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Studies of ice extent, volume and dynamics during former glaciations are important for understanding past climates and evolution of the Earth’s surface, and also provide analogies for present-day ice sheets and their subglacial environments. This includes observations of glacial erosion, glacial transport and deposition of sediments, formation of fjords and their relation to ice streams, evidence for migration of ice divides, former locations of subglacial lakes, relations between high geothermal heat flow, basal ice melt and rapid ice flow, and other aspects of paleo glacier extent and behaviour. This session will bring together the interdisciplinary scientific community working on former ice covers from the perspectives of glacial geomorphology, quaternary geology, and numerical modeling. It will provide a forum in which field-based reconstructions and model-based simulations can be compared and contrasted. We particularly welcome contributions that shed light on ancient and more recent glaciations on Earth and their interaction with other components of the Earth System.

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Co-organized by GM7
Convener: Andy EmeryECSECS | Co-conveners: Eef van DongenECSECS, Jorge BernalesECSECS, Elisa MantelliECSECS, April DaltonECSECS, Samuel E. KelleyECSECS, Tom JordanECSECS, Kelly Hogan
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| Attendance Tue, 05 May, 14:00–18:00 (CEST)

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Session materials Download all presentations (259MB)

Chat time: Tuesday, 5 May 2020, 14:00–15:45

Chairperson: Andy Emery, Elisa Mantelli
D2589 |
EGU2020-19740
| solicited
Ricarda Winkelmann, Torsten Albrecht, Julius Garbe, Jonathan Donges, and Anders Levermann

The Antarctic Ice Sheet has undergone extensive retreat and re-advance in its glacial-interglacial history. With progressing anthropogenic climate change, the associated ice dynamics and feedbacks could further lead to persistent and potentially irreversible ice loss from Antarctic drainage basins in the future.

Process-based models, in combination with paleo and modern records, provide the tools to reconstruct the glacial-interglacial history of the Antarctic Ice Sheet, to improve our understanding of the involved processes and critical thresholds, and to better anticipate possible future pathways.

Here we present simulations of the Antarctic Ice Sheet over the past two glacial cycles using the Parallel Ice Sheet Model PISM. As the conditions in particular at the base of the ice sheet are weakly constrained, and proxy data for the climatic forcing over the last glacial cycles is sparse, we assess the sensitivity of the model response with respect to the choice of boundary conditions. We further conduct an ensemble analysis in order to systematically constrain uncertainties with respect to representative model parameters associated with ice dynamics, climatic forcing, basal sliding and bed deformation.

Based on the insights into the dynamic threshold behavior and estimates of the ice sheet’s contributions to global sea-level changes in the past, we investigate the long-term future stability of the Antarctic Ice Sheet under different levels of global warming. We show that the ice sheet exhibits a multitude of temperature thresholds beyond which ice loss into the ocean becomes irreversible. Each of these thresholds gives rise to hysteresis behavior, meaning that the currently observed ice-sheet configuration cannot be regained even if temperatures were to be reversed to their present-day levels.

How to cite: Winkelmann, R., Albrecht, T., Garbe, J., Donges, J., and Levermann, A.: Antarctic ice dynamics - from deep past to deep future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19740, https://doi.org/10.5194/egusphere-egu2020-19740, 2020

D2590 |
EGU2020-1296
Eliza Dawson, Dustin Schroeder, Winnie Chu, Elisa Mantelli, and Helene Seroussi

Glacial thermal processes exert a fundamental control on ice flow, governing viscosity and frozen-to-thawed transitions at the ice-bed interface. Across Antarctica, frozen bed regions characterized by numerical models and geophysical observations, can also reduce ice flow by increasing basal traction. Some frozen bed regions can separate or confine fast-flowing glaciers and ice streams. Others separate inland catchments with thawed beds from the grounding zone of marine ice-sheet sectors. If regions with frozen bed experienced thawing, such a transition may lead to ice-sheet acceleration, reconfiguration, or retreat. To investigate the potential impact of such a thermal transition, we use the JPL/UCI Ice Sheet System Model (ISSM) to identify vulnerable regions across Antarctica that are close to the basal melting point. We assess the impact of thawing these regions by quantifying resulting volume changes and surface expressions. This allows us to identify the areas of the ice sheet where the thermal regime at the ice-bed interface has the largest potential impact on ice-sheet stability and sea-level contribution. We also examine the potential basal temperature and thaw-propagation thresholds governing this process. We then compare the ISSM results to a selection of ice-penetrating radar sounding observations to refine our constraints of the configuration, distribution, and extent of these thermally critical areas.

How to cite: Dawson, E., Schroeder, D., Chu, W., Mantelli, E., and Seroussi, H.: Investigating basal thaw as a potential driver of ice flow acceleration in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1296, https://doi.org/10.5194/egusphere-egu2020-1296, 2019

D2591 |
EGU2020-4188
| solicited
Felicity McCormack, Roland Warner, Adam Treverrow, and Helene Seroussi

Viscous deformation is the main process controlling ice flow in ice shelves and in slow-moving regions of polar ice sheets where ice is frozen to the bed. However, the role of deformation in flow in ice streams and fast-flowing regions is typically poorly represented in ice sheet models due to a major limitation in the current standard flow relation used in most large-scale ice sheet models – the Glen flow relation – which does not capture the steady-state flow of anisotropic ice that prevails in polar ice sheets. Here, we highlight recent advances in modeling deformation in the Ice Sheet System Model using the ESTAR (empirical, scalar, tertiary, anisotropic regime) flow relation – a new description of deformation that takes into account the impact of different types of stresses on the deformation rate. We contrast the influence of the ESTAR and Glen flow relations on the role of deformation in the dynamics of Thwaites Glacier, West Antarctica, using diagnostic simulations. We find key differences in: (1) the slow-flowing interior of the catchment where the unenhanced Glen flow relation simulates unphysical basal sliding; (2) over the floating Thwaites Glacier Tongue where the ESTAR flow relation outperforms the Glen flow relation in accounting for tertiary creep and the spatial differences in deformation rates inherent to ice anisotropy; and (3) in the grounded region within 80km of the grounding line where the ESTAR flow relation locally predicts up to three times more vertical shear deformation than the unenhanced Glen flow relation, from a combination of enhanced vertical shear flow and differences in the distribution of basal shear stresses. More broadly on grounded ice, the membrane stresses are found to play a key role in the patterns in basal shear stresses and the balance between basal shear stresses and gravitational forces simulated by each of the ESTAR and Glen flow relations. Our results have implications for the suitability of ice flow relations used to constrain uncertainty in reconstructions and projections of global sea levels, warranting further investigation into using the ESTAR flow relation in transient simulations of glacier and ice sheet dynamics. We conclude by discussing how geophysical data might be used to provide insight into the relationship between ice flow processes as captured by the ESTAR flow relation and ice fabric anisotropy.

How to cite: McCormack, F., Warner, R., Treverrow, A., and Seroussi, H.: Recent developments in modeling ice sheet deformation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4188, https://doi.org/10.5194/egusphere-egu2020-4188, 2020

D2592 |
EGU2020-18618
Alexios Theofilopoulos and Andreas Born

Our knowledge of the past surface mass balance on Greenland depends on scarce paleoclimate reconstructions and uncertain climate simulations. However, reconstructions of the internal layering of the ice sheet can provide an independent dataset of accumulation. The thickness of isochronal layers is directly affected by accumulation, but modified over time by the flow of ice. Existing methods can disentangle these two effects only near the ice divide where assumptions of stationarity may be justified. To solve this problem and to obtain a spatially comprehensive reconstruction of accumulation, we use an ice sheet model with an isochronal grid. Thinning rates are calculated prognostically by the model and can be used to define an inverse problem that can be solved iteratively. The only input data is the final layer thickness of the target, e.g., reconstructed radio echo layers from the Greenland ice sheet. To test this method and its limitations, we reconstruct the accumulation histories from the stratigraphies of simulations for which the idealized accumulation time series and spatial distributions are known. These simulations represent a two-dimensional cross section of the Greenland ice sheet. The results are robust to a wide range of realistic variations in accumulation for all but the layers closest to the bedrock where the deformation by the flow is most severe.

