Basal Water Research Articles

Body composition changes in a 12-week exercise intervention for breast cancer patients.

e12500 Background: Evidence has linked weight gain and obesity to increased breast cancer risk, poorer outcomes, decreased survivorship, and increased risk of recurrence. Adjuvant therapies can increase weight gain, making tailored exercise interventions beneficial in maintaining a healthy weight. In this study, body composition changes were examined after a 12-week exercise program in a cohort of breast cancer survivors. Methods: The Breast Cancer Exercise Rehabilitation Research Study recruited breast cancer survivors to undergo a 12-week exercise program (NCT04013568) and examine body composition changes. Measurements taken included anthropometry (waist circumference, waist-to-hip ratio, BMI), DXA body composition measurements (fat mass-visceral and subcutaneous, trunk to limb, muscle mass-appendicular, and whole body), and BIA (Bio-electrical Impedance Analysis-muscle, fat, and water). 34 participants completed the exercise program and baseline and post-12-week measurements were obtained. Descriptive statistics and a paired t-test analysis was done to analyze changes in body composition using SAS onDemand. A correlation analysis between measurements simple to do in clinic and DXA measurements were run to determine proxy use for DXA. Results: After a 12-week exercise program, reductions in body fat via DXA scan, BIA, and InBody (whole body fat, whole body fat %, trunk fat, leg fat, body fat %, hip width at maximum girth, body fat mass, and percent body fat) were observed. Additionally, increases in lean mass (Appendicular Lean Mass (ALM)/height2, Appendicular Lean/height2, ALM index, and lean body mass), whole body mass measured by DXA, basal metabolic rate, water retention (extracellular water and total body water), and skeletal muscle mass were observed. Correlation analysis revealed BMI can be used as a surrogate measure for whole body mass measured by DXA (r=0.91, p<0.001) and can be utilized to measure change over time. Skinfold sum showed moderate correlation for measuring subcutaneous fat mass by DXA (r=0.45, p=0.0096). Conclusions: In our population of breast cancer survivors, a 12-week exercise program did show various changes in body composition according to InBody, DXA, and BIA measurements. DXA and InBody measurements were feasible, making it readily available for patients. Additionally, simple measures such as BMI and skinfold sum showed moderate to strong correlation with DXA measurements, validating use of these measurements in routine practice. Clinical trial information: NCT04013568. [Table: see text]

Interaction effects of desiccation and temperature stress resistance across Spodoptera frugiperda (Lepidoptera, Noctuidae) developmental stages

Insects encounter multiple overlapping physiologically challenging environmental stressors in their habitats. As such, the ability of insects to withstand these stressors singly or interactively is fundamental in population persistence. Following its invasion in Africa, Spodoptera frugiperda (Lepidoptera: Noctuidae) has successfully established and spread in most parts of the continent. However, the mechanisms behind its successful survival across arid and semi-arid African environments are relatively unknown. Here, we investigated the water balance of S. frugiperda across its developmental stages. Given the relationships between desiccation stress, temperature stress and other life history traits in arid ecosystems, we also measured interaction effects across metrics of these traits. Specifically, we measured basal body water content (BWC), water loss rates (WLRs) and the effects of desiccation pre-treatment on critical thermal minimum (CTmin), critical thermal maximum (CTmax) and fecundity. Body water content and WLR increased with age across larval instars. However, the effects of desiccation environments on WLRs were more dramatic for 5th and 6th larval instars. The 5th and 6th instars exhibited highest BWC and magnitude of WLRs plastic responses following desiccation treatment. The effects of desiccation pre-treatment on temperature tolerance were less apparent, only significantly improving CTmin in 2nd and 3rd larval instars and reducing CTmax in 5th instars. In addition, desiccation pre-treatment showed no significant effects on fecundity. These results show that water balance traits differ with developmental stage, while the effects of desiccation pre-treatment were more dramatic and inconclusive. The differential desiccation resistance, high proportional BWC and no desiccation pre-treatment effects on fecundity may help the species survive in arid and semi-arid environments. This information provides insights into understanding S. frugiperda survival under desiccating arid and semi-arid tropical environments and is significant in predicting pest outbreaks.

