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Bed topography is a critical parameter for determining the modern-day and future dynamics of ice sheets and their outlet glaciers. This is because the topography controls the state of stress for glaciers. At glacier termini, topography can influence the timing of terminus retreat by controlling access to warm ocean waters and/or by influencing the ability of a glacier terminus to retreat over bed bumps (moraines). Inland from the terminus, the topography can also influence where glacier retreat and thinning can stabilize. In part, this is because of knickpoints in bed topography created through glacial erosion that may influence the extent to which thinning can diffuse inland for an individual glacier and thus, the timing and magnitude of long-term mass loss. Here we provide a review of the current literature on these topics. While much of the reviewed literature assumes that topography is stable on relevant timescales to humans, new research suggests that topography may change much faster than previously thought and this further complicates our ability to project future outlet glacier change. [ABSTRACT FROM AUTHOR]

Glacial sediment research using thin sections began post-1945. Microsedimentology examines sediments at the microscopic level deriving insights into the processes of glacial erosion, transport, and deposition. Two issues exist (1) the difficulty by some in recognizing microstructures in thin section and (2) the absence of quantitative data making data reproduction difficult. The latter is hard to resolve but more image capture and software methodologies are now becoming available at reasonable costs. Thin sections are two-dimensional sections of three-dimensional objects, and this must be considered when measurements, fabrics and other data are assessed. Research into the microaspects of glacial sediments followed a typical scientific trajectory: thin sections description with little uniformity or common "language" for observed microstructures: standardization allowed comparison between different sediments; with standardization, came an open-ended classification; and with cross-comparison with multiple thin sections—a quantitative means of study needs developed. It has become apparent that the basic principles of structural geology had to be applied. Thus, micromorphology has subsumed into a microsedimentological study of glacial sediments where stress parameters, structural fabrics and the mapping of deformation structures and contextual integration allows an understanding of how these sediments have been formed. Examples of the development stages of glacial micromorphology/sedimentology are presented here as well as discussion of future avenues of study. In addition, multiple thin sections are used to illustrate the many aspects of glacial micromorphology and the parameters necessary to understand glacial sedimentology and the processes of glacial sedimentation. [ABSTRACT FROM AUTHOR]

Bed topography is a critical parameter for determining the modern-day and future dynamics of ice sheets and their outlet glaciers. This is because the topography controls the state of stress for glaciers. At glacier termini, topography can influence the timing of terminus retreat by controlling access to warm ocean waters and/or by influencing the ability of a glacier terminus to retreat over bed bumps (moraines). Inland from the terminus, the topography can also influence where glacier retreat and thinning can stabilize. In part, this is because of knickpoints in bed topography created through glacial erosion that may influence the extent to which thinning can diffuse inland for an individual glacier and thus, the timing and magnitude of long-term mass loss. Here we provide a review of the current literature on these topics. While much of the reviewed literature assumes that topography is stable on relevant timescales to humans, new research suggests that topography may change much faster than previously thought and this further complicates our ability to project future outlet glacier change. [ABSTRACT FROM AUTHOR]

Evacuation of basal sediment by subglacial drainage is an important mediator of rates of glacial erosion and glacier flow. Glacial erosion patterns can produce closed basins (i.e., overdeepenings) in glacier beds, thereby introducing adverse bed gradients that are hypothesized to reduce drainage system efficiency and thus favour basal sediment accumulation. To establish how the presence of a terminal overdeepening might mediate seasonal drainage system evolution and glacial sediment export, we measured suspended sediment transport from Findelengletscher, Switzerland during late August and early September 2016. Analyses of these data demonstrate poor hydraulic efficiency of drainage pathways in the terminus region but high sediment availability. Specifically, the rate of increase of sediment concentration with discharge was found to be significantly lower than that anticipated if channelized flow paths were present. Sediment availability to these flow paths was also higher than would be anticipated for discrete bedrock‐floored subglacial channels. Our findings indicate that subglacial drainage in the terminal region of Findelengletscher is dominated by distributed flow where entrainment capacity increases only marginally with discharge, but flow has extensive access to an abundant sediment store. This high availability maintains sediment connectivity between the glacial and proglacial realm and means daily sediment yield is unusually high relative to yields exhibited by similar Alpine glaciers. We present a conceptual model illustrating the potential influence of ice‐bed morphology on subglacial drainage evolution and sediment evacuation mechanics, patterns and yields, and recommend that bed morphology should be an explicit consideration when monitoring and evaluating glaciated basin sediment export rates. [ABSTRACT FROM AUTHOR]

Glacial erosion is the basic process that has shaped the landscapes of the Alps. Despite intense research over centuries, and the use of various techniques, determination of glacial erosion rates remains challenging. This is not only because the location where the process occurs is almost inaccessible, but also because it is dependent on many different factors, including ice thickness and velocity, glacier thermal regime and lithology. Reported glacial erosion rates range over several orders of magnitude (0.01 to >10 mm a−1). Most studies focus on crystalline bedrock, whereas few researchers have investigated glacial erosion on limestone. Here we analyse glacially polished bedrock surfaces at the recently deglaciated forefield of the Tsanfleuron glacier, Swiss Alps. The nearly horizontally bedded limestone hosts a well‐developed karst system. Meltwater from the glacier drains into the subsurface within a few metres of the ice margin. By combining geomorphological mapping, measurement of cosmogenic 36Cl concentrations of glacially eroded bedrock surfaces and a numerical model (MECED), we quantify at each sample location the amount of rock removed during glacier occupation. The glacial erosion rates calculated from these values range from 0 to 0.08 mm a−1. These are orders of magnitude lower than values measured at comparable sites on crystalline bedrock. The high 36Cl concentrations we measured show that the Tsanfleuron glacier was unable to effectively erode the gently dipping, strongly karstified limestone. We suggest that this effect may play a key role in formation and preservation over many glacial cycles of high‐elevation, low‐relief limestone plateaus in the Alps. © 2020 John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

We evaluate changes to subglacial sediment discharge during glacier retreat by considering ice dynamics, bedrock erosion, and sediment transport processes. Coupling these components together within a single framework, we simulate sediment discharge from synthetic alpine glaciers experiencing accelerated glacier melt for 100 years. We find that sediment discharge increases by about 8 times the steady glacier values by the end of the simulation. The enhanced sediment discharge persists through peak water discharge and despite annual bedrock erosion volume decreasing by approximately 30% from the initial value. The greater sediment discharge results from increased melt at the glaciers' higher region, where transport was limited prior to glacier retreat. These findings suggest that large increases in sediment discharge may occur as glaciers retreat. The magnitude of the sediment discharge increase primarily depends on the quantity of sediment stored subglacially. Plain Language Summary: Changes to sediment discharge from glaciers can dramatically impact downstream communities and ecosystems. We account for two primary processes that largely control to sediment discharge from glaciers: (1) bedrock erosion, which creates sediment below the glacier and (2) the ability of meltwater below the glacier to carry this sediment. To understand the potential changes in sediment discharge as glaciers retreat, we link numerical models of both processes and run them in a scenario that complies with ongoing climate warming. In the scenario, we find that sediment discharge increases dramatically, despite smaller quantities of sediment being produced by bedrock erosion. This is because more meltwater higher on the glaciers increases sediment transport in these upper regions. Results here suggest that future subglacial sediment discharge depends on the amount of sediment that already exists below glaciers. Large increases in subglacial sediment discharge are possible. Key Points: We present a coupled system of models that represent ice dynamics, bedrock erosion, and sediment transport processesLarge increases in subglacial sediment discharge occur in response to simulated glacier retreatRising equilibrium line altitudes drive increased sediment discharge by allowing meltwater to access greater amounts of subglacial sediment [ABSTRACT FROM AUTHOR]

