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Glacial movements shaped vast northern parts, offering critical insights into glacial dynamics in a changing climate. Located on the island of Rügen in NE Germany, the Jasmund Glacitectonic Complex (JGC) is a key area to study the dynamics of past glaciations. Previous reconstructions focused primarily on the onshore realm, resulting in some areas remaining unexplored. Here we use more than 140 high‐resolution marine multi‐channel seismic profiles to map the erosional unconformity surrounding the JGC for the first time. Submarine glacial features match features observed onshore, allowing a consistent land‐to‐sea reconstruction of the evolution of the JGC. Our results indicate a single SW‐directed Weichselian glacier advance, suggesting that the JGC formed through three distinct glacier lobes exerting pressure from multiple directions. The ice advance encircled the Jasmund peninsula and overthrusted Cretaceous sediments on the JGC perpendicularly and laterally. Plain Language Summary: The Jasmund Glacitectonic Complex on Rügen island, northeast Germany, is a popular tourist destination and a key area for studying how deformations and erosion by former ice sheets shape our landscapes. Previous studies were limited to the onshore area and suggested that the complex formed in three separate phases. Our study uses marine seismic imaging techniques that suggest an alternative development. By creating detailed maps of the proposed glacial erosional surface from seismic data, we discovered depressions of different shapes that were carved by glaciers moving southwestwards during the last ice age. The erosional feature is 100 m deep and matches earlier predictions of the ground's response to glacial movement. The mapping indicates that the glacial traces on the seabed extend onto the land. We propose that a single glacier movement was responsible for shaping the entire area in one dynamic phase. This shows that the sediments were compressed and displaced in varying directions during the ongoing (single) ice advance. Key Points: Seismic mapping, offshore channels and depressions, thrust‐fault structures, ice advance dynamics, Jasmund Glacitectonic Complex, Rügen Island and surrounding Baltic Sea, NE Germany [ABSTRACT FROM AUTHOR]

Here we present the first Lateglacial and Holocene glacial history from Rotsunddalen, northern Troms and western Finnmark county, northern Norway, based on both relative and numerical moraine dating using Schmidt hammer, soil chronosequencing and terrestrial cosmogenic nuclide dating. We combine these chronological data with a regional map of the glacial geomorphology to hypothesize key events in the glacial history from around 14 ka to present. Our reconstruction shows that, following deglaciation of the main ice sheet across central Troms and Finnmark, mountain glaciers were terminating on land, close to the coast, between around 12.1 and 10.6 ka. Continued recession of the main Fennoscandian Ice Sheet margin towards the SE led to the isolation of several large plateau icefields and outlet glaciers that generated moraines at around 10.2–9.2 ka, which we ascribe to the Erdalen Event, and 8.4–8.2 ka, which is broadly contemporaneous with the 8.2 ka cold event. Although the latter corresponds with the Scandinavian Finse Event, very few moraines have been dated to this time and we therefore view it as a tentative hypothesis for future work to test. During the Holocene Thermal Maximum (~6.6 to 6.3 ka) most (if not all) glaciers in the region disappeared, but then regrew during the Neoglaciation and produced large moraines dated to around 4.7 ka that lie a few hundred metres distal to the prominent Little Ice Age moraines (previously dated to AD 1810s–1870s). Given the limitations of our dating approach, the preservation of moraines dated to this period in northern Norway also warrants further investigation. We also highlight that terrestrial cosmogenic nuclide dating of the moraines is not consistent with other dating approaches and the widely established deglaciation history of the region, probably owing to cosmogenic inheritance and insufficient glacial erosion. [ABSTRACT FROM AUTHOR]

The subglacial landscape of Antarctica records and influences the behaviour of its overlying ice sheet. However, in many places, the evolution of the landscape and its control on ice sheet behaviour have not been investigated in detail. Using recently released radio-echo sounding data, we investigate the subglacial landscape of the Evans–Rutford region of West Antarctica. Following quantitative analysis of the landscape morphology under ice-loaded and ice-unloaded conditions, we identify 10 flat surfaces distributed across the region. Across these 10 surfaces, we identify two distinct populations based on clustering of elevations, which potentially represent remnants of regionally coherent pre-glacial surfaces underlying the West Antarctic Ice Sheet (WAIS). The surfaces are bounded by deeply incised glacial troughs, some of which have potential tectonic controls. We assess two hypotheses for the evolution of the regional landscape: (1) passive-margin evolution associated with the break-up of the Gondwana supercontinent or (2) an extensive planation surface that may have been uplifted in association with either the West Antarctic Rift System or cessation of subduction at the base of the Antarctic Peninsula. We suggest that passive-margin evolution is the most likely of these two mechanisms, with the erosion of glacial troughs adjacent to, and incising, the flat surfaces likely having coincided with the growth of the WAIS. These flat surfaces also demonstrate similarities to other identified surfaces, indicating that a similar formational process may have been acting more widely around the Weddell Sea embayment. The subsequent fluctuations of ice flow, basal thermal regime, and erosion patterns of the WAIS are therefore controlled by the regional tectonic structures. [ABSTRACT FROM AUTHOR]

Inheritance from prior exposure often complicates the interpretation of terrestrial cosmogenic nuclide (TCN) inventories in glaciated terrain. Lochnagar, a mountain in eastern Scotland, holds a clear geomorphological record of corrie glaciation and the thinning of the last Scottish ice sheet over the last ~15 ka. Yet attempts to date the main stages in deglaciation after sampling of 21 granite boulders for 10Be, 26Al and 14C from corrie moraines, an ice sheet lateral moraine and boulder spreads revealed widespread, but variable, TCN inheritance. Only the youngest boulder ages fit within the range of expected deglaciation ages. To identify the sources of geological uncertainty, we provide simple models of ice cover duration and erosion histories for plateau, corrie and strath landscape domains, identify the variable nuclide inheritance that derives from different sources for boulders in these domains, and outline the effects of rotation, splitting and erosion of boulders during glacial transport. The combined effects increase clustering around arbitrary mean TCN values that exceed deglaciation ages. A further implication is that boulders have survived beneath overriding ice sheets. Such boulder trapping at Lochnagar may have resulted from topographic controls on katabatic winds and surface ablation acting on a thinning, cold‐based ice sheet. [ABSTRACT FROM AUTHOR]

Glacial erosion rates on the Iceland landscape throughout the Pleistocene are not well quantified. Ice scour lakes provide an opportunity to investigate glacial erosive activity and relative intensity because they commonly form in areas beneath ice sheets due to intense quarrying. This study evaluates ice scour lake morphology and density as a potential proxy for paleo‐ice flow direction and basal thermal regime for parts of the Iceland Ice Sheet. Using GIS analysis, properties of ice scour lakes are examined in regions that experienced different rates of ice flow during and following the Last Glacial Maximum (LGM), as interpreted from streamlined subglacial landforms. The primary input datasets were topographic, hydrologic and bedrock data. Lake distribution and morphology were quantified for all natural lakes of Iceland (n = 30 169), with close examination of three 400 km2 sub‐regions in Vestfirðir (n = 904), Húnaflói (n = 69) and Bakkaheiði (n = 232). Lake distribution parameters include density, packing and centroid elevation. PolyMorph‐2D was used to quantify lake morphology including orientation, area and elongation ratio. Ice scour lake density, packing and elevation were all greatest on Vestfirðir. The high density and packing of lakes across Vestfirðir suggests unique ice dynamics relative to the other two sub‐regions, and multidirectional flow of lake axes supports the presence of an independent ice cap covering Vestfirðir. Differential intensity of glacial erosion interpreted from regions of high and low lake density on Bakkaheiði supports a proposed ice divide in Northeast Iceland. The orientation of lakes align with the flow directions of proposed LGM ice streams in Northern and Northeast Iceland. Ice scour lakes were most elongate on average on Bakkaheiði, which supports fast ice flow. Improving understanding of former ice sheet basal thermal regime and paleo‐ice flow velocity serves to inform modern controls on ice sheet stability and ice sheet basal processes. [ABSTRACT FROM AUTHOR]

