Mega-scale Glacial Lineations Research Articles

Iceberg ploughmarks and glacial lineations on Jan Mayen Ridge: Evidence for past iceberg and possible ice-shelf grounding in deep water

Jan Mayen Ridge, south of the isolated island of Jan Mayen (71°N 8°W), is located strategically near the centre of the Polar North Atlantic and surrounded by deep-water seas. Examination of about 4,100 km2 of multibeam bathymetric data allowed identification of 1700 chaotic seafloor depressions at 300–1000 m modern water depth and two sets of lineations at 400–600 m and 750–900 m deep. The chaotic depressions are interpreted as ploughmarks produced as iceberg keels impinged on a sedimentary seafloor. The deepest ploughmarks reach 1010 m depth. Multi-keel ploughmarks indicate the presence of tabular icebergs of minimum widths 0.5–2.3 km. Ploughmark orientations were W/E and SW/NE on the northern and southern ridge, respectively, suggesting that deep-keeled icebergs drifting across Jan Mayen Ridge were probably calved mainly from short floating tongues at the margins of full-glacial Greenland ice streams. The mapped seafloor lineations are morphologically similar to mega-scale glacial lineations and flutes formed by soft-sediment deformation beneath active ice. They are interpreted to indicate the possible grounding of glacier ice on Jan Mayen Ridge. Their W-E orientation precludes ice flow from a full-glacial Jan Mayen ice cap. A possible interpretation is that they may represent grounding of a large floating ice shelf probably fed by ice from the Greenland Ice Sheet during one of the very large pre-Weichselian glaciations of the Quaternary. Whereas these lineations at 70°N do not provide direct evidence for a huge ice-shelf complex flowing southwards from the Arctic Ocean, the general climatic conditions required to form and maintain large ice shelves suggest that the development of an Arctic Ocean ice shelf at some point during Quaternary full-glacials remains a possibility.

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

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

Laurentide Ice Sheet configuration in southern Ontario, Canada during the last glaciation (MIS 4 to 2) from stratigraphic drilling and LIDAR-based surficial mapping

Regional subsurface mapping of glacial depositional systems preserved in buried bedrock paleovalleys, and quantitative analysis of new LiDAR imagery of surface glacial landforms using machine learning techniques, when combined, are powerful tools for assessing the dynamics of the Laurentide Ice Sheet (LIS) during the last (Wisconsinan) glaciation in southern Ontario. While age dating of deposits preserved below Last Glacial Maximum tills (LGM: MIS 2 < c.24,000 years before present; ybp) is still sparse, newly available sedimentological data derived by cored drilling, combined with legacy outcrop data, identifies thick (100 m +) successions of glaciolacustrine sediments and a lack of till(s) indicating that the ice sheet margin did not extend beyond the Niagara Escarpment at the western end of Lake Ontario, during the earliest phases of the glaciation (MIS 4) or the ensuing mid-Wisconsinan (MIS 3). Ice was able to extend into New York State blocking the Rome outlet to the Hudson Valley ponding deep proglacial lakes in the glacio-isostatically depressed Huron-Ontario-Erie basins recorded by thick glaciolacustrine sediments in paleovalleys. These were cannibalized by an expanding Late Wisconsinan ice sheet after ~ 24,000 ybp recorded by extensive till sheets resting on a marked erosional unconformity, with drumlinized surfaces. Analysis and visualization of LiDAR data identifies discrete statistically validated flow sets of highly elongated streamlined bedforms (mega-scale glacial lineations; MSGLs). These provide key evidence of a major reorganization of the ice sheet margin during deglaciation into lobate paleo ice streams shortly after 17,400 ybp.