The article presents a research on transient glacial incision in the Patagonian Andes. Topics discussed include decline in local erosion rates may represent a return toward a balance between rock uplift and erosion; spatially averaged erosion rate of the source region after the onset of alpine glaciations; and negative feedback operates at the scale of the glacial network.

Glaciers are highly effective agents of erosion that have profoundly shaped Earth's surface, but there is uncertainty about how glacial erosion should be parameterised in landscape evolution models. Glacial erosion rate is usually modelled as a function of glacier sliding velocity, but the empirical basis for this relationship is weak. In turn, climate is assumed to control sliding velocity and hence erosion, but this too lacks empirical scrutiny. Here, we present statistically robust relationships between erosion rates, sliding velocities, and climate from a global compilation of 38 glaciers. We show that sliding is positively and significantly correlated with erosion, and derive a relationship for use in erosion models. Our dataset further demonstrates that the most rapid erosion is achieved at temperate glaciers with high mean annual precipitation, which serve to promote rapid sliding. Precipitation has received little attention in glacial erosion studies, but our data illustrate its importance. Glaciers have profoundly shaped Earth's surface, but glacial erosion models lack a strong empirical basis. Cook et al. have compiled a dataset that illustrates how the speed at which glaciers move controls the rate at which they erode, and that climate is crucial in modulating glacier sliding speed and erosion rates. [ABSTRACT FROM AUTHOR]

Glacial erosion produces vast quantities of fine-grained sediment that has a far-reaching impact on Earth surface processes. To gain a better understanding of the production of glacial silt and clay, we use automated mineralogy to quantify the microstructure and mineralogy of rock and sediment samples from 20 basins in the St. Elias Mountains, Yukon, Canada. Sediments were collected from proglacial streams, while rock samples were collected from ice marginal outcrops and fragmented using electrical pulse disaggregation. For both rock fragments and sediments, we observe a log-normal distribution of grain sizes and a sub-micrometer terminal grain size. We find that the abrasion of silt and clay results in both rounding and the exploitation of through-going fractures. The abundance of inter- versus intragranular fractures depends on mineralogy and size. Unlike the relatively larger grains, where crushing and abrasion are thought to exploit and produce discrete populations of grain sizes, the comminution of fines leads to a grain size, composition and rounding that is continuously distributed across size, and highly dependent on source-rock properties. [ABSTRACT FROM AUTHOR]

The Upper Miocene interval of the AND‐1B sediment core is a muddy ca 300 m thick succession of glacimarine strata that was recovered from the McMurdo sector of the Ross Ice Shelf, Antarctica. This succession comprises lithofacies consistent with those formed in modern polythermal glacial systems with large volumes of subglacial meltwater. In particular, meltwater‐associated facies and iceberg‐rafted debris suggest that these late Miocene glacial systems were similar to subpolar glaciers like those in Svalbard today. Modern subpolar systems in Svalbard accumulate sediments at rates of ca 50 to 100 mm a−1 within ca 1 km of their grounded tidewater cliffs in waters up to hundreds of metres deep. Here, the rifted tectonic setting and glacio‐isostatic load of the Antarctic Ice Sheet enhanced accommodation for this succession. Based on these interpretations, the glacial sequence stratigraphic model of Powell & Cooper (2002) is applied to the study interval in an effort to better understand ice dynamics during this time. Base level is defined as the grounding line (where the ice sheet is grounded on the sea floor) and the surface that projects basinward (a correlative conformity). Glacial sequence stratigraphic description of the sediment core reveals 10 glacial sequences bounded by glacial erosion surfaces and two lower‐ranked glacial sequences bounded by correlative conformities. These glacial sequences occur in regular fining‐upward stratigraphic patterns and consist of two distinct styles of glacial retreat: packages with grounding‐line fan deposits and those without them. Lastly, in an effort to fill the gap between the middle Miocene and Plio‐Pleistocene climate histories of Antarctica, comparison of the AND‐1B Upper Miocene interval with the obliquity curve reveals one glacial–interglacial cycle and identifies erosion surfaces along which significant time may be missing. [ABSTRACT FROM AUTHOR]

Glacier thinning and retreat drives initial acceleration of glacier sliding and erosion, de-buttressing of steep valley walls, and destabilization of ice-marginal deposits and bedrock, which can lead to massive rock avalanching and accelerated incision of tributary watersheds. A compelling example of these changes occurred in Taan Fjord in SE Alaska due to the rapid thinning and retreat of Tyndall Glacier over the past half century. Increased glacier sliding speeds led to both increased rates of subglacial erosion and the evacuation of subglacially stored sediments into the proglacial basins. The shrinking glacier also exposed proglacial tributary watersheds to rapid incision and denudation driven by >350 m of baselevel fall in a few decades. Moreover, in October 2015 a large tsunamigenic landslide occurred at the terminus of Tyndall Glacier, largely due to thinning exposing oversteepened, unstable slopes. Sediment yields from the glacier, the landslide and the tributary watersheds, measured from surveys of the sediments in the fjord collected in 1999 and 2016, are compared to ongoing changes in glacier and fjord geometry to investigate the magnitude of glacial and paraglacial denudation in Taan Fjord during retreat. In the last 50 years, sediment yields from the glacier and non-glacial tributaries kept pace with the rapid rate of retreat, and were on par with each other. Notably, basin-averaged erosion rates from the paraglacial landscape were twice that from the glacier, averaging 58 ± 9 and 26 ± 5 mm a−1, respectively. The sharp increases in sediment yields during retreat observed from both the glacier and the adjacent watersheds, including the landslide, highlight the rapid evolution of landscapes undergoing glacier shrinkage. [ABSTRACT FROM AUTHOR]