Reconstructions of the southwestern Laurentide Ice Sheet (LIS) from geomorphology have revealed complex cross‐cutting ice streams, indicative of surging and flow switching. This flow pattern and behaviour is distinct from the rest of the ice sheet where ice streams flowed radially to the ice sheet margin. Many ice streams in the southwestern sector originate around the Alberta Oil Sands (AOS). Previous reports have detected oil sands material in surficial and glacial sediments south of the AOS, demonstrating potential glacial mobilisation of the oil sands. In this study, we use geochemical fingerprinting to systematically investigate surficial sediments from the former Central Alberta Ice Stream (CAIS) flow track. We compare the geochemical signatures of 82 sediments from within and outside the CAIS limits with those of the AOS (from mines and natural exposures), using gas chromatography–mass spectrometry oil–oil correlation techniques. Our results provide geochemical evidence of glacial erosion and long‐distance mobilisation of AOS producing contamination signatures in sediments throughout the CAIS flow track. The strength of the AOS signature is particularly strong in sediments along the terminating margins, to the east of Calgary and in the Cooking Lake area to the southeast of Edmonton. These results inform theoretical models of enhanced slipperiness, inspired by slippery liquid infused porous surfaces (SLIPS), whereby oil lubrication of the basal sediment influences the degree of sliding and basal deformation in the ice stream. We hypothesise that naturally occurring hydrocarbons at the basal interface exerted control on the location of the onset zone of the CAIS and surrounding ice streams in Alberta. The enhanced slipperiness caused by oil contamination may also explain ice streaming and surging in other ice sheets, such as the Barents Sea Ice Sheet, where hydrocarbons are known to have been driven to the sedimentary interface during glaciation. [ABSTRACT FROM AUTHOR]

The subglacial landscape of Antarctica records and influences the behaviour of its overlying ice sheet. However, in many places, the evolution of the landscape and its control on ice sheet behaviour has not been investigated in detail. Using recently released radio-echo sounding data, we investigate the subglacial landscape of the Evans-Rutford region of West Antarctica. Following quantitative analysis of the landscape morphology under ice-loaded and unloaded conditions, we identify ten flat surfaces distributed across the region. Across these ten surfaces, we identify two distinct populations based on clustering of elevations, which potentially represent remnants of regionally coherent pre-glacial surfaces underlying the West Antarctic Ice Sheet (WAIS). The surfaces are bounded by deeply incised glacial troughs, some of which have potential tectonic controls. We assess two hypotheses for the evolution of the regional landscape: (1) passive margin evolution associated with the breakup of the Gondwana supercontinent, or (2) an extensive planation surface that may have been uplifted either in association with the West Antarctic Rift System or cessation of subduction at the base of the Antarctic Peninsula. We suggest that passive margin evolution is most likely of these two mechanisms, with the erosion of glacial troughs adjacent to, and incising, the flat surfaces likely having coincided with the growth of the WAIS. These flat surfaces also demonstrate similarities to other identified surfaces, indicating that a similar formational process may have been acting more widely around the Weddell Sea Embayment. The subsequent fluctuations of ice flow, basal thermal regime and erosion patterns of the WAIS are therefore controlled by the regional tectonic structures. [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]

We present the first extensive high-resolution glacial geomorphic map west of the Andean Cordillera in southernmost Chile (52.8–53.1°S, 73.0–73.9°W). The map extends over 1565 km² and is based on high-resolution satellite images and aerial photographs. At selected locations, the remotely mapped geomorphology was corroborated by field observations. The study area is dominated by glacial erosional landforms (77%) over depositional landforms (23%), with published submarine depositional landforms having been included (e.g. moraines). Glacial drift, kettle kame topography and lateral and frontal moraines form the primary depositional landforms and sediment associations. Glacial cirques, wide U-shaped valleys, whalebacks, roches moutonnées and scoured bedrock characterize most of the mapped area. The spatial distribution of whalebacks and roches moutonnées in the study area indicates a lack of lithological control on their formation and a warm-based, dynamic ice velocity and thickness regime during Patagonian Ice Sheet cover and retreat during the last glacial cycle. [ABSTRACT FROM AUTHOR]

Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet — the third largest Quaternary ice mass that spanned 49°N to 82°N — to decipher its erosional footprint during the entire last ~100 ka glacial cycle. Our results demonstrate extreme spatial and temporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5 mm a−1 and a net volume equating to ~130,000 km3 of bedrock excavated to depths of ~190 m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion — critically modulated by transient ice-sheet dynamics — with its capacity to impart a profound but piecemeal geological legacy across mid- and high latitudes. Glacial erosion processes over geological timescales are poorly understood. Here the authors apply an observationally constrained model to reconstruct the evolving thermodynamics and transient erosional signature of the Eurasian Ice Sheet over the last 100,000-year ice age to reveal how it profoundly sculpted but also protected the landscape visible today [ABSTRACT FROM AUTHOR]

Ice sheet interiors are conventionally regarded as non‐erosive. Yet subglacial conditions may be transformed during deglaciation by the arrival of large volumes of meltwater at the ice sheet bed. The development of a dynamic meltwater drainage system and the onset of basal sliding have potential to increase erosion rates in bedrock and sediment. Here, we examine the impact of late deglacial thawing on the Rogen plateau, located near the former ice divide of the Fennoscandian Ice Sheet. We provide new maps of glacial and glacifluvial landforms which we combine with existing data on Quaternary sediments and landforms. Cross‐cutting and overlapping relations allow for an event sequence to be established of the deglaciation period. In the Early Holocene (< 11 ka), an ice lobe onset zone developed at the Rogen plateau. In places where meltwater reached the bed and where pressures rose to overpressure, it caused fracture dilation in horizontally bedded sandstones and rock brecciation. The onset of sliding and application of drag resulted in the mobilization of bedrock sheets. The establishment of meltwater corridors led to fluidization of sediments at the bed, dissection and modification of ribbed moraines and formation of murtoos and hummock corridors. During final stagnation of the ice sheet, meltwater drained through channels forming axial eskers. Bedrock erosion during deglaciation reached depths up to 4 m, and in conjunction with some recycling of till, generated ~ 317 km2 of boulder cover. The average erosion depths by removal and reworking of sediment are ~ 0.9–1.1 m across areas below 900 m elevation. This study shows that when the cold‐based interiors of ice sheets become briefly activated by large subglacial meltwater delivery late in deglaciation, there can be significant reworking and erosion of rock and sediment. [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]

The lack of evidence for large‐scale glacial landscapes on Mars has led to the belief that ancient glaciations had to be frozen to the ground. Here we propose that the fingerprints of Martian wet‐based glaciation should be the remnants of the ice sheet drainage system instead of landforms generally associated with terrestrial ice sheets. We use the terrestrial glacial hydrology framework to interrogate how the Martian surface gravity affects glacial hydrology, ice sliding, and glacial erosion. Taking as reference the ancient southern circumpolar ice sheet that deposited the Dorsa Argentea formation, we compare the theoretical behavior of identical ice sheets on Mars and Earth and show that, whereas on Earth glacial drainage is predominantly inefficient, enhancing ice sliding and erosion, on Mars the lower gravity favors the formation of efficient subglacial drainage. The apparent lack of large‐scale glacial fingerprints on Mars, such as drumlins or lineations, is to be expected. Plain Language Summary: Water accumulates under ice masses, including glaciers and ice sheets, lubricating the base of the ice and accelerating ice motion. On Earth, this glacial motion has produced scoured landscapes in northern Europe and North America. Mars lacks such large‐scale glacial erosion even in areas with other signs of widespread glaciation. This paper uses the existing framework describing the physical interactions of water and ice, and how they affect ice motion, to show that a lack of landforms recording glacial erosion is expected even if glaciation were widespread on Mars. Key Points: Glacial hydrology feedback dynamics can explain the lack of glacial sliding on the Martian geological recordSubglacial water drainage develops faster, and is more resilient under lower Martian gravityThe fingerprints of Martian wet‐based glaciation are predicted to be channels and eskers [ABSTRACT FROM AUTHOR]