How to cite: Theofilopoulos, A. and Born, A.: Reconstructing surface mass balance from the Greenland ice sheet stratigraphy., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18618, https://doi.org/10.5194/egusphere-egu2020-18618, 2020

D2593 |
EGU2020-19036
Vjeran Višnjević, Frederic Herman, and Günther Prasicek

 

During the pinnacle of the last glacial period 21 kyr ago, the Alps and the Pyrenees were largely covered by ice. Climate was colder and most likely drier, but the magnitudes of temperature and precipitation changes remain poorly constrained. This is in part because climate proxies are not sufficiently accurate, and because there are unknowns on the past position of the Westerly winds and, consequently, the intensity of the moisture flow towards Europe. A new inverse method combined with an ice flow model enables us to infer past climate from mapped ice extents. In the case of the Alps, all of the presented scenarios recover an increase in the position of the ELA across the mountain range from west to east, and a decrease from north to south, pointing to a dominantly zonal circulation with Westerlies bringing moisture from the Atlantic. This is supported by the Pyrenees reconstruction, where the method recovers a clear N-S gradient for all scenarios, indicating that the moisture source from the direction of the Atlantic. While the precipitation pattern was probably not much different from today, mean temperatures were ~9.3 ± 2.97˚C lower in the Alps and ~6.6 ± 1.6˚C lower in the Pyrenees. Our results match pollen-based reconstructions if the climate was 60% dryer than today.

 

How to cite: Višnjević, V., Herman, F., and Prasicek, G.: Reconstruction of LGM ice extents in Europe indicates a cold and dry climate with precipitation patterns similar to present day, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19036, https://doi.org/10.5194/egusphere-egu2020-19036, 2020

D2594 |
EGU2020-480
Helen Dulfer and Martin Margold

The Cordilleran Ice Sheet (CIS) repeatedly covered western Canada during the Pleistocene and attained a volume and area similar to that of the present-day Greenland Ice Sheet. Deglaciation of the CIS following the Last Glacial Maximum (LGM) directly affected atmosphere and ocean circulation, eustatic sea level, and human migration from Asia to North America. It has recently been shown that the rapid climate oscillations at the end of the Pleistocene had a dramatic effect on the CIS. Data on glacial isostatic adjustment and cosmogenic nuclide exposure ages indicate that abrupt warming at the onset of the Bølling-Allerød caused significant thinning of the ice sheet, resulting in a fifty percent reduction in mass, while the Younger Dryas cooling caused the expansion of alpine glaciers across the mountains of western Canada. However, the mountainous subglacial terrain makes it challenging to reconstruct the regional-scale deglaciation dynamics of the ice sheet, and its configuration during this period of rapid change remains poorly constrained. 

Here we use the glacial landform record to reconstruct the ice sheet configuration for the central sector of the CIS, over the Cassiar and Omineca Mountains in northern British Columbia, during the Late Pleistocene climate reversals. We present the first regional-scale reconstruction of the CIS following the Bølling-Allerød warming, whereby the ice sheet was reduced to a labyrinth of valley glaciers fed by ice dispersal centres located over the Skeena Mountains in the south and Coast Mountains in the west. Additionally, numerous lateral and terminal late glacial moraines delineate the extent of alpine glaciers, ice caps and ice fields that regrew on mountain peaks above the CIS during the Younger Dryas. Cross-cutting relationships indicate that the valley glaciers of the CIS were slower to respond to the Younger Dryas cooling than the mountain glaciers.

How to cite: Dulfer, H. and Margold, M.: Reconstructing the Cordilleran Ice Sheet in northern British Columbia during the Late Pleistocene climate reversals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-480, https://doi.org/10.5194/egusphere-egu2020-480, 2019

D2595 |
EGU2020-20521
Edward Gasson, Heather Stoll, and Isabel Cacho

Compared with the intensely studied interval of the last glacial maximum and termination, significantly less attention has been given to the preceding glacial period and Termination 2. This is perhaps understandable as the Greenland ice cores do not stretch this far back in time and the terrestrial record of the ice sheets has in part been lost during the subsequent glacial period. However, there are many questions remaining about how these two glacial intervals differed and whether this was important in driving some of the differences between the last interglacial and our current interglacial. Here I will focus on a new speleothem record from northern Spain which records the meltwater-driven d18O anomaly in the eastern North Atlantic and provides an absolutely dated chronology (U/Th) during the penultimate glacial and Termination 2. The character of which differs dramatically from a record for Termination 1 recovered from speleothems at the same site. This record also shows structure during Termination 2 that has not been seen previously. Here I’ll discuss some possible reasons for the differences between the two glacial terminations and focus on recent ice sheet model experiments that have been run to try and test these hypotheses.

 

How to cite: Gasson, E., Stoll, H., and Cacho, I.: Contrasting style and retreat rates of the northern hemisphere ice sheets during the past two glacial terminations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20521, https://doi.org/10.5194/egusphere-egu2020-20521, 2020

D2596 |
EGU2020-6021
| solicited
Daniel Goldberg, Paul Holland, and Mathieu Morlighem

In recent years, there have been great advances in coupled ice sheet-ocean modelling, to the point where ice-ocean interactions can be represented in global climate models — with potential to greatly improve forecasting of marine ice-sheet loss and sea level rise in the coming century and beyond. However, initialisation of coupled ice sheet-ocean models has not yet been properly examined; and initialisation approaches applied to ocean and coupled atmosphere-ocean models may not be appropriate due to the long time scales inherent in dynamic ice sheets. Moreover, as ocean melt rates and ice-shelf geometry strongly influence each other, nonphysical transients in incorrectly initialised coupled ice-ocean models may persist for longer than in ice-sheet models alone.

In this work, two approaches to coupled initialisation are considered using a synchronously coupled ice-ocean model. The two approaches are based on two commonly used approaches to ice sheet model initialisation: “snapshot” calibration, where ice-sheet basal and internal parameters are configured to optimise fit with observed surface velocity; and “transient” calibration, where these parameters are configured to jointly optimise fit with velocity and geometry change; however, the transient calibration makes use of the ocean component to ensure the ice model is not subject to “initialisation shock” from ocean melting. The approaches are applied to Smith Glacier, a small but fast-thinning glacier in West Antarctica, and the model is forced under ocean warming scenarios in multidecadal runs. Initially there is much faster retreat seen in the Snapshot-calibrated simulation, but this difference decays over several decades, and ultimately the Transiently-calibrated model sees more retreat.

The experiments further suggest that Smith Glacier is not likely to exhibit Marine Ice Sheet instability in the next century. But the methods discrepancy has strong implications for glaciers which are susceptible to this instability.

How to cite: Goldberg, D., Holland, P., and Morlighem, M.: Impacts of initialisation of coupled ice sheet-ocean models forecasting., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6021, https://doi.org/10.5194/egusphere-egu2020-6021, 2020

D2597 |
EGU2020-17640
Michele Petrini, Colleoni Florence, Kirchner Nina, Hughes Anna L. C., Camerlenghi Angelo, Rebesco Michele, Lucchi Renata G., Forte Emanuele, Colucci Renato R., Noormets Riko, and Mangerud Jan

An interconnected complex of ice sheets, collectively referred to as the Eurasian ice sheets, covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP), connecting to the Scandinavian Ice Sheet to the south. Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. Investigating key processes driving the last deglaciation of the Barents Sea Ice Sheet represents an important tool to interpret recent observations in Antarctica over the multi-millennial temporal scale of glaciological changes. We present results from a statistical ensemble of ice sheet model simulations of the last deglaciation of the Barents Sea Ice Sheet, all forced with transient atmospheric and oceanic conditions derived from AOGCM simulations. The ensemble of transient simulations is evaluated against the data-based DATED-1 reconstruction. We find that the simulated deglaciation of the Barents Sea Ice Sheet is primarily driven by the oceanic forcing, with sea level rise and surface melting amplifying the ice sheet sensitivity to ocean warming over relatively short intervals. Despite a large model/data mismatch at the western and eastern ice sheet margins, the simulated and DATED-1 deglaciation scenarios agree well on the timing of the deglaciation of the central and northern Barents Sea. The primary role played by ocean forcing in our simulations suggests that the long-term stability of the West Antarctic Ice Sheet could be at stake if the current trend in ocean warming will continue.

How to cite: Petrini, M., Florence, C., Nina, K., Anna L. C., H., Angelo, C., Michele, R., Renata G., L., Emanuele, F., Renato R., C., Riko, N., and Jan, M.: Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17640, https://doi.org/10.5194/egusphere-egu2020-17640, 2020

D2598 |
EGU2020-10118
| solicited
Christine Batchelor, Dag Ottesen, Benjamin Bellwald, Sverre Planke, Helge Løseth, Sverre Henriksen, Ståle Johansen, and Julian Dowdeswell

The North Sea has arguably the most extensive geophysical data coverage of any glacier-influenced sedimentary regime on Earth, enabling detailed investigation of the thick (up to 1 km) sequence of Quaternary sediments that is preserved within the North Sea Basin. At the start of the Quaternary, the bathymetry of the northern North Sea was dominated by a deep depression that provided accommodation for sediment input from the Norwegian mainland and the East Shetland Platform. Here we use an extensive database of 2D and 3D seismic data to investigate the geological development of the northern North Sea through the Quaternary.