Antarctic Basal Water Storage Variation Inferred from Multi-Source Satellite Observation and Relevant Models

Antarctic basal water storage variation (BWSV) refers to mass changes of basal water beneath the Antarctic ice sheet (AIS). Identifying these variations is critical for understanding Antarctic basal hydrology variations and basal heat conduction, yet they are rarely accessible due to a lack of direct observation. This paper proposes a layered gravity density forward/inversion iteration method to investigate Antarctic BWSV based on multi-source satellite observations and relevant models. During 2003–2009, BWSV increased at an average rate of 43 ± 23 Gt/yr, which accounts for 29% of the previously documented total mass loss rate (−76 ± 20 Gt/yr) of AIS. Major uncertainty arises from satellite gravimetry, satellite altimetry, the glacial isostatic adjustment (GIA) model, and the modelled basal melting rate. We find that increases in basal water mainly occurred in regions with widespread active subglacial lakes, such as the Rockefeller Plateau, Siple Coast, Institute Ice Stream regions, and marginal regions of East Antarctic Ice Sheet (EAIS), which indicates the increased water storage in these active subglacial lakes, despite the frequent water drainage events. The Amundsen Sea coast experienced a significant loss during the same period, which is attributed to the basal meltwater discharging into the Amundsen Sea through basal channels.

Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow

Abstract. Due to increasing surface melting on the Greenland ice sheet, better constraints on seasonally evolving basal water pressure and sliding speed are required by models. Here we assess the potential of using inverse methods on a dense time series of surface speeds to recover the seasonal evolution of the basal conditions in a well-documented region in southwest Greenland. Using data compiled from multiple satellite missions, we document seasonally evolving surface velocities with a temporal resolution of 2 weeks between 2015 and 2019. We then apply the inverse control method using the ice flow model Elmer/Ice to infer the basal sliding and friction corresponding to each of the 24 surface velocity data sets. Near the margin where the uncertainty in the velocity and bed topography are small, we obtain clear seasonal variations that can be mostly interpreted in terms of an effective-pressure-based hard-bed friction law. We find for valley bottoms or “troughs” in the bed topography that the changes in modelled basal conditions directly respond to local modelled water pressure variations, while the link is more complex for subglacial “ridges” which are often non-locally forced. At the catchment scale, in-phase variations in the water pressure, surface velocities, and surface runoff variations are found. Our results show that time series inversions of observed surface velocities can be used to understand the evolution of basal conditions over different timescales and could therefore serve as an intermediate validation for subglacial hydrology models to achieve better coupling with ice flow models.

Generation and fate of basal meltwater during winter, western Greenland Ice Sheet

Abstract. Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modeling with results strongly dependent upon assumptions with poor observational constraints. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or nonexistent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains manyfold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying that a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in western Greenland.

Topographic Controls on Channelized Meltwater in the Subglacial Environment

AbstractRealistic characterization of subglacial hydrology necessitates knowledge of the range in form, scale, and spatiotemporal evolution of drainage networks. A relict subglacial meltwater corridor on the deglaciated Antarctic continental shelf encompasses 80 convergent and divergent channels, many of which are hundreds of meters wide and several of which lack a definable headwater source. Without significant surface‐melt contributions to the bed like similarly described landforms in the Northern Hemisphere, channelized drainage capacity varies non‐systematically by three orders of magnitude downstream. This signifies apparent additions and losses of basal water to the bed‐channelized system that relates to bed topography. Larger magnitude grounding‐line retreat events occurred while the channel system was active than once channelized drainage had ceased. Overall, this corridor demonstrates that meltwater drainage styles co‐exist in time and space in response to bed topography, with prolonged impacts on grounding‐line behavior.