Roches moutonnées are typical landforms of glacial erosion developed in hard rocks, with an asymmetric profile caused by abrasion and lee-side plucking. In eastern Sweden, some roches moutonnées show extensive damage, including open fractures, disintegration into blocks, fracture caves and short boulder trains. Disintegration increases along ice-flow directions during deglaciation of the last Weichselian Fennoscandian Ice Sheet, indicating a subglacial origin: limited edge rounding can be explained by a combination of hard rock, slow abrasion rates and disintegration just prior to deglaciation. The roches moutonnées initially developed in kernels of gneissic rocks with a wide fracture spacing (large block size) and interlocking fracture pattern, and hence high overall rock mass strength. Dilated fractures and 'fracture caves' occur up to 15 m below the ice-bed interface. It is proposed that hydraulic jacking by overpressured water opened up the rock mass along pre-existing fractures. Jacking reduced rock mass strength, allowing glaciotectonic deformation of the roches moutonnées. Uneven hydraulic jacking led to uplift of individual fracture-bound blocks above the pre-existing smooth, abraded surface of the roches moutonnées, creating blunt, step-like edges. These edges allowed high ice pushing forces to act on large blocks: where blocks extend into the deeper rock mass, they further aided the disintegration of the rock mass. The disintegrated roches moutonnées can be regarded as transient features between intact bedrock and complete disintegration into boulders. The jacking-disintegration-transport sequence is characteristic of glacial ripping and very different from classic lee-side plucking. [ABSTRACT FROM AUTHOR]

The geometry of glacial overdeepenings on the Swiss Plateau close to Bern was inferred through a combination of gravity data with a 3D gravity modelling software. The target overdeepenings have depths between 155 and > 270 m and widths between 860 and 2400 m. The models show incisions characterized by U-shaped cross-sectional geometries and steep to over-steepened lateral flanks. Existing stratigraphic data reveals that the overdeepenings were formed and then filled during at least two glacial stages, which occurred during the Last Glacial Maximum (LGM) within the Marine Isotope Stage (MIS) 2, and possibly MIS 6 or before. The U-shaped cross-sectional geometries point towards glacial erosion as the main driver for the shaping of the overdeepenings. The combination of the geometries with stratigraphic data suggests that the MIS 6 (or older) glaciers deeply carved the bedrock, whereas the LGM ice sheet only widened the existing valleys but did not further deepen them. We relate this pattern to the different ice thicknesses, where a thicker MIS 6 ice was likely more powerful for wearing down the bedrock than a thinner LGM glacier. Gravity data in combination with forward modelling thus offers robust information on the development of a landscape formed through glaciers. [ABSTRACT FROM AUTHOR]

Climate has been viewed as a primary control on the rates and patterns of glacial erosion, yet our understanding of the mechanisms by which climate influences glacial erosion is limited. We hypothesize that climate controls the patterns of glacial erosion by altering the basal thermal regime of glaciers. The basal thermal regime is a first-order control on the spatial patterns of glacial erosion. Polythermal glaciers contain both cold-based portions that protect bedrock from erosion and warm-based portions that actively erode bedrock. In this study, we model the impact of various climatic conditions on glacier basal thermal regimes and patterns of glacial erosion in mountainous regions. We couple a sliding-dependent glacial erosion model with the Parallel Ice Sheet Model (PISM) to simulate the evolution of the glacier basal thermal regime and glacial erosion in a synthetic landscape. We find that both basal thermal regimes and glacial erosion patterns are sensitive to climatic conditions, and glacial erosion patterns follow the patterns of the basal thermal regime. Cold temperature leads to limited glacial erosion at high elevations due to cold-based conditions. Increasing precipitation can overcome the impact of cold temperature on the basal thermal regime by accumulating thick ice and lowering the melting point of ice at the base of glaciers. High precipitation rates, therefore, tend to cause warm-based conditions at high elevations, resulting in intensive erosion near the peak of the mountain range. Previous studies often assessed the impact of climate on the spatial patterns of glacial erosion by integrating climatic conditions into the equilibrium line altitudes (ELAs) of glaciers, and glacial erosion is suggested to be maximal around the ELA. However, our results show that different climatic conditions produce glaciers with similar ELAs but different patterns of basal thermal regime and glacial erosion, suggesting that there might not be any direct correlation between ELAs and glacial erosion patterns. [ABSTRACT FROM AUTHOR]

The landscape of Antarctica, hidden beneath kilometre‐thick ice in most places, has been shaped by the interactions between tectonic and erosional processes. The flow dynamics of the thick ice cover deepened pre‐formed topographic depressions by glacial erosion, but also preserved the subglacial landscapes in regions with moderate to slow ice flow. Mapping the spatial variability of these structures provides the basis for reconstruction of the evolution of subglacial morphology. This study focuses on the Jutulstraumen Glacier drainage system in Dronning Maud Land, East Antarctica. The Jutulstraumen Glacier reaches the ocean via the Jutulstraumen Graben, which is the only significant passage for draining the East Antarctic Ice Sheet through the western part of the Dronning Maud Land mountain chain. We acquired new bed topography data during an airborne radar campaign in the region upstream of the Jutulstraumen Graben to characterise the source area of the glacier. The new data show a deep relief to be generally under‐represented in available bed topography compilations. Our analysis of the bed topography, valley characteristics and bed roughness leads to the conclusion that much more of the alpine landscape that would have formed prior to the Antarctic Ice Sheet is preserved than previously anticipated. We identify an active and deeply eroded U‐shaped valley network next to largely preserved passive fluvial and glacial modified landscapes. Based on the landscape classification, we reconstruct the temporal sequence by which ice flow modified the topography since the beginning of the glaciation of Antarctica. [ABSTRACT FROM AUTHOR]

The Scandinavian Ice Sheet reached the Sudetes and Carpathian Mountains during the Elsterian glaciation. A long ice‐sheet piedmont marginal zone affected by the rugged mountain foreland topography and associated slopes originated. This study focuses on the hilly Rychleby Mts. foreland (Eastern Sudetes, Czechia), which was a part of the piedmont marginal foreland zone of the ice sheet. The basal regime was reconstructed through an investigation of the sedimentology, structural features, and the nature of ice‐sheet erosion of preglacial landscapes evident at two sites located ~3–5 km inside the maximum ice‐sheet extent. These sites show a preglacial relief buried by sub‐ to supraglacial sediments. The sites were located under an ice cover of max. 200 m. Evidence of cold‐based conditions (including palaeotors with delicate structures on the bedrock, almost absent striations on clasts, originally frozen unlithified sedimentary rafts) exists at both sites. Permafrost composed of coarse‐grained sediments was subject to brittle deformation at the base of the ice sheet, whereas permafrost composed of fine‐grained sediments underwent ductile deformation. The margin of the Scandinavian Ice Sheet in the Rychleby Mts. foreland was cold‐based, therefore glacial erosion was not sufficient to significantly remodel the palaeotors into roches moutonnées. During ice‐sheet decay, the preglacial landscape was partially buried by melt‐out tills and meltwater sediments. [ABSTRACT FROM AUTHOR]

