Glacial geomorphology of the northern Kivalliq region, Nunavut, Canada, with an emphasis on meltwater drainage systems

This paper presents a glacial geomorphological map of glacial lineations, ribbed terrain, moraines, meltwater channels (subglacial and ice-marginal/proglacial), eskers, glaciofluvial deposits, ice-contact outwash fans and deltas and abandoned shorelines on the bed of the former Laurentide Ice Sheet in northern Canada. Mapping was compiled from satellite imagery and digital elevation data and landforms were digitised directly into a Geographical Information System. The map reveals a complex glacial history characterised by multiple ice-flow events, including fast-flowing ice-streams. Moraines record a series of pauses or re-advances during overall SE retreat towards the Keewatin Ice Divide. The distribution of subglacial meltwater landforms indicates that several distinctive scales and modes of drainage system operated beneath the retreating ice sheet. This includes a large (>100 km) integrated network of meltwater channels, eskers, ice-contact outwash fans and deltas and glaciofluvial deposits that originates at the northern edge of Aberdeen Lake. The map comprises zone 66 of the Canadian National Topographic System, which encompasses an area of 160,000 km2. It is presented at a scale of 1:500,000 and is designed to be printed at A0 size

Reconstructing dynamics of the Baltic Ice Stream Complex during deglaciation of the Last Scandinavian Ice Sheet

Landforms left behind by the last Scandinavian Ice Sheet (SIS) offer an opportunity to investigate controls governing ice sheet dynamics. Terrestrial sectors of the ice sheet have received considerable attention from landform and stratigraphic investigations. In contrast, despite its geographical importance, the Baltic Sea remains poorly constrained due to limitations in bathymetric data. Both ice-sheet-scale investigations and regional studies at the southern periphery of the SIS have considered the Baltic depression to be a preferential route for ice flux towards the southern ice margin throughout the last glaciation. During the deglaciation the Baltic depression hosted the extensive Baltic Ice Lake, which likely exerted a considerable control on ice dynamics. Here we investigate the Baltic depression using newly available bathymetric data and peripheral topographic data. These data reveal an extensive landform suite stretching from Denmark in the west to Estonia in the east and from the southern European coast to the Åland Sea, comprising an area of 0.3 million km2. We use these landforms to reconstruct aspects of the ice dynamic history of the Baltic sector of the ice sheet. Landform evidence indicates a complex retreat pattern that changes from lobate ice margins with splaying lineations to parallel mega-scale glacial lineations (MSGLs) in the deeper depressions of the Baltic Basin. Ice margin still-stands on underlying geological structures indicate the likely importance of pinning points during deglaciation, resulting in a stepped retreat signal. Over the span of the study area we identify broad changes in the ice flow direction, ranging from SE–NW to N–S and then to NW–SE. MSGLs reveal distinct corridors of fast ice flow (ice streams) with widths of 30 km and up to 95 km in places, rather than the often-interpreted Baltic-wide (300 km) accelerated ice flow zone. These smaller ice streams are interpreted as having operated close behind the ice margin during late stages of deglaciation. Where previous ice-sheet-scale investigations inferred a single ice source, our mapping identifies flow and ice margin geometries from both Swedish and northern Bothnian sources. We anticipate that our landform mapping and interpretations may be used as a framework for more detailed empirical studies by identifying targets to acquire high-resolution bathymetry and sediment cores and also for comparison with numerical ice sheet modelling.</p

A revision of the British Chronostratigraphy within the Last Glacial-Interglacial Cycle based on new evidence from Arclid, Cheshire UK

Of the 24 Greenland interstadials (GI) in the Last Glacial-interglacial cycle (LGIC) only five are conventionally recognised in Britain. This paper aims to improve understanding of the LGIC in Britain from a site at Arclid, Cheshire. Sediments were characterised and luminescence used to establish a chronology. This found that the Chelford Sand Formation spans 77-47 ka with sand deposited initially by aeolian but later by fluvial transportation. Coleoptera and Diptera from the basal peat lens provided a reconstruction for a heather-rich heathland environment grazed by large herbivores, with summer temperatures between 13-18° C, and winter temperatures between -14 and 1°C. Flies included the earliest records of the blood-sucking horsefly Haematopota pluvialis, and the soldierfly Chloromyia formosa. The overlying Stockport Sand Formation was deposited fluvioglacially between 47-41 ka with the upper Stockport Till formed by the advance of the last British icesheet after ~33 ka. Stenothermic beetle analysis from Arclid indicate similarities with results from other British mid LGIC sites, some of which are at or beyond the limit of radiocarbon dating and may be of a similar age to Arclid. Basal organic sediments found at Arclid along with other reassigned sites are proposed as a new Arclid Interstadial. A revised British LGIC chronostratigraphy has the Wretton, Chelford and Brimpton Interstadials and the previously suggested but not widely recognised Cassington Interstadial. The Arclid Interstadial occurred after these, but prior to the Upton Warren Interstadial complex. This closes the previous gap in interstadials between the Brimpton Interstadial and the Upton Warren Interstadial complex within the British chronostratigraphy

