Glacier-like forms on Mars

More than 1300 glacier-like forms (GLFs) are located in Mars' mid-latitudes. These GLFs are predominantly composed of ice–dust mixtures and are visually similar to terrestrial valley glaciers, showing signs of downhill viscous deformation and an expanded former extent. However, several fundamental aspects of their behavior are virtually unknown, including temporal and spatial variations in mass balance, ice motion, landscape erosion and deposition, and hydrology. Here, we investigate the physical glaciology of martian GLFs. We use satellite images of specific examples and case studies to build on existing knowledge relating to (i) GLF current and former extent, exemplified via a GLF located in Phlegra Montes; (ii) indicators of GLF motion, focusing on the presence of surface crevasses on several GLFs; (iii) processes of GLF debris transfer, focusing on mapping and interpreting boulder trains on one GLF located in Protonilus Mensae, the analysis of which suggests a best-estimate mean GLF flow speed of 7.5 mm a−1; and (iv) GLF hydrology, focusing on supra-GLF gulley networks. On the basis of this information, we summarize the current state of knowledge of the glaciology of martian GLFs and identify future research avenues

Landscapes of polyphase glaciation: eastern Hellas Planitia, Mars

<p>The mid-latitudes of Mars host numerous ice-related landforms that bear many similarities to terrestrial ice masses. This collection of landforms, termed viscous flow features (VFFs), is composed primarily of H₂O ice and shows evidence of viscous deformation. Recent work has hypothesised that VFFs are the diminishing remains of once larger ice masses, formed during one or more previous ice ages, and the landscape therefore records evidence of polyphase glaciation. However, debate persists concerning the former extent and volume of ice, and style of former glaciations. The accompanying map (1:100,000 scale) presents a geomorphic and structural assessment of a glacial landscape in eastern Hellas Planitia, Mars. Here, we present a description of the features identified, comprising four geomorphic units (plains, lobate debris apron, degraded glacial material, and glacier-like form) and 16 structures (craters, moraine-like ridges, flow unit boundaries, arcuate transvers structures, longitudinal surface structures, ring-mold craters, terraces, medial moraine-like ridges, raised textured areas, flow-parallel and flow-transverse lineations, crevasses and crevasse traces, and ridge clusters).</p

Observing iceberg size distributions and implications for calving processes

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Atmospheric drivers of melt-related ice speed-up events on the Russell Glacier in Southwest Greenland

The Greenland ice sheet is a major contributor to current and projected sea level rise in the warming climate. However, uncertainties in Greenland&rsquo;s contribution to future sea level rise remain, partly due to challenges in constraining the role of ice dynamics. One process that has the potential to indirectly affect the mass budget of the ice sheet are transient ice accelerations, or ice speed-up events, lasting from one day to a week and triggered by overloading the subglacial drainage system with an increase in water supply. In this study, we identify melt-induced ice speed-up events at the Russell Glacier, Southwest Greenland, in order to analyse synoptic patterns driving these events. The short-term speed-up events are identified from daily ice velocity time series collected from six GPS stations along the glacier, for each summer (May&ndash;September) from 2009 to 2012. In total, 45 ice speed-up events are identified, of which 36 are considered melt-induced events where melt is derived from two in-situ observational datasets and one regional climate model forced by ERA5 reanalysis. 16 out of the 45 speed-up events co-occur with lake drainage events, and only four are linked with extreme rainfall events. The 36 melt-induced speed-up events occur during synoptic patterns that can be grouped into three main clusters: (1) patterns that resemble atmospheric rivers with a landfall in Southwest Greenland, (2) patterns with anticyclonic blockings centred over Southwest Greenland, and (3) patterns that show low pressure systems centred either south or southeast of Greenland. Out of these clusters, the one resembling atmospheric river patterns is linked to the strongest speed-up events induced by a 2&ndash;3 day continuously increasing surface melt driven by anomalously high sensible heat flux and incoming longwave radiation. In the other two clusters, the net shortwave radiation dominates the contribution to the melt energy. As the frequency and intensity of these weather patterns may change in the warming climate, so may the frequency and intensity of ice speed-up events, ultimately altering the mass loss of the ice sheet.</p

Identification of Trypanocidal Activity for Known Clinical Compounds Using a New <i>Trypanosoma cruzi</i> Hit-Discovery Screening Cascade

<div><p>Chagas disease is a significant health problem in Latin America and the available treatments have significant issues in terms of toxicity and efficacy. There is thus an urgent need to develop new treatments either via a repurposing strategy or through the development of new chemical entities. A key first step is the identification of compounds with anti-<i>Trypanosoma cruzi</i> activity from compound libraries. Here we describe a hit discovery screening cascade designed to specifically identify hits that have the appropriate anti-parasitic properties to warrant further development. The cascade consists of a primary imaging-based assay followed by newly developed and appropriately scaled secondary assays to predict the cidality and rate-of-kill of the compounds. Finally, we incorporated a cytochrome P450 CYP51 biochemical assay to remove compounds that owe their phenotypic response to inhibition of this enzyme. We report the use of the cascade in profiling two small libraries containing clinically tested compounds and identify Clemastine, Azelastine, Ifenprodil, Ziprasidone and Clofibrate as molecules having appropriate profiles. Analysis of clinical derived pharmacokinetic and toxicity data indicates that none of these are appropriate for repurposing but they may represent suitable start points for further optimisation for the treatment of Chagas disease.</p></div

Exceptional Retreat of Kangerlussuaq Glacier, East Greenland, Between 2016 and 2018

Kangerlussuaq Glacier is one of Greenland’s largest tidewater outlet glaciers, accounting for approximately 5% of all ice discharge from the Greenland ice sheet. In 2018 the Kangerlussuaq ice front reached its most retreated position since observations began in 1932. We determine the relationship between retreat and: (i) ice velocity; and (ii) surface elevation change, to assess the impact of the retreat on the glacier trunk. Between 2016 and 2018 the glacier retreated ∼5 km and brought the Kangerlussuaq ice front into a major (∼15 km long) overdeepening. Coincident with this retreat, the glacier thinned as a result of near-terminus acceleration in ice flow. The subglacial topography means that 2016–2018 terminus recession is likely to trigger a series of feedbacks between retreat, thinning, and glacier acceleration, leading to a rapid and high-magnitude increase in discharge and sea level rise contribution. Dynamic thinning may continue until the glacier reaches the upward sloping bed ∼10 km inland of its current position. Incorporating these non-linear processes into prognostic models of the ice sheet to 2100 and beyond will be critical for accurate forecasting of the ice sheet’s contribution to sea level rise