Drumlin sedimentology in a hard-bed, lowland setting, Connemara, western Ireland: implications for subglacial bedform generation in areas of sparse till cover

Cores of coastal drumlins in Connemara contain stratified diamictons that interdigitate with gravelly clinoforms and finer grained rhythmites. The diamictons are interpreted as subaqueous mud apron deposits delivered by subglacial till advection to continuously failing subaqueous ice-contact fans, whose strata were being syn-depositionally over-steepened by glacitectonic deformation. The localized nature of the stratified sediments reflects the emergence of subglacial deforming tills and meltwater deposits in a glacilacustrine environment to produce interdigitated mass flow diamictons and grounding line fans/wedges. These depo-centres became glacitectonized and subglacially streamlined during glacier overriding and hence regional drumlin sedimentology reflects the varying degrees of inheritance of pre-existing glacigenic deposits and suggests that drumlin production relates more to the position of localized sediment accumulations at the glacier bed than full-depth till deformation processes (e.g. instability mechanisms) within the same drumlin field. Till cored drumlins give way down ice to stratified cored drumlins with till caps and then to stratified drumlins. This zonation is compatible with the increased lateral variability in drumlin composition that would arise from the occurrence of linear assemblages of glacifluvial (esker) and subaqueous (grounding line) sediments in an otherwise marginal-thickening till sheet

Glacial geomorphology of the Great Glen Region of Scotland

This paper presents a detailed glacial Main Map of the Great Glen region of Scotland, UK, covering an area of over 6800 km2 extending from 56°34′7″ to 57°41′1″ N and from 3°44′2″ to 5°33′24″ W. This represents the first extensive mapping of the glacial geomorphology of the Great Glen and builds upon previous studies that conducted localised field mapping or ice-sheet wide mapping using remote sensing. Particular emphasis is placed on deriving medium-scale glacial retreat patterns from these data, and examining differences in landsystem assemblages across the region. Features were typically mapped at a scale of 1:8000 to 1:10,000 and will be used to investigate the pattern and dynamics of the British-Irish Ice Sheet during deglaciation. Mapping was conducted using the NEXTMap digital terrain model. In total, 17,637 glacial landforms were mapped, with 58% identified as moraines, 23% as meltwater channels, 10% as bedrock controlled glacial lineations, 3% as eskers, 2% as cirques or arêtes, 2% as kame topography or kame terraces, and 1% as drumlins. Additionally, 10 palaeo-lake shorelines were identified. Complex landform assemblages in the form of streamlined subglacial bedforms, moraines and glaciofluvial features exist across the region. Extensive subglacial meltwater networks are found over the Monadhliath Mountain Range. Transverse and longitudinal moraine ridges generally arc across valley floors or are located on valley slopes respectively. Hummocky moraines are found almost exclusively across Rannoch Moor. Finally, eskers, meltwater channels and kame landforms form spatial relationships along the axis of Strathspey. These glacial landsystems reveal the dynamics and patterns of retreat of the British-Irish Ice Sheet during the last deglaciation

Submarine landform assemblages and sedimentary processes related to glacier surging in Kongsfjorden, Svalbard

High-resolution swath-bathymetry data from inner Kongsfjorden, Svalbard, reveal characteristic landform assemblages formed during and after surges of tidewater glaciers, and provide new insights into the dynamics of surging glaciers. Glacier front oscillations and overriding related to surge activity lead to the formation of overridden moraines, glacial lineations of two types, terminal moraines, associated debris lobes and De Geer moraines. In contrast to submarine landform assemblages from other Svalbard fjords, the occurrence of two kinds of glacial lineations and the presence of De Geer moraines suggest variability in the landforms produced by surge-type tidewater glaciers. All the landforms in inner Kongsfjorden were deposited during the last c. 150 years. Lithological and acoustic data from the innermost fjord reveal that suspension settling from meltwater plumes as well as ice rafting are dominant sedimentary processes in the fjord, leading to the deposition of stratified glacimarine muds with variable numbers of clasts. Reworking of sediments by glacier surging results in the deposition of sediment lobes containing massive glacimarine muds. Two sediment cores reveal minimum sediment accumulation rates related to the Kongsvegen surge from 1948; these were 30 cm a-1 approximately 2.5 km beyond the glacier front shortly after surge termination, and rapidly dropped to an average rate of 1.8 cm a-1 in ∼ 1950, during glacier retreat

Glacial geomorphology of Marguerite Bay Palaeo-Ice stream, western Antarctic Peninsula