Glacier-erosion rates range across orders of magnitude, and much of this variation cannot be attributed to basal sliding rates. Subglacial till acts as lubricating 'fault gouge' or 'sawdust', and must be removed for rapid subglacial bedrock erosion. Such erosion occurs especially where and when moulin-fed streams access the bed and are unconstrained by supercooling or other processes. Streams also may directly erode bedrock, likely with strong time-evolution. Erosion is primarily by quarrying, aided by strong fluctuations in the water system driven by variable surface melt and by subglacial earthquakes. Debris-bed friction significantly affects abrasion, quarrying and general glacier flow. Frost heave drives cirque headwall erosion as winter cold air enters bergschrunds, creating temperature gradients to drive water flow along premelted films to growing ice lenses that fracture rock, and the glacier removes the resulting blocks. Recent subglacial bedrock erosion and sediment flux are in many cases much higher than long-term averages. Over glacial cycles, evolution of glacial-valley form feeds back strongly on erosion and deposition. Most of this is poorly quantified, with parts open to argument. Glacial erosion and interactions are important to tectonic and volcanic processes as well as climate and biogeochemical fluxes, motivating vigorous research. [ABSTRACT FROM AUTHOR]

Glacial cirques are widely used palaeoenvironmental indicators, and are key to understanding the role of glaciers in shaping mountain topography. However, notable uncertainty persists regarding the rate and timing of cirque erosion. In order to address this uncertainty, we analyse the dimensions of 2208 cirques in Britain and Ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth. Results indicate that during the last ~120 ka, cirques were glacier‐free for an average of 52.0 ± 21.2 ka (43 ± 18%); occupied by small (largely cirque‐confined) glaciers for 16.2 ± 9.9 ka (14 ± 8%); and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka (43 ± 16%). Over the entire Quaternary (i.e. 2.6 Ma), we estimate that cirques were glacier‐free for 1.1 ± 0.5 Ma; occupied by small glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. Comparing occupation times to cirque depths, and calculating required erosion rates, reveals that continuous cirque growth during glacier occupation is unlikely. Instead, we propose that cirques attained much of their size during the first occupation of a non‐glacially sculpted landscape (perhaps during the timeframe of a single glacial cycle). During subsequent glacier occupations, cirque growth may have slowed considerably, with the highest rates of subglacial erosion focused during periods of marginal (small glacier) glaciation. We propose comparatively slow rates of growth following initial cirque development because a 'least resistance' shape is formed, and as cirques deepen, sediment becomes trapped subglacially, partly protecting the bedrock from subsequent erosion. In support of the idea of rapid cirque growth, we present evidence from northern British Columbia, where cirques of comparable size to those in Britain and Ireland developed in less than 140 ka. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reconstructions of past ice-flow provide useful insights into the long-term behaviour of past ice sheets and help to understand how glaciated landscapes are shaped. Here, we present reconstruction of a 10-phase ice-flow history from southwestern Hudson Bay in northeastern Manitoba (Canada), a dynamic region situated between two major ice dispersal centres of the Laurentide Ice Sheet. We utilize a diverse geologic dataset including 1900 field-based erosional indicators, 12 streamlined-landform flowsets, esker and meltwater corridor orientations, 103 till-fabrics analyses, and 1344 till-clast lithology counts. Our reconstruction suggests that both pre-MIS 2 and MIS 2 glaciations followed similar growth patterns, where ice advanced into study area from ice centered to the east (probably in northern Quebec), followed by a switch in ice-flow direction indicating flow from the Keewatin ice centre to the northwest and north. The cause for this switch in ice-flow orientation is uncertain, but the youngest switch may relate to retreat of ice during MIS 3 that then left space for Keewatin-sourced ice to advance over the study area. While modelling experiments indicate widespread cold-based conditions in the study area during the last glacial cycle, uniformly relict landscapes are not common. Instead, the glaciated landscape is palimpsest and commonly fragmented, forming a subglacial bed mosaic of erosional and depositional assemblages that record both shifting ice-flow direction through time and shifting subglacial conditions. Each assemblage formed, or modified, during times of dynamic (warm-based) ice, and later preserved under conditions below or close to the pressure melting point (slow and sluggish, or cold-based). • Regionally integrated multi-scale observations provide insights into the evolution of core regions of ice sheets. • Ten phases of ice-flow reconstructed based on four different proxies. • Fragmented, complex, landscape due to subglacial bed mosaic of glacial erosion and deposition. • Half of the landscape in northeastern Manitoba is a palimpsest record of older glacial events. [ABSTRACT FROM AUTHOR]

Sediment export from glaciated basins involves complex interactions between ice flow, basal erosion and sediment transfer in subglacial and proglacial streams. In particular, we know very little about the processes associated with sediment transfer by subglacial streams. The Haut Glacier d'Arolla (VS, Switzerland) was investigated during the summer melt season of 2015. LiDAR survey revealed positive surface changes in the ablation zone, indicating glacier uplift, at the end of the morning during the period of peak ablation. Instream measures of sediment transport showed that suspended load and bedload responded differently to diurnal flow variability. Suspended load depended on the availability of fine material whereas bedload depended mainly on the competence of the flow. Interpretation of these results allowed development of a conceptual model of subglacial sediment transport dynamics. It is based upon the mechanisms of clogging (deposition) and flushing (transport/erosion) in sub‐glacial channels as forced by diurnal flow variability. Through the melt season, the glacier hydrological response evolves from being buffered by glacier snow cover with a poorly developed subglacial drainage system to being dominated by more rapid ice melt with a more hydraulically efficient subglacial channel system. The resultant changes in the shape of diurnal discharge hydrographs, and notably higher peak flows and lower base flows, causes sediment transport to become discontinuous, with overnight clogging and late morning flushing of subglacial channels. Overnight clogging may be sufficient to reduce subglacial channel size, creating temporarily pressurized flow and lateral transfer of water away from the subglacial channels, leading to the late morning glacier surface uplift. However, without further data, we cannot exclude other hypotheses for the uplift. © 2018 John Wiley & Sons, Ltd. Conceptual model of the daily subglacial sediment transport dynamics with flow cycle induced by melting ice integrating the glacial surface uplift. Phase c: before the critical transport capacity of coarse sediments is achieved (schematic cross‐section East–West of glacial tongue of the Haut Glacier d'Arolla with median supgraglacial moraine). [ABSTRACT FROM AUTHOR]

Continuity of sediment transfer through glacial systems is essential to maintain subglacial bedrock erosion, yet transfer at temperate glaciers with overdeepened beds, where subglacial fluvial sediment transport should be greatly limited by adverse slopes, remains poorly understood. Complex multiple transfer processes in temperate overdeepened systems has been indicated by the presence of large frontal moraine systems, supraglacial debris of mixed transport origin, thick basal ice sequences, and englacial thrusts and eskers. At Svínafellsjökull, thrusts comprising decimetre-thick debris-rich bands of stratified facies ice of basal origin, with a coarser size distribution and higher clast content than that observed in basal ice layers, contribute substantially to the transfer of subglacial material in the terminal zone. Entrainment and transfer of material occurs by simple shear along the upper surface of bands and by strain-induced deformation of stratified and firnified glacier ice below. Thrust material includes rounded and well-rounded clasts that are also striated, indicating that fluvial bedload is deposited as subglacial channels approach the overdeepening and then entrained along thrusts. Substantial transfer also occurs within basal ice, with facies type and debris content dependent on the hydrological connectedness of the adverse slope. A process model of transfer at glaciers with terminal overdeepenings is proposed, in which the geometry of the overdeepening influences spatial patterns of ice deformation, hydrology, and basal ice formation. We conclude that the significance of thrusting in maintaining sediment transfer continuity has likely been overlooked by glacier sediment budgets and glacial landscape evolution studies. [ABSTRACT FROM AUTHOR]