Chad's cabinet of icy curiosities: Sharpening the interpretation of subglacial and ice marginal environments during the LPIA glaciation of the Ennedi Plateau

The Ennedi Plateau in Chad in north-central Africa exposes an outstanding example of a palaeo-ice stream glacial landsystem of late Palaeozoic age, with an assemblage of geomorphological structures of comparable preservation quality to those found in Quaternary deglaciated landscapes. Satellite images and various methods to combine acquired satellite data (e.g. band-ratio technique) have been used to interpret proglacial, ice-marginal and subglacial structures. The main goal of the study is to produce a detailed and more in-depth analysis of newly found structures that enhance our understanding of ice sheet behaviour in the Ennedi Plateau during the LPIA.We report the first known evidence of soft-sediment striated surfaces from outcrop, testifying to the existence of a soft-deformable bed. This deformable bed interpretation can probably be upscaled to explain the extensive swarms of mega-scale glacial lineations mapped previously across the plateau. Furthermore, we identify the first known fully preserved grounding zone wedge (GZW), replete with three-dimensional geometry, in the rock record. This unique structure exhibits a well pronounced slope and a convex topography. Its presence allows the position of the former coastline to be reconstructed as it is assumed that ice streams terminated into a former ocean basin. Building on the studies by Le Heron (2018) and Kettler et al. (this issue), our analyses permit unprecedented insights into the behaviour of a significant, mid-latitude, marine-terminating ice sheet during the LPIA.

A world-class example of a Late Palaeozoic glaciated landscape in Chad

Continental glacial deposits are rarely preserved in nature. Recent studies of the LPIA reveal the presence of periglacial deposits in Northern Chad covering an area of 20,000 km2. Using satellite maps, this project managed to examine the entirety of the Ennedi Plateau. 3D reconstructions of this mountain range reveal complex glacial morphological features. This paper presents large-scale subglacial features interbedded with proglacial fluvial features and discussed the variables at play during the progressive, repetitive, and perhaps cyclical nature of the Carboniferous glaciation. Using remote sensing techniques, this paper shows that there are three major ice advance–retreat cycles that led to the deposition of mega-scale glacial lineations with a complex fluvial channel belt. Palaeo-geomorphological mapping of satellite images in northern Chad reveals that the Late Carboniferous Chadian ice sheet covered at least 20,000 km2, a much greater extent than previously thought (ca. 6000 km2). Glacial lineations (GLs) are dominant and extensive on the plateau. They are arranged in widespread ice stream networks and developed at multiple stratigraphic levels. This broadly indicates palaeo-ice flow to the north. We report a newly discovered pristine channel belt, covering at least 300 km2 of a plateau in the Ennedi Plateau. A swarm of N–S trending channels, up to 250 m wide, is recognised. These are of both braided and meandering characters and are organised into channel belts of up to 500 m width. The mapped palaeo-morphology shows complex crosscutting relationships. The channel belt is intercalated with zones of GLs; hence, ice activity preceded and succeeded fluvial activity. Preserved planform sinuous channel geometries show distinctive point bar deposits and scroll bar geometries therein, which testify to a terrestrial, subaerial environment, rather than to their evolution in the subglacial realm, e.g. as eskers. Therefore, we find that cross-cutting, amalgamated channel systems record the complex phases of meltwater release during glacial retreat in the advance–retreat cycles of the Late Palaeozoic Ice Age in Chad.

Reconstructing terrestrial ice sheet retreat dynamics from hummocky topography using multiscale evidence: An example from central Ireland

The research reported here combines high-resolution digital elevation models (DEMs) derived from airborne LiDAR with ground-penetrating radar (GPR) surveys and macro- and micro-scale sedimentological analyses to study the geomorphology and internal structure and composition of ridges and mounds within an area of hummocky topography in the Brosna basin, central Ireland. Our evidence indicates that much of the hummocky topography consists of fragmented mega-scale glacial lineations (MSGLs) indicating a phase of accelerated ice flow, overlain by groups of small ridges composed of subglacially derived till and sediment gravity flow deposits. Subtle differences in ridge morphology indicate they may be multi-genetic and formed both ice-marginally as moraines and subglacially as small ribbed moraine. We interpret MSGL-ridge associations as a subglacial bedform continuum reflecting the evolution from a deforming bed to brittle deformation, due to changing thermal and hydrological conditions at the ice-bed interface during ice sheet retreat. Adjacent glaciofluvial landforms indicate initial en- and supra-glacial meltwater drainage, possibly directly related to changing basal thermal/hydrological characteristics and subglacial ridge formation. Subsequently a subglacial conduit system evolved, and later retreat involved formation of ice-marginal ridges. The partially preserved landsystem reflects formation at a polythermal to active temperate ice marginal zone, rather than the stagnating temperate margin previously assumed for this area. Our work demonstrates the usefulness of hummocky topography in identifying changes in ice sheet bed thermal/hydrological characteristics during deglaciation and the importance of combining multiple evidence strands in reconstructing the processes involved in glacial landform construction.