Here we present the first compilation of sediment volumes, sedimentation rates, and chronology of Quaternary sediment packages along the entire marine margin of the Eurasian ice sheets (EurIS; British-Irish, Kara-Barents Sea-Svalbard, and Fennoscandian). This compilation allows for a subdivision of the EurIS development into three phases (2.6-1.5 Ma, 1.5-0.78 Ma, and 0.78-0 Ma). At the start of the Quaternary, sedimentation rates increased, relative to pre-Quaternary rates, by an order of magnitude. This abruptness in rate change excludes tectonic raising of landmasses as the main factor, but more likely reflects climate change through increased glacial erosion. The sediment distribution data suggest that the Kara-Barents Sea-Svalbard Ice Sheet (KBSIS) already was quite large at the beginning of the Quaternary, and well before 1.5 Ma it extended to the shelf edge and coalesced with the Fennoscandian Ice Sheet (FIS), which prior to 1.5 Ma most likely was located near the coast. Large ice streams and intense glacial erosion characterized the KBSIS in the 1.5-0.78 Ma time period, whereas the FIS at that time extended farther out on the continental shelf. After 0.78 Ma, a north-south change in EurIS development occurred. In the FIS and the British-Irish Ice Sheet (BIIS), large ice streams developed and shelf-edge glaciations occurred nearly 1 m.y. later compared to the KBSIS. The FIS and BIIS also repetitively coalesced in the North Sea. A significant drop in sediment input along the KBSIS marine margin, to the lowest Quaternary level, suggests a less erosive KBSIS. [ABSTRACT FROM AUTHOR]

In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultant boulder spreads are covers of large, angular boulders, many with glacial transport distances of 1–100 m. Boulder spreads occur alongside partly disintegrated roches moutonnées and associated fracture caves, and are associated with disrupted bedrock, which shows extensive fracture dilation in the near surface. These features are distributed in ice-flow parallel belts up to 10 km wide and extend over distances of >500 km. Our hypothesis is that the assemblage results from (1) hydraulic jacking and bedrock disruption, (2) subglacial ripping and (3) displacement, transport and final deposition of boulders. Soft sediment fills indicate jacking and dilation of pre-existing bedrock fractures by groundwater overpressure below the ice sheet. Overpressure reduces frictional resistance along fractures. Where ice traction overcomes this resistance, the rock mass strength is exceeded, resulting in disintegration of rock surfaces and ripping apart into separate blocks. Further movement and deposition create boulder spreads and moraines. Short boulder transport distances and high angularity indicate that glacial ripping operated late in the last deglaciation. The depths of rock mobilized in boulder spreads are estimated as 1–4 m. This compares with 0.6–1.6 m depths of erosion during the last glaciation derived from cosmogenic nuclide inventories of samples from bedrock surfaces without evidence of disruption. Glacially disrupted and ripped bedrock is also made ready for removal by future ice sheets. Hence glacial ripping is a highly effective process of glacial erosion. [ABSTRACT FROM AUTHOR]

Ice sheet behavior is strongly influenced by the bed topography. However, the effect of the progressive temporal evolution of Antarctica's subglacial landscape on the sensitivity of the Antarctic Ice Sheet (AIS) to climatic and oceanic change has yet to be fully quantified. Here we investigate the evolving sensitivity of the AIS using a series of data‐constrained reconstructions of Antarctic paleotopography since glacial inception at the Eocene‐Oligocene transition. We use a numerical ice sheet model to subject the AIS to schematic climate and ocean warming experiments and find that bed topographic evolution causes a doubling in ice volume loss and equivalent global sea level rise. Glacial erosion is primarily responsible for enhanced ice sheet retreat via the development of increasingly low‐lying and reverse sloping beds over time, particularly within near‐coastal subglacial basins. We conclude that AIS sensitivity to climate and ocean forcing has been substantially amplified by long‐term landscape evolution. Plain Language Summary: The Antarctic Ice Sheet is situated above a large landmass, the geometry of which is an important control on the behavior of the ice sheet and how it responds to climatic change. However, Antarctica's subglacial landscape has evolved significantly since the formation of the first ice sheets approximately 34 million years ago, which implies that the sensitivity of the ice sheet to climate change may also have changed over time. Our ice sheet model experiments show that the progressive evolution of Antarctica's bed topography has enhanced the sensitivity of the Antarctic Ice Sheet to climate and ocean warming, meaning that a greater volume of ice is lost for a given warming scenario when using the modern topography compared to past topographies. In particular, the lowering of bed elevations by glacial erosion has caused a notable increase in ice sheet sensitivity within subglacial basins close to the ice sheet margin. Key Points: We investigate the influence of the progressive evolution of bed topography on the sensitivity of the Antarctic Ice Sheet to climatic changeBed topographic evolution since 34 Ma causes a doubling in Antarctic ice volume loss in our schematic ice sheet model experimentsAntarctic Ice Sheet sensitivity to climate and ocean forcing has been substantially amplified by long‐term landscape evolution [ABSTRACT FROM AUTHOR]

Pleistocene glaciations have promoted important landscape transformations as a result of high rates of erosion and rapid sediment evacuation to adjacent marine basins. In the Patagonian Andes the role of the Patagonian Ice Sheet on landscape evolution, in particular the spatial patterns of glacial erosion and its influence on sediment fluxes, is poorly documented. Here, we investigate the Middle and Late Pleistocene sedimentary record of the continental slope from Ocean Drilling Program (ODP) Site 861, offshore Patagonia (46°S), to evaluate the link between glaciations, mountain range erosion and continental margin strata formation. Petrographic analysis of the sand‐size fraction (0.063–2 mm) and ɛNd and 87Sr/86Sr measurements in the silt‐size fraction (10–63 µm) indicate that glacial erosion over the last 350,000 years has focused within the Patagonian Batholith, with a minor influence of a proximal source to the drilling site, the Chonos Metamorphic Complex. This shows that erosion has focused in the core of the northern Patagonian Andes, coinciding roughly with the location of the Liquiñe‐Ofqui Fault Zone and the zone of concentrated precipitation during glaciations, suggesting a combined climatic and structural control on glacial erosion. Temporal variation in the provenance signal is contemporaneous with a marked change in the stratigraphy of ODP Site 861 that occurred after the glaciation of MIS 8 (~240 kyr ago). Before MIS 8, a restricted provenance signal and coarse lithofacies accumulated on the continental slope indicates spatially restricted erosion and efficient transfer of sediment towards the ocean. In contrast, very high provenance variability and finer continental slope lithofacies accumulation after MIS 8 suggest a disorganized expansion of the areas under erosion and a more distal influence of ice sediment discharge to this site. We argue that this change may have been related to a re‐organization of the drainage patterns of the Patagonian Ice Sheet and flow of outlet glaciers to the continental margin during the last two glaciations. [ABSTRACT FROM AUTHOR]

The present marine Baltic Sea basin (BSB) occupies an eroded Proterozoic intra-cratonic basin on the Fennoscandian shield. Competing models propose a Neogene fluvial origin, with later modification by glacial erosion, or a much younger development, with overdeepening beneath the Fennoscandian Ice Sheet (FIS). We test these alternatives using a first order source to sink sediment budget for the catchment of the BSB. Best estimates derived from geomorphic and cosmogenic nuclide evidence suggest depths of erosion over the last 1 Ma of 20 m in basement and 40 m in sedimentary rocks that surround the BSB. As the BSB has been overdeepened below a regional base level provided by the shallow Darss Sill at the boundary with the Kattegat, erosion of the BSB may be interpreted as glacial in origin, without a fluvial component. The estimated total volume of source area erosion is 30,628 km3 of which 87% is derived from the present BSB. Sediment volumes in the sink area within the limits of maximum Pleistocene glaciation are estimated at a minimum of 37,629 km3, after correction for local erosion, porosity, and carbonate losses. Marine Isotope Stage 12 and younger sediments account for 87% of the total Pleistocene sediment volume in the sink in Poland. Although significant uncertainties remain, the sediment budget is consistent with erosion of the BSB entirely by the FIS, mainly when the ice sheet reached its maximum extent and thickness during the Middle and Late Pleistocene glaciations. [ABSTRACT FROM AUTHOR]

