will investigate the effect of changing atmospheric/oceanic conditions on ice-rise evolution and divide migration using for the first time a fully coupled 3D ice-sheet model. This approach will permit to unambiguously show if and how much changes in external forcing influence divide position and internal stratigraphy, a proxy that has been widely used to deduce stable ice-flow and grounding-line conditions, but from studies that either use simplified model physics or omit the coupling between ice rise and ice shelf. Our novel modelling set-up will help to unravel the importance of ice rises for the past and future timing of sea-level rise, and represents a first step towards using ice rises as a Pan-Antarctic archive to constrain paleo ice-sheet simulations

Assessment of sub-shelf melting parameterisations using the ocean–ice-sheet coupled model NEMO(v3.6)–Elmer/Ice(v8.3)

Oceanic melting beneath ice shelves is the main driver of the current mass loss of the Antarctic ice sheet and is mostly parameterised in stand-alone ice-sheet modelling. Parameterisations are crude representations of reality, and their response to ocean warming has not been compared to 3-D ocean–ice-sheet coupled models. Here, we assess various melting parameterisations ranging from simple scalings with far-field thermal driving to emulators of box and plume models, using a new coupling framework combining the ocean model NEMO and the ice-sheet model Elmer/Ice. We define six idealised one-century scenarios for the far-field ocean ranging from cold to warm, and representative of potential futures for typical Antarctic ice shelves. The scenarios are used to constrain an idealised geometry of the Pine Island glacier representative of a relatively small cavity. Melt rates and sea-level contributions obtained with the parameterised stand-alone ice-sheet model are compared to the coupled model results. The plume parameterisations give good results for cold scenarios but fail and underestimate sea level contribution by tens of percent for warm(ing) scenarios, which may be improved by adapting its empirical scaling. The box parameterisation with five boxes compares fairly well to the coupled results for almost all scenarios, but further work is needed to grasp the correct number of boxes. For simple scalings, the comparison to the coupled framework shows that a quadratic as opposed to linear dependency on thermal forcing is required. In addition, the quadratic dependency is improved when melting depends on both local and non-local, i.e. averaged over the ice shelf, thermal forcing. The results of both the box and the two quadratic parameterisations fall within or close to the coupled model uncertainty. All parameterisations overestimate melting for thin ice shelves while underestimating melting in deep water near the grounding line. Further work is therefore needed to assess the validity of these melting parameteriations in more realistic set-ups

The effects of auditory enrichment on zebrafish behavior and physiology

Environmental enrichment is widely used to improve welfare and behavioral performance of animal species. It ensures housing of laboratory animals in environments with space and complexity that enable the expression of their normal behavioral repertoire. Auditory enrichment by exposure to classical music decreases abnormal behaviors and endocrine stress responses in humans, non-humans primates, and rodents. However, little is known about the role of auditory enrichment in laboratory zebrafish. Given the growing importance of zebrafish for neuroscience research, such studies become critical. To examine whether auditory enrichment by classical music can affect fish behavior and physiology, we exposed adult zebrafish to 2 h of Vivaldi’s music (65–75 dB) twice daily, for 15 days. Overall, zebrafish exposed to such auditory stimuli were less anxious in the novel tank test and less active, calmer in the light-dark test, also affecting zebrafish physiological (immune) biomarkers, decreasing peripheral levels of pro-inflammatory cytokines and increasing the activity of some CNS genes, without overt effects on whole-body cortisol levels. In summary, we report that twice-daily exposure to continuous musical sounds may provide benefits over the ongoing 50–55 dB background noise of equipment in the laboratory setting. Overall, our results support utilizing auditory enrichment in laboratory zebrafish to reduce stress and improve welfare in this experimental aquatic organism

Farm and farmer characteristics and off-farm work: Evidence from Algeria

© 2019 Australasian Agricultural and Resource Economics Society Inc. Off-farm work is a widespread, two-edged, phenomenon that can help both the survival and the demise of small- and medium-sized agricultural exploitations. Given the prevalence of poverty in rural areas, nonfarm income has been credited with helping farmers to survive. But the observed shrinking of rural areas has also raised the question of whether off-farm work is pulling farmers permanently away from farming. This paper explores the impact of farmer characteristics on the decision to work off-farm in developing countries where this phenomenon has been largely neglected. A review of theory and prior empirical work suggests four main hypotheses which we test empirically. The results suggest that while some farmer characteristics appear to be universal, others appear to be country- or culture-specific

Sensitivity of basal conditions in an inverse model : Vestfonna ice cap, Nordaustlandet/Svalbard

Peer reviewe

Ice fabric in an Antarctic ice stream interpreted from seismic anisotropy

Here we present new measurements of an anisotropic ice fabric in a fast moving (377 ma−1) ice stream in West Antarctica. We use ∼6000 measurements of shear wave splitting observed in microseismic signals from the bed of Rutford Ice Stream, to show that in contrast to large-scale ice flow models, which assume that ice is isotropic, the ice in Rutford Ice Stream is dominated by a previously unobserved type of partial girdle fabric. This fabric has a strong directional contrast in mechanical properties, shearing 9.1 times more easily along the ice flow direction than across flow. This observed fabric is likely to be widespread and representative of fabrics in other ice streams and large glaciers, suggesting it is essential to consider anisotropy in data-driven models to correctly predict ice loss and future flow in these regions. We show how passive microseismic monitoring can be effectively used to provide these data