Characteristics and formation of bedrock mega-grooves (BMGs) in glaciated terrain: 1 - morphometric analyses

Bedrock mega-grooves (BMGs) are subglacial landforms of erosion that occur in glaciated terrain in various geological and (palaeo)glaciological settings. Despite a significant literature on BMGs, no systematic morphometric analysis of these landforms has been undertaken. This is a necessary step towards exploring BMG formation and has been successfully applied to other subglacial landforms of similar magnitude (e.g. mega-scale glacial lineations (MSGLs) and drumlins). In this study, BMGs from ten locations across the world are systematically mapped, sampled and measured. Based on the 10th–90th percentile of the aggregated global population (n = 1242), BMGs have lengths of 224–2269 m, widths of 21–210 m, depths of 5–15 m, elongation ratios of 5:1–41:1, and the spacing between adjacent grooves is 35–315 m. Frequency distributions for all metrics are unimodal, strongly suggesting that the sampled BMGs form a single landform population. This establishes the BMG as a geomorphic entity, distinctive from other subglacial landforms. The variability of the metrics and their correlations between and within sites most likely reflect site-specific geological characteristics. At sites which have been associated with fast-ice flow, BMGs display the largest dimensions (especially in terms of length, depth and width) but lowest elongation ratios, whereas BMGs formed under a primary geological control occupy smaller size ranges and have higher elongation ratios. Morphometrically, BMGs and MSGLs plot as different populations, with BMGs being on average 4 × shorter, 3.5 × narrower, 3.5 × more closely spaced and about 2 × deeper. It is suggested that future research focuses on numerical modelling experiments to test rates of erosion in different bedrock lithologies under varying glaciological conditions, and on adding to the body of existing field-derived empirical observations. The latter remains key to validating geological controls over BMG formation and assessing the efficiency of erosion mechanisms.

Numerical modelling of subglacial ribs, drumlins, herringbones, and mega‐scale glacial lineations reveals their developmental trajectories and transitions

AbstractInitially a matter of intellectual curiosity, but now important for understanding ice‐sheet dynamics, the formation of subglacial bedforms has been a subject of scientific enquiry for over a century. Here, we use a numerical model of the coupled flow of ice, water, and subglacial sediment to explore the formation of subglacial ribs (i.e., ribbed moraine), drumlins and mega‐scale glacial lineations (MSGLs). The model produces instabilities at the ice–bed interface, which result in landforms resembling subglacial ribs and drumlins. We find that a behavioural trajectory is present. Initially subglacial ribs form, which can either develop into fields of organized drumlins, or herringbone‐type structures misaligned with ice flow. We present potential examples of these misaligned bedforms in deglaciated landscapes, the presence of which means caution should be taken when interpreting cross‐cutting bedforms to reconstruct ice flow directions. Under unvarying ice flow parameters, MSGLs failed to appear in our experiments. However, drumlin fields can elongate into MSGLs in our model if low ice–bed coupling conditions are imposed. The conditions under which drumlins elongate into MSGLs are analogous to those found beneath contemporary ice streams, providing the first mechanism, rather than just an association, for linking MSGLs with ice stream flow. We conclude that the instability theory, as realized in this numerical model, is sufficient to explain the fundamental mechanics and process‐interactions that lead to the initiation of subglacial bedforms, the development of the distinctive types of bedform patterns, and their evolutionary trajectories. We therefore suggest that the first part of the longstanding ‘drumlin problem’ – how and why they come into existence – is now solved. However, much remains to be discovered regarding the exact sedimentary and hydrological processes involved.

