Fig 3 - uploaded by Brian Jeremy Todd
Content may be subject to copyright.
The varying preservation of glacial landforms in marine and sub-aerial environments after deglaciation less than 100 years ago. (a) Multibeam-bathymetric image of the seafloor of Borebukta in western Svalbard, adjacent to two tidewater glaciers. Five types of glacial landform (1, oldest, to 5, youngest) are superimposed, illustrating a very well-preserved assemblage of submarine landforms (modified from Ottesen & Dowdeswell 2006). (b) Photograph of the forefield of Kotlujökull, Iceland (courtesy of D.J.A. Evans). The glacier is on the right. Note the erosion of the glacier forefield and moraine ridges by braided meltwater streams.
Source publication
Glacial landforms and sediments exposed sub-aerially have been the subject of description, analysis and interpretation for more than a century (e.g. De Laski 1864; De Geer 1889). Indeed, such features provided important initial observations informing Louis Agassiz’s ideas that ice was a key instrument in sculpting the landscape and that glaciers an...
Contexts in source publication
Context 1
... illustrate the excellent preservation of seafloor landforms, submarine and sub-aerial glacial landforms produced beneath gla- ciers that have retreated a few kilometres from a Little Ice Age maximum only about 100 years ago may be compared (Fig. 3). It can be seen that whereas the glacier-derived sediments and land- forms on a fjord floor remain largely unaltered (Fig. 3a), the land- forms and sediments beyond the modern margin of a terrestrial glacier are being eroded and degraded by fluvial and mass-wasting processes (Fig. 3b). In addition, the potential for longer-term pres- ...
Context 2
... preservation of seafloor landforms, submarine and sub-aerial glacial landforms produced beneath gla- ciers that have retreated a few kilometres from a Little Ice Age maximum only about 100 years ago may be compared (Fig. 3). It can be seen that whereas the glacier-derived sediments and land- forms on a fjord floor remain largely unaltered (Fig. 3a), the land- forms and sediments beyond the modern margin of a terrestrial glacier are being eroded and degraded by fluvial and mass-wasting processes (Fig. 3b). In addition, the potential for longer-term pres- ervation of submarine landforms in the geological record is far greater, given their likely burial by subsequent glacimarine and ...
Context 3
... Little Ice Age maximum only about 100 years ago may be compared (Fig. 3). It can be seen that whereas the glacier-derived sediments and land- forms on a fjord floor remain largely unaltered (Fig. 3a), the land- forms and sediments beyond the modern margin of a terrestrial glacier are being eroded and degraded by fluvial and mass-wasting processes (Fig. 3b). In addition, the potential for longer-term pres- ervation of submarine landforms in the geological record is far greater, given their likely burial by subsequent glacimarine and normal-marine ...
Similar publications
The East
Antarctic Ice Sheet discharges into the Weddell Sea via the Coats Land ice
margin. We have used geophysical data to determine the changing ice-sheet
configuration in this region through its last glacial advance and Holocene
retreat and to identify constraints on its future stability. Methods included
high-resolution multibeam bathymetry, s...
The East Antarctic Ice Sheet discharges into the Weddell Sea via the Coats Land ice margin. We have used geophysical data to determine the changing ice sheet configuration in this region through its last advance and retreat, and identify constraints on its future stability. Methods included high-resolution multibeam-bathymetry, sub-bottom profiles,...
Sedimentation processes influenced by late Cenozoic ice-sheet dynamics and bottom-current activity can be extracted from the seismic stratigraphic record of the Ross Sea continental slope and rise, where more continuous sedimentary successions are preserved compared to the continental shelf. In this study, we present a seismic stratigraphic analysi...
Citations
... During the Wisconsinan glaciation, large portions of North America were covered by the Laurentide Ice Sheet (LIS). The study of its glacial remnants allows the understanding of deglaciation processes of this former ice sheet, which is essential for an insight into the coupling between ice, ocean and climate (e.g.: Batchelor and Dowdeswell, 2015;Dowdeswell et al., 2016a). In the discussion on global climate warming and expected glacial melting, it is important to improve our knowledge of the processes and feedbacks associated with deglaciation (e.g.: Carlson et al., 2008;Briner et al., 2020). ...