Glacial erosion has long been recognized as a significant factor contributing to continental denudation during the Ediacaran Period, consequently leading to geochemical perturbations and biotic evolution in marine environments. However, the role of Ediacaran glaciation in the oceanic geochemical perturbations remains controversial due to ambiguous geochronological correlations and unresolved paleogeographic and tectonic settings. A total of 45 Ediacaran glacial records have been reviewed and categorized into four Ediacaran glaciations: Gaskiers (581–579 Ma), Fauquier (ca. 571 Ma), Bou-Azzer (ca. 565–560 Ma), and Hankalchough (ca. 562–551 Ma) glaciations. Of these glacial records, 53% have been reported in the Avalonian–Cadomian and Altaids accretionary orogenic belts, recognized as representing Cordilleran-type mountain ice sheets (CMISs). This study reports an Ediacaran glaciation in the southern Altaids, NW China, with 18 glacial and non-glacial facies and 1173 new U-Pb-Hf data from detrital zircons. The maximum ages of deposition based on detrital zircons from the Ediacaran to Lower Cambrian strata indicate an age range from 591.1 to 561.9 Ma for the glacial and deglacial sequences. The glacial sequences consist mostly of proglacial marine facies associated with ice-rafted diamictites and turbidite facies. The unimodal detrital zircon feature of these proglacial facies suggests that the glaciation center was located proximal to a ca. 644 Ma magmatic arc. A statistical comparison of detrital zircon facies was conducted on a regional Ediacaran dataset compiled from 12,291 U-Pb-Hf data points from the Altaids, Siberia, Tarim, North China and South China Cratons. The result suggests the presence of CMISs extending from Beishan to Yili Tianshan and Kyrgyz Tianshan along an active margin of the Paleo-Asian Ocean (PAO). The provenance shift and exhumation of a ca. 967 and 2469 Ma granitic basement suggests that erosion by the Ediacaran ice sheets provided a greater contribution to the terrestrial influx and geochemical perturbations in the late Ediacaran oceans compared with other glacial and tectonic events. [ABSTRACT FROM AUTHOR]

The shallow Chukchi-East Siberian margin of the Arctic Ocean was repeatedly impacted by Pleistocene glaciations and related changes in sea level and circulation. The depositional history across the last two Arctic glacial cycles is investigated in sediment core ARC6-C15 from the foot of the Chukchi Rise, an extension of the Chukchi Sea shelf that was impacted by the East Siberian Ice Sheet (ESIS). Our proxy data indicate a large extent of the ESIS, likely blocking the westward sediment transport from the Laurentide Ice Sheet (LIS) during the penultimate glaciation estimated to have occurred within an age span from Marine Isotope Stage (MIS) 4 to 6. The deglacial environments are characterized by enhanced sediment inputs from the East Siberian and Chukchi shelves, while overlying interstadial/interglacial sediments have a signature of the Chukchi Sea and the Beaufort Gyre. During the last glaciation, the ESIS had a smaller impact on the Chukchi margin, and the deglaciation was dominated by the LIS sediment sources. Glacial discharge from the Mackenzie area is identified in the Bølling/Allerød interval, while later deglacial pulses can be tracked to the Canadian Arctic Archipelago. In addition to glacigenic sediment inputs, both deglacial intervals contain Fe Mn micronodules, possibly formed under the influence of meltwater pulses during sea level rise. An increase in the chlorite content that likely marks the flooding of the Bering Strait is identified at the start of the Holocene. A pronounced oxygen and carbon isotope excursion in the early Holocene may indicate hydrographic changes in the Arctic Ocean related to the 8.2 ka meltwater discharge event. • Detailed comparison of glacial, deglacial, interglacial/interstadial environments during the last two Arctic glacial cycles at the Chukchi-East Siberian margin • More intensive glacial erosion at the Chukchi-East Siberian margin during penultimate compared to the last glacial • East Siberian-Chukchi Sea sources dominate penultimate deglaciation in contrast to North American sources for the last deglaciation • Meltwater/terrestrial organic pulses from the adjacent shelf facilitate Fe-Mn micronodules during deglaciations at the Chukchi margin [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]

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]

Drumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high‐resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo‐ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600‐800 m long, 200‐250 m wide, 3‐6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down‐slope and where thick fine‐grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up‐slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre‐date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The timing and extent of early glaciations in Greenland and their co-evolution with the underlying landscape remain elusive. Here we use the concept of geophysical relief to estimate fjord erosion and the subsequent flexural isostatic response to erosional unloading in Northeast and North Greenland between Scoresby Sund (70°N) and Independence Fjord (82°N). The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene-early Pleistocene age that are now exposed on land between ~24 m and 230 m above sea level. By determining the timing of fjord formation, we can establish the early history of the Greenland Ice Sheet. We find that the Independence Fjord system must have formed by glacial erosion at average rates of ~0.5-1 mm/yr since ca. 2.5 Ma in order to explain the current elevation of the marine Kap København Formation by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of Scoresby Sund commenced before the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene by progressive inland fjord formation. Our results demonstrate that the inception of the Greenland Ice Sheet began in the central parts of Northeast Greenland before the Pleistocene and spread to North Greenland only at the onset of the Pleistocene. [ABSTRACT FROM AUTHOR]

Subglacial groundwater flow was an integral part of glaciological systems of past ice sheets, but its impact on the origin of active‐ice landforms remains unexplored. Using numerical experiments, we attempt to constrain groundwater flow dynamics under a major paleo‐ice stream of the southern Scandinavian Ice Sheet and its impact on the formation of the Stargard drumlin field. Flow models show a total reorganization of groundwater dynamics under the advancing ice stream to a depth of up to ~200 m. A mosaic of intervening groundwater recharge and discharge areas originates, whereby the same areas may experience multiple shifts in flow directions. A prominent time‐ and space‐transgressive pressure pump recharges groundwater in a subglacial zone up to about 20 km within the ice margin and discharges it in front of the ice sheet. The simulated groundwater flow pattern suggests that drumlins occupying a portion of the ice stream area occur preferentially where groundwater upwells and discharges at the ice/bed interface. Consistent with the geological composition, a possible drumlin‐forming mechanism involves an excess of pressurized water under the ice reducing the strength of the subglacial deposits and facilitating glacial erosion, erosion by turbulent meltwater flows or both, streamlining antecedent deposits into drumlin shapes. This study emphasizes the importance of causal feedback between subglacial groundwater flow and the ice sheet dynamics and suggests an impact of the former on the formation of streamlined subglacial landforms in general. Key Points: Numerical simulations show that subglacial groundwater flow under a major paleo‐ice stream is entirely reorganized compared with nonglacial timesA mosaic of subglacial groundwater recharge and discharge areas moves time‐transgressively with the advancing ice sheet with highest fluxes around the ice marginDrumlin formation is likely facilitated by upwelling groundwater weakening subglacial deposits and enhancing erosion [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]

Tors represent one of the most characteristic landforms in the uplands and mountains of Central Europe, including the Sudetes, Czech-Moravian Highlands, Šumava/Bayerischer Wald, Fichtelgebirge or Harz. These features occur in a range of lithologies, although granites and gneisses are particularly prone to tor formation. Various models of tor formation and development have been presented, and for each model the tors were thought to have evolved under specific environmental conditions. The two most common theories emphasised their progressive emergence from pre-Quaternary weathering mantles in a two-stage scenario, and their development across slopes under periglacial conditions in a one-stage scenario. More recently, tors have been analysed in relation to ice sheet extent, the selectivity of glacial erosion, and the preservation of landforms under ice. In this paper we describe tor distribution across Central Europe along with hypotheses relating to their formation and development, arguing that specific evolutionary histories are not supported by unequivocal evidence and that the scenarios presented were invariably model-driven. Several examples from the Sudetes are presented to demonstrate that tor morphology is strongly controlled by lithology and structure. The juxtaposition of tors of different types is not necessarily evidence that they differ in their mode of origin or age. Pathways of tor remodelling and degradation under subaerial conditions are identified and it is argued that processes of tor formation and development are ongoing. Thus, tors are not reliable indicators of past environments, because they are considerably influenced by both geological factors, such as lithology and structure, and geomorphological factors such as hillslope setting.. [ABSTRACT FROM AUTHOR]