Three main sedimentary processes were dominant within the northern North Sea during the early Quaternary: 1) the delivery and associated basinward transfer of glacier-derived sediments from an ice mass centred over mainland Norway; 2) the delivery of fluvio-deltaic sediments from the East Shetland Platform; and 3) contourite deposition and the reworking of sediments by contour currents. The infilling of the North Sea Basin during the early Quaternary increased the width and reduced the water depth of the continental shelf, facilitating the initiation of the Norwegian Channel Ice Stream.

How to cite: Batchelor, C., Ottesen, D., Bellwald, B., Planke, S., Løseth, H., Henriksen, S., Johansen, S., and Dowdeswell, J.: Quaternary evolution of the northern North Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10118, https://doi.org/10.5194/egusphere-egu2020-10118, 2020

D2599 |
EGU2020-12243
Andrew Christ, Paul Bierman, Dorthe Dahl-Jensen, Jørgen Steffensen, Dorothy Peteet, Elizabeth Thomas, Owen Cowling, Eric Steig, Lee Corbett, Joerg Schaefer, Alan Hidy, Marc Caffee, Tammy Rittenour, Jean-Louis Tison, Pierre-Henri Blard, Marie Protin, and John Southon

The Greenland Ice Sheet (GrIS) is melting in response to a rapidly warming climate.  It is imperative to understand GrIS sensitivity to past climate, especially during periods when the ice sheet was smaller than present or possibly absent. The Camp Century ice core from NW Greenland, collected in 1966 and the first ice core to be drilled to the bed of the GrIS, revolutionized our understanding of global paleoclimate since 125 ka. However, basal sediment from the ice core was not fully explored and then sat in storage for decades – until it was re-discovered two years ago. We are now investigating these unique samples from the sub-glacial environment using modern analyses. 

Here, we present initial results from two samples, the upper and lower portions of >4 m of basal sediment. We applied an array of geochemical analyses to characterize paleoenvironment (lipid biomarkers, δ13C, δ15N), to infer past climatic conditions (δ18O, δD) from frozen pore water, and to determine the exposure and burial history of the sediments below the ice sheet (optically stimulated luminescence [OSL], cosmogenic 10Be, 26Al, and 21Ne). 

The sub-glacial sediment consists of poorly sorted, reddish-brown, quartz-rich diamict, with paleo-permafrost features in some layers. This material contains woody macrofossils, fungal sclerotia (Cenococcum geophilum), and mosses (Tomenthypnum nitens, Polytrichum juniperinum) that yield a 14C age >55 ka. Woody tissue from the upper and lower samples yield stable δ13C ratios of -26.7±0.1‰ and -29.6±0.1‰ and δ15N ratios of 2.4±0.8‰ and -2.3±0.8‰. Leaf wax (n-alkanoic acid) distributions are similar to modern Arctic shrubs. Frozen pore water yielded δ18O ratios of -23.06±0.08‰ and -21.49±0.08‰, enriched relative to all overlying ice (<-27‰). Deuterium-excess values are 4.3±0.8 ‰ and 13.4±0.4 ‰, respectively.  These stable isotope measurements of pore water suggest snowfall precipitation at temperatures similar to today if the site were ice-free. OSL measurements from the lower sediment suggest a minimum depositional age >600 ka. In situ 10Be concentrations in quartz decrease with depth from 7.7±0.1 x104 atoms/g (500-850 µm) and  6.6±0.2 x104 (250-500 µm) in the upper sediment to 1.6±0.1 x104 atoms/g (500-850 µm) and 1.8±0.1 x104 (250-500 µm) in the lower sediment. The 26Al/10Be ratio also decreases with depth. In the upper sediment, 26Al/10Be ratios range between 4.2 and 4.9 indicating > 900 ka of burial. In the lower sediment, 26Al/10Be ratios range from 1.4 to 2.0 indicating >2 Ma of burial. Measured 21Ne/10Be ratios in quartz exceed 1000, which could indicate long-term burial and/or the presence of nucleogenic 21Ne.

These results demonstrate that Camp Century basal sediment was exposed under ice-free conditions that supported vegetation similar to today. Cosmogenic data indicate the deeper sediment has been buried for most of the Pleistocene and the OSL date rules out surface exposure of the deeper material at MIS 11. Cosmogenic analysis indicates that the upper sample experienced less burial or more recent re-exposure. These data are consistent with a growing body of evidence indicating a dynamic Pleistocene GrIS, even under a pre-industrial climate system in which atmospheric CO2 concentrations did not exceed ~300 ppm.

How to cite: Christ, A., Bierman, P., Dahl-Jensen, D., Steffensen, J., Peteet, D., Thomas, E., Cowling, O., Steig, E., Corbett, L., Schaefer, J., Hidy, A., Caffee, M., Rittenour, T., Tison, J.-L., Blard, P.-H., Protin, M., and Southon, J.: Camp Century ice core basal sediments record the absence of the Greenland Ice Sheet within the last million years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12243, https://doi.org/10.5194/egusphere-egu2020-12243, 2020

D2600 |
EGU2020-8691
Arne Lohrberg, Sebastian Krastel, Daniel Unverricht, and Klaus Schwarzer

Glaciotectonic disturbance of sediments and tunnel valleys are often found near the margin of former ice sheets. Hence, these landforms can be used to reconstruct the dynamics of former ice sheet margins. The direction of thrusts usually points perpendicular to the ice front. Considering heterogeneity due to local ice advances, this relation can be used to infer the regional forward direction of large ice lobes. Here, we present a dense grid of high-resolution 2D multi-channel reflection seismic data from the German sector of the southeastern North Sea imaging a buried glaciotectonic complex and tunnel valleys in unprecedented detail.

We have identified individual thrust sheets in an area of approx. 650 km² (combined with recent results of Winsemann et al. (2020)). All thrust sheets are buried and partly eroded at their top. Two major phases of thrusting with two corresponding detachment surfaces have been identified in the subsurface, of which the younger phase led to the deformation of sediments several kilometers further into the foreland. The thickness of individual thrust sheets differs between 180 and 240 m. Some thrust sheets have been cut by the subsequent formation of tunnel valleys with an overall incision direction ranging from east-west to northeast-southwest. The glaciotectonic complex is limited to its southeast by an updipping reflector, which represents the margin of a source depression.

The restauration of cross-sections shows that the thrust sheets transported sediments over more than a kilometer towards the northwest to west, which relates the formation of the thrust sheets and the source depression. The landforms are very similar to a hill-hole pair that led to the foreland thrust sheets, probably as a result of combined bulldozing and gravity spreading in the foreland of the ice margin. Their occurrence and the adjacent tunnel valleys leads us to assume that we identified the marginal position of an Elsterian ice lobe in the southeastern North Sea.

Reference:
Winsemann, J., Koopmann, H., Tanner, D.C., Lutz, R., Lang, J., Brandes, C., Gaedicke, C., 2020. Seismic interpretation and structural restoration of the Heligoland glaciotectonic thrust-fault complex: Implications for multiple deformation during (pre-)Elsterian to Warthian ice advances into the southern North Sea Basin. Quat. Sci. Rev. 227, 1–15. https://doi.org/10.1016/j.quascirev.2019.106068

How to cite: Lohrberg, A., Krastel, S., Unverricht, D., and Schwarzer, K.: Glaciotectonics and tunnel valleys in the southeastern North Sea imaged by high-resolution multi-channel seismics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8691, https://doi.org/10.5194/egusphere-egu2020-8691, 2020

D2601 |
EGU2020-334
Benjamin Boyes, Lorna Linch, and Danni Pearce

The glacial history of the Kola Peninsula, northwest Arctic Russia, during the Last Glacial-Interglacial Transition (LGIT; c. 18-10 ka) is poorly understood, with some researchers suggesting that the region was glaciated by the Fennoscandian Ice Sheet (FIS; e.g. Hughes et al., 2016), and others suggesting that it was glaciated by an independent Ponoy Ice Cap (e.g. Astakhov et al., 2016). Furthermore, it is unclear if and where there was a periodic ice standstill during the Younger Dryas (c. 12.9-11.7 ka) cold stadial. This is the largest sector of Fennoscandia where glaciation is poorly constrained, which stems from low resolution geomorphological mapping, a lack of sedimentary analyses, and limited dating of glacial landforms and deposits on the Kola Peninsula.