Glacial cirques are armchair-shaped erosional hollows, typified by steep headwalls and, often, overdeepened floors. They reflect former regions of glacier initiation, and their distribution is, therefore, linked to palaeoclimate. Because of this association, cirques can be analysed for the information they provide about past environments, an approach that has a strong heritage, and has seen resurgence over recent years. This paper provides a critical assessment of what cirques can tell us about past environments, and considers their reliability as palaeoenvironmental proxies. Specific focus is placed on information that can be obtained from consideration of cirque distribution, aspect, altitude, and morphometry. The paper highlights the fact that cirques potentially provide information about the style, duration and intensity of former glaciation, as well as information about past temperatures, precipitation gradients, cloud-cover and wind directions. In all, cirques are considered a valuable source of palaeoenvironmental information (if used judiciously), particularly as they are ubiquitous within formerly glaciated mountain ranges globally, thus making regional or even global scale studies possible. Furthermore, cirques often occupy remote and inaccessible regions where other palaeoenvironmental proxies may be limited or lacking. [ABSTRACT FROM AUTHOR]

This paper investigates the controls on the formation of subglacially eroded bedrock bedforms beneath the topographically confined region upstream of the Uummannaq Ice Stream (UIS). During the last glacial cycle, palaeoglaciological conditions are believed to have been similar for all sites in the study, characterised by thick, fast-flowing ice moving over a rigid bedrock bed. Classic bedrock bedforms indicative of glacially eroded terrain were mapped, including p-forms, roches moutonnées, and whalebacks. Bedform long axes and plucked face orientations display close correlation (parallel and perpendicular) to palaeo-ice flow directions inferred from striae measurements. Across all sites, elongation ratios (length to width) varied by an order of magnitude between 0.8:1 and 8.4:1. Bedform properties (length, height, width, and long axis orientation) from four subsample areas, form morphometrically distinct populations, despite their close proximity and hypothesised similarity in palaeoglaciological conditions. Variations in lithology and geological structures (e.g., joint frequency; joint dip; joint orientation; bedding plane thickness; and bedding plane dip) provide lines of geological weakness, which focus the glacial erosion, in turn controlling bedform geometries. Determining the relationship (s) between bedding plane dip relative to palaeo-ice flow and bedform shape, relative length, amplitude, and wavelength has important ramifications for understanding subglacial bed roughness, cavity formation, and likely erosion style (quarrying and/or abrasion) at the ice-bed interface. This paper demonstrates a direct link between bedrock bedform geometries and geological structure and emphasises the need to understand bedrock bedform characteristics when reconstructing palaeoglaciological conditions. [ABSTRACT FROM AUTHOR]

Field data and numerical modeling show that glaciations have the potential either to enhance relief or to dampen topography. We aim to model the effect of the subglacial hydraulic system on spatiotemporal patterns of glacial erosion by abrasion and quarrying on time scales commensurate with drainage system fluctuations (e.g., seasonal to annual). We use a numerical model that incorporates a dual-morphology subglacial drainage system coupled to a higher-order ice-flow model and process-specific erosion laws. The subglacial drainage system allows for a dynamic transition between two morphologies: the distributed system, characterized by an increase in basal water pressure with discharge, and the channelized system, which exhibits a decrease in equilibrium water pressure with increasing discharge. We apply the model to a simple synthetic glacier geometry, drive it with prescribed meltwater input variations, and compute sliding and erosion rates over a seasonal cycle. When both distributed and channelized systems are included, abrasion and sliding maxima migrate ~20% up-glacier compared to simulations with distributed drainage only. Power-law sliding generally yields to a broader response of abrasion to water pressure changes along the flowline compared to Coulomb-friction sliding. Multi-day variations in meltwater input elicit a stronger abrasion response than either diurnal- or seasonal variations alone for the same total input volume. An increase in water input volume leads to increased abrasion. We find that ice thickness commensurate with ice sheet outlet glaciers can hinder the up-glacier migration of abrasion. Quarrying patterns computed with a recently published law differ markedly from calculated abrasion patterns, with effective pressure being a stronger determinant than sliding speeds of quarrying rates. These variations in calculated patterns of instantaneous erosion as a function of hydrology-, sliding-, and erosion-model formulation, as well as model forcing, may lead to significant differences in predicted topographic profiles on long time scales. [ABSTRACT FROM AUTHOR]

Tunnel valleys are an erosional channel characterized by anastomosing, steep-sided channel systems formed by subglacial, confined meltwater flow. Our study uses two-dimensional (2D) industry reflection seismic on the Scotian Shelf near Sable Island to better constrain the geometry of tunnel valleys in the area. Here, U- to V-shaped buried channels north and west of Sable Island extensively branch, reconnect, and meander. They average 2-5 km wide and 150-700 m deep (below sea level) and have a dominantly north-south orientation. Immediately to the south and southwest of Sable Island, the channels become narrower (1-1.5 km), shallower (300-400 m maximum) and more widely spaced. Multiple tunnel valley generations may be present, but could not be separately mapped. There is a notable gap of 20-30 km between the ends of the detectable tunnel valleys and the shelf edge south of Sable Island. An exception is erosive features at the shelf edge at the head of Logan Canyon, but these channels are disconnected from the tunnel valley network further north and may not be tunnel valleys. The reason for the gap south of Sable Island is not clear; however, we do not believe it is due to data coverage or resolution issues. If the tunnel valleys genuinely end south of Sable Island, then the gap between them and the shelf edge means that between The Gully and Logan Canyon these subglacial meltwater channels did not empty directly at the shelf edge. This implies direct meltwater and sediment delivery by tunnel valleys to the Scotian Slope during the Pleistocene may have been limited in this area. [ABSTRACT FROM AUTHOR]

The morphometry of glaciated valleys has been of considerable significance in evaluating models and processes of valley form development, and is typically evaluated using a power law function fit to topographic data. Results of the power law method are sensitive to the location of the coordinate system origin, but most previous research has used a coordinate system centered, on the valley midpoint and has not systematically assessed alternative approaches. Here, we test four options for selecting the coordinate system origin, using cross-section profiles from glacial, fluvial, and transitional valleys in the Dalijia Mountains, China: (A) the lowest elevation point, (B) the valley midpoint, (C) the lowest point on the valley side wall, and (D) the highest point on the valley side. Option A produces results that are most consistent with expected values and trends for shape parameters in the Dalijia Mountains. Over half of the values calculated using Option B overestimate key valley-shape parameters compared to Option A. Options C and D produce similar values to each other, but these values are very different from Option A and less useful for landform interpretation. In morphometric studies designed to evaluate impacts of glacial erosion using the power law approach, we recommend that alternate coordinate system origins be evaluated, including the lowest elevation point on a cross-profile. [ABSTRACT FROM AUTHOR]