PSIV-B-21 Broilers as an animal model to assess different copper, manganese and zinc mineral sources on absorption

Abstract The study objective was to evaluate absorption differences between different sources of Copper (Cu), Manganese (Mn) and Zin (Zn) in broiler diets. Cobb500 chicks (n = 130, 0-d old) were housed in colony brooders and offered basal diet and water ad libitum for eight days. Following the transition phase, 96 straight-run chicks were randomly assigned to one of 48 battery cages (2 chicks/cage; 12 cages/treatment) and offered one of three soy-corn based diets for three weeks: Negative Control (NC; Basal diet at 6 mg/kg Cu, 35 mg/kg Mn, and 36 mg/kg Zn); Positive Control (PC; NC + 15 mg/kg Cu, 100 mg/kg Mn, and 100 mg/kg Zn from Sulfate sources); Treatment 1 (T1; NC + 15 mg/kg Cu, 100 mg/kg Mn, and 100 mg/kg Zn from hydroxychloride Product 1); and Treatment 2 (T2; NC + 15 mg/kg Cu, 100 mg/kg Mn, and 100 mg/kg Zn from hydroxychloride sources Product 2). Week three birds were bled and dissected to obtain liver, breast and femur samples for mineral absorption status. Data were analyzed using RV3.6.1 procedures with non-repeated measures. Plasma and breast tissue were not (P ≥ 0.05) impacted by mineral source, however numerical increases were reported in PC, T1 and T2 over NC. Liver Cu and Zn concentrations were non-significant (P ≥ 0.05) for all treatments. However liver Mn concentrations increased (P ≤ 0.05) in Pc and T1. Copper bone concentrations were not (P ≥ 0.05) affected, but an increase (P ≤ 0.05) in Mn and Zn was reported for PC, T1 and T2 versus NC. These results indicate increased absorption occurs when mineral sources are adequately supplemented beyond basal diet levels and that source may impact absorption rate. Additional research is needed to address the absorption ability of different mineral sources to better understand the impact on bird performance.

Illuminating Active Subglacial Lake Processes With ICESat‐2 Laser Altimetry

AbstractAntarctica's basal water system contains more than 130 active lakes, and its evolution remains a major uncertainty in future ice sheet dynamics. Most of our current understanding has come from using satellite radar and laser altimetry acquired since 2003. NASA's ICESat‐2 laser altimetry mission, launched in September 2018, provides a new, small‐footprint altimetry data set with which to investigate Antarctic active subglacial lake processes. Here, we demonstrate the ability to continue monitoring active subglacial lakes at timescales shorter than the ICESat‐2's repeat cycle and generate self‐consistent time series of subglacial lake surface‐height anomalies from combined ICESat, CryoSat‐2, and ICESat‐2 altimetry. Focusing on three regions with the known significant lake activity, we show that ICESat‐2 laser altimetry can not only extend the record of subglacial lake activity but also provides better understanding of hydrological processes by capturing denser and more precise spatial detail.

Velocity Anomaly of Campbell Glacier, East Antarctica, Observed by Double-Differential Interferometric SAR and Ice Penetrating Radar

Regional changes in the flow velocity of Antarctic glaciers can affect the ice sheet mass balance and formation of surface crevasses. The velocity anomaly of a glacier can be detected using the Double-Differential Interferometric Synthetic Aperture Radar (DDInSAR) technique that removes the constant displacement in two Differential Interferometric SAR (DInSAR) images at different times and shows only the temporally variable displacement. In this study, two circular-shaped ice-velocity anomalies in Campbell Glacier, East Antarctica, were analyzed by using 13 DDInSAR images generated from COSMO-SkyMED one-day tandem DInSAR images in 2010–2011. The topography of the ice surface and ice bed were obtained from the helicopter-borne Ice Penetrating Radar (IPR) surveys in 2016–2017. Denoted as A and B, the velocity anomalies were in circular shapes with radii of ~800 m, located 14.7 km (A) and 11.3 km (B) upstream from the grounding line of the Campbell Glacier. Velocity anomalies were up to ~1 cm/day for A and ~5 cm/day for B. To investigate the cause of the two velocity anomalies, the ice surface and bed profiles derived from the IPR survey crossing the anomalies were analyzed. The two anomalies lay over a bed hill along the glacial valley where stick-slip and pressure melting can occur, resulting in temporal variation of ice velocity. The bright radar reflection and flat hydraulic head at the ice bed of A observed in the IPR-derived radargram strongly suggested the existence of basal water in a form of reservoir or film, which caused smaller friction and the reduced variation of stick-slip motion compared to B. Crevasses began to appear at B due to tensile stress at the top of the hill and the fast flow downstream. The sporadic shift of the location of anomalies suggests complex pressure melting and transportation of the basal water over the bed hill.