Initial interpretations of geomorphological mapping and sedimentological analyses are presented. High resolution geomorphological mapping has, so far, demonstrated that the Kola Peninsula was glaciated by the FIS, which flowed from the Scandinavian mountains in the west and across the shield terrain of the Kola Peninsula, and not an independent Ponoy Ice Cap, as indicated by the west-east orientation of glacial lineations (e.g. drumlins, crag and tails, mega-scale glacial lineations), moraines, and meltwater channels. Up to four ice streams located in the western Kola Peninsula and the White Sea demonstrated in the glacial lineation record have also been identified. Furthermore, the Younger Dryas margin is proposed to be aligned north-south across the Kola Peninsula, flowing around the Khibiny Mountains, and forming an ice lobe in the White Sea, which is demonstrated by the moraine and meltwater landform assemblage. Moraines and lateral meltwater channels also suggest the Monche-tundra Mountains were exposed as nunataks, and that there were independent cirque and valley glaciers in the Lovozero and Khibiny Mountains at the periphery of the FIS during the Younger Dryas. In addition, glaciotectonised sediments identified in sedimentary analyses indicates the FIS underwent sustained readvances during retreat. This research will provide crucial empirical data for validating numerical model simulations of the FIS, which in turn will further our understanding of (de)glacial dynamics in other Arctic, Antarctic, and Alpine regions.

 

Astakhov, V., Shkatova, V., Zastrozhnov, A. and Chuyko, M. (2016). Glaciomorphological map of the Russian Federation. Quaternary International, 420, pp.4-14.

Hughes, A.L., Gyllencreutz, R., Lohne, Ø.S., Mangerud, J. and Svendsen, J.I. (2016). The last Eurasian ice sheets - a chronological database and time-slice reconstruction, DATED-1. Boreas, 45(1), pp.1-45.

How to cite: Boyes, B., Linch, L., and Pearce, D.: Deglaciation of the Kola Peninsula, Arctic Russia, during the Last Glacial-Interglacial Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-334, https://doi.org/10.5194/egusphere-egu2020-334, 2019

D2602 |
EGU2020-1832
Bethan Davies and the PATICE Team

We present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronostratigraphic data. PATICE includes 58,823 landforms and 1,669 ages, and extends from 38°S to 55°S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka (synchronous with the “Little Ice Age”) and 2011 AD. At 35 ka, the PIS covered of 492.6 x103 km2, had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent at 33 – 28 ka from 38°S to 48°S, and earlier, around 47 ka from 48°S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation at 21 – 18 ka, followed by rapid deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at 14 – 13 ka, 11 ka, 5 – 6 ka, 1 – 2 ka, and 0.2 ka. We suggest that 20th century glacial recession is occurring faster than at any time documented during the Holocene. 

How to cite: Davies, B. and the PATICE Team: The evolution of the Patagonian Ice Sheet from 35 ka to the Present Day (PATICE), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1832, https://doi.org/10.5194/egusphere-egu2020-1832, 2019

D2603 |
EGU2020-118
James Kirkham, Kelly Hogan, Robert Larter, Ed Self, Ken Games, Mads Huuse, Margaret Stewart, Dag Ottesen, Neil Arnold, and Julian Dowdeswell

Tunnel valleys are large (kilometres wide, hundreds of metres deep) channels incised into bedrock and soft sediments by the action of pressurised subglacial meltwater. Discovered over a century ago, they are common across large swathes of North-West Europe and North America. However, many aspects of tunnel valley formation, and the processes by which they are infilled, remain poorly understood. Here, we use new high-resolution 3D seismic reflection data, collected by the geohazard assessment industry, to examine the infill lithology and architecture of buried tunnel valleys located in the central North Sea. The spatial resolution of our seismic data (3.125-6.25 m bin size) represents an order of magnitude improvement in the data resolution that has previously been used to study tunnel valleys in this region, allowing us to examine their infill in unprecedented detail. Inside the tunnel valleys, we identify a suite of buried subglacial landforms, some of which have rarely been reported inside tunnel valleys before. These landforms include a 14-km-long system of segmented eskers, crevasse-squeeze ridges, subsidiary meltwater channels and retreat moraines. Their presence suggests that, in some cases, tunnel valleys in the North Sea were reoccupied by ice following their initial formation, casting doubt on hypotheses which invoke catastrophic releases of water to explain tunnel valley creation.

How to cite: Kirkham, J., Hogan, K., Larter, R., Self, E., Games, K., Huuse, M., Stewart, M., Ottesen, D., Arnold, N., and Dowdeswell, J.: New insights into North Sea tunnel valley infill and genesis from high-resolution 3D seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-118, https://doi.org/10.5194/egusphere-egu2020-118, 2019

D2604 |
EGU2020-18701
Benjamin Bellwald, Sverre Planke, Sunil Vadakkepuliyambatta, Stefan Buenz, Christine Batchelor, Ben Manton, Dmitry Zastrozhnov, Reidun Myklebust, and Bent Kjølhamar

Sediments deposited by marine-based ice sheets are dominantly fine-grained glacial muds, which are commonly known for their sealing properties for migrating fluids. However, the Peon and Aviat hydrocarbon discoveries in the North Sea show that coarse-grained glacial sands can occur over large areas in formerly glaciated continental shelves. In this study, we use conventional and high-resolution 2D and 3D seismic data combined with well information to present new models for large-scale fluid accumulations within the shallow subsurface of the Norwegian Continental Shelf. The data include 48,000 km2 of high-quality 3D seismic data and 150 km2 of high-resolution P-Cable 3D seismic data, with a vertical resolution of 2 m and a horizontal resolution of 6 to 10 m in these data sets. We conducted horizon picking, gridding and attribute extractions as well as seismic geomorphological interpretation, and integrated the results obtained from the seismic interpretation with existing well data.

The thicknesses of the Quaternary deposits vary from hundreds of meters of subglacial till in the Northern North Sea to several kilometers of glacigenic sediments in the North Sea Fan. Gas-charged, sandy accumulations are characterized by phase-reserved reflections with anomalously high amplitudes in the seismic data as well as density and velocity decreases in the well data. Extensive (>10 km2) Quaternary sand accumulations within this package include (i) glacial sands in an ice-marginal outwash fan, sealed by stiff glacial tills deposited by repeated glaciations (the Peon discovery in the Northern North Sea), (ii) sandy channel-levee systems sealed by fine-grained mud within sequences of glacigenic debris flows, formed during shelf-edge glaciations, (iii) fine-grained glacimarine sands of contouritic origin sealed by gas hydrates, and (iv) remobilized oozes above large evacuation craters and sealed by megaslides and glacial muds. The development of the Fennoscandian Ice Sheet resulted in a rich variety of depositional environments with frequently changing types and patterns of glacial sedimentation. Extensive new 3D seismic data sets are crucial to correctly interpret glacial processes and to analyze the grain sizes of the related deposits. Furthermore, these data sets allow the identification of localized extensive fluid accumulations within the Quaternary succession and distinguish stratigraphic levels favorable for fluid accumulations from layers acting as fluid barriers.

How to cite: Bellwald, B., Planke, S., Vadakkepuliyambatta, S., Buenz, S., Batchelor, C., Manton, B., Zastrozhnov, D., Myklebust, R., and Kjølhamar, B.: Extensive, Gas-charged Quaternary Sand Accumulations of the Northern North Sea and North Sea Fan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18701, https://doi.org/10.5194/egusphere-egu2020-18701, 2020

D2605 |
EGU2020-5410
Samuel E. Kelley, Brent Ward, Jason Briner, Martin Ross, Philippe Normandeau, and Barrett Elliott

The Laurentide Ice Sheet (LIS) during the Pleistocene-Holocene transition provides a useful natural laboratory for examining the behavior of a mid- to high-latitude ice sheet during a period of climatically driven ice sheet thinning and retreat. While the timing and pattern of Pleistocene recession of the LIS are well-constrained along the southern and eastern margins, there is limited chronology constraining the ice margin retreat along the northwestern margin. Here we present new cosmogenic 10Be exposure ages retreat of the western margin of the LIS during the Pleistocene-Holocene transition. Sampling was performed along three transects located between the northern shore of Great Slave Lake and Lac de Gras. Each of the transects is oriented parallel to the inferred ice retreat direction in an attempt to capture a regional rate of retreat. Our new 10Be cosmogenic exposure ages from the southeastern Northwest Territories demonstrate that regional deglaciation occurred around 11,000 years ago. The population of ages broadly overlaps, indicating that either the retreat occurred within the resolution of our chronology or that the ice sheet experienced widespread stagnation and rapid down-wasting. These ages, not corrected for changes in atmospheric depth due to isostatic rebound, are older than minimum limiting radiocarbon constraints by ~1000 years, indicating that existing LIS reconstructions may underestimate the timing and pace of ice margin recession for this sector. Constraining the timing of the recession of the northwest sector of the LIS has the potential to inform our understanding about the damming of large proglacial lakes, such as Glacial Lake McConnell. The ages from our southern transect, collected from elevated bedrock hills, indicate LIS retreat from through the McConnell basin occurred after 12,000 years ago, and thus constitute maximum limiting constraints on the expansion of Glacial Lake McConnell southeastward into the present-day Great Slave Lake basin. Our chronology, combined with other emerging cosmogenic exposure ages constraining LIS deglaciation indicates retreat of the ice margin over 100s of kilometres during the Pleistocene-Holocene transition, exhibiting no evidence of a significant readvance during the Younger Dryas stadial.