This paper presents a glacial geomorphological map of over 17,000 landforms on the bed of a major palaeo-ice stream in Marguerite Bay, western Antarctic Peninsula. The map was compiled using various geophysical datasets from multiple marine research cruises. Eight glacial landform types are identified: mega-scale glacial lineations, crag-and-tails, whalebacks, gouged, grooved and streamlined bedrock, grounding-zone wedges, subglacial meltwater channels, gullies and channels, and iceberg scours. The map represents one of the most complete marine ice-stream signatures available for scrutiny, and these data hold much potential for reconstructing former ice sheet dynamics, testing numerical ice sheet models, and understanding the formation of subglacial bedforms beneath ice streams. In particular, they record a complex bedform signature of palaeo-ice stream flow and retreat since the last glacial maximum, characterised by considerable spatial variability and strongly influenced by the underlying geology. The map is presented at a scale of 1: 750,000, designed to be printed at A2 size, and encompasses an area of 128,420 km2

Antarctic palaeo-ice streams

We review the geomorphological, sedimentological and chronological evidence for palaeo-ice streams on the continental shelf of Antarctica and use this information to investigate basal conditions and processes, and to identify factors controlling grounding-line retreat. A comprehensive circum-Antarctic inventory of known palaeo-ice streams, their basal characteristics and minimum ages for their retreat following the Last Glacial Maximum (LGM) is also provided. Antarctic palaeo-ice streams are identified by a set of diagnostic landforms that, nonetheless, display considerable spatial variability due to the influence of substrate, flow velocity and subglacial processes. During the LGM, palaeo-ice streams extended, via bathymetric troughs, to the shelf edge of the Antarctic Peninsula and West Antarctica, and typically, to the mid-outer shelf of East Antarctica. The retreat history of the Antarctic Ice Sheet since the LGM is characterised by considerable asynchroneity, with individual ice streams exhibiting different retreat histories. This variability allows Antarctic palaeo-ice streams to be classified into discrete retreat styles and the controls on grounding-line retreat to be investigated. Such analysis highlights the important impact of internal factors on ice stream dynamics, such as bed characteristics and slope, and drainage basin size. Whilst grounding-line retreat may be triggered, and to some extent paced, by external (atmospheric and oceanic) forcing, the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

Stratified glacimarine basin-fills in West Greenland fjords

Acoustically stratified sediments that infill glacially eroded bedrock basins are common in fjords (Seramur et al. 1997; Gilbert et al. 1998; Hogan et al. 2012; Dowdeswell & Vasquez, 2013). Internally, such stratified sediments are often characterised by relatively smooth reflections that parallel the seafloor. Sills between basins usually comprise bedrock, sometimes covered by a thin veneer of glacimarine sediment and/or till. Fjords in West Greenland, including Rink Fjord and the Vaigat, contain bedrock basins infilled by acoustically stratified sediment (Fig. 1). The basin fills are a product of rain-out from turbid meltwater plumes, probably supplemented by iceberg-rafting and downslope resedimentation.This is the author accepted manuscript. The final version is available from Geological Society of London via https://doi.org/10.1144/M46.8

Holocene history of the 79° N ice shelf reconstructed from epishelf lake and uplifted glaciomarine sediments

Acknowledgements This work was funded by a NERC standard grant (grant no. NE/N011228/1), and some radiocarbon analysis was funded by NEIF (grant NE/S011587/1; allocation number 2169.1118). We thank the Alfred Wegener Institute, particularly Angelika Humbert and Hicham Rafiq, for significant logistic support through the iGRIFF project. Additional support was provided by Station Nord (Jorgen Skafte), Nordlandair, Air Greenland, and the Joint Arctic Command. Naalakkersuisut (government of Greenland) provided scientific survey (VU-00121) and export (046/2017) licences for this work. Finally, we would like to thank our (Nanu Travel) field ranger Isak (and dog Ooni) for keeping us safe in the field and taking great pleasure in beating James A. Smith at cards. Financial support This research has been supported by the Natural Environment Research Council (grant no. NE/N011228/1).Peer reviewedPublisher PD

Holocene history of the 79°N ice shelf reconstructed from epishelf lake and uplifted glaciomarine sediments