... Helpful internal reviews were provided by Brendan Brooke (GA), Reidulv Bøe (NGU) and Gareth Carter (BGS). Selected definitions of submarine glacial landforms from Bell et al. (2016; adapted from Bell et al., 1997) in the Dowdeswell et al., (2016) Atlas of Submarine Glacial Landforms are reproduced with permission from The Geological Society. This report is published with permission of the Chief Executive Officer, Geoscience Australia. ...
Maps of seabed geomorphology derived from bathymetry data provide foundational information that is used to support the sustainable use of the marine environment across a range of activities that contribute to the Blue Economy. The global recognition of the value of the Blue Economy and several key global initiatives, notably the Seabed 2030 project to map the global ocean and the United Nations Decade of Ocean Science for Sustainable Development, are driving the proliferation and open dissemination of these data and derived map products. To effectively support these global efforts, geomorphic characterisation of the seabed requires standardised multi-scalar and interjurisdictional approaches that can be applied locally, regionally and internationally. This document describes and illustrates a geomorphic lexicon for the full range of coastal to deep ocean geomorphic Settings and related Processes that drive the formation, modification and preservation of geomorphic features on the seabed. Terms and Settings/Processes have been selected from the literature and structured to balance established terminology with the need for consistency between the range of geomorphic environments and processes. This document also presents a glossary of 406 geomorphic terms and identifies the insights that can be gained by mapping each unit type, from an applied perspective.
... The Antarctic ice sheet is dominated by marine-terminating glacier outlets (Dowdeswell and others, 2016). Numerous paleosubglacial channels incised into crystalline bedrock are exposed on the seafloor of the Antarctic continental shelf and indicate channelized subglacial meltwater drainage fed by upstream subglacial lakes (Lowe and Anderson, 2003;Livingstone and others, 2013;Simkins and others, 2017;Munoz and Wellner, 2018). ...
... The Greenland ice sheet, on the other hand, comprises both marine-and land-terminating outlets (Dowdeswell and others, 2016). The proglacial hydrologic environment of Greenland consists of rivers and lakes draining the ice margin (Chu, 2014), with Journal of Glaciology 13 a total of 434 proglacial meltwater outlets from land-terminating portions of the ice sheet (Lewis and Smith, 2009). ...
Proglacial braided river systems discharge large volumes of meltwater from ice sheets and transport coarse-grained sediments from the glaciated areas to the oceans. Here, we test the hypothesis if high-energy hydrological events can leave distinctive signatures in the sedimentary record of braided river systems. We characterize the morphology and infer a mode of formation of a 25 km long and 1–3 km wide Early Pleistocene incised valley recently imaged in 3-D seismic data in the Hoop area, SW Barents Sea. The fluvial system, named Bjørnelva River Valley, carved 20 m deep channels into Lower Cretaceous bedrock at a glacial paleo-surface and deposited 28 channel bars along a paleo-slope gradient of ~0.64 m km ⁻¹ . The landform morphologies and position relative to the paleo-surface support that Bjørnelva River Valley was formed in the proglacial domain of the Barents Sea Ice Sheet. Based on valley width and valley depth, we suggest that Bjørnelva River Valley represents a braided river system fed by violent outburst floods from a glacial lake, with estimated outburst discharges of ~160 000 m ³ s ⁻¹ . The morphological configuration of Bjørnelva River Valley can inform geohazard assessments in areas at risk of outburst flooding today and is an analogue for landscapes evolving in areas currently covered by the Greenland and Antarctic ice sheets.
... Glacial landforms such as drumlins, moraines and eskers [56], [57], arise as a consequence of glacial advance, retreat or flow. They influence the ice flow as grounding-line wedges, and also are important for inferring the ancient flow direction of ice streams in areas close to the grounding line transitions, in regions where the internal layers are so disrupted that they cannot be traced [42]. ...