How to cite: Kelley, S. E., Ward, B., Briner, J., Ross, M., Normandeau, P., and Elliott, B.: The recession of the Laurentide Ice Sheet in southeast Northwest Territories during the Pleistocene-Holocene transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5410, https://doi.org/10.5194/egusphere-egu2020-5410, 2020

D2606 |
EGU2020-3902
Mark Coughlan, Andy Wheeler, Mike Long, Ronan O'Toole, and Matthew Service

The onshore exposures on the northeast coast of the island of Ireland have been well studied in relation to regional glacial advances of the British and Irish Ice Sheet (BIIS) and changes in relative sea level change. These includes sites around Dundalk Bay, Carlingford Lough and Kilkeel in particular. During deglaciation of the BIIS, two important readvance phases are recorded locally; the Clogher Head and Killard Point Stadials. However, the offshore extent and record of these events is still poorly constrained. Understanding the nature and pattern of deglaciation of the offshore sectors of the BIIS is important to any attempt to reconstruct its history after the Last Glacial Maximum.

This study presents a new seismo-stratigraphic analysis of submarine Quaternary deposits nearshore, off the northeast coast of the island of Ireland. This includes multibeam echosounder (MBES), sparker seismic and core data from the areas of offshore Dundalk Bay, Carlingford Lough, Kilkeel and Dundrum Bay. Preliminary analysis of the data reveals a series of geomorphic features in each area including moraines, eskers, drumlinised landscapes, exposed till surfaces and infilled channels. Sediment cores will be used to further groundtruth these features and provide insights into their formation processes and timing. Initial inspection of these cores suggest two diamicton facies, assumed to be subglacial till, in the area of Kilkeel. This presentation will include results to date from this study with the aim of elucidating the glaciation and deglaciation history of geomorphologically complex area.

How to cite: Coughlan, M., Wheeler, A., Long, M., O'Toole, R., and Service, M.: Offshore stratigraphic and geomorphological record of northeastern Ireland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3902, https://doi.org/10.5194/egusphere-egu2020-3902, 2020

D2607 |
EGU2020-5561
Quentin Glaude and Christoph Kittel

 

Remote sensing has long been used as a powerful tool for the observation in cryospheric sciences. With the advances brought by the ESA Copernicus program, Earth observation goes a step further in its ability to get acquisitions at very high temporal rate. This is even amplified in polar regions due to heliosynchronism of satellites’ orbits. Earth observation shifts from sporadic observations to Earth monitoring.

Observations are a critical aspect for the assessment of geophysical models. The ability of a model to replicate observations is crucial as a benchmark. It also allows to refine our comprehension of Earth systems, such as in cryospheric sciences.

In this work, we are using the regional climate model MAR to compute the surface melt on a domain focusing on the Roi Baudouin Ice Shelf, Queen Maud Land, East Antarctica. From the results, we extract the number of days with surface melt in a region. In parallel, we employ remote sensing to obtain comparison data. Synthetic aperture radar appears as a solution of choice thanks to its day-and-night (critical in polar regions) and atmospheric-free capabilities. Radar backscattering anomalies between different dates are witnesses of substantial increase of soil moisture. Using Sentinel-1 in its wide-swath modes (namely Interferometric Wide Swath and Extra Wide Swath modes) and multiple satellite paths, near-daily acquisitions can be obtained. By comparing the two independent results, we better constraint model’s outputs while also better interpret SAR acquisitions. 

How to cite: Glaude, Q. and Kittel, C.: Comparison Between Surface Melt Days Estimation from a Regional Climate Model and Near-Daily Synthetic Aperture Radar Backscattering, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5561, https://doi.org/10.5194/egusphere-egu2020-5561, 2020

D2608 |
EGU2020-6995
Hans Petter Sejrup, Berit Oline Hjelstuen, Mariana Ramos Esteves, Henry Patton, Monica Winsborrow, Karin Andreassen, Tine Rasmussen, and Alun Hubbard

 The timing, rates and patterns of retreat of western sectors of the last Eurasian Ice Sheet (EurIS) are poorly constrained, hampered by limited observations from the marine domain. A better knowledge of the deglaciation of the NW European marine areas/continental margins is essential for efforts to understand the role of different controlling factors (such as ice streams, atmospheric and oceanic conditions, relative sea level, morphology and substrate) on the stability of the EurIS, and also for ice-sheet stability in general. Based on new and existing mapping of glacial landforms, together with a compilation of existing and recalibrated dates from the NW European shelf, a new reconstruction of the retreating EurIS between 20 and 14 ka BP will be presented. Our reconstruction suggests an initial modest withdrawal from maximum extent to c. 19 ka BP along the entire western marine-terminating margin. From 19ka the two major marine-terminating ice streams, in the Norwegian Channel and Bear Island Trough, begin to retreat/collapse. This destabilisation leads to rapid interior downdraw and the eventual unzipping of the British-Irish and Fennoscandian ice sheets at c. 18.5 ka BP, and the Barents-Kara and Fennoscandian ice sheets between 16 and 15 ka BP. Based on our new reconstruction and modelling results, the importance of factors controlling the nonsynchronous and rapid deglaciation of marine-based sectors and the implications for the stability of the ice sheet, will be discussed. The chronology and patterns of past marine deglaciations provide contextual insight into ice sheet instabilities and the mechanisms behind, underpinning the ongoing retreat of the Greenland and Antarctic ice sheets today.

 

How to cite: Sejrup, H. P., Hjelstuen, B. O., Esteves, M. R., Patton, H., Winsborrow, M., Andreassen, K., Rasmussen, T., and Hubbard, A.: Disintegration of the marine based parts of the last Eurasian Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6995, https://doi.org/10.5194/egusphere-egu2020-6995, 2020

Chat time: Tuesday, 5 May 2020, 16:15–18:00

D2609 |
EGU2020-7294
Thomas Jordan, Alex Brisbourne, Carlos Martin, Rebecca Schlegel, Dustin Schroeder, and Andrew Smith

Lateral shear margins provide resistance to ice flow within ice streams and play an important role in the overall dynamics of ice sheets. The strength and location of shear margins are known to be influenced by both subglacial factors (e.g. bed roughness, meltwater availability) and ice rheology (ice temperature, ice fabric, and damage). Assessing the relative contribution of these factors upon ice-stream flow is complex but can be aided by geophysical measurements (e.g. radar-sounding and seismic imaging) of the ice-stream subsurface. There are, however, ongoing challenges in obtaining geophysical information in an appropriate form to be incorporated into ice-flow models. This is true of ice fabric, and its direction-dependent effect upon ice viscosity is typically neglected in models of ice streams.

Here we develop a framework to relate ice fabric measurements from polarimetric radar sounding to ice-flow enhancement within ice streams. First, we extend a `polarimetric coherence’ radar method to automate the extraction of ice fabric using quad-polarized data.  Second, using a previously developed anisotropic flow-law formulation, we relate the radar fabric measurements to direction-dependent enhancement factors of glacier ice. We demonstrate the approach using a radar ground survey, collected by the British Antarctic Survey, which traverses between the centre and shear margin of Rutford Ice Stream. The data indicate that a vertical girdle fabric is present in the near-surface of the ice stream (approximately the top 300 m) which azimuthally rotates and strengthens toward the shear margin. We then assess the effect that the girdle fabric has upon shear and compression and the impact upon ice-flow models of Rutford Ice Stream.

