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Subglacial meltwater landforms found on palaeo‐ice sheet beds allow the properties of meltwater drainage to be reconstructed, informing our understanding of modern‐day subglacial hydrological processes. In northern Canada and Fennoscandia, subglacial meltwater landforms are largely organized into continental‐scale networks of subglacial meltwater corridors (SMCs), interpreted as the relics of subglacial drainage systems undergoing variations in meltwater input, effective pressure and drainage efficiency. We review the current state of knowledge of bedforms (hummocks, ridges, murtoos, ribbed bedforms) and associated landforms (channels, eskers) described along SMCs and use selected high‐resolution DEMs in Canada and Fennoscandia to complete the bedform catalogue and categorize their characteristics, patterning and spatial distributions. We synthesize the diversity of bedform and formation processes occurring along subglacial drainage routes in a conceptual model invoking spatiotemporal changes in hydraulic connectivity, basal meltwater pressure and ice‐bed coupling, which influences the evolution of subglacial processes (bed deformation, erosion, deposition) along subglacial drainage systems. When the hydraulic capacity of the subglacial drainage system is overwhelmed glaciofluvial erosion and deposition will dominate in the SMC, resulting in tracts of hummocks and ridges arising from both fragmentation of underlying pre‐existing bedforms and downstream deposition of sediments in basal cavities and crevasses. Re‐coupling of ice with the bed, when meltwater supply decreases, facilitates deformation, transforming existing and producing new bedforms concomitant with the wider subglacial bedform imprint. We finally establish a range of future research perspectives to improve understanding of subglacial hydrology, geomorphic processes and bedform diversity along SMCs. These perspectives include the new acquisition of remote‐sensing and field‐based sedimentological and geomorphological data, a better connection between the interpreted subglacial drainage configurations down corridors and the mathematical treatments studying their stability, and the quantification of the scaling, distribution and evolution of the hydraulically connected drainage system beneath present‐day ice masses to test our bedform‐related conceptual model. [ABSTRACT FROM AUTHOR]

We develop a mathematical model for esker formation by the continuous deposition of sediments near the mouth of water‐filled subglacial tunnels. We assume a retreating ice sheet margin and prescribe meltwater and sediment supply to a channelized subglacial drainage system. The hydrodynamic model for the subglacial channel has its cross section governed by wall melting, creep closure, and sediment deposition. Sediment‐carrying capacity typically increases downstream, before decreasing rapidly near the margin, suggesting that most deposition occurs there. This can lead to "choking" near the margin, which is offset by enhanced melting to keep the channel open. The model shows that the deposition rate varies roughly quadratically with sediment supply and inversely with water flux. For given sediment supply, the model suggests esker formation is most prevalent in smaller channels. Larger ice sheet melt rates likely produce more closely spaced eskers, but with smaller cross sections. Key Points: We develop a quantitative physically based model for esker deposition in subglacial channelsThe model predicts relationships between melt rate, sediment supply, retreat rate, and esker size and spacingLarger ice sheet melt rates are expected to produce smaller, more closely spaced, eskers [ABSTRACT FROM AUTHOR]

Eskers are long sedimentary ridges that are widespread in current and previously glaciated landscapes. Eskers are believed to form when sediment carried by glacial meltwater gets deposited in subglacial tunnels, which given the importance of subglacial water for ice dynamics means that eskers can provide important information about the shape and dynamics of ice sheets and glaciers. To date, however, no physical model for their formation has been developed. Beaud et al. (2018, https://doi.org/10.1029/2018JF004779) present the first such model; they have linked an existing model for subglacial water flow with one for sediment transport, erosion, and deposition in mixed sediment/bedrock streams. The results of the model add new insights into the conditions which promote esker formation, the rate of supply of sediment to proglacial environments, and also suggest possible links between the water flow regime and the likely esker morphology. Plain Language Summary: This commentary discusses the paper by Beaud et al. (2018) which presents the first numerical, physically based model for esker formation. Eskers are long sedimentary ridges that are widespread in current and previously glaciated landscapes. They are believed to form within subglacial tunnels; this commentary discusses the importance of the configuration of the "plumbing system" of glaciers and ice sheets for their flow patterns and highlights how the model could change how esker deposits are interpreted and how the model results could be used to help infer subglacial water flow characteristics from eskers. Key Points: A new model for esker formation by Beaud et al. (2018) links sediment processes with subglacial tunnel dynamicsThe model shows sediment deposition as eskers is caused by a bottleneck in sediment transport near the snout of glaciersThe model develops realistic sedimentation patterns and will allow better understanding of the links between esker formation and ice dynamics [ABSTRACT FROM AUTHOR]

Sediment yields from glacierized basins are used to quantify erosion rates on seasonal to decadal timescales as well as conditions at the glacier bed, and eskers hold valuable information about past subglacial hydraulic conditions in their spatial organization, geometry, and sedimentary structures. Ultimately, eskers are a record of past glacio‐fluvial sediment transport, but there is currently no physical model for this process. We develop a 1‐D model of morphodynamics in semicircular bedrock‐floored subglacial channels. We adapt a sediment conservation law developed for mixed alluvial‐bedrock conditions to subglacial channels. Channel evolution is a function of melt opening by viscous heat dissipation from flowing water and creep closure of the overlying ice, to which we add the closure or enlargement due to sediment deposition or removal, respectively. We apply the model to an idealized land‐terminating glacier and find that temporary sediment accumulation in the vicinity of the terminus, or the formation of an incipient esker, is inherent to the dynamics of the channelized water flow. The alluviation of the bed combined with the pressurized channel flow produces unexpected patterns of sediment evacuation: We show that the direction of hysteresis between sediment and water discharge is not necessarily linked to a supply‐ or transport‐limited system, as has been hypothesized for proglacial sediment yields. We also find that the deposition of an incipient esker is a function of a compromise between water discharge and sediment supply, but perhaps more importantly, ice‐surface slope and the temporal pattern of water delivery to the bed. Plain Language Summary: Glaciers and ice sheets are changing rapidly, impacting sea levels, landscapes, and ecosystems. These changes are tightly linked to the meltwater routing through glaciers' plumbing systems. If this plumbing is pressurized by water flowing into crevasses and moulin (which act like water wells), the ice base can move faster downstream, possibly leading to enhanced ice loss, or vice versa. As glaciers retreated at the end of the last glaciation, they left clues of their passage, including sediment casts of their plumbing system: eskers. Eskers are elongated ridges that snake across the landscape and can be hundreds of kilometers long. Although understanding their deposition can help us understand contemporary ice sheet plumbing systems, their origin has been puzzling for several decades. We build a numerical model tracking sediment as they move with the water under ice. Glaciers naturally produce a sediment bottleneck and tend to form such eskers, producing the first process‐based model for their deposition. We identify ice geometry and temporal patterns of water input into the plumbing system as critical factors, when combined with sufficient sediment and water supplies. This model helps to reconcile contemporary glacier processes and sediment records, which is key to better understand glaciers' plumbing system. Key Points: A framework is presented for sediment transport in subglacial channels over semialluvial bedsHysteresis in sediment and water flux is inherent to R‐channels regardless of bed alluviationThe formation of eskers is caused by a sediment bottleneck at the glacier terminus [ABSTRACT FROM AUTHOR]

This paper uses detailed mapping of eskers to address three questions which are important for reconstructing meltwater behaviour beneath contemporary and ancient ice masses: 'What controls the morphology of simple and complex esker systems?', 'How do esker systems evolve through time?' and 'Are esker patterns compatible with groundwater controlled hydraulic spacing of esker tunnels?'. Esker crestlines and widths are mapped on the Breiðamerkurjökull foreland for eight time slices between 1945 and 2007, from high resolution (~50 cm) aerial photography, permitting their long-term morphological evolution to be analysed in a high level of detail. We find that complex eskers develop where meltwater and sediment is abundant, such that sediment clogs channels, forming distributary eskers. Isolated eskers are simpler and smaller and reflect less abundant meltwater and sediment, which is unable to clog channels. Eskers may take several decades to emerge from outwash deposits containing buried ice and can increase or decrease in size when ice surrounding and underlying them melts out. It has been suggested that groundwater-channel coupling dictates the spacing between eskers at Breiðamerkurjökull. Our results do not dispute this, but suggest that the routing of sediment and meltwater through medial moraines is an additional important control on esker location and spacing. These results may be used to better understand the processes surrounding esker formation in a variety of geographical settings, enabling a more detailed understanding of the operation of meltwater drainage systems in sub-marginal zones beneath glaciers and ice sheets. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

African tick-bite fever ( ATBF), a tickborne disease endemic in rural areas of sub-Saharan Africa and the West Indies caused by Rickettsia africae, has been recognized as an emerging health problem in recent years. ATBF has been reported as the second most commonly documented etiology of fever, after malaria, in travelers who return ill from sub-Saharan Africa. Most cases reported in the literature occurred in middle-aged adults, so the incidence of ATBF in children is unclear. We report a cluster of three cases of ATBF that occurred in children ages 7 to 16 years after returning from a game-hunting safari in South Africa. [ABSTRACT FROM AUTHOR]

Papain, a phytotherapeutic agent, has been used in the treatment of eschars and as a debriding chemical agent to remove damaged or necrotic tissue of pressure ulcers and gangrene. Its benefits in these treatments are deemed effective, since more than 5000 patients, at the public university hospital at Rio de Janeiro, Brazil, have undergone papain treatment and presented satisfactory results. Despite its extensive use, there is little information about toxic and mutagenic properties of papain. This work evaluated the toxic and mutagenic potential of papain and its potential antioxidant activity against induced-H2O2 oxidative stress in Escherichia coli strains. Cytotoxicity assay, Growth inhibition test, WP2-Mutoxitest and Plasmid-DNA treatment, and agarose gel electrophoresis were used to investigate if papain would present any toxic or mutagenic potential as well as if papain would display antioxidant properties. Papain exhibited negative results for all tests. This agent presented an activity protecting cells against H2O2- induced mutagenesis. [ABSTRACT FROM AUTHOR]

The article outlines the study conducted by Richard C. A. Hindmarsh and colleagues on the ice-stream lateral shear formation. Research shows that such structures were formed by differential erosion rates related to lateral variations in the stream velocity and lateral incursion from inter-stream ridges after the thinner stream retreats. Till continuity/deforming bed mechanisms offer a feasible explanation for lateral shear margin moraines but other possible mechanisms require testing and there is an urgent need to examine the internal structure of shear margin moraines.