We seek to quantify glacial erosion in a low relief shield landscape in northern Sweden. We use GIS analyses of digital elevation models and field mapping of glacial erosion indicators to explore the geomorphology of three granite areas with the same sets of landforms and of similar relative relief, but with different degrees of glacial streamlining. Area 1, the Parkajoki district, shows no streamlining and so is a type area for negligible glacial erosion. Parkajoki retains many delicate pre-glacial features, including tors and saprolites with exposure histories of over 1 Myr. Area 2 shows the onset of significant glacial erosion, with the development of glacially streamlined bedrock hills. Area 3 shows extensive glacial streamlining and the development of hill forms such as large crag and tails and roches moutonnées. Preservation of old landforms is almost complete in Area 1, due to repeated covers of cold-based, non-erosive ice. In Area 2, streamlined hills appear but sheet joint patterns indicate that the lateral erosion of granite domes needed to form flanking cliffs and to give a streamlined appearance is only of the order of a few tens of metres. The inheritance of large-scale, pre-glacial landforms, notably structurally controlled bedrock hills and low relief palaeosurfaces, remains evident even in Area 3, the zone of maximum glacial erosion. Glacial erosion here has been concentrated in valleys, leading to the dissection and loss of area of palaeosurfaces. Semi-quantitative estimates of glacial erosion on inselbergs and palaeosurfaces and in valleys provide mean totals for glacial erosion of 8 ± 8 m in Area 1 and 27 ± 11 m in Area 3. These estimates support previous views that glacial erosion depths and rates on shields can be low and that pre-glacial landforms can survive long periods of glaciation, including episodes of wet-based flow. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the influence of the “Little Ice Age” (LIA) glacier advance on hillslope morphometry and development in selected U-shaped and (para)glacial tributary valleys, which are still occupied in their upper parts by outlet glaciers of the Jostedalsbreen ice cap in Western Norway. Especially the morphometric influences and geomorphic consequences of the LIA glacier advance on the development of the valley-side hillslope systems and associated denudative processes are assessed by comparing hillslope systems located inside and outside of the LIA glacier maximum extent. The process-based approach applied includes orthophoto- and topographical map interpretation as well as hillslope profile surveying in field for morphometric analyses and detailed geomorphological mapping for process analyses. In addition GIS and DEM computing as well as geophysical measurements (georadar) for storage analyses are performed. It is found that hillslopes inside the LIA glacier limit have steepened lower hillslope segments due to a negative sediment net balance of removal and deposition of material by the advancing LIA glacier front. There are significant differences in the present-day slope debris thickness and composition between hillslopes inside or outside the LIA glacier limit. Slope debris from hillslopes inside the glacier maximum extent are clearly less thick and display a different internal structure originating from a combination of debris from gravitational processes and reworked modern glacial deposits. Compared to that slope debris covers on hillslopes outside the LIA glacier limit are in general noticeable thicker and less influenced by glacial deposits. The combined effects of modified slope morphometry and altered composition of material covering lower hillslope segments have generated a higher intensity of post-LIA denudative hillslope processes. [Copyright &y& Elsevier]

Seismic stratigraphic and drill data from Antarctic continental margins have provided much direct evidence concerning ice sheet evolution as Earth's climate cooled from the warmth of the Eocene. Seismic facies analyses and correlations to sediment cores from Deep Sea Drilling Project Leg 28 drill sites show that the Ross Sea, the southwestern Pacific gateway of West Antarctica, was still mostly free of grounded ice for ~ 6 million years after Oi-1, the large-amplitude oxygen-isotope shift that signaled the abrupt onset of the current Antarctic glaciation. In the Ross Sea, our analysis shows that West Antarctic glaciation had begun by the late Oligocene, much earlier than usually interpreted from the paleoceanographic proxy data. Continental ice probably existed on Marie Bird Land and other highland areas of the West Antarctica. In the central Ross Sea, ice caps nucleated on the subaerially elevated basement horst blocks of the Central and Coulman Highs. Ice caps waxed and waned across the shallow-marine platforms rimming these broad basement uplifts. These temperate glacial systems delivered much sediment to the surrounding deepwater shelf basins. Ice cap oscillations during the early and middle Miocene also included significant intervals of grounded ice retreat and resumption of widespread marine sedimentation. By the end of the middle Miocene, glaciation intensified, local ice caps coalesced, and grounded ice with cross-shelf ice streams eventually extended across the entire Ross Sea continental shelf. Antarctic climate shifted from polar to temperate conditions during this time and ice streams advanced to the shelf edge. Full-bodied West Antarctic Ice Sheet advances continued and even occurred during the warmer-than-present early Pliocene. As a consequence of widespread and progressive glacial erosion, the shelf overdeepened in the latest Miocene. The surprisingly few advances of grounded ice preserved in Plio- Pleistocene strata suggest that the record is amalgamated and/or otherwise below the resolution of seismic data. [ABSTRACT FROM AUTHOR]

Abstract: Alpine glacial landforms (such as U-shaped troughs, hanging valleys, and cirques) have been linked to the meltwater-modulated sliding motion of glaciers. Several of these alpine landforms are associated with characteristic length scales for width and spacing, indicating that the viscosity of ice exerts a first-order control on the processes responsible for their formation. Here we present the results of three-dimensional computational experiments focusing on the influence of higher order ice dynamical effects, such as horizontal stress gradients, on long-term glacial landscape evolution. Some of the experiments presented have highly simplified bed conditions; other experiments use topography from an existing mountain range as basis for simulating glacial erosion. The experiments demonstrate how gradients in horizontal stress play a primary role in scaling the bed shear stress of glaciers. We also demonstrate how higher order ice dynamics may influence the feedback between glacial sliding and erosion, hereby providing important stabilization mechanisms that prevent runaway effects associated with the steepening of longitudinal profiles and the formation of overdeepenings. [Copyright &y& Elsevier]