Nioghalvfjerdsbrae, or 79∘ N Glacier, is the largest marine-terminating glacier draining the Northeast Greenland Ice Stream (NEGIS). In recent years, its ∼ 70 km long fringing ice shelf (hereafter referred to as the 79∘ N ice shelf) has thinned, and a number of small calving events highlight its sensitivity to climate warming. With the continued retreat of the 79∘ N ice shelf and the potential for accelerated discharge from NEGIS, which drains 16 % of the Greenland Ice Sheet (GrIS), it has become increasingly important to understand the long-term history of the ice shelf in order to put the recent changes into perspective and to judge their long-term significance. Here, we reconstruct the Holocene dynamics of the 79∘ N ice shelf by combining radiocarbon dating of marine molluscs from isostatically uplifted glaciomarine sediments with a multi-proxy investigation of two sediment cores recovered from Blåsø, a large epishelf lake 2–13 km from the current grounding line of 79∘ N Glacier. Our reconstructions suggest that the ice shelf retreated between 8.5 and 4.4 ka cal BP, which is consistent with previous work charting grounding line and ice shelf retreat to the coast as well as open marine conditions in Nioghalvfjerdsbrae. Ice shelf retreat followed a period of enhanced atmospheric and ocean warming in the Early Holocene. Based on our detailed sedimentological, microfaunal, and biomarker evidence, the ice shelf reformed at Blåsø after 4.4 ka cal BP, reaching a thickness similar to present by 4.0 ka cal BP. Reformation of the ice shelf coincides with decreasing atmospheric temperatures, the increased dominance of Polar Water, a reduction in Atlantic Water, and (near-)perennial sea-ice cover on the adjacent continental shelf. Along with available climate archives, our data indicate that the 79∘ N ice shelf is susceptible to collapse at mean atmospheric and ocean temperatures ∼ 2 ∘C warmer than present, which could be achieved by the middle of this century under some emission scenarios. Finally, the presence of “marine” markers in the uppermost part of the Blåsø sediment cores could record modern ice shelf thinning, although the significance and precise timing of these changes requires further work

Holocene history of the 79°N ice shelf reconstructed from epishelf lake and uplifted glaciomarine sediments

Nioghalvfjerdsbrae, or 79°N Glacier, is the largest marine-terminating glacier draining the Northeast Greenland Ice Stream (NEGIS). In recent years, its ∼70 km long fringing ice shelf (hereafter referred to as the 79°N ice shelf) has thinned, and a number of small calving events highlight its sensitivity to climate warming. With the continued retreat of the 79°N ice shelf and the potential for accelerated discharge from NEGIS, which drains 16 % of the Greenland Ice Sheet (GrIS), it has become increasingly important to understand the long-term history of the ice shelf in order to put the recent changes into perspective and to judge their long-term significance. Here, we reconstruct the Holocene dynamics of the 79°N ice shelf by combining radiocarbon dating of marine molluscs from isostatically uplifted glaciomarine sediments with a multi-proxy investigation of two sediment cores recovered from Blåsø, a large epishelf lake 2-13 km from the current grounding line of 79°N Glacier. Our reconstructions suggest that the ice shelf retreated between 8.5 and 4.4 kacalBP, which is consistent with previous work charting grounding line and ice shelf retreat to the coast as well as open marine conditions in Nioghalvfjerdsbrae. Ice shelf retreat followed a period of enhanced atmospheric and ocean warming in the Early Holocene. Based on our detailed sedimentological, microfaunal, and biomarker evidence, the ice shelf reformed at Blåsø after 4.4 kacalBP, reaching a thickness similar to present by 4.0 kacalBP. Reformation of the ice shelf coincides with decreasing atmospheric temperatures, the increased dominance of Polar Water, a reduction in Atlantic Water, and (near-)perennial sea-ice cover on the adjacent continental shelf. Along with available climate archives, our data indicate that the 79°N ice shelf is susceptible to collapse at mean atmospheric and ocean temperatures ∼2 °C warmer than present, which could be achieved by the middle of this century under some emission scenarios. Finally, the presence of "marine"markers in the uppermost part of the Blåsø sediment cores could record modern ice shelf thinning, although the significance and precise timing of these changes requires further work

Glacial geomorphology of the north-west sector of the Laurentide Ice Sheet

This paper presents a new map of the glacial geomorphology of $\sim$ 800,000 km\up{2} of north-west Canada. The mapped area includes parts of Northwest Territories and Nunavut which were covered by the Laurentide Ice Sheet during the Late Wisconsinan glaciation. It has been hypothesized that ice streaming occurred here during this time and the area has also been identified as a potential drainage pathway of glacial Lake Agassiz. Mapping was carried out remotely using a range of spaceborne imagery with varying spatial resolutions, including Landsat ETM+, ASTER and SRTM. Aerial photography was also used in areas where cloud obscured the Landsat imagery. The map records 94,780 individual landforms including moraines, eskers, large meltwater channels and lineations. Highly elongate bedforms with convergent flow traces and abrupt lateral margins are abundant throughout the mapped area and most likely represent former zones of streaming flow. Numerous eskers can be traced for tens of kilometres and are found both parallel and sub-parallel to abundant lineations. Moraine ridges are also identified which mark Late Wisconsinan ice margin positions and a series of smaller ridges are also identified within areas of hummocky topography. The map is intended to form the basis of a regional ice sheet reconstruction from the Last Glacial Maximum through to deglaciation, which we suggest is likely to involve marked changes in the spatial and temporal activity of ice streams