Stratigraphic and palaeo-geomorphological evidence for the glacial-deglacial history of the last British-Irish Ice Sheet in the north-western Irish Sea

During its maximum extent around 25–23 ka BP, the British-Irish Ice Sheet extended to near the present-day shelf break with a large ice stream, the Irish Sea Ice Stream, occupied much of the present-day Celtic and Irish Seas. The different episodes of advance and retreat of the ice sheet have been extensively constrained onshore, with models based on feature characterisation and dating helping to understand the retreat pattern of the ice sheet. Offshore, glacial geomorphologies in the Irish Sea have been mostly recognised on the United Kingdom side but remains poorly constrained on the Irish side. In this paper, based on the analysis of an extensive seismic dataset, an update of the stratigraphic model of the northern Irish Sea, with new sub-units, is proposed with a mapping of newly discovered buried geomorphology. Characterisation of the geomorphology, including megascale glacial lineations, subglacial meltwater channels, moraines, and iceberg scours, has been used to extend the constraints on ice sheet retreat offshore. The transition from late glacial to marine setting has been constrained based on the mapping of marine sediment subunits and their terminations. This paper brings new constraints offshore, in a previously understudied area, and synthesises all the results into an updated conceptual model highlighting stratigraphic units succession and associated processes linked to geomorphology, within the context of a rapidly retreating ice stream.

LiDAR‐based semi‐automated mapping of drumlins and mega‐scale glacial lineations of the Green Bay Lobe, Wisconsin, USA: Ice sheet beds as glaciotribological systems

AbstractA machine learning methodology for processing and visualizing high‐resolution LiDAR digital data is used to map drumlins and mega‐scale glacial lineations (MSGLs) on the bed of the Late Wisconsin Green Bay Lobe in Wisconsin, USA, which exhibited surge‐like behaviour during deglaciation. Previous work has shown that streamlined bedforms are the product of erosional streamlining of pre‐existing sediment. Analysis of bedform height and elongation ratio using curvature‐based relief separation (CBRS) andK‐means clustering of 32,003 bedforms reveals a continuum of six morphotypes ranging from drumlins, through “channeled” more elongated multi‐crested drumlins, to MSGLs. Further statistical analysis shows that morphotypes cluster into six types of streamlined surfaces (S1–S6) recording progressive elimination of an antecedent overridden topography to produce a smoother bed. Initial, relatively high‐relief drumlinized surfaces (S1, S2) occur around the slower‐flowing lateral flanks of the lobe, where a pre‐existing hummocky morainal topography was only partially modified by subglacial erosion. More streamlined surfaces (S3, S4) dominated by multi‐crested more elongate drumlins of reduced relief amplitude are transitional to flow sets of MSGL‐dominated surfaces (S5, S6) indicative of much faster‐flowing ice streaming along the lobe's axis. Estimates of basal drag based on roughness calculations for each surface type identify a 61% reduction in frictional retardation from poorly streamlined surfaces S1 and S2 to MSGL‐dominated surfaces S5 and S6, with a step‐like reduction between drumlins and channeled drumlins (S3, S4) possibly recording the rapid onset of fast flow. Subglacial streamlining is argued to be accomplished by a thin (<1 m) “third layer” of deforming subglacial debris between ice and its bed which functioned as an erodent layer. A thin (<3 m) till cap, formed by aggradation of deforming debris, rests unconformably on heterogeneous core sediments. Streamlined subglacial surfaces are comparable to the “functional” surfaces resulting from erosion by a “third layer” of wear debris in engineering tribological systems, and also by gouge on faults. Pleistocene ice sheets expanded over pre‐existing landsystems, pointing to the broader relevance of the methodology and findings reported here.

Drumlins and mega-scale glacial lineations as a continuum of subglacial shear marks: A LiDAR based morphometric study of streamlined surfaces on the bed of a Canadian paleo-ice stream