Abstract The location and setting of the continental shelf break along the Antarctic continental shelves influences the paleoceanographic circulation patterns as well as sedimentation and ice sheet dynamics. By evaluating the available multichannel seismic reflection data and drill core information, we mapped the base of progradational features associated with the first advances of grounded ice sheet to the outer shelf. The distance between the modern shelf edge and the pre-glacial shelf edge varies from >200 km (e.g. Ross Sea) to <6 km (e.g. Thurston Island, West Antarctica). We identified multiple processes and mechanisms which influence the amount of shelf progradation during the establishment of a grounded ice sheet on the outer Antarctic shelves. The tectonic structure of the shelves proves to be a key factor by establishing the width of the shelf as well as local tectonics such as horst/graben and fault systems, which guide the ice stream flow and therefore the resulting sedimentation. Unlike expected, the erosional potential of the hinterland seems to play a minor role in building progradational sequences, whereas fewer long-term grounding events on the shelf edge result in more continental shelf progradation than presumed from a more dynamic ice sheet. By using these observed relationships to extrapolate the former shelf edge to unmapped regions around the Antarctic continent, we estimate an overall seaward growth of the continental shelves by 7% in area and 1.28 ∗ 106 km3 of approximated sedimentary volume deposited along the shelf edge and upper slope. Highlights • The continental shelf increased by 7% due to sediment deposition by advancing grounded ice since late Oligocene or Miocene. • The tectonic architectures of the continental shelves strongly influence the build-up of glacial prograding sequences. • Ice sheet dynamics and sediment availability play only minor roles in the development of prograding sequences. [ABSTRACT FROM AUTHOR]

Concentrations of boulders are a common feature of landscapes modified by former mid-latitude ice sheets. In many cases, the origin of the boulders can be traced in the up-ice direction to a cliff only tens to hundreds of metres distant. The implication is that a pulse of plucking and short boulder transport occurred beneath thin ice at the end of the last glacial cycle. Here we use a case study in granite bedrock in the Dee Valley, Scotland, to constrain theory and explore the factors involved in such a late phase of plucking. Plucking is influenced by ice velocity, hydrology, effective ice pressure, the extent of subglacial cavities and bedrock characteristics. The balance between these factors favours block removal beneath thin ice near a glacier margin. At Ripe Hill in the Dee Valley, a mean exposure age of 14.2 ka on blocks supports the view that the boulder train formed at the end of ice sheet glaciation. The late pulse of plucking was further enhanced by ice flowing obliquely across vertical joints and by fluctuations in sub-marginal meltwater conditions. An implication of the study is that there is the potential for a wave of ice-marginal plucking to sweep across a landscape as an ice sheet retreats. [ABSTRACT FROM AUTHOR]

Ice-stream networks constitute the arteries of ice sheets through which large volumes of glacial ice are rapidly delivered from the continent to the ocean. Modifications in ice-stream networks have a major impact on ice sheet mass balance and global sea level. Reorganizations in the drainage network of ice streams have been reported in both modern and paleo-ice sheets and usually result in ice streams switching their trajectory and/or shutting down. While some hypotheses for the reorganization of ice streams have been proposed, the mechanisms that control the switching of ice streams remain poorly understood and documented. Here, we interpret a flow switch in an ice-stream system that occurred prior to the last glaciation on the northeastern Baffin Island shelf (Arctic Canada) through glacial erosion of a marginal trough, i.e., deep parallel-to-coast bedrock moats located up-ice of a cross-shelf trough. Shelf geomorphology imaged by high-resolution swath bathymetry and seismo-stratigraphic data in the area indicate the extension of ice streams from Scott and Hecla & Griper troughs towards the interior of the Laurentide Ice Sheet. Up-ice propagation of ice streams through a marginal trough is interpreted to have led to the piracy of the neighboring ice catchment that in turn induced an adjacent ice-stream flow switch and shutdown. These results suggest that competition for ice discharge between the two ice streams, which implies piracy of ice drainage basins via marginal troughs, was the driving mechanism behind ice flow switching. In turn, the enlargement of the ice catchment by piracy increased the volume and discharge of Scott Ice Stream, allowing it to erode deeper and flow farther on the continental shelf. Similar trough systems observed on many other glaciated continental shelves may be the product of such competition for ice discharge between catchments. [ABSTRACT FROM AUTHOR]

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

Abstract Bedrock mega-grooves are assemblages of straight and parallel troughs eroded in bedrock, typically over 1000 m in length; most sites occur within the limits of the Last Glacial Maximum, both on- and off-shore. In this paper, we review the current understanding of these important yet enigmatic landforms and propose a framework for their future research. Mega-grooves are important to our understanding of ice sheet dynamics, ice–bedrock interactions and bedrock landscape evolution in glaciated areas. The overall straightness of mega-grooves across the landscape, their parallel alignment to palaeo-ice flow direction, and occurrence below the general land-surface level, has led to their unanimous interpretation as landforms of subglacial erosion. Scenarios proposed for mega-groove formation focus on either glacier ice or subglacial meltwater as the principal agent of erosion, yet none offers a comprehensive explanation. At locations where mega-grooves occur along lines of structural geology, their location, formation and morphology were largely controlled by the bedrock characteristics. Where no underlying structural control is apparent, mega-grooves were likely initiated through glacial abrasion, and subsequently modified through a range of erosional processes, potentially involving multiple morphogenetic agencies and feedbacks operating between bedrock topography and basal ice flow. In the absence of absolute dates, morphostratigraphic analyses suggest mega-groove survival through multiple glacial cycles. No specific ice-flow characteristics have been identified as a condition for bedrock grooving, but it has been suggested that some bedrock mega-grooves are related to ice streaming, which deserves further study. An initial analysis of bedrock grooves with seemingly similar morphology at a range of scales hints at a bedrock – groove landform size continuum, which could be a useful framework for exploring process - landform relationships. Future research could usefully focus on quantitative analysis of mega-groove morphology, augmented with detailed field analysis of landform relationships to bedrock structure and lithology, and thereby potentially provide further insight into the age and glaciological significance of these landforms. [ABSTRACT FROM AUTHOR]

Recently obtained geophysical data show sets of parallel erosional features on the Lomonosov Ridge in the central Arctic Basin, indicative of ice grounding in water depths up to 1280 m. These features have been interpreted as being formed by an ice shelf-either restricted to the Amerasian Basin (the "minimum model") or extending across the entire Arctic Basin. Here, we use a numerical ice sheet-shelf model to explore how such an ice shelf could form. We rule out the "minimum model" and suggest that grounding on the Lomonosov Ridge requires complete Arctic ice shelf cover; this places a minimum estimate on its volume, which would have exceeded that of the modern Greenland Ice Sheet. Buttressing provided by an Arctic ice shelf would have increased volumes of the peripheral terrestrial ice sheets. An Arctic ice shelf could have formed even in the absence of a hypothesised East Siberian Ice Sheet. [ABSTRACT FROM AUTHOR]

Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets. [ABSTRACT FROM AUTHOR]

Glacier bed overdeepenings are ubiquitous in glacier systems and likely exert significant influence on ice dynamics, subglacial hydrology, and ice stability. Understanding of overdeepening formation and evolution has been hampered by an absence of quantitative empirical studies of their distribution and morphology, with process insights having been drawn largely from theoretical or numerical studies. To address this shortcoming, we first map the distribution of potential overdeepenings beneath the Antarctic and Greenland ice sheets using a GIS-based algorithm that identifies closed-contours in the bed topography and then describe and analyse the characteristics and metrics of a subset of overdeepenings that pass further quality control criteria. Overdeepenings are found to be widespread, but are particularly associated with areas of topographically laterally constrained ice flow, notably near the ice sheet margins where outlet systems follow deeply incised troughs. Overdeepenings also occur in regions of topographically unconstrained ice flow (for example, beneath the Siple Coast ice streams and on the Greenland continental shelf). Metrics indicate that overdeepening growth is generally allometric and that topographic confinement of ice flow in general enhances overdeepening depth. However, overdeepening depth is skewed towards shallow values – typically 200–300 m – indicating that the rate of deepening slows with overdeepening age. This is reflected in a decline in adverse slope steepness with increasing overdeepening planform size. Finally, overdeepening long-profiles are found to support headward quarrying as the primary factor in overdeepening development. These observations support proposed negative feedbacks related to hydrology and sediment transport that stabilise overdeepening growth through sedimentation on the adverse slope but permit continued overdeepening planform enlargement by processes of headward erosion. [ABSTRACT FROM AUTHOR]