A quasi-annual record of time-transgressive esker formation: implications for ice sheet reconstruction and subglacial hydrology

We identify and map chains of esker beads (series of aligned mounds) up to 15 m high and on average ~ 65 m wide across central Nunavut, Canada from the high-resolution (2 m) ArcticDEM. Based on the close one-to-one association with regularly spaced, sharp crested ridges interpreted as De Geer moraines, we interpret the esker beads to be quasi-annual ice-marginal deposits formed time-transgressively at the mouth of subglacial conduits during deglaciation. Esker beads therefore preserve a high-resolution record of ice-margin retreat and subglacial hydrology. The well-organised beaded esker network implies that subglacial channelised drainage was relatively fixed in space and through time. Downstream esker bead spacing constrains the typical pace of deglaciation in central Nunavut between 7.2 and 6 ka 14C BP to 165–370 m yr−1, although with short periods of more rapid retreat (> 400 m yr−1). Under our time-transgressive interpretation, the lateral spacing of the observed eskers provides a true measure of subglacial conduit spacing for testing mathematical models of subglacial hydrology. Esker beads also record the volume of sediment deposited in each melt season, thus providing a minimum bound on annual sediment fluxes, which is in the range of 103–104 m3 yr−1 in each 6–10 km wide subglacial conduit catchment. We suggest the prevalence of esker beads across this predominantly marine terminating sector of the former Laurentide Ice Sheet is a result of sediment fluxes that were unable to backfill conduits at a rate faster than ice-margin retreat. Esker ridges, conversely, are hypothesised to form when sediment backfilling of the subglacial conduit outpaced retreat resulting in headward esker growth close to but behind the margin. The implication, in accordance with recent modelling results, is that eskers in general record a composite signature of ice-marginal drainage rather than a temporal snapshot of ice-sheet wide subglacial drainage

An ice-sheet scale comparison of eskers with modelled subglacial drainage routes

Eskers record a time-integrated signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage. In this paper, we compare the spatial pattern of eskers beneath the former Laurentide Ice Sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical icesheet model. Perhaps surprisingly, we show that eskers predominantly occur in regions where modelled subglacial water flow is low. Eskers and modelled subglacial drainage routes were found to typically match for lengths <10 km, and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation. This supports a time-transgressive esker pattern, with formation in short (<10 km) segments of conduit close behind a retreating ice margin, and probably associated with thin, stagnant or sluggish ice. Esker forming conduits were probably dominated by supraglacially fed meltwater inputs. We also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo-ice stream locations. The paucity of eskers along the terrestrial portion of these palaeo-ice streams and meltwater routes is probably due to the prevalence of distributed drainage and the high erosion potential of fast-flowing ice

Be‐10 dating of ice‐marginal moraines in the Khumbu Valley, Nepal, Central Himalaya, reveals the response of monsoon‐influenced glaciers to Holocene climate change

The dynamic response of large mountain glaciers to climatic forcing operates over timescales of several centuries and therefore understanding how these glaciers change requires observations of their behavior through the Holocene. We used Be-10 exposure-age dating and geomorphological mapping to constrain the evolution of glaciers in the Khumbu Valley in the Everest region of Nepal. Khumbu and Lobuche Glaciers are surrounded by high-relief lateral and terminal moraines from which seven glacial stages were identified and dated to 7.4 ± 0.2, 5.0 ± 0.3, 3.9 ± 0.1, 2.8 ± 0.2, 1.3 ± 0.1, 0.9 ± 0.02, and 0.6 ± 0.16 ka. These stages correlate to each of the seven latest Holocene regional glacial stages identified across the monsoon-influenced Himalaya, demonstrating that a coherent record of high elevation terrestrial palaeoclimate change can be extracted from dynamic mountain landscapes. The time-constrained moraine complex represents a catchment-wide denudation rate of 0.8–1.4 mm a−1 over the last 8 kyr. The geometry of the ablation area of Khumbu Glacier changed around 4 ka from a broad, shallow ice tongue to become narrower and thicker as restricted by the topographic barrier of the terminal moraine complex

Risk of cardiovascular disease and total mortality in adults with type 1 diabetes: Scottish registry linkage study