 

 

 

How to cite: Jordan, T., Brisbourne, A., Martin, C., Schlegel, R., Schroeder, D., and Smith, A.: Relating polarimetric radar measurements of ice fabric to ice-flow enhancement of Rutford Ice Stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7294, https://doi.org/10.5194/egusphere-egu2020-7294, 2020

D2610 |
EGU2020-9048
Aleksandr Montelli and Jonathan Kingslake

Present-day englacial temperatures are the product of the millennial-scale histories of ice flow and thermal boundary conditions experienced by an ice sheet. Vertical englacial temperature profiles extracted from boreholes drilled at ice divides record past ice dynamics and changing external forcings. Bindschadler (1990) estimated the timing of grounding of Crary Ice Rise, Ross Sea, by minimizing the mismatch between modelled and measured temperature profiles. This approach has huge potential if future boreholes are drilled at Antarctic ice rises in locations suspected of undergoing significant dynamics change. Yet, the uncertainties inherent in this approach must be carefully assessed to target and maximize the utility of borehole drilling. Here, using a 1D vertical heat flux model, we simulate the evolution of temperature as a function of depth in six locations with slow-flowing, cold-based ice in the Weddell and Ross Sea sectors of the West Antarctic Ice Sheet. The locations were chosen using output from the Parallel Ice Sheet Model (PISM) as which are most likely to have ungrounded and regrounded during the last deglaciation (i.e., through last 20 k.y.). We use the shallow ice approximation assuming horizontally isothermal ice and no basal sliding. Several parameters, accounting for timing and duration of grounding/ungrounding events, surface temperature evolution, accumulation rate, ice-thickness change, geothermal heat flux and vertical velocity, are varied to generate a range of different temperature profile outputs. Uncertainties associated with each parameter are then evaluated using a Monte-Carlo approach, yielding a statistical account of model sensitivity to key variables. We highlight that the precision needed to infer timing of grounding increases with the duration of grounded ice flow. Results presented here can help in choosing future ice drilling sites, and provide useful constraints on inferring past forcings and changing boundary conditions from in-situ temperature-depth measurements.

How to cite: Montelli, A. and Kingslake, J.: Modelling ice rise englacial temperature profiles to constrain past ice-sheet dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9048, https://doi.org/10.5194/egusphere-egu2020-9048, 2020

D2611 |
EGU2020-9829
Arjen P. Stroeven, Ramona A.A. Schneider, Robin Blomdin, Natacha Gribenski, Marc W. Caffee, Chaolu Yi, Xiangke Xu, Xuezhen Zeng, Martina Hättestrand, Ping Fu, and Lewis A. Owen

Paleoglaciological data is a crucial source of information towards insightful paleoclimate reconstructions by providing vital boundary conditions for regional and global climate models. In this context, the Third Pole Environment is considered a key region because it is highly sensitive to global climate change and its many glaciers constitute a diminishing but critical supply of freshwater to downstream communities in SE Asia. Despite its importance, extents of past glaciation on the Tibetan Plateau remain poorly documented or controversial largely because of the lack of well define glacial chronostratigraphies and reconstructions of former glacier extent. This study contributes to a better documentation of the extent and improved resolution of the timing of past glaciations on the southeastern margin of the Tibetan Plateau. We deploy a high-resolution TanDEM-X Digital Elevation Model (12 m resolution) to produce maps of glacial and proglacial fluvial landforms in unprecedented detail. Geomorphological and sedimentological field observations complement the mapping while cosmogenic nuclide exposure dating of quartz samples from boulders on end moraines detail the timing of local glacier expansion. Additionally, samples for optically stimulated luminescence dating were taken from extensive and distinct terraces located in pull-apart basins downstream of the end moraines to determine their formation time. We compare this new dataset with new and published electron spin resonance ages from terraces. Temporal coherence between the different chronometers strengthens the geochronological record while divergence highlights limitations in the applicability of the chronometers to glacial research or in our conceptual understanding of landscape changes in tectonic regions. Results highlight our current understanding of paleoglaciation, landscape development, and paleoclimate on the SE Tibetan Plateau.

How to cite: Stroeven, A. P., Schneider, R. A. A., Blomdin, R., Gribenski, N., Caffee, M. W., Yi, C., Xu, X., Zeng, X., Hättestrand, M., Fu, P., and Owen, L. A.: Extending the paleoglaciological record of the southeastern Tibetan Plateau by combining geochronological and high-resolution remote sensing techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9829, https://doi.org/10.5194/egusphere-egu2020-9829, 2020

D2612 |
EGU2020-11714
Fabio Magrani, Pierre Valla, and David Egholm

Numerical modeling already demonstrated to be a powerful tool for investigating the role of surface processes, including glaciation, in landscape evolution. Ice model developments from 1-D simulations (Oerlemans, 1984; MacGregor et al., 2000) to more recent 2-/3D models (e.g. Egholm et al., 2011) allow investigating glacier dynamics and landscape erosion over various timescales by also incorporating the effects of rugged topography and feedbacks between erosion by glacial sliding and the extent of glaciation.

Precipitation and temperature are primary controls on glacier mass balance, driving basal sliding and erosion in response to changes in both ice thickness and extent. However, still little is known on how erosion patterns behave under temporally- and spatially-varying combinations of these two climatic parameters. Since ice basal sliding and fluctuations of water-pressure peak around the equilibrium-line altitude (ELA) (MacGregor et al., 2000; Herman et al., 2011), erosion would be expected to follow similar patterns due to their relationship with abrasion and quarrying. However, modeled glaciers with similar geographical extents may present significant differences in either ice thickness and/or ELA, depending on the simulated climate scenarios (i.e. combinations of precipitation/temperature). This will in turn affect ice dynamics and thus erosion patterns, especially differences between the accumulation and ablation areas.

In this study we aim to numerically explore how both ice dynamics and erosion patterns are influenced by specific climatic scenarios (i.e. precipitation and temperature conditions). Towards this, we used the Integrate Second Order Shallow Ice Approximation - iSOSIA (Egholm et al., 2011) model, which uses a positive degree-day (PDD) model for mass balance and a depth-integrated computation for ice flux with irregular Voronoi cell grids, allowing local mesh adjustments in selected topographic areas. In addition, this model is capable to couple ice, water and sediments which permits to explore erosion feedbacks onto ice dynamics.

Using a synthetic Alpine landscape, we performed a set of simulations with mass balance scenarios preserving similar ELAs and ice extents between runs. From these simulations, we generated glacial erosion patterns (e.g. steady-state erosion, total erosion integrated over a glacial cycle), testing different erosion laws (abrasion, quarrying) as well as the role of subglacial water and sediment entrainment. From the different scenarios, we also investigated how ice dynamics (i.e. ice flux and thickness) and erosion rates vary spatially and differ between the accumulation/ablation areas. Our ultimate goal is to understand how glacial erosion patterns, combined with classic paleo-glacial reconstructions and paleo-ELA estimates, can be used as proxies for paleoclimate reconstruction.

 

References:

Egholm, D.L. et al. (2011). Modeling the flow of glaciers in steep terrains: The integrated second‐order shallow ice approximation (iSOSIA). Journal of Geophysical Research. Vol. 116.

Herman, F. et al. (2011). Glacial hydrology and erosion patterns: A mechanism for carving glacial valleys. Earth and Planetary Science Letters. Vol. 310.

MacGregor, K.R. et al. (2000). Numerical simulations of glacial-valley longitudinal profile evolution. Geology. Vol. 28. No. 11.

Oerlemans, J. (1984). Numerical experiments on large-scale glacial erosion: Zeitschrift für Gletscherkunde und Glazialgeologie. Vol. 20.

How to cite: Magrani, F., Valla, P., and Egholm, D.: Numerically simulated ice dynamics and erosion patterns under specific climate scenarios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11714, https://doi.org/10.5194/egusphere-egu2020-11714, 2020

D2613 |
EGU2020-11787
Christopher Halsted, Jeremy Shakun, Lee Corbett, Paul Bierman, P. Thompson Davis, Brent Goehring, Alexandria Koester, and Marc Caffee

In the northeastern United States, there are extensive geochronologic and geomorphic constraints on the deglaciation of the southeastern Laurentide Ice Sheet; thus, it is an ideal area for large-scale ice volume reconstructions and comparison between different ice retreat chronometers. Varve chronologies, lake and bog-bottom radiocarbon ages, and cosmogenic nuclide exposure ages constrain the timing of ice retreat, but the inferred ages exhibit considerable noise and sometimes disagree. Additionally, there are few empirical constraints on ice thinning, forcing ice volume reconstructions to rely on geophysically-based ice thickness models. Here, we aim to improve the understanding of the southeastern Laurentide Ice Sheet recession by (1) adding extensive ice thickness constraints and (2) compiling all available deglacial chronology data in the region to investigate discrepancies between different chronometers.