A slip law for hard-bedded glaciers derived from observed bed topography.

Ice-sheet responses to climate warming and associated sea-level rise depend sensitively on the form of the slip law that relates drag at the beds of glaciers to their slip velocity and basal water pressure. Process-based models of glacier slip over idealized, hard (rigid) beds with water-filled cavities yield slip laws in which drag decreases with increasing slip velocity or water pressure (rate-weakening drag). We present results of a process-based, three-dimensional model of glacier slip applied to measured bed topographies. We find that consideration of actual glacier beds eliminates or makes insignificant rate-weakening drag, thereby uniting process-based models of slip with some ice-sheet model parameterizations. Computed slip laws have the same form as those indicated by experiments with ice dragged over deformable till, the other common bed condition. Thus, these results may point to a universal slip law that would simplify and improve estimations of glacier discharges to the oceans.

Joint Inversion for Surface Accumulation Rate and Geothermal Heat Flow From Ice‐Penetrating Radar Observations at Dome A, East Antarctica. Part I: Model Description, Data Constraints, and Inversion Results

AbstractIce‐penetrating radar data contain a wealth of information about the bed and internal structure of the ice sheet. While these data have long been used to diagnose the presence of basal water, infer attenuation rates, or explore the internal stratigraphy of the ice sheet, they have rarely been used jointly in a formal inverse model for the ice sheet temperature structure. Here, we invert a coupled thermomechanical ice sheet and basal hydrology model to infer both geothermal heat flow (GHF) and accumulation rate from multiple classes of radar observations in the area around Dome A, East Antarctica. Our forward model solves for a coupled steady state between the ice sheet flow field, temperature, and basal hydrology, including melt, water transport, and freeze‐on. We fit radar observations of basal water, freeze‐on, and internal layers, along with a GHF prior based on aeromagnetic observations. We minimize the combined misfit function by first using an evolutionary algorithm followed by localized perturbation tests. In addition to inferring the spatial distribution of GHF and accumulation rate, we are also able to estimate the uncertainty about our best‐fit answer, as well as quantify how our result depends on each individual data constraint. Our results demonstrate a new method for combining multiple glaciological constraints into a single inverse model of the ice sheet, and give us a more rigorous picture of the information content provided by each data set. In a companion paper we analyze and interpret the best‐fit model.

Sudden large-volume detachments of low-angle mountain glaciers – more frequent than thought?

Abstract. The detachment of large parts of low-angle mountain glaciers resulting in massive ice–rock avalanches have so far been believed to be a unique type of event, made known to the global scientific community first for the 2002 Kolka Glacier detachment, Caucasus Mountains, and then for the 2016 collapses of two glaciers in the Aru range, Tibet. Since 2016, several so-far unrecognized low-angle glacier detachments have been recognized and described, and new ones have occurred. In the current contribution, we compile, compare, and discuss 20 actual or suspected large-volume detachments of low-angle mountain glaciers at 10 different sites in the Caucasus, the Pamirs, Tibet, Altai, the North American Cordillera, and the Southern Andes. Many of the detachments reached volumes in the order of 10–100 million m3. The similarities and differences between the presented cases indicate that glacier detachments often involve a coincidental combination of factors related to the lowering of basal friction, high or increasing driving stresses, concentration of shear stress, or low resistance to exceed stability thresholds. Particularly soft glacier beds seem to be a common condition among the observed events as they offer smooth contact areas between the glacier and the underlying substrate and are prone to till-strength weakening and eventually basal failure under high pore-water pressure. Partially or fully thawed glacier bed conditions and the presence of liquid water could thus play an important role in the detachments. Surface slopes of the detached glaciers range between around 10∘ and 20∘. This may be low enough to enable the development of thick and thus large-volume glaciers while also being steep enough to allow critical driving stresses to build up. We construct a simple slab model to estimate ranges of glacier slope and width above which a glacier may be able to detach when extensively losing basal resistance. From this model we estimate that all the detachments described in this study occurred due to a basal shear stress reduction of more than 50 %. Most of the ice–rock avalanches resulting from the detachments in this study have a particularly low angle of reach, down to around 5∘, likely due to their high ice content and connected liquefaction potential, the availability of soft basal slurries, and large amounts of basal water, as well as the smooth topographic setting typical for glacial valleys. Low-angle glacier detachments combine elements and likely also physical processes of glacier surges and ice break-offs from steep glaciers. The surge-like temporal evolution ahead of several detachments and their geographic proximity to other surge-type glaciers indicate the glacier detachments investigated can be interpreted as endmembers of the continuum of surge-like glacier instabilities. Though rare, glacier detachments appear to be more frequent than commonly thought and disclose, despite local differences in conditions and precursory evolutions, the fundamental and critical potential of low-angle soft glacier beds to fail catastrophically.