The aim of the thesis is the software processing of data acquired by PASIN2 (Polarimetric Airborne Scientific Instrument, mark 2). It is a 150-MHz coherent pulsed synthetic aperture radar (SAR) for 3D imagery beneath the ice thickness of the Antarctic, designed and operated by the British Antarctic Survey (BAS) to map the overflown regions of the continent in a single pass. In conventional single SAR imaging (2D), along-track and range coordinates are obtained. For 3D mapping, the remaining across-track angle dimension is estimated after processing several SAR images, exploiting the multiple-input multiple-output (MIMO) capabilities, with 8 underwing elements (4 below each wing) switching between transmit- and receive-modes, and 4 receive-only below the fuselage. The array is non-uniformly distributed along the wing orientation, perpendicular to the aircraft trajectory. Using Matlab® software, the off-line processing of PASIN2 data consists firstly in amplitude, phase and delay calibration of the different channels; secondly, single SAR imaging resulting from Backprojection algorithm, assuming homogeneous ice medium, and electromagnetic propagation based on refraction and diffraction according to the surveyed area; and finally, the direction of arrival estimation, by combining the available images and applying a high-resolution non-linear technique called MUSIC. To deal with the spatial distribution of PASIN2 array, a pre-processing has been implemented to improve MUSIC outputs. The results lead to 3D map estimations of the bedrock, ice-water interface or subglacial channels, correcting the topography regarding models in which a vertical direction of arrival was wrongly assumed. These observations will be used by environmental scientist to design, optimise or validate climate models. The thesis is framed within a major project of the Natural Environment Research Council (NERC) called ‘Ice shelves in a warming world: Filchner Ice Shelf System, Antarctica’ (NERC reference NE/L013770/1), in which UCL and BAS participate, among others.
... Maximum ice sheet extent has been reconstructed from subglacial and proglacial bedforms preserved on the continental shelf and dated using radiocarbon ages from carbonate material in marine sediment cores Mackintosh et al., 2014;Ó Cofaigh et al., 2016;Smith et al., 2019). High-resolution mapping of glacial bedforms on the Antarctic continental shelves provides unequivocal evidence for the expansion of grounded ice sheets, although improved chronological constraints are required to understand the spatial variability of the timing at which the maximum extent was reached in each sector (Arndt et al., 2017;Dowdeswell et al., 2016;Fernandez et al., 2018;Halberstadt et al., 2016;Hodgson et al., 2018;Klages et al., 2014;Larter et al., 2019;Lee et al., 2017;Lynch et al., 2014;Simkins et al., 2017;The RAISED Consortium et al., 2014;Wise et al., 2017). Quantifying the LGM extent, and the timing of subsequent retreat, is required to test hypotheses regarding the climate or oceanographic mechanisms for initiating widespread Antarctic marine ice sheet retreat. ...
The Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic‐enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern observations by contrast suggest that the AIS has only just started to respond to climate change in recent decades. The maximum projected sea level contribution from Antarctica to 2100 has increased significantly since the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report, although estimates continue to evolve with new observational and theoretical advances. This review brings together recent literature highlighting the progress made on the known processes and feedbacks that influence the stability of the AIS. Reducing the uncertainty in the magnitude and timing of the future sea level response to AIS change requires a multidisciplinary approach that integrates knowledge of the interactions between the ice sheet, solid Earth, atmosphere, and ocean systems and across time scales of days to millennia. We start by reviewing the processes affecting AIS mass change, from atmospheric and oceanic processes acting on short time scales (days to decades), through to ice processes acting on intermediate time scales (decades to centuries) and the response to solid Earth interactions over longer time scales (decades to millennia). We then review the evidence of AIS changes from the Pliocene to the present and consider the projections of global sea level rise and their consequences. We highlight priority research areas required to improve our understanding of the processes and feedbacks governing AIS change.
... Improvements in geophysical methods and analytical techniques over the last two decades resulted in multiple publications describing glaciogenic sequences. Especially worth mentioning are Special Publications and Memoirs from The Geological Society, London including: "Glaciogenic reservoirs and hydrocarbon systems" ; "Glaciated margins: the sedimentary and geophysical archive" (Le Heron et al., 2019); "Glacier influenced sedimentation on high-latitude continental margins" (Dowdeswell and Cofaigh, 2002); "Engineering Geology and Geomorphology of Glaciated and Periglaciated Terrains: Engineering Group Working Party Report" (Griffiths and Martin, 2017); "Atlas of Submarine Glacial Landforms" (Dowdeswell et al., 2016a). From these, and other, publications it is clear that the distribution and nature of glaciogenic sediments is more complex, and less predictable, than more traditional clastic sequences. ...