We employ and further develop quantitative analytical techniques used to map roughness on fault planes, to map and classify drumlins and mega-scale glacial lineations (MSGLs) on the bed of a terrestrially-terminating Late Wisconsin paleo ice stream lobe exposed near Peterborough in Southern Ontario, Canada. Geological data show these bedforms are erosional remnants of older sediments, principally coarse-grained proximal outwash, capped by a thin (<2 m) upper till. Our earlier work ascribed the formation of drumlins and MSGLs to differential erosion of antecedent sediment by a thin layer of deforming subglacial debris (the Erodent Layer Hypothesis) which we now test using new geostatistical and unsupervised machine learning techniques applied to large LiDAR-derived digital topographic datasets. Analysis of more than 1739 streamlined bedforms mapped by Curvature-Based Relief Separation, reveals a statistically-validated continuum of eight morphotypes (M1 to M8) ranging from drumlins to grooved multi-crested drumlins to MSGLs. Furthermore, cluster analysis of the entire morphotype population, reveals three statistically-validated groups that define three streamlined surface types (S1 to S3) which record progressive erosional lowering of the ice stream bed, as drumlins evolve into multi-crested morphotypes, and ultimately MSGLs. Calculation of surface roughness using a technique called Median Absolute Differences (MAD) shows the frictional drag of mega-scale glacially lineated surfaces (S3) is 60% less than drumlinized surfaces (S1). Our findings support earlier ideas that drumlins and MSGLs are ‘longitudinal shear marks’ akin to those cut by extended frictional wear on fault planes, to which can now also be added analogous streamlined surfaces cut by wear debris mobilized at the base of landslides, ejecta blankets and pyroclastic flows, and on engineered man-made surfaces.

Geomorphology and shallow sub-sea-floor structures underneath the Ekström Ice Shelf, Antarctica

Abstract. The Ekström Ice Shelf is one of numerous small ice shelves that fringe the coastline of western Dronning Maud Land, East Antarctica. Reconstructions of past ice-sheet extent in this area are poorly constrained, due to a lack of geomorphological evidence. Here, we present a compilation of geophysical surveys in front of and beneath the Ekström Ice Shelf, to identify and interpret evidence of past ice-sheet flow, extent and retreat. The sea floor beneath the Ekström Ice Shelf is dominated by an incised trough, which extends from the modern-day grounding line onto the continental shelf. Our surveys show that mega-scale glacial lineations cover most of the mouth of this trough, terminating 11 km away from the continental shelf break, indicating the most recent minimal extent of grounded ice in this region. Beneath the front ∼30 km of the ice shelf measured from the ice shelf edge towards the inland direction, the sea floor is characterised by an acoustically transparent sedimentary unit, up to 45 m thick. This is likely composed of subglacial till, further corroborating the presence of past grounded ice cover. Further inland, the sea floor becomes rougher, interpreted as a transition from subglacial tills to a crystalline bedrock, corresponding to the outcrop of the volcanic Explora Wedge at the sea floor. Ice retreat in this region appears to have happened rapidly in the centre of the incised trough, evidenced by a lack of overprinting of the lineations at the trough mouth. At the margins of the trough uniformly spaced recessional moraines suggest ice retreated more gradually. We estimate the palaeo-ice thickness at the calving front around the Last Glacial Maximum to have been at least 305 to 320 m, based on the depth of iceberg ploughmarks within the trough and sea level reconstructions. Given the similarity of the numerous small ice shelves along the Dronning Maud Land coast, these findings are likely representative for other ice shelves in this region and provide essential boundary conditions for palaeo ice-sheet models in this severely understudied region.

Radar Derived Subglacial Properties and Landforms Beneath Rutford Ice Stream, West Antarctica

AbstractBasal properties beneath ice streams and glaciers are known to be a control for ice flow dynamics, hence knowledge of them is crucial for predicting sea level due to changes in glacial dynamics. Basal properties, processes and topography also drive the formation of subglacial landforms. Bed properties beneath Rutford Ice Stream (West Antarctica) have previously been described using seismic acoustic impedance measurements at a sparse spatial coverage. Here, we derive bed properties in a 15 × 17 km grid of surface radar data with coverage and sampling much higher than previous seismic studies. Bed reflection amplitudes in surface radar data were calibrated using sediment porosities (ranging from 0.4–0.5) derived from seismic acoustic impedance. We find the bed properties are spatially variable, consisting of low porosity material in some areas and soft sediment in other areas. Comparison of seismic and surface radar data imply the low porosity material to be a consolidated sediment or sedimentary rock. Mega‐scale glacial lineations (MSGLs) are ubiquitous on the bed and consist of soft, high porosity, probably deforming sediment, consistent with previous interpretations of MSGLs. We find some MSGLs have high reflectivity on their crest, interpreted as water bodies overlying high porosity sediment, whereas the trough around and the upstream end of some landforms consist of low porosity material. Integrating these different observations, we place constraints on possible explanations for the occurrence of water on the crest of landforms.