Swift, D. A., Sanderson, D. C. W., Nienow, P. W., Bingham, R. G. & Cochrane, I. C. 2010: Anomalous luminescence of subglacial sediment at Haut Glacier d'Arolla, Switzerland - a consequence of resetting at the glacier bed? Boreas, Vol. 40, pp. 446-458. 10.1111/j.1502-3885.2010.00196.x. ISSN 0300-9483. Luminescence has the potential to elucidate glacial geomorphic processes because primary glacial sediment sources and transport pathways are associated with contrasting degrees of exposure to light. Most notably, sediment entrained from extraglacial sources should be at least partially reset, whereas sediment produced by glacial erosion of subglacial bedrock should retain substantial luminescence commensurate with a geological irradiation history. We set out to test the validity of this assumption at Haut Glacier d'Arolla, Switzerland using sediment sampled extraglacially and from the glacier bed. Contrary to our expectations, the subglacial samples exhibited natural signals that were substantially lower than those of other sample groups, and further (albeit limited) analyses have indicated no obvious differences in sample-group luminescence characteristics or behaviour that could account for this observation. For glaciological reasons, we can eliminate the possibilities that the subglacial sediment has been extraglacially reset or exposed in situ to heat or light. We therefore advocate investigation of possible resetting processes related to subglacial crushing and grinding, and speculate that such processes, if more generally present, may enable the dating of subglacially deposited tills using luminescence-based techniques. [ABSTRACT FROM AUTHOR]

Glacial outburst floods or ‘jökulhlaups’ are a key part of deglaciation of both alpine mountains and of ice sheet margins. They produce widespread and intense landscape change through erosion and deposition and are a hazard to populations and infrastructure. This article reviews these aspects with an emphasis on the current ‘state of play’ of research on the phenomena. Three case studies are presented: the 2010 Eyafjallajökull and 2007 Mt Ruapehu events, and the recent jökulhlaups in western Greenland. These illustrate that, where there is sufficient lead-in time for the development of projects, the application of modern technology and of multi-disciplinary research teams enables unprecedented acquisition quality, resolution and extent of data to be gained. These exciting data should enable development of new insights towards jökulhlaup impacts and flow phenomena. [ABSTRACT FROM AUTHOR]

Mountain geodynamics represent highly scale-dependent interactions involving climate, tectonic, and surface processes. The central Karakoram in Pakistan exhibit strong climate-tectonic feedbacks, although the detailed tectonic and topographic responses to climate perturbations need to be systematically explored. This study focuses on understanding climate variations in relation to glacier erosion and relief production. Field data, climate modeling, remote sensing, geomorphometry, geochronology, glaciology, and geomorphological assessment are utilized to characterize climate change and geomorphic response. Climate simulations suggest that the region has experienced significant climate change due to radiative forcing over at least the past million years due to changes in Earth's orbital configuration, as well as more temporally rapid climate dynamics related to the El Nino Southern Oscillation. Paleoclimate simulations support geomorphological evidence of multiple glaciations and long-term glacier retreat. Mesoscale relief patterns clearly depict erosion zones that are spatially coincident with high peaks and rapid exhumation. These patterns depict extreme spatial and temporal variability of the influence of glacier erosion in the topographic evolution of the region. Results support the interpretation of high-magnitude glacial erosion as a significant denudational agent in the exhumation of the central Karakoram. Consequently, a strong linkage is seen to occur between global, or at least hemispheric, climate change and the topographic evolution of the Karakoram and the western Himalaya. [ABSTRACT FROM AUTHOR]

In a gravel pit near Hultsfred, at the eastern margin of the South Swedish Upland, gravelly, sandy and silty-sandy beds covered by a thick, stratified gravelly diamicton are exposed. Large folds and shear-planes indicate post-depositional deformation of the sorted sediments, which according to OSL dating have a maximum Middle Weichselian (∼60 ka) age. The sand and gravel are interpreted as glaciofluvial sediments that were deposited laterally during a Middle Weichselian deglaciation, or possibly subglacially during the Late Weichselian. The large-scale deformation was due to glaciotectonics, caused by an overriding wet-based ice sheet during the last deglaciation. The subglacial hydrostatical pressure was high and led to the formation of downward-injected clastic dykes. A basal till, which forms the cover moraine in the area, caps the succession. The fairly frequent occurrence of sub-till sediments on the South Swedish Upland demonstrates the limited effect of glacial erosion in parts of this area. During the Last Glacial Maximum, the South Swedish Upland was an 'island' of slow-moving, polythermal and at least partly non-erosive ice, surrounded by faster ice-streams in the Baltic and in the Skagerrak. The ice sheet may have left its main impact on the landscape during short periods during advance and deglaciation only. [ABSTRACT FROM AUTHOR]

The article provides information on the rapid decrease of mass balance observed in the Xiao (Lesser) Dongkemadi Glacier, in the central Tibetan Plateau. Since 1989 the status of the mass balance in the Xiao (Lesser) Dongkemadi Glacier has been closely observed. According to the observation the mass balance on the plateau has shown a deficit trend and that the glacier terminus was also retreating. In 1989-1993, it was said that the positive mass balance of the glacier was dominant during the period, and the accumulated mass balance reached by 970 mm. However, in 1994 a negative mass balance has occurred, except for the unusual large positive mass balance in 1997. Moreover, Meteorological data suggest that the decreasing in the mass balance of the glacier was due to summer season warming.

Abstract: A key problem in understanding valley evolution in alpine landscapes has been the lack of an independent timescale against which to measure morphological change. Here, we outline that by using space as a proxy for time, the role of glaciation in producing ‘classic’ U-shaped valleys can be quantified. The Two Thumb Range in New Zealand''s central Southern Alps is undergoing rapid tectonic transport and uplift as it is advected towards the Alpine Fault. Repeated cycles of glacial erosion during the Quaternary have fashioned an alpine landscape in the north of the range, close to the Main Divide and Alpine Fault, while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross-profiles. Using known rates of tectonic transport and uplift of the Southern Alps, coupled with an offshore oxygen isotope (δ 18O) record from the Chatham Rise and glacio-geological reconstructions, time constraints can be applied to the erosional development of valleys. It is possible to estimate the duration of glacial occupancy of valleys in the Two Thumb Range, and the pattern is one of very limited glaciation of the southern valleys, with glacial occupancy increasing northwards. The key trend identifiable is that valley cross-profiles become U-shaped with c. 400–600 kyr of glacial occupancy. Other models have shown a “flattening” of valley long-profiles with increased glaciation, implying glaciers erode larger volumes of rock from mountains than rivers. From a cross-profile perspective, the simple change in geometry from V- to U-shape concurs with these models. Indeed, the transition from V- to U-shape with increasing relief and glaciation indicates glaciers may erode greater volumes of rock from mountain belts than rivers. [Copyright &y& Elsevier]

Glacial retreat on the Tibetan Plateau and surrounding regions is characteristic since the 1960s and has intensified in the past 10 yr. The magnitude of glacial retreat is relatively small in the interior of the Tibetan Plateau and increases to the margins of the plateau, with the greatest retreat around the edges. Glacial retreat in this region is impacting the hydrological processes in the Tibetan Plateau and surrounding regions. The glacial retreat has caused an increase of more than 5.5% in river runoff from the plateau. In some areas, such as the Tarim River basin, the increase in river runoff is greater. Glacial retreat has also caused rising lake levels in the areas with large coverage of glaciers, such as the Nam Co Lake and Selin Co Lake areas. Rising lake levels are devastating grasslands and villages near the lakes. [ABSTRACT FROM AUTHOR]