Glaciogenic sediments are present in many hydrocarbon-producing basins across the globe but their complex nature makes it difficult to characterise the reservoir-quality sedimentary units. Despite this, Ordovician glacial deposits in North Africa, and Carboniferous-Permian glaciogenic sequences in the Middle East, have been proven to host significant, economical, hydrocarbon accumulations. Additionally, discoveries have been made in the shallow (<1000 m below seabed), glacial, Pleistocene sedimentary succession of the North Sea (e.g. Peon and Aviat). This paper provides a predictive exploration framework in the form of a conceptual model of glaciogenic sediment-landform distributions. The model is based on the extensive onshore glacial sedimentary record integrated with available offshore data. It synthesises the published knowledge, drawing heavily on glacial landsystem models, glacial geomorphology and sedimentology of glaciogenic deposits to provide a novel conceptual model allowing for the efficient description and interpretation of glacial sediments and landforms in the subsurface. Subsequently, land-terminating and water-terminating ice sheet depositional systems are described and discussed, with respect to ice advance and retreat cycles. This detailed description focuses on the macro-scale stratigraphic organisation of glacial sediments with relation to the ice margin, aiding the prediction of glaciogenic sediment distributions, and their likely geometry, architecture and connectivity as reservoirs.
... Our theory would be testable against idealized laboratory experiments of thin film flow over granular beds in a Hele-Shaw cell, which, to our knowledge, are not currently available. Comparing the fastest growing wavelengths of this instability to observations of subglacial morphologies in the field [76] would require follow-up work that captures the nonlinear evolution of the incipient bed-form into its fully fledged form, for example, through a depth-resolved, direct numerical simulation. ...
The distribution and drainage of meltwater at the base of glaciers sensitively affects fast ice flow. Previous studies suggest that thin meltwater films between the overlying ice and a hard-rock bed channelize into efficient drainage elements by melting the overlying ice. However, these studies do not account for the presence of soft deformable sediment observed underneath many West Antarctic ice streams, and the inextricable coupling that sediment exhibits with meltwater drainage. Our work presents an alternate mechanism for initiating drainage elements such as canals where meltwater films grow by eroding the sediment beneath. We conduct a linearized stability analysis on a meltwater film flowing over an erodible bed. We solve the Orr-Sommerfeld equation for the film flow, and we compute bed evolution with the Exner equation. We identify a regime where the coupled dynamics of hydrology and sediment transport drives a morphological instability that generates spatial heterogeneity at the bed. We show that this film instability operates at much faster time scales than the classical thermal instability proposed by Walder. We discuss the physics of the instability using the framework of ripple formation on erodible beds.
... Describing and interpreting the seismic stratigraphy of unlithified sediments in glacier-influenced settings provides the largescale geometries of deposits that can then be related to glacial landforms observed in bathymetry datasets and with sediments directly sampled by seafloor coring (cf. Dowdeswell et al., 2016). In high-latitude fjords and glacial troughs beyond the coastline, the unlithified sediment accumulation may be taken to represent material deposited since these areas were last 360 occupied by grounded ice, during ice retreat following the LGM (e.g., Aarseth, 1997;Gilbert et al., 1998;Hjelstuen et al., 2009;Hogan et al., 2012). ...
Petermann Fjord is a deep (> 1000 m) fjord that incises the coastline of northwest Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5–70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deglacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line-km of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to: bedrock or till surfaces (Facies I); subglacial deposition (Facies II); deposition from meltwater plumes and icebergs in quiescent glaciomarine conditions (Facies III, IV); deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V); and the redeposition of material down slopes (Facies IV). These sediment units represent the total volume of glacial sediment delivered to the mapped marine environment during retreat. We calculate a glacial sediment flux for the former Petermann Ice Stream as 1080–1420 m³ a−1 per meter of ice stream width and an average deglacial erosion rate for the basin of 0.29–0.34 mm a−1. Our deglacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system and we conclude that glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in these rates over a glacial-deglacial transition. Our new fluxes and erosion rates show that the Petermann Ice Stream was approximately as efficient as the palaeo-Jakobshavn Isbrae at eroding, transporting and delivering sediment to its margin during early deglaciation.