To provide insight about ice sheet thinning history, we collected 120 samples for in-situ 10Be and 10 samples for in-situ 14C cosmogenic exposure dating from various elevations at 13 mountains in the northeastern United States. By calculating ages of exposure at different elevations across this region, we reconstruct paleo-ice surface lowering of the southeastern Laurentide Ice Sheet during deglaciation. Where we suspect that 10Be remains from pre-Last Glacial Maximum periods of exposure, in-situ 14C is used to infer the erosional history and minimum exposure age of samples.

Presently, we have measured 10Be in 73 samples. Mountain-top exposure ages located within 150 km of the southeastern Laurentide Ice Sheet terminal moraine indicate that near-margin thinning began early in the deglacial period (~19.5 to 17.5 ka), coincident with the slow initial margin retreat indicated by varve records. Exposure ages from several mountains further inland (>400 km north of terminal moraine) collected over ~1000 m of elevation range record rapid ice thinning between 14.5 and 13 ka. Ages within each of these vertical transects are similar within 1σ internal uncertainty, indicating that ice thinned quickly, less than a few hundred years at most. This rapid thinning occurred at about the same time that varve records indicate accelerated ice margin retreat (14.6–12.9 ka), providing evidence of substantial ice volume loss during the Bølling-Allerød warm period.

Our critical evaluation of deglacial chronometers, including valley-bottom 10Be ages from this project, is intended to constrain ice margin retreat rates and timing in the region. Ultimately, we will integrate our ice thickness over time constraints with the existing network of deglacial ages to create a probabilistic reconstructions of the southeastern Laurentide Ice Sheet volume during its recession through the northeastern United States.

How to cite: Halsted, C., Shakun, J., Corbett, L., Bierman, P., Davis, P. T., Goehring, B., Koester, A., and Caffee, M.: Improved reconstruction of the southeastern Laurentide Ice Sheet deglaciation: constraining ice thinning using in-situ cosmogenic 10Be and 14C and critically evaluating different retreat rate chronometers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11787, https://doi.org/10.5194/egusphere-egu2020-11787, 2020

D2614 |
EGU2020-9886
Devin Harrison, Neil Ross, Andrew Russell, and Stuart Jones

The sedimentary record of Icelandic ice-contact environments provides valuable information about glacier margin dynamics and position, relative sea-level and the geomorphic processes driving proglacial environments. This important archive has been little exploited, however, with most glacier and sea level reconstructions based on limited sedimentary exposures and surface geomorphic evidence. Although geophysical surveys of Icelandic sandur have been conducted, they have often been of limited spatial scale and focused on specific landforms. Here, we report an extensive (42 km of data) detailed low-frequency (40 and 100 MHz) ground-penetrating radar (GPR) survey of the Sandgigúr moraine complex, SE Iceland, which transforms our understanding of this landform, with implications for the Holocene history of Skeiðarársandur and SE Iceland.

The Sandgigúr moraines are located on Skeiðarársandur, SE Iceland, down-sandur of large Little Ice Age-moraines of Skeiðarárjökull. They have a relatively subtle surface geomorphic expression (typically 125 m wide and 7 m high), and knowledge of their formation is limited, with no dating control on their age or detailed geomorphic or sedimentological investigations.  GPR investigations reveal a much larger (60 m high and 1200 m wide) and extensive buried moraine complex than that suggested by surface morphology, suggesting that the moraine was a major Holocene ice margin of Skeiðarárjökull.

GPR reflections interpreted as large progradational foresets (up to 20 m in height) beneath the morainic structure are consistent with a sub-aqueous depositional environment before moraine formation, providing potential controls on former sea-level.  The GPR data also provide information on the internal structure of the moraine, with evidence for glacitectonism within the proximal side of the moraine, multiphase moraine formation, and possible buried ice at depth. A 30-40 m thick package of down-sandur dipping GPR reflections drape the leeside of the moraine, evidencing glaciofluvial deposition during and after moraine development. Potential moraine breaches, possibly caused by glaciofluvial (e.g. jökulhlaup) events, are also apparent within the GPR data and the surface geomorphology.

We combine GPR-derived subsurface architecture with the current surface morphology to develop a conceptual model detailing the geomorphic evolution of the moraines and surrounding region, from pre-moraine morphology, to their formation and breaching, resulting in the subsequent present-day morphology. These results provide new insights into the Holocene to present-day evolution of Skeiðarársandur and Skeiðarárjökull, with implications for reconstructions of the Holocene environmental history of SE Iceland.

How to cite: Harrison, D., Ross, N., Russell, A., and Jones, S.: Geophysical evidence for a large Holocene ice marginal moraine of Skeiðarárjökull, SE Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9886, https://doi.org/10.5194/egusphere-egu2020-9886, 2020

D2615 |
EGU2020-12713
Jorie Clark, Anders Carlson, Alberto Reyes, and Glenn Milne

During the last glacial maximum, the Cordilleran and Laurentide ice sheets met just to the east of the Canadian Rocky Mountains, forming an ice-sheet saddle. When this saddle disappeared has implications on deglacial global sea-level rise and abrupt climate change as well as human migration patterns to the Americas. We will present new 10-Be boulder ages from six sites on a ~1100 km transect along the ice-sheet suture zone, to date Cordilleran-Laurentide ice-sheet separation. Results will directly test whether or not Cordilleran-Laurentide separation contributed to abrupt sea-level rise during meltwater pulse 1a (14.6-14.3 ka) in response to abrupt Bølling warming (14.6-14.0 ka).

How to cite: Clark, J., Carlson, A., Reyes, A., and Milne, G.: 10Be dating Cordilleran-Laurentide ice-sheet separation during the last deglaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12713, https://doi.org/10.5194/egusphere-egu2020-12713, 2020

D2616 |
EGU2020-13198
Alberto Reyes, Anders Carlson, and Jesse Reimink

The timing of northwest Laurentide ice-sheet deglaciation is important for understanding how ice-sheet retreat, and associated meltwater discharge, may have been involved in abrupt climate change and rapid sea-level rise at the end of the last glaciation. However, the deglacial chronology across the western Canadian Shield is poorly understood, with only a handful of minimum-limiting 14C dates and sparse cosmogenic nuclide exposure dates constraining the timing and pattern of northwest Laurentide ice-sheet retreat across >1000 km of ice-sheet retreat to the marine limit west of Hudson Bay. We present cosmogenic 10Be surface exposure dating of glacial erratics at two sites, within a ~160,000 km2 region with no reliable temporal constraints on ice-margin retreat, to directly date the timing of northwest Laurentide ice-sheet deglaciation. Six erratics perched directly on bedrock at a site on the western edge of the Slave Craton have exposure ages between 12.8±0.6 and 12.2±0.6 thousand years ago (ka; ±1sigma). Five erratics on bedrock, sampled at a site 115 km up-ice to the east, yielded exposure ages between 10.8±0.5 and 11.6±0.5 ka. When corrected for decreased atmospheric depth due to isostatic uplift since deglaciation, the error-weighted mean ages for the two sites indicate that the Laurentide ice sheet retreated through this region of the western Canadian Shield between 13.3±0.2 and 11.8±0.2 ka, or at least 1 kyr earlier than inferred from the canonical compilation of minimum-limiting 14C dates for deglaciation and paleo-glaciological models. We tentatively infer a preliminary ice-margin retreat rate of ~0.1 m kyr-1 over this interval spanning much of the Younger Dryas which, compared to earlier estimates, implies a substantially lower volume of meltwater flux from the retreating northwest Laurentide ice sheet at this time.  Additional exposure ages on glacial erratics across this data-poor region are needed for validation of existing deglacial ice-sheet models, which can in turn contribute to comprehensive testing of hypotheses related to northwest Laurentide ice-sheet retreat rate, abrupt deglacial sea-level rise, and potential forcing of associated climate change events.

How to cite: Reyes, A., Carlson, A., and Reimink, J.: Revised chronology of northwest Laurentide ice-sheet deglaciation from beryllium-10 exposure-dated erratics on the western Canadian Shield, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13198, https://doi.org/10.5194/egusphere-egu2020-13198, 2020

D2617 |
EGU2020-3417
| solicited
Christine Batchelor, Julian Dowdeswell, Eric Rignot, and Romain Millan

The Southeast (SE) Greenland margin, which includes the SE sector of the Greenland Ice Sheet (GIS) and the eastern Julianehåb Ice Cap (JIC), is drained by a number of fast‐flowing, marine‐terminating outlet glaciers. Although the SE Greenland margin is suggested to have been highly sensitive to past climatic changes, mountainous terrain and a lack of ice‐free areas have largely prevented analysis of the deglacial and Holocene behaviour of these outlet glaciers. Here we use bathymetric data, from multibeam echo-sounding acquired by NASA’s Earth Venture Sub‐orbital Oceans Melting Greenland (OMG) mission and from gravity inversion derived from Operation Icebridge (OIB) gravity data, from 36 fjords along the SE Greenland margin to map the distribution of more than 50 major submarine moraines. The moraines are up to 3 km long in the former ice‐flow direction, reach up to 150 m above the surrounding seafloor, and span the width of the fjord.