GIS dataset: geomorphological record of terrestrial-terminating ice streams, southern sector of the Baltic Ice Stream Complex, last Scandinavian Ice Sheet, Poland

Abstract. Here we present a comprehensive dataset of glacial geomorphological features covering an area of 65 000 km2 in central west Poland, located along the southern sector of the last Scandinavian Ice Sheet, within the limits of the Baltic Ice Stream Complex. The GIS dataset is based on mapping from a 0.4 m high-resolution digital elevation model derived from airborne light detection and ranging data. Ten landform types have been mapped: mega-scale glacial lineations, drumlins, marginal features (moraine chains, abrupt margins, edges of ice-contact fans), ribbed moraines, tunnel valleys, eskers, geometrical ridge networks, and hill–hole pairs. The map comprises 5461 individual landforms or landform parts, which are available as vector layers in GeoPackage format at https://doi.org/10.5281/zenodo.4570570 (Szuman et al., 2021a). These features constitute a valuable data source for reconstructing and modelling the last Scandinavian Ice Sheet extent and dynamics from the Middle Weichselian Scandinavian Ice Sheet advance, 50–30 ka, through the Last Glacial Maximum, 25–21 ka, and Young Baltic advances, 18–15 ka. The presented data are particularly useful for modellers, geomorphologists, and glaciologists.

LiDAR-based quantitative assessment of drumlin to mega-scale glacial lineation continuums and flow of the paleo Seneca-Cayuga paleo-ice stream

Shortly after 14,500 ybp during the deglaciation of the Laurentide Ice Sheet in eastern North America, the 80 km wide Seneca-Cayuga paleo ice stream occupied the overdeepened New York State Finger Lake basins. The topography of the former ice stream bed can be evaluated from high-resolution LiDAR DEM data, allowing mapping of almost four thousand subglacially streamlined bedforms such as drumlins and mega-scale glacial lineations using Curvature-based Relief Separation. Qualitative and quantitative techniques were then applied to the statistical analysis of bedform elongation ratio and orientation using Natural Neighbor Interpolation and unsupervised machine learning-based data clustering. Analysis reveals a geomorphic continuum of as many as seven morphotypes of streamlined bedforms from drumlins to mega-scale glacial lineations with intermediate ‘channeled drumlins’ possibly recording erosion of parent drumlins. Spatial analysis using orientation Grouping Analysis identifies several flow-parallel sets of bedforms reflecting the presence of multiple ice flow units in the ice stream up to 10 km wide that were topographically controlled by glacially-overdeepened basins of lakes Canandaigua, Seneca, and Cayuga (−151, −306, −242 below mean sea level respectively). Longitudinal variation in bedform elongation along as much as 60 km length of flow lines is provisionally interpreted as a proxy for ice flow velocities which ranged from steady state flow (drumlins), intermediate velocities (channeled drumlins) to fast flow (mega-scale glacial lineations). Evolution in bedforms occurred rapidly likely over a time frame of several hundred years. Quantitative data also identifies faster axial flow and slower flow along the margins of each ice flow unit. Fast flow was triggered at the grounding lines of flow units terminating in deep (as much as 600 m) proglacial lakes at the southern end of each overdeepened Finger Lake basin and propagated northwards along each flow unit at different rates reflecting the size and depth of frontal waterbodies. Petrographic data from tills derived from distinctive Paleozoic quartzites outcropping in a narrow west-east belt perpendicular to flow of each ice stream identifies extended longitudinal subglacial advection during fast flow consistent with very rapid bedform evolution.

Seismic geomorphology and evolution of the Melville Bugt trough mouth fan, northwest Greenland