&lt;p&gt;Background: Randomized controlled trials have shown the importance of tight glucose control in type 1 diabetes (T1DM), but few recent studies have evaluated the risk of cardiovascular disease (CVD) and all-cause mortality among adults with T1DM. We evaluated these risks in adults with T1DM compared with the non-diabetic population in a nationwide study from Scotland and examined control of CVD risk factors in those with T1DM.&lt;/p&gt; &lt;p&gt;Methods and Findings: The Scottish Care Information-Diabetes Collaboration database was used to identify all people registered with T1DM and aged ≥20 years in 2005–2007 and to provide risk factor data. Major CVD events and deaths were obtained from the national hospital admissions database and death register. The age-adjusted incidence rate ratio (IRR) for CVD and mortality in T1DM (n = 21,789) versus the non-diabetic population (3.96 million) was estimated using Poisson regression. The age-adjusted IRR for first CVD event associated with T1DM versus the non-diabetic population was higher in women (3.0: 95% CI 2.4–3.8, p&#60;0.001) than men (2.3: 2.0–2.7, p&#60;0.001) while the IRR for all-cause mortality associated with T1DM was comparable at 2.6 (2.2–3.0, p&#60;0.001) in men and 2.7 (2.2–3.4, p&#60;0.001) in women. Between 2005–2007, among individuals with T1DM, 34 of 123 deaths among 10,173 who were &#60;40 years and 37 of 907 deaths among 12,739 who were ≥40 years had an underlying cause of death of coma or diabetic ketoacidosis. Among individuals 60–69 years, approximately three extra deaths per 100 per year occurred among men with T1DM (28.51/1,000 person years at risk), and two per 100 per year for women (17.99/1,000 person years at risk). 28% of those with T1DM were current smokers, 13% achieved target HbA1c of &#60;7% and 37% had very poor (≥9%) glycaemic control. Among those aged ≥40, 37% had blood pressures above even conservative targets (≥140/90 mmHg) and 39% of those ≥40 years were not on a statin. Although many of these risk factors were comparable to those previously reported in other developed countries, CVD and mortality rates may not be generalizable to other countries. Limitations included lack of information on the specific insulin therapy used.&lt;/p&gt; &lt;p&gt;Conclusions: Although the relative risks for CVD and total mortality associated with T1DM in this population have declined relative to earlier studies, T1DM continues to be associated with higher CVD and death rates than the non-diabetic population. Risk factor management should be improved to further reduce risk but better treatment approaches for achieving good glycaemic control are badly needed.&lt;/p&gt

Near-margin ice thickness from a portable radar: implications for subglacial water routing, Leverett Glacier, Greenland

Ice thickness measurements near the margin of the Greenland Ice Sheet (GrIS) are relatively sparse, presenting issues for modelling ice flow dynamics, ice sheet change and subglacial hydrology. We acquired ice thickness data at Leverett Glacier, western Greenland, using a highly portable, low power commercially-available ice-penetrating radar operating at 10-80 MHz. Imaging of the bed to depths of 270 m was possible using this system. Our ice thickness measurements were incorporated into the BedMachine model of bed elevation created using mass conservation methods. The new data significantly modified the modelled ice thickness and routing of subglacial water in both the Leverett and adjacent Russell Glacier. Though changes to the modelled basal topography and subglacial hydrology are consistent with observations, our new data unrealistically reduced the overall size of the Leverett hydrological catchment. Additional ice thickness measurements are therefore required to realistically constrain subglacial topography and subglacial hydrological routing in this area. Our work has significantly enhanced our understanding of basal topography and subglacial hydrology of Leverett Glacier, with implications for glacier dynamics and assessments of water piracy between catchments in the marginal zone of the GrIS

Rapid accelerations of Antarctic Peninsula outlet glaciers driven by surface melt

J.C.E. acknowledges a NERC independent research fellowship grant number NE/R014574/1. J.M.W. acknowledges financial contributions made by the Netherlands Organization for Scientific Research (grant 866.15.201) and the Netherlands Earth System Science Center (NESSC).Atmospheric warming is increasing surface melting across the Antarctic Peninsula, with unknown impacts upon glacier dynamics at the ice-bed interface. Using high-resolution satellite-derived ice velocity data, optical satellite imagery and regional climate modelling, we show that drainage of surface meltwater to the bed of outlet glaciers on the Antarctic Peninsula occurs and triggers rapid ice flow accelerations (up to 100% greater than the annual mean). This provides a mechanism for this sector of the Antarctic Ice Sheet to respond rapidly to atmospheric warming. We infer that delivery of water to the bed transiently increases basal water pressure, enhancing basal motion, but efficient evacuation subsequently reduces water pressure causing ice deceleration. Currently, melt events are sporadic, so efficient subglacial drainage cannot be maintained, resulting in multiple short-lived (<6 day) ice flow perturbations. Future increases in meltwater could induce a shift to a glacier dynamic regime characterised by seasonal-scale hydrologically-driven ice flow variations.Publisher PDFPeer reviewe

Conceptual model for the formation of bedforms along subglacial meltwater corridors (SMCs) by variable ice‐water‐bed interactions

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