Abstract: Limestone and ophiolite rocks are common across the eastern Mediterranean and many of the highest mountains are formed in these rock types. In northwest Greece, Pleistocene glacial erosion was much more effective on limestone terrain where pronounced glacial incision and subglacial glacio-karst processes produced locally-complex topography. This enabled Pleistocene glaciers to form on a range of slope orientations in contrast to ophiolite terrains, where glaciers were strongly controlled by aspect. On limestone terrains, the largest ice masses formed on south-facing slopes, whereas in neighbouring higher mountains formed in ophiolite, glaciers were much more restricted and predominantly formed on north- and east-facing slopes. [Copyright &y& Elsevier]

Alpine glaciers are efficient agents of erosion and capable of significantly modifying topography. Despite recent advances in theoretical and field studies that quantify glacial erosion processes, few studies have documented glacial erosion rates over long (>106 yr) or large (more than tens of kilometers) scales. We use apatite (U-Th)/He (AHe) and apatite fission track (AFT) cooling ages to address the late Miocene to Holocene erosion history across two 60-km-long transects of the heavily glaciated southern Coast Mountains, British Columbia. Observed AHe cooling ages from equal elevation samples range between 1.5 and 8 Ma and suggest that thick alpine glaciers resulted in a 16 km shift of the highest point in the topography in the past 1.5-4.0 m.y. We evaluated temporal and spatial variations in erosion rates using a three-dimensional thermal-kinematic model that predicted AHe and AFT ages at the surface for different erosion histories. Comparison of model predicted and observed cooling ages suggests an increase in erosion rates of as much as 300% over the past 1.5-7 m.y., coincident with the onset of glaciation of this range. [ABSTRACT FROM AUTHOR]

Abstract: In the coastal mountains of Marie Byrd Land, Antarctica, there is a juxtaposition of ice moulded landforms at lower altitudes and upstanding summits with weathered surfaces bearing tors. This paper uses geomorphological mapping and exposure dating to test two hypotheses commonly used to explain such a landscape contrast: either the pattern reflects contrasts in glacial erosion related to the basal thermal regime beneath a former ice sheet or it represents a periglacial trimline marking the upper limit of ice cover during the Last Glacial Maximum (LGM). Cosmogenic nuclide measurements on erratics show that the mountains were covered by ice on several occasions, most recently during the LGM. Similar measurements on bedrock show that fragile landforms on weathered surfaces survived many glaciations. Nuclide concentrations in bedrock indicate both that subglacial erosion is insignificant and that ice-free periods of periglacial weathering are longer at higher elevations. We conclude that the pattern of landscape modification reflects both topographically controlled contrasts in the basal thermal regime of overriding ice and the longer exposure to periglacial conditions at higher elevations. In addition, the combination of nuclide data and the wider pattern of striations shows that the LGM ice cover was thinner than predicted by ice sheet models assuming equilibrium conditions, that ice sheet thinning has occurred from 10,400 years ago to the present, and that regional flow by overriding ice has been replaced by radial ice flow from local glaciers centred on individual mountain massifs. [Copyright &y& Elsevier]

Variations of global and regional silicate weathering rates and paleo-ocean circulation patterns are estimated by using radiogenic isotope records, but the effects of changes in provenance are generally ignored. Here sediment provenance has been constrained through the use of Ar-Ar ages for individual detrital minerals from the Labrador Sea, which can be compared directly to the radiogenic isotope compositions from the same core material. Dramatic changes in the radiogenic isotope composition of North Atlantic Deep Water through the Quaternary Period are shown to reflect discrete changes in both sources and weathering processes accompanying Northern Hemisphere glaciation. Chang- es in the different radiogenic isotope systems reflect the influence of source, physical weathering, and chemical weathering, and not simply changes in the underlying weathering rate or ocean circulation patterns that are typically inferred. [ABSTRACT FROM AUTHOR]

An emerging paradigm that equates glaciers to "buzz saws" of exceptional erosional efficiency has been strengthened by shortterm (<10² yr) sediment yields from southern Alaska. New lowtemperature cooling ages from this area, the glaciated ChugachSt. Elias Mountains, constrain long-term (106 yr) exhumation rates. Vertically averaged exhumation rates reach ∼3 mm/yr, but are an order of magnitude lower than rates based on short-term sediment yields. Whereas these exhumation rates are not exceptional for orogenic belts, denudation patterns are strongly correlated with the distribution of glaciers, and erosion appears to keep pace with convergence and uplift. These findings imply a coupling between glacially dominated erosion and tectonics. [ABSTRACT FROM AUTHOR]

Previous work indicates that large variations in the power-law relationship, relating glacial outlet valley size to ice drainage area, may occur between different glaciological settings. In this paper, we take issue with methods used to quantify the relationships of outlet valley size to drainage area size and propose a general method for comparing power-law relationships between study areas, to determine whether or not such power-law scalings are similar. Based on this method, we demonstrate that outlet valleys have a similar sensitivity to variation in ice-contributing area irrespective of their glaciological setting, contrary to earlier findings. Minor variation in such relationships may reflect the different lithological and glaciological settings of the study sites and provide an insight into the physics of glacial erosional development of landscapes. Despite their limitations, we conclude that power-law relationships are valid and, when interpreted carefully, provide a useful basis for comparing the efficiency of glacial erosion processes in different locations. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study assesses the effects of glaciation on a drift-buried cuesta in southeast Michigan through analysis of detailed data for the underlying bedrock surface. Four separate areas of the cuesta affected differently by glaciation are examined. These illustrate (1) proximal lowering through abrasion, (2) lateral smoothing and trimming, (3) distal plucking and (4) pro- tection resulting from local structural-topographic relationships. It is shown that glacial effects on the cuesta vary in a meaningful way with changes in relationships between bedrock structure, lithology, surface configuration, and the direction of ice movement. [ABSTRACT FROM AUTHOR]