Trough mouth fans on glaciated margins are a common sedimentary feature that contain a record of ice sheet advance and retreat across the continental shelf. This study uses 2D and 3D seismic reflection data across the Melville Bugt Trough Mouth Fan (MB-TMF), offshore northwest Greenland, to document its stratigraphic architecture, glacigenic landforms, and marine deposits. The MB-TMF stratigraphy is characterised by rapid progradation of the continental shelf (over 100 km since ∼2.7 Ma) and heterogeneous truncation or subsidence of topset strata. The variable topset character relates to the repeated growth and retreat of the Greenland Ice Sheet across the shelf since ∼2.7 Ma. Seismic geomorphology and facies analysis of the prograding clinoforms show repeated sequences of debris flow deposits and gullies that are taken to infer gravity-driven processes and the presence of meltwater-related hyperpycnal flows in areas proximal to the ice sheet on the outer shelf. Several sets of mega-scale glacial lineations confirm the presence and flow pathways of successive ice streams since ∼1.3 Ma. Evolution of the MB-TMF can be summarised into four stages that were controlled by variations in ice sheet erosion, topographic forcing of ice stream flow, and changes in accommodation related to glacigenic deposition and tectonic subsidence. These results show that during the Middle Pleistocene Transition there is an apparent switch from a meltwater-dominated depositional regime, to one with greater emplacement of materials by ice directly at the palaeo-shelf edge. These results provide significant new detail about the large-scale glacigenic and marine depositional processes during the repeated fluctuations of the northwest Greenland Ice Sheet into Melville Bugt since ∼2.7 Ma.

Landform evolution of Oudemans crater and its bounding plateau plains on Mars: Geomorphological constraints on the Tharsis ice-cap hypothesis

In this study we address the question of whether the Tharsis rise that occupies ~25 % of the surface area of Mars was once covered by an ice cap, and the sudden ice-cap melting was responsible for the catastrophic development of the Late Hesperian (3.5-3.6 Ga) circum-Tharsis giant (>1000s km in length) outflow channels. To achieve this goal, we conducted geomorphologic mapping across the Oudemans crater basin (~125 km in diameter) at elevations of ~2.7 km to ~5.0 km and its bounding plateau plains at elevations of ~5.3 km to ~6.7 km in the central Tharsis rise. Our work shows that the Oudemans-impact-induced landforms were superposed by a suite of younger landform assemblages, which consist of horn-like peaks, arête-like ridges, cirque-like depressions, hanging-valley-like features, trim-line-like escarpments, lobate ridges, striated, pitted and hummocky terrains, and features resembling drumlins, crag-and-tails and roches moutonnées. A plateau-plain striated terrain on a hummocky surface exhibits streamlined linear ridges that are 400-2000 m wide and up to ~17 km long. The average length-width ratio (~9), shape, surface texture, and associated washboard landform pattern of the linear morphological features in the striated terrain on Mars are comparable to mega-scale glacial lineations (MSGLs) on Earth. Using well-understood Earth analogues as a guide, we interpret the post-Oudemans-impact landform assemblages to have formed during regional ice-sheet-style glaciation. We further suggest the striated terrain on the plateau plains to have been generated by a fast-moving ice stream in a regional ice sheet that filled 4-km deep Oudemans crater and covered the crater-bounding plateau plains in the central Tharsis rise. The volume of the glacier ice stored in the Oudemans crater basin alone is estimated on the order of ~200,000 km3. The shape of the inferred glacier-induced landforms and their cross-cutting relationships require early northward-flowing northward-advancing glaciation, followed by southward-flowing northward-retreating glaciation. The size-frequency distribution of the craters superposed on top of the interpreted glaciated landforms in the mapped area yields a glaciation age of ca. 3.5 Ga, coeval with the estimated age of the interpreted glacial landforms along the 2000-km long Valles Marineris trough zone east of the study area. The inferred glaciation age is also coeval with the development of the circum-Tharsis outflow channels. Although our work supports the Tharsis ice-cap hypothesis, the full extent of the ice cap within and possibly beyond the Tharsis rise remains unconstrained.

Evidence of ice streaming and ice tongue shutdown in western Latvia: revealed from the mapping of crevasse-squeeze ridges

Glacial geomorphological mapping of western Latvia using a 1-m-resolution digital elevation model generated from airborne LiDAR data has revealed two sets of mega-scale glacial lineations (MSGLs), one of which is superimposed by crevasse-squeeze ridges (CSRs). CSRs occur as a dense ridge network with a dominant orientation of ridges perpendicular to the ice flow direction. The landform assemblage is interpreted as evidence for two separate phases of fast ice flow with different ice flow directions during the overall deglaciation of the Fennoscandian Ice Sheet (FIS). The first fast ice flow phase occurred from the northwest by the Usma Ice Lobe that extended in the Eastern Kursa Upland. The second fast ice flow occurred from the north by the Venta Ice Tongue in a narrow flow corridor limited mainly to the Kursa Lowland. Active ice streaming caused ice crevassing perpendicular to the ice flow direction and formation of CSRs by squeezing of subglacial till into basal crevasses. A good preservation of the CSRs and general lack of recessional moraines suggest widespread stagnation and ice mass melting after the shutdown of the Venta Ice Tongue followed by the formation of the Venta-Usma ice-dammed lake and glaciolacustrine deposition in the lowest areas of lowland. Our data provide the first evidence of CSRs in the south-eastern terrestrial sector of the FIS suggesting the dynamic ice streaming or surging behaviour of the ice lobes and tongues in this region during deglaciation.