... Svalbard has a cooler climate than South Alaska or South Georgia (next section) ( Dowdeswell et al., 2016b), thereby reducing the likelihood of channel formation as a consequence of lower melt production. Here, high resolution bathymetry has been published for 30 fjords and outlets Dowdeswell, 2006, 2009;Ottesen et al., 2008Ottesen et al., , 2017Baeten et al., 2010;Forwick et al., 2010Forwick et al., , 2016Robinson and Dowdeswell, 2011;Kempf et al., 2013;Hansen, 2014;Burton et al., 2016aBurton et al., , 2016bFarnsworth et al., 2017;Flink et al., 2017Flink et al., , 2018Streuff et al., 2017Streuff et al., , 2018Leister, 2018). ...
Submarine channels, and the sediment density flows which form them, act as conduits for the transport of sediment, macro-nutrients, fresher water and organic matter from the coast to the deep sea. These systems are therefore significant pathways for global sediment and carbon cycles. However, the conditions that permit or preclude submarine channel formation are poorly understood, especially when in association with marine-terminating glaciers. Here, using swath-bathymetric data from the inner shelf and fjords of northwest and southeast Greenland, we provide the first paper to analyse the controls on the formation of submarine channels offshore of numerous marine-terminating glaciers. These data reveal 37 submarine channels: 11 offshore of northwest Greenland and 26 offshore of southeast Greenland. The presence of channels is nearly always associated with: (1) a stable glacier front, as indicated by the association with either a moraine or grounding-zone wedge; and (2), a consistent seaward sloping gradient. In northwest Greenland, turbidity current channels are also more likely to be associated with larger glacier catchments with higher ice and meltwater fluxes which provide higher volumes of sediment delivery. However, the factors controlling the presence of channels in northwest and southeast Greenland are different, which suggest some complexity about predicting the occurrence of turbidity currents in glacier-influenced settings. Future work on tidewater glacier sediment delivery rates by different subglacial processes, and the role of grain size and catchment/regional geology is required to address uncertainties regarding the controls on channel formation.
... We infer that the two curved ridges at 2 and 5 km from the shelf edge (Fig. 2) described in Sect. "The upper reaches of the INBIS channel system" are shelf-edge moraines, subglacial landforms located in areas of slow-moving ice, similar to those observed west of the Lofoten Islands on the western Norwegian margin [9,10,87]. Another hypothesis is that these ridges are margin moraines formed in the transition zones between fast-flowing ice (ice streams) and slowerflowing ice (or absence of ice), similar to those observed in the Vestfjorden Trough by Ottesen et al. [61]. ...
The INBIS (Interfan Bear Island and Storfjorden) channel system is a rare example of a deep-sea channel on a glaciated margin. The system is located between two trough mouth fans (TMFs) on the continental slope of the NW Barents Sea: the Bear Island and the Storfjorden–Kveithola TMFs. New bathymetric data in the upper part of this channel system show a series of gullies that incise the shelf break and minor tributary channels on the upper part of the continental slope. These gullies and channels appear far more developed than those on the rest of the NW Barents Sea margin, increasing in size downslope and eventually merging into the INBIS channel. Morphological evidence suggests that the Northern part of the INBIS channel system preserved its original morphology over the last glacial maximum (LGM), whereas the Southern part experienced the emplacement of mass transport glacigenic debris that obliterated the original morphology. Radiometric analyses were applied on two sediment cores to estimate the recent (~ 110 years) sedimentation rates. Furthermore, analysis of grain size characteristics and sediment composition of two cores shows evidence of turbidity currents. We associate these turbidity currents with density-driven plumes, linked to the release of meltwater at the ice-sheet grounding line, cascading down the slope. This type of density current would contribute to the erosion and/ or preservation of the gullies’ morphologies during the present interglacial. We infer that Bear Island and the shallow morphology around it prevented the flow of ice streams to the shelf edge in this area, working as a pin (fastener) for the surrounding ice and allowing for the development of the INBIS channel system on the inter-ice stream part of the slope. The INBIS channel system was protected from the burial by high rates of ice-stream derived sedimentation and only partially affected by the local emplacement of glacial debris, which instead dominated on the neighbouring TMF systems.