Well-dated paleorecords from periods prior to the Last Glacial Maximum (LGM) are important for validating models of ice sheet build-up and growth. However, owing to glacial erosion, most Late Pleistocene records lie outside of the previously glaciated region, which limits their ability to inform about the dynamics of paleo-ice sheets. Here, we evaluate new and previously published chronology data from the Missinaibi Formation, a Pleistocene-aged deposit in the Hudson Bay Lowlands (HBL), Canada, located near the geographic center of the Laurentide Ice Sheet (LIS). Available radiocarbon (AMS = 44, conventional = 36), amino acid (n = 13), uranium-thorium (U-Th, n = 14), thermoluminescence (TL, n = 15) and optically stimulated luminescence (OSL, n = 5) data suggest that an ice-free HBL may have been possible during parts of Marine Isotope Stage 7 (MIS 7; ca. 243,000 to ca. 190,000 yr BP), MIS 5 (ca. 130,000 to ca. 71,000 yr BP) and MIS 3 (ca. 29,000 to ca. 57,000). While MIS 7 and MIS 5 are well-documented interglacial periods, the development of peat, forest bed and fluvial deposits dating to MIS 3 (n = 20 radiocarbon dates; 4 TL dates, 3 OSL dates), suggests that the LIS retreated and remained beyond, or somewhere within, the boundaries of the HBL during this interstadial. Ice sheet models approximate the margin of the LIS to Southern Ontario during this time, which is 700 km south of the HBL. Therefore, if correct, our data help constrain a significantly different configuration and dynamicity for the LIS than previously modelled. We can find no chronological basis to discount the MIS 3 age assignments. However, since most data originate from radiocarbon dates lying close to the reliable limit of this geochronometer, future work on dating the Missinaibi Formation using other geochronological methods (e.g. U-Th, OSL) is necessary in order to confirm the age estimates and strengthen the boundaries of the LIS during this period. [ABSTRACT FROM AUTHOR]

We describe glacial-geological observations and cosmogenic-nuclide exposure ages from the Schmidt, Williams, and Thomas Hills in the Pensacola Mountains of Antarctica adjacent to the Foundation Ice Stream (FIS). Our aim is to learn about changes in the thickness and grounding line position o f the Antarctic Ice Sheet in the Weddell Sea embayment between the Last Glacial Maximum (LGM) and the present. Glacial-geological observations from all three regions indicate that currendyice- free areas were covered by ice during one or more past ice sheet expansions, and that this ice was typically frozen to its bed and thus non-erosive, permitting the accumulation of multiple generations of glacial drift. Cosmogenic-nuclide exposureage data from glacially transported erratics are consistent with this interpretation in that we observe both (i) samples with Holocene exposure ages that display a systematic age-elevation relationship recording LGM-to-present deglaciation, and (ii) samples with older and highly scattered apparent exposure ages that were deposited in previous glacial-interglacial cycles and have experienced multiple periods of surface exposure and ice cover. Holocene exposure ages at the Thomas and Williams Hills, upstream o f the present grounding line o f the FIS, show that the FIS was at least 500 m thicker prior to 11 ka, and that 500 m of thinning took place between 11 and 4 ka. However, exposure-age data from the Schmidt Hills, downstream of the present grounding line of the FIS, show no evidence for LGM thickening of the FIS and, in fact, provide some evidence that the FIS could have been no more than 200 m thicker than present at the LGM. If all these observations are correct, they imply that the LGM and early Holocene ice surface slope in the vicinity of the present grounding line was steeper than present, which is inconsistent with glaciological model predictions o f possible LGM ice sheet configurations. Specifically, scenarios in which the LGM grounding line of the FIS advanced to the outer continental shelf appear inconsistent with exposureage data from the Schmidt Hills, whereas scenarios in which the FIS grounding line did not advance at the LGM appear inconsistent with exposure-age data from the Williams and Thomas Hills. [ABSTRACT FROM AUTHOR]

An extensive tract of glacially-streamlined terrain across a large part of Southern Ontario, Canada, is recognized as the footprint of the paleo-Ontario Ice Stream (OIS) within the easternmost Great Lakes sector of the last Laurentide Ice Sheet. The upstream part is a drumlinized and megagrooved ‘hard bed’ underlain by Cambro-Ordovician carbonates and sandstones. Subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base, recorded by sporadic spreads of hummocky rubble moraine. Downstream, the hard bed passes underneath a streamlined ‘soft’ bed of till-cored (‘drift’) drumlins and megaridges of the classic Peterborough and New York State drumlin fields. The boundary between the two bed types is a ~ 10 km wide ‘mixed bed’ of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin. Spatial variation in the geomorphology of ~ 2500 drift drumlins, indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins. A large moraine system may mark the final collapse and melt of the ice stream, accompanying abrupt flow switching of its margin. [ABSTRACT FROM AUTHOR]

The erodent layer hypothesis (ELH) proposes that drumlinization leaves no substantial stratigraphic record because it is primarily an erosional process that cuts an unconformity across pre-existing bed materials. Drumlins most commonly have autochthonous cores of antecedent till(s), other stiff and coarse-grained sediment and rock or any combination thereof, and are also found closely juxtaposed with rock drumlins within the same flow sets (‘mixed beds’). This is at odds with the suggested growth of drumlins by vertical accretion (‘emergence’) from deforming subglacial till (‘soft beds’). ELH argues that drumlins ‘grow down’ by erosional carving of pre-existing stiff till, sediment and/or rock by a thin (< 1 m) layer of deforming subglacial debris which abrades its substrate. This process is well known to the science of tribology (the study of wearing surfaces) where remnant micro-drumlins, ridges and grooves comparable to drumlins and megaridges are cut by debris (‘erodent layers’) between surfaces in relative motion. In the subglacial setting the erodent layer comprises deforming diamict containing harder ‘erodents’ such as boulders, clast-rich zones or frozen rafts. Similar, till-like erodent layers (cataclasites) cut streamlined surfaces below gravity-driven mass flows such as rock avalanches, landslides and slumps, pyroclastic flows and debris flows; streamlined surfaces including drumlin-like ‘ellipsoidal bumps’ and ridges are also common on the surfaces of faults. Megadrumlins, drumlins and megaridges comprise an erosional continuum in many flow sets. This records the progressive dissection of large streamlined bedforms to form successively more elongate daughter drumlins and megaridges (‘clones’) as the bed is lowered to create a low-slip surface that allows fast ice flow and ice streaming. Clones are the ‘missing links’ in the continuum. ELH predicts preservation within drumlins of antecedent remnant tills and stratigraphies deposited earlier in the glacial cycle under sluggish or steady-state ice flows that were then streamlined by erosion under streaming ice flows. The erodent layer may be preserved as a relatively thin, loosely-consolidated surficial till that drapes the streamlined bedform (the ‘upper till’, ‘cap till’, ‘till veneer’, ‘till mantle’, ‘retreat till’, or ‘englacial debris’ of many previous reports). ELH suggests that there is a fundamental commonality of all forms of erosional wear and streamlining on sliding interfaces from the microscopic scale to the macroscopic scale of ice sheet beds. [ABSTRACT FROM AUTHOR]