New insights into the formation of submarine glacial landforms from high-resolution Autonomous Underwater Vehicle data

Autonomous Underwater Vehicles (AUVs) deployed close to the seafloor can acquire high-resolution geophysical data about the topography and shallow stratigraphy of the seabed, yet have had limited application within the fields of glacial geomorphology and ice sheet reconstruction. Here, we present multibeam echo-sounding, side-scan sonar, sub-bottom profiler and High-Resolution Synthetic Aperture Sonar (HISAS) data acquired during three AUV dives on the northeast Antarctic Peninsula continental shelf. These data enable glacial landforms, including mega-scale glacial lineations (MSGLs), grounding-zone wedges (GZWs) and iceberg ploughmarks, to be imaged at a horizontal resolution of a few tens of centimetres, allowing for the identification of subtle morphological features. We map tidal ridges that are interpreted as having been formed 1) along the ice-sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles, and 2) by the tidally driven motion of grounded or near-grounded icebergs. These data also enable the mapping of small GZWs that show the location of short-term still-stands or re-advances of the ice-sheet grounding zone. No meltwater channels are identified from our data, suggesting that free-flowing meltwater may not be essential for the formation of GZWs or MSGLs. The examples presented here show how high-resolution AUV-derived geophysical data provide a step-change in our ability to image seafloor glacial landforms, enabling new interpretations about past ice dynamics and glacial sedimentation at fine temporal and spatial scales.

Bed erosion during fast ice streaming regulated the retreat dynamics of the Irish Sea Ice Stream

Marine-terminating ice stream behaviour often defines the stability of ice sheets and is driven by a complex interplay of climatic, oceanic, topographic and glaciological factors. Here, we use new integrated high resolution, extensive (2100 km2) and continuous geophysical, sedimentological and geotechnical data to reconstruct past glacial environments during the Last Glacial Maximum from a well-preserved palaeo-landscape. The data is from the axial centre of the Irish Sea Ice Stream (ISIS), which drained > 17% of the former British-Irish Ice Sheet. Recent geochronological data of the palaeo-ISIS show a build-up and advance of ice to marine-terminating maximum limits in the southern Celtic Sea 27–25 ka BP, followed by rapid ice margin retreat into the northern Irish Sea Basin (ISB) by 20.8 ± 0.7 ka BP. However, the flow dynamics in the central and axial bed of the ISIS through this timeframe are not well understood. Here, we use our new glacial landscape reconstruction to identify the spatial and temporal patterns of flow re-organisation and re-activations for the marine-terminating ISIS. From this we infer how ice streaming was driven by a variety of factors through advance, deglaciation and towards a temporary lift-off of ice from its bed and an ultimate demise. Overprinted subglacial bedforms with differing ice flow directions indicate an on/off behaviour to the ice-streaming, an increasing topographical influence and substantial realignment of ice flows. Subsurface geophysical data reveal the erosive capability of the ice stream through time, with a first erosive component in the formation of mega-scale glacial lineations leaving bedrock exposed at the ice stream bed. The depositional component of MSGL crest building occurred in the same ice-flow phase. Whilst the ice stream was laterally constricted in two locations, likely contributing to changes in ice margin retreat rates, we also propose that changes in basal drag associated with exposed bedrock at the ice‒bed interface influenced the retreat dynamics, particularly when this exposure was near the grounding zone. The wider implications of this work are that episodic and highly erosive ice streaming during ice advance and early retreat can change ice‒bed conditions radically and in turn influence glacial dynamics during later retreat episode, thus constituting a feedback process to be considered in modelling the dynamics of marine-terminating ice streams.