Inner‐fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords of the SE GIS and the JIC. Their locations beyond the oldest ice‐margin position where it is known from aerial photographs and correlation with prominent terrestrial moraines suggest that the inner‐fjord moraines were produced sometime during the Neoglacial (since approximately 4 ka).

Major moraine ridges are present in a midfjord setting in all of the nine fjords of the eastern JIC yet are generally absent from the deeper and wider fjords of the SE GIS. Given the distribution of published deglacial ages, we hypothesize that the midfjord moraines of the eastern JIC were formed during an ice‐margin still‐stand or advance that occurred during the early Holocene. It is possible that this still‐stand or advance had a climatic control, for example, the 8.2‐ka event that has been recorded from Greenland ice cores. The absence of midfjord moraines from the deeper and wider fjords of the SE GIS to the north suggests relatively rapid and continuous ice retreat occurred during the last deglaciation. The contrasting behaviour of the SE GIS and the eastern JIC during the last deglaciation probably reflects differences in fjord geometry and exposure to ocean heat.

How to cite: Batchelor, C., Dowdeswell, J., Rignot, E., and Millan, R.: Submarine glacial landforms in Southeast Greenland fjords reveal contrasting outlet-glacier behaviour since the Last Glacial Maximum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3417, https://doi.org/10.5194/egusphere-egu2020-3417, 2020

D2618 |
EGU2020-15076
Daniel Moreno, Javier Blasco, Jorge Álvarez-Solas, Alexander Robinson, and Marisa Montoya

The climate during the last glacial period was far from stable. Evidence has shown the presence of layers of ice-rafted debris (IRD) in deep sea sediments, which have been interpreted as quasi-periodic episodes of massive iceberg calving from the Laurentide Ice Sheet (LIS). Several mechanisms have been proposed, yet the ultimate cause of these events is still under debate. In fact, one of the main sources of uncertainty and diversity in model response is the choice of basal friction law. Therefore, it is essential to determine the impact of this feature in glacial transport and erosion, deposition of sediments and ice streams among others. We herein study the effect of a wide range of basal friction parameters and laws under glacial conditions over the LIS. In addition, the impact of the thermodynamic state of the ice is taken into account by means of two independent procedures: a two-valued friction coefficient approach and an active basal hydrology. The aim is to determine under what conditions, if any, physically-based oscillations are possible in a three-dimensional hybrid ice-sheet model. Increasing our understanding of both basal friction laws and basal hydrology will improve not only reconstructions of paleo ice dynamics but also help to constrain the potential future evolution of current ice sheets.

How to cite: Moreno, D., Blasco, J., Álvarez-Solas, J., Robinson, A., and Montoya, M.: Physically-based oscillations of the Laurentide under glacial conditions., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15076, https://doi.org/10.5194/egusphere-egu2020-15076, 2020

D2619 |
EGU2020-17965
Jane L. Andersen, Jennifer C. Newall, Robin Blomdin, Sarah E. Sams, Derek G. Fabel, Alexandria J. Koester, Finlay M. Stuart, Nathaniel A. Lifton, Ola Fredin, Marc W. Caffee, Neil F. Glasser, Irina Rogozhina, Yusuke Suganuma, Jonathan M. Harbor, and Arjen P. Stroeven

Reconstructing past ice surface changes is key to test and improve ice-sheet models. Yet, data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past and future climate changes. Here, we attempt to test whether the ice-sheet margin in western Dronning Maud Land has thinned since the last glacial maximum or whether it perhaps thickened in places due to increased precipitation associated with warmer climates. We report cosmogenic multi-nuclide (10Be, 26Al, 36Cl, 21Ne) data from bedrock and erratics on nunataks along Jutulstraumen ice stream and the Penck Trough in western Dronning Maud Land, East Antarctica. Spanning elevations between 751-2387 m above sea level, and between 5 and 450 m above the contemporaneous local ice sheet surface, the samples record apparent exposure ages between 2 ka and 5 Ma. The highest bedrock sample indicates (near-) continuous exposure since at least the Pliocene, with a very low apparent erosion rate of 15±3 cm Ma-1. However, there are also clear indications of a thicker-than-present ice sheet within the last glacial cycle, thinning ~35-120 m at several nunataks during the Holocene (~2-11 ka). Owing to difficulties in retrieving suitable sample material from the often rugged and quartz-poor mountain summits, and due to the presence of inherited nuclides in many of our samples, we are unable to present robust thinning estimates from elevational profiles. Nevertheless, the results clearly indicate ice-surface fluctuations of several hundred meters within the last glacial cycle in this sector of the EAIS, between the current grounding line and the edge of the polar plateau. Finally, inverse modelling of the cosmogenic multi-nuclide inventories in bedrock yields estimates of total erosion and ice cover across multiple glacial cycles. Our results show that the EAIS in western Dronning Maud Land was thicker than present during most of the Quaternary, covering sample sites up to 200 m above the present-day ice sheet for ~80 % of this period. Thinning of the ice since the last glacial maximum, combined with a long-term record of thicker-than-present ice, indicate that the ice sheet below the polar plateau in western Dronning Maud Land generally expands and thickens during climate cooling, despite decreasing precipitation associated with a cooler Southern Ocean.

How to cite: Andersen, J. L., Newall, J. C., Blomdin, R., Sams, S. E., Fabel, D. G., Koester, A. J., Stuart, F. M., Lifton, N. A., Fredin, O., Caffee, M. W., Glasser, N. F., Rogozhina, I., Suganuma, Y., Harbor, J. M., and Stroeven, A. P.: New constraints on Plio-Pleistocene East Antarctic Ice Sheet thickness: cosmogenic exposure data from western Dronning Maud Land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17965, https://doi.org/10.5194/egusphere-egu2020-17965, 2020

D2620 |
EGU2020-19779
Songtao Ai, Zemin Wang, Jiachun An, Yuande Yang, Chunxia Zhou, Tingting Liu, Hao Ke, Weifeng Hao, and Hong Geng

Ice flow velocity is sensitive to glacier variations both controlling and representing the delivery of ice and affecting the future stability of ice masses in a warming climate. Austre Lovénbreen (AL) is one of the poly-thermal glaciers in the high Arctic and located on the northwestern coast of Spitsbergen, Svalbard. The ice flow velocity of AL was investigated using in situ global positioning system (GPS) observations over 15 years and numerical modelling with Elmer/Ice. First, the ice flow velocity field of AL along central flow line was presented. While AL moves slowly at a speed of approximate 4 m/a, obvious seasonal changes of ice flow velocity can be found in the middle of the glacier, where the velocity in spring-summer is 47% larger than in autumn–winter in 2016, and the mean annual velocity variation in different seasons is 14% from 2009 until 2016. Second, the numerical simulation was performed considering the poly-thermal character of the glacier, and indicated that there are two peak ice flow regions on the glacier, and not just one peak ice flow region as previously believed. The new peak ice flow zone found by simulation was verified by field work, which also demonstrated that the velocity of the newly identified zone is 8% faster than the previously identified zone. Third, although our field observations showed that the ice flow velocity is slowly increasing recently, the maximum ice flow velocity will soon begin to decrease gradually in the long term according to glacier evolution modelling of AL.

How to cite: Ai, S., Wang, Z., An, J., Yang, Y., Zhou, C., Liu, T., Ke, H., Hao, W., and Geng, H.: How much can we benefit from the combination of numerical simulation and in situ observations? A case study on an Arctic polythermal valley glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19779, https://doi.org/10.5194/egusphere-egu2020-19779, 2020

D2621 |
EGU2020-6774
Harunur Rashid, Mary Smith, Min Zeng, Yang Wang, Julie Drapeau, and David Piper

Hughes et al. (1977) hypothesized of a pan-Arctic Ice Sheet that behaved as a single dynamic system during the Last Glacial Maximum. Moreover, the authors suggested a nearly grounded ice shelf in Davis Strait implying that little or no exchange between Baffin Island and the Labrador Sea. Here we present data at 1-cm (<100 years) resolution between ~12 ka and 45 ka that shed light on the discharge from Hudson Strait