Distinct Younger Dryas (YD) moraines are mapped more-or-less continuously around the Scandinavian Ice Sheet. In most areas there is no evidence to suggest that a glacial re-advance took place during the YD, either because it did not happen or because older deposits have been removed by glacial erosion. In contrast we here present 90 radiocarbon dates from 36 different sites that were overrun by a major ice sheet advance in the area between Hardangerfjorden and Sognefjorden, SW Norway. Thus this region is exceptional for examining the glacial response to the climate shifts across Allerød-YD. The re-growth of the ice sheet in this sector commenced during the Allerød Interstadial. It expanded along 600–800 m deep fjords reaching a thickness of up to 2000 m. We produce time–distance diagrams for two lobes; for both the outermost coast became ice free close to 15 cal ka BP, i.e. at the onset of the Bølling. The Hardangerfjorden Lobe re-advanced during the Older Dryas (14 cal ka BP), an event that was not replicated for the Herdla Lobe farther north. Both lobes reached their most landward position before re-advancing at 13.5–13.0 cal ka and obtained their maximum extent at the very end of the YD, 11.5 cal ka. The late culmination of the advance is accurately dated and differs from most of the Scandinavian Ice Sheet margin where the maximum was reached during early or middle YD. We also present a time–distance diagram from the Last Glacial Maximum to the ice divide showing two-step retreat; fast retreat occurs 21–20 and 11.5–10 cal ka BP separated by a period of almost no net retreat 20–11.5 cal ka BP, which contrasts with much more even retreat in other parts of the Scandinavian Ice Sheet. [ABSTRACT FROM AUTHOR]

The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a portion of Baffin Island, eastern Canadian Arctic, between 68° and 72°N and 66° and 80°W. This tilted shield block was covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined with GIS analyses using two geomorphic parameters: lake density and terrain ruggedness. The resulting patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages, and the distribution of the chemical index of alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west-east-oriented band at around 350-400 m a.s.l., and in fjord-onset zones in the uplifted eastern region. Above the 350-400 m a.s.l. band and between the fjord-onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception - where lake density and terrain ruggedness indicate that ice-sheet erosion had a scouring effect all across the study area - was in an area from Foxe Basin to Home Bay with elevations <400 m a.s.l. These morphological contrasts link to former ice-sheet basal thermal regimes during the Pleistocene. The zone of low glacial erosion surrounding the cold-based Barnes Ice Cap probably represents the ice cap's greater extent during successive Pleistocene cold stages. Inter-fjord plateaus with few ice-sheet bedforms remained cold-based throughout multiple Pleistocene glaciations. In contrast, zones of high lake density and high terrain ruggedness are a result of the repeated development of fast-flowing, erosive ice in warm-based zones beneath the Laurentide Ice Sheet. These zones are linked to greater ice thickness over western lowland Baffin Island. However, adjacent lowland surfaces with similar elevations of non-eroded, weakly eroded, and ice-scoured shield bedrock indicate that-even in areas of high lake density and terrain ruggedness-the total depth of ice sheet erosion did not exceed 50 m. [ABSTRACT FROM AUTHOR]

The nature of the regolith that existed on the shields of the Northern Hemisphere at the onset of ice sheet glaciation is poorly constrained. In this paper, we provide the first detailed account of an exceptionally preserved, deeply weathered late Neogene landscape in the ice sheet divide zone in northern Finland. We mine data sets of drilling and pitting records gathered by the Geological Survey of Finland to reconstruct regional preglacial deep weathering patterns within a GIS framework. Using a large geochemical data set, we give standardised descriptions of saprolite geochemistry using a variant of the Weathering Index of Parker (WIP) as a proxy to assess the intensity of weathering. We also focus on mineral prospects and mines with dense pit and borehole data coverage in order to identify links between geology, topography, and weathering. Geology is closely linked to topography on the preglacial shield landscape of northern Finland and both factors influence weathering patterns. Upstanding, resistant granulite, granite, gabbro, metabasalt, and quartzite rocks were associated with fresh rock outcrops, including tors, or with thin (< 5 m) grusses. Plains developed across less resistant biotite gneisses, greenstones, and belts of alternating rock types were mainly weathered to thick (10–20 m) grusses with WIP fines values above 3000 and 4000. Beneath valley floors developed along mineralised shear and fracture zones, weathering penetrated locally to depths of > 50 m and included intensely weathered kaolinitic clays with WIP fines values below 1000. Late Neogene weathering profiles were varied in character. Tripartite clay–gruss–saprock profiles occur only in limited areas. Bipartite gruss–saprock profiles were widespread, with saprock thicknesses of > 10 m. Weathering profiles included two discontinuities in texture, materials and resistance to erosion, between saprolite and saprock and between saprock and rock. Limited core recovery when drilling below the soil base in mixed rocks of the Tana Belt indicates that weathering locally penetrated deep below upper fresh rock layers. Such deep-seated weathered bands in rock represent a third set of discontinuities. Incipient weathering and supergene mineralisation also extended to depths of > 100 m in mineralised fracture zones. The thin weathering crusts found extensively beneath till may represent types of early or middle Pleistocene palaeosols. We confirm that glacial erosion has been very limited (< 20 m) in northern Finland and has been widely restricted to the partial stripping of saprolith. The Fennoscandian Ice Sheet in this ice-divide zone remained cold-based and unerosive throughout the Pleistocene. The large-scale shield geomorphology developed before glaciation and is a product of differential weathering and erosion acting on diverse rock types and structures through the Neogene. The first ice sheets did not advance across planar, uniformly soft, deeply kaolinised beds as proposed in recent models of the Laurentide ice sheet. Instead, in northern Finland, the shield topography comprised broad plains and valleys with isolated hills and hill masses, with a relative relief of several hundred metres. Weathered rock was restricted in its distribution and thickness and provided diverse bed materials for ice sheets, including rock, broken saprock, permeable gruss, and linear zones of impermeable clay, with multiple discontinuities. Glacial erosion and local glacial transport led to widespread incorporation of this saprolith material into tills. [ABSTRACT FROM AUTHOR]

Glacial erosion is fundamental to our understanding of the role of Cenozoic-era climate change in the development of topography worldwide, yet the factors that control the rate of erosion by ice remain poorly understood. In many tectonically active mountain ranges, glaciers have been inferred to be highly erosive, and conditions of glaciation are used to explain both the marked relief typical of alpine settings and the limit on mountain heights above the snowline, that is, the glacial buzzsaw. In other high-latitude regions, glacial erosion is presumed to be minimal, where a mantle of cold ice effectively protects landscapes from erosion. Glacial erosion rates are expected to increase with decreasing latitude, owing to the climatic control on basal temperature and the production of meltwater, which promotes glacial sliding, erosion and sediment transfer. This relationship between climate, glacier dynamics and erosion rate is the focus of recent numerical modelling, yet it is qualitative and lacks an empirical database. Here we present a comprehensive data set that permits explicit examination of the factors controlling glacier erosion across climatic regimes. We report contemporary ice fluxes, sliding speeds and erosion rates inferred from sediment yields from 15 outlet glaciers spanning 19 degrees of latitude from Patagonia to the Antarctic Peninsula. Although this broad region has a relatively uniform tectonic and geologic history, the thermal regimes of its glaciers range from temperate to polar. We find that basin-averaged erosion rates vary by three orders of magnitude over this latitudinal transect. Our findings imply that climate and the glacier thermal regime control erosion rates more than do extent of ice cover, ice flux or sliding speeds. [ABSTRACT FROM AUTHOR]

Longitudinal ice-surface structures in the Antarctic Ice Sheet can be traced continuously down-ice for distances of up to 1200 km. A map of the distribution of ~3600 of these features, compiled from satellite images, shows that they mirror the location of fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of metres per annum and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. They can be traced continuously through crevasse fields and through blue-ice areas, indicating that they represent the surface manifestation of a three-dimensional structure, interpreted as foliation. Flow lines are linear and undeformed for all major flow units described here in the Antarctic Ice Sheet except for the Kamb Ice Stream and the Institute and Möller Ice Stream areas, where areas of flow perturbation are evident. Parcels of ice along individual flow paths on the Lambert Glacier, Recovery Glacier, Byrd Glacier and Pine Island Glacier may reside in the glacier system for ~2500 to 18 500 years. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow configuration of the ice sheet may have remained largely unchanged for the last few hundred years, and possibly even longer. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition. [ABSTRACT FROM AUTHOR]