A long-lasting question in glacial geology is how and how fast glaciers were able to shape the distinctive landscapes of the Alps. This study contributes to the understanding on the formation of overdeepened basins, especially the processes and the amount of time involved. We examine the remarkably high (150 m) cross-valley bedrock riegel and the associated overdeepening located in front of the Trift glacier in the central Swiss Alps. A combined approach of field survey with measurements of two cosmogenic nuclides, 10Be and in-situ 14C, and a numerical model was used to determine the spatial glacial erosion patterns on the bedrock riegel. Ten samples were taken along two transects; one perpendicular to the glacier flow direction, from outside of the Little Ice Age (LIA) extent down to the centre of the riegel, and the other following the former ice-flow direction across the riegel. Analysis of measured nuclide concentrations shows that the sample outside of the LIA was constantly exposed since the retreat of the Egesen stadial Trift glacier (~11.5 ka). The samples inside the LIA extent indicate a distinct trend of increasing glacial erosion rates from 0 mm/a near the LIA ice margin to high erosion all across the top of the riegel. The resulting minimum glacial erosion rates from samples on the riegel are 0.5–1.1 mm/a (10Be) and 0.6–>1.8 mm/a (in-situ 14C) which correspond to minimum erosion depths of 1.6–>3 m (10Be) and 1–>5 m (14C). The extremely low nuclide concentrations measured at the riegel highlight the substantial erosion (predominantly abrasion) of the bedrock surface during late Holocene glacier coverage. Field observations suggest that the formation of the overdeepening and, as a consequence, the riegel is due to a combination of valley shape, bedrock structures, glacier confluence and hydrology. We further hypothesise that the gorge is a key factor responsible for this impressive overdeepening, by lowering the threshold for the subglacial meltwater, effectively decoupling the height of the riegel from the depth of the overdeepening. Unlabelled Image • Deep glacial erosion on the Trift riegel during the late Holocene • Erosion depth quantification with cosmogenic 10Be and in-situ 14C in bedrock • Gorges play key factor in formation of high riegels and deep overdeepenings. • New insights into Alpine landscape evolution [ABSTRACT FROM AUTHOR]

The multi‐million year history of the Greenland Ice Sheet remains poorly known. Ice‐proximal glacial marine diamict provides a direct but discontinuous record of ice sheet behavior; it is underutilized as a climate archive. Here, we present a novel multiproxy analysis of an Early Pleistocene marine diamict from northwestern Greenland. Low cosmogenic nuclide concentrations indicate minimal near‐surface exposure, similar to modern terrestrial sediment. Detrital apatite (U‐Th‐Sm)/He (AHe) ages all predate glaciation by >150 million years, suggesting the northwestern Greenland Ice Sheet had, by 1.9 Ma, not yet incised fjords of sufficient depth to excavate grains with young AHe ages. The diamict contains terrestrial plant leaf wax, likely from land surfaces surrounding the ice sheet. These data indicate that a persistent, dynamic ice sheet existed in northwestern Greenland by 1.9 Ma and that diamict is a useful archive of ice sheet history and process. Plain Language Summary: The behavior of the Greenland Ice Sheet over the past several million years is poorly known. We analyzed 1.9 million‐year‐old sediment, deposited by glacial ice on the seafloor, to understand long‐term ice sheet history. Low cosmogenic isotope concentrations indicate persistent ice cover and at least meters of glacial erosion. Old apatite ages suggest deep glacial valleys had not yet been eroded. Leaf waxes produced by plants and algae indicate less than complete ice cover. By 1.9 million years ago, the Greenland Ice Sheet was a persistent, dynamic, erosive feature of Earth's climate and landscape. Key Points: By the Early Pleistocene, the northwestern Greenland Ice Sheet had removed preglacial soil and regolith but had not yet incised deep fjordsSimilar to today, ice‐free areas harbored vegetation that was incorporated into glacial marine sediment during ice advancesGlacial marine diamict is an underutilized, but promising paleoclimate archive; existing archives should be re‐examined [ABSTRACT FROM AUTHOR]

Alpine overdeepenings consist of widespread hidden geomorphic features shaped by glacial erosion, with up to hundreds of meters incision over the Quaternary. Their occurrence and geometry in the Swiss foreland have been investigated and mapped (Dürst-Stucki & Schlunegger 2013), however, their spatial distribution, morphometric characteristics and Quaternary evolution during successive glaciations remain poorly constrained (e.g. Preusser et al. 2010). This study consists on the morphometric analysis of glacial overdeepenings (ODs) in the Swiss Alpine foreland to get quantitative constrains on both their shape characteristics and spatial occurrence. The aim is to understand how much the bedrock resistance, local settings (lithological contrasts, faults, foreland vs. mountain) or drainage network control the location and geometry of ODs. A combined bedrock model derived from subsurface mapping of Mey et al. (2016) and Dürst-Stucki & Schlunegger (2013) was generated to better constrain the Quaternary sediment thickness both in the low-relief regions (Swiss Alpine foreland) and in the high-relief areas (Swiss Alps). For bedrock regions under modern glaciers, we also collected data from Haeberli et al. (2016) and used them for quantitative comparisons with ODs in ice-free areas. For establishing the ODs shapes, an automated GIS-routine was designed with four different criteria for filtering: area, maximum depth, slope and basin connectivity. Differences in the spatial trends of the ODs (area, length, width, sediment thickness, elongation and orientation) and the potential influence of lithology, faults/folds and hydrological network were investigated for all Switzerland. A more detailed analysis was conducted for large overdeepened features (area > 4 km2), in which cross-section profiles, shape-factor computation, relationships with drainage confluences and valley asymmetry were further computed. Preliminary results show that subglacial hydrology seems to play a decisive role on local erosion patterns, while bedrock resistance explains well maximum depths and width of ODs. On the other hand, no clear relationship between area and elongation or between width and length was found for our datasets. Further steps using a more detailed drainage, as well as enhanced features-delimitation routines will be performed. The analysis will, ultimately, provide an overview of the main spatial trends and possible controls related to formation and development of overdeepenings, allowing a broader understanding of erosive processes by glaciers during Quaternary times. REFERENCESDürst-Stucki, M. & Schlunegger, F. 2013: Identification of erosional mechanisms during past glaciations based on a bedrock surface model of the Central European Alps. Earth Planet. Sci. Lett, 384, 57.Haeberli, W., Linsbauer, A., Cochachin, A., Salazar, C., Fischer, U. H. 2016: On the morphological characteristics of overdeepenings in high-mountain glacier beds. Earth Surface Processes and Landforms, 41(13), 1980–1990.Mey, J., Scherler, D., Wickert, A.D., Egholm, D.L., Tesauro, M., Schildgen, T.F., Stecker, M.R. 2016: Glacial isostatic uplift of the European Alps. Nature Communications, 7, 10. Preusser, F., Reitner, J.M., Schlüchter, C. 2010: Distribution, geometry, age and origin of overdeepened valleys and basins in the Alps and their foreland. Swiss J. Geoscience, 103, 407. [ABSTRACT FROM AUTHOR]

When a continental sized ice sheet first formed on Antarctica across the Eocene-Oligocene boundary the bed topography was significantly different to the modern day bed. As the bed evolved due to the effects of glacial erosion, sedimentation, subsidence and tectonics, it is hypothesised that the ice sheet sensitivity to climate forcing also changed. This hypothesis has been tested in a number of recent ice sheet modelling studies, but these efforts have been limited by the use of idealised bed topography estimates. Here we explore the ice sheet sensitivity to evolving bed topography using a recently produced suite of palaeotopographies for the Eocene-Oligocene and Oligocene-Miocene transitions, the mid-Miocene climatic optimum, and the late Miocene to early Pliocene. Although we present results for all of these intervals, we are particularly interested in whether bed topography played a role in Antarctic ice sheet stabilisation following the mid-Miocene climatic optimum and the final descent into the icehouse. [ABSTRACT FROM AUTHOR]