Complex Basal Conditions and Their Influence on Ice Flow at the Onset of the Northeast Greenland Ice Stream

AbstractThe ice stream geometry and large ice surface velocities at the onset region of the Northeast Greenland Ice Stream (NEGIS) are not yet well reproduced by ice sheet models. The quantification of basal sliding and a parametrization of basal conditions remains a major gap. In this study, we assess the basal conditions of the onset region of the NEGIS in a systematic analysis of airborne ultra‐wideband radar data. We evaluate basal roughness and basal return echoes in the context of the current ice stream geometry and ice surface velocity. We observe a change from a smooth to a rougher bed where the ice stream widens, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. In the upstream region, the excess ice mass flux through the shear margins is evacuated by ice flow acceleration and along‐flow stretching of the ice. At the downstream part, the generally rougher bed topography correlates with a decrease in flow acceleration and lateral variations in ice surface velocity. Together with basal water routing pathways, this hints to two different zones in this part of the NEGIS: the upstream region collecting water, with a reduced basal traction, and downstream, where the ice stream is slowing down and is widening on a rougher bed, with a distribution of basal water toward the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.

Native-like membrane models of E. coli polar lipid extract shed light on the importance of lipid composition complexity

BackgroundLipid-protein interactions stabilize protein oligomers, shape their structure, and modulate their function. Whereas in vitro experiments already account for the functional importance of lipids by using natural lipid extracts, in silico methods lack behind by embedding proteins in single component lipid bilayers. However, to accurately complement in vitro experiments with molecular details at very high spatio-temporal resolution, molecular dynamics simulations have to be performed in natural(-like) lipid environments.ResultsTo enable more accurate MD simulations, we have prepared four membrane models of E. coli polar lipid extract, a typical model organism, each at all-atom (CHARMM36) and coarse-grained (Martini3) representations. These models contain all main lipid headgroup types of the E. coli inner membrane, i.e., phosphatidylethanolamines, phosphatidylglycerols, and cardiolipins, symmetrically distributed between the membrane leaflets. The lipid tail (un)saturation and propanylation stereochemistry represent the bacterial lipid tail composition of E. coli grown at 37∘C until 3/4 of the log growth phase. The comparison of the Simple three lipid component models to the complex 14-lipid component model Avanti over a broad range of physiologically relevant temperatures revealed that the balance of lipid tail unsaturation and propanylation in different positions and inclusion of lipid tails of various length maintain realistic values for lipid mobility, membrane area compressibility, lipid ordering, lipid volume and area, and the bilayer thickness. The only Simple model that was able to satisfactory reproduce most of the structural properties of the complex Avanti model showed worse agreement of the activation energy of basal water permeation with the here performed measurements. The Martini3 models reflect extremely well both experimental and atomistic behavior of the E. coli polar lipid extract membranes. Aquaporin-1 embedded in our native(-like) membranes causes partial lipid ordering and membrane thinning in its vicinity. Moreover, aquaporin-1 attracts and temporarily binds negatively charged lipids, mainly cardiolipins, with a distinct cardiolipin binding site in the crevice at the contact site between two monomers, most probably stabilizing the tetrameric protein assembly.ConclusionsThe here prepared and validated membrane models of E. coli polar lipids extract revealed that lipid tail complexity, in terms of double bond and cyclopropane location and varying lipid tail length, is key to stabilize membrane properties over a broad temperature range. In addition, they build a solid basis for manifold future simulation studies on more realistic lipid membranes bridging the gap between simulations and experiments.