The article features the study conducted by Chris R. Stokes and colleagues on the impact of ice stream dynamics and shutdown in the superimposition of ribbed moraines on palaeo-ice-stream bed. Research shows that the sediments and landforms preserved on the stream beds can furnish important information about their subglacial conditions and flow mechanisms. They concluded that both sets of landforms were formed by ice flow but the overlying eskers suggest a subtle change in flow direction after ribbed moraine formation prior to deglaciation.

The article elaborates on the study conducted by Arthur S. Dyke on deglaciation of Northern Baffin Island of Eastern Arctic Canada. Research shows that such an event involve several large ice streams with contrasting histories wherein the north-flowing, marine-based ice streams were in place during the Last Glacial Maximum but it retreated at widely varying rates at early and middle Holocene. The Steensby Inlet Ice Stream was formed due to over-steepening of ice front during deglaciation of Foxe Basin.

Mature dead-ice has been overridden repeatedly by the Brúarjökull glacier, and multiple generations of ice-cored landforms occur, with ice cores originating at least from glacier surges in 1963-1964, 1890 and 1810. Ice-cores are located on the proximal slopes of end moraines and in the valleys, as ice-cored outwash and eskers, ice-cored drumlins and ice-cored moraine patches. This dictates that the sediments and internal architecture might not always match their end-products as de-icing progresses. Analysis of multi-temporal aerial photographs integrated with annual field measurements showed that the time required for a total de-icing in the forefield exceeds the duration of the quiescent phases between the surges, even in the current climate at the limit of permafrost. Quantifying melting progression suggests that complete de-icing of ice-cored landforms is not likely to occur. The mean de-icing rate is c. 9.8 cm/yr in 1890 ice-cored moraines, and c. 17.7 cm/yr in 1963-1964 ice-cored moraines. Backwasting of ice-cored slopes (c. 30 cm/yr) is the fastest melt process. Long-term downwasting rates derived from multi-temporal digital elevation models provide a superior insight into the impact of multiple glacier surges on the formation of dead-ice moraines in front of Brúarjökull. [ABSTRACT FROM AUTHOR]

ABSTRACT Evidence of conspicuous repeated seasonal to annual deposition of glaciofluvial and glaciolacustrine sequences within a structurally complex interlobate esker segment in SW Finland is presented. The time-transgressive, overlapping depositional sequences consist of deposits from two successive melt seasons, including three vertically stacked lithofacies associations: (1) massive to stratified coarse gravels = summer deposits; (2) trough and ripple cross-stratified fine-grained deposits = autumn to winter deposits; and (3) sandy stratified beds = spring deposits. The depositional environment of each lithofacies association involves a transition from subglacial or submarginal tunnel to a subaqueous re-entrant environment, which then passes to a proglacial glaciolacustrine environment. The study also presents evidence of headward extension of subglacial tunnel deposits, related to the rapid shifting of a tunnel expansion point during the increasing spring discharge, which occupied the old tunnel exit: this mode of annual deposition has not been reported previously in esker studies. The good preservation of the rhythmic lithofacies associations is suggested as resulting from interlobate depositional conditions associated with rapidly decaying icestreams. Therefore, the depositional model may provide a key to recognizing time-transgressive interlobate eskers that form an important geomorphological and sedimentological record of meltwater activity during the last deglaciation of the Fennoscandian and Laurentide ice sheets. The identification of time-transgressive interlobate eskers and associated palaeo-icestream behaviour is an essential step forward for more accurate models of ice sheet behaviour and palaeoclimatic reconstructions. [ABSTRACT FROM AUTHOR]

Although eskers are frequently described glaciofluvial landforms, they are poorly understood. To assist with the interpretation of Pleistocene examples, modern analogue data are required. This paper documents the morphology, sedimentology and formation of a 650 m long esker system in front of the high-arctic glacier Vegbreen in Svalbard. The esker is located between the Neoglacial maximum and the present ice front and appears to have formed both as a supraglacial trough-fill and as a channel/conduit-fill along the suture formed by two confluent glacier lobes. A range of sedimentary facies is preserved within this ridge system providing evidence for braided rivers, ephemeral lakes, episodic flow regimes and sediment gravity flows. This case study provides an important analogue for glaciofluvial sedimentation between retreating ice lobes. [ABSTRACT FROM AUTHOR]

Studies the sliding bed facies in esker sands and gravels. Criteria for full-pipe tunnel flow; Analysis of key issues of interest; Implications on sedimentology.