Possible impacts of a 1000 km long hypothetical subglacial river valley towards Petermann Glacier in northern Greenland

Abstract. Greenland basal topographic data show a segmented valley extending from Petermann Fjord into the centre of Greenland; however, the locations of radar scan lines, used to create the bedrock topography data, indicate that valley segmentation is due to data interpolation. Therefore, as a thought experiment, simulations where the valley is opened are used to investigate its effects on basal water movement and distribution. The simulations indicate that the opening of this valley can result in an uninterrupted water pathway from the interior to Petermann Fjord. Along its length, the path of the valley progresses gradually down an ice surface slope, causing a lowering of ice overburden pressure that could enable water flow along its path. The fact that the valley base appears to be relatively flat and follows a path near the interior ice divide that roughly intersects the east and west basal hydrological basins is presented as evidence that its present day form may have developed in conjunction with an overlying ice sheet. Experiments where basal melting is increased solely within the deep interior near the known large area of basal melting result in an increase in the flux of water northwards along the entire valley. The results are consistent with a long subglacial river; however, considerable uncertainty remains over aspects such as whether adequate water is available at the bed, whether water escapes from the valley or is refrozen, and over what form a hydrological conduit could take along the valley base.

The Effect of Groundnut Shells Supplementation on Selected Biochemical Parameters of Confined Indigenous Cattle during Winter Season in the North West Province of South Africa

Background: The use of groundnut shells (GNS) in animal feeding is a common practice in tropical countries and most researchers have evaluated the nutritive values of GNS and their effects on animal performance. They are cheap and widely available in South Africa. However, most communal farmers in Mogosane village lack the knowledge nutritive values of such, and therefore do not use GNS to improve the performance of their cattle. Determination of the nutritional status of cattle is important especially when quantifying the effects of a dietary treatment. Blood metabolite concentrations indicate the animal’s nutritional status and they are commonly assessed in dairy than beef cattle, such that there are no reference values for the blood constituents of indigenous cattle in South Africa, suggesting a need for research in this area.Methods: An eight-week feeding trial was therefore, conducted to determine effect of different levels of groundnut shells (GNS) on biochemical parameters. Forty cattle were used and were allocated into Groups: A, B, C, D and E with eight animals in each group. Treatment group A was given basal diet and water only. Treatment group B was supplemented with 700 g/kg of GNS, C with 1050 g/kg of GNS, D with 1400 g/kg of GNS and E with 1750 g/kg of GNS. Blood samples were collected into anticoagulant free, allowed to coagulate at room temperature for 24 hours and then centrifuged at 1000 rpm for 10 minutes. The supernatant sera were harvested and stored in a freezer. Samples were collected once a week for eight weeks and were then analysed using Anision-300 Auto-Analyzer system. Results: Significant values were observed in urea and lipase in animals receiving 1050g/kg of GNS and were significantly (P less than 0.05) higher when compared to control group and all other treatment groups, and even for those animals in treatment group E. These significant values found in urea and lipase, on animals receiving 1050 g/kg, confirmed effect of GNS on metabolic functions on animals depending on natural pasture.

Brecciation of glacially overridden palaeokarst (Lower Aare Valley, northern Switzerland): result of subglacial water‐pressure peaks?

Water pressures at the base of active glacial overdeepenings are known to fluctuate strongly on various time scales. Rapid peaks in basal water pressure can lead to fracturing of the glacier bed, a process that has been described at numerous sites around the world, mostly based on large hydrofracture systems. This article presents drill‐cores from the base of a >100‐m‐deep glacial overdeepening in the Lower Aare Valley in northern Switzerland that were investigated with high‐resolution imaging (including X‐ray computed tomography) as well as compositional and microstructural analyses. The drill‐cores recovered Jurassic limestones hosting palaeokarst voids infilled with blue clay. We identify this clay, based on its kaolinitic composition, as siderolithic Bolus Clay but in a rather atypical variety formed under reducing conditions. The surfaces of the palaeokarst walls show smoothly undulating as well as brecciated sections with form‐fit interlocking clasts, which are the result of an in situ brecciation process. We argue that these particular fractures are not related to (glacio‐)tectonics or frost action. Instead, we suggest an explanation by involving water‐pressure peaks that were transmitted to the void walls by the clayey karst filling, resulting in hydrofracturing. In addition to pervasive karstification and tectonic overprinting, this water pressure‐driven fracturing may have enhanced the deep incision of the overdeepening into the rheologically competent bedrock.

Radar Sounding Confirms a Hydrologically Active Deep-Water Subglacial Lake in East Antarctica

Lake CookE2, upstream of Cook Glacier in East Antarctica is an ‘active’ subglacial lake, which experiences episodic discharge and recharge of basal water. Although around 130 active lakes are known to exist, the majority are not able to be identified by radar sounding techniques, suggesting they are ephemeral and/or distributed stores of small amounts of water rather than permanent significant singular features. Airborne ice-sounding radar data from Lake CookE2, a known ‘active’ subglacial lake, reveal a bright and flat ice-bed interface, providing clear evidence of deep (>10 m) water surrounded by elevated topography, however. The data reveal the lake area is ~46 km2; 3 times less than a previous estimated (145 km2) from ICESat surface altimetry, indicating a possible bias in identifying subglacial lake area from surface depressions. Using time-series altimetry from ICESat, Cryosat-2 data, and the Reference Elevation Model of Antarctica, we re-estimate the lake discharged ~2.93 km3 of water (or ~63.8 m in lake level) between February 2006 and January 2011. Subsequently, the ice surface over the lake rose steadily and experienced a mean uplift of ~11 m between January 2011 and November 2016, indicating continuous recharge with total volume increase of ~0.51 km3. The lake is recharging at a rate of ~1.33 m/year, which means it will take another ~39 years to reach the lake level that triggered the previous discharge.

The Surge of the Hispar Glacier, Central Karakoram: SAR 3‐D Flow Velocity Time Series and Thickness Changes

AbstractThe Hispar Glacier is a useful site for studying surge mechanisms. Prior to this study, only two‐dimensional (2‐D) flow velocities having low temporal resolution were available for this glacier, providing inadequate information about its surge evolution. In this study, 139 synthetic aperture radar (SAR) images from Sentinel‐1A were used to obtain 3‐D flow velocity time series for the Hispar Glacier during the recent surge (2014–2016). The 3‐D flow velocities were sampled at an interval of 11 days, which is much greater than in previous studies. Besides, the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) and two TanDEM‐X images were used to determine glacier thickness changes prior to and following the recent surge. Combining the results and geomorphologic features, we deduced that the recent surge was because of saturated basal water pressure in the Yutmaru tributary. The mass from the Yutmaru tributary squeezed into the trunk and rapidly flowed downslope along the northern margin, generating strong normal pressure to the trunk mass. Pushed by the Yutmaru tributary, the trunk began to surge in September 2014. The flow velocity reached a first peak in May 2015 and then decreased in October 2015, as part of the basal meltwater ran off. However, basal meltwater accumulated again during the following 4 months, and correspondingly, the trunk accelerated again after October 2015. Finally, as kinetic energy was released and resisting force increased, the trunk became almost stagnant in August 2016. The surge mass was blocked downstream in the trunk by the mass transferred from the Kunyang tributary, and consequently, the glacier did not advance.

Large-scale englacial folding and deep-ice stratigraphy within the West Antarctic Ice Sheet

Abstract. It has been hypothesized that complex englacial structures identified within the East Antarctic and Greenland ice sheets are generated by (i) water freezing to the ice sheet base and evolving under ice flow, (ii) deformation of ice of varying rheology, or (iii) entrainment of basal material. Using ice-penetrating radar, we identify a widespread complex of deep-ice facies in West Antarctica that exist in the absence of basal water. These deep-ice units are extensive, thick (>500 m), and incorporate multiple highly reflective englacial layers. At the lateral margin of an enhanced flow tributary of the Institute Ice Stream, these units are heavily deformed and folded by the action of lateral flow convergence. Radar reflectivity analysis demonstrates that the uppermost reflector of the deep-ice package is highly anisotropic, due to abrupt alternations in crystal orientation fabric, and consequently will have a different rheology to the ice above and below it. Deformation and folding of the deep-ice package is an englacial response to the combination of laterally-convergent ice flow and the physical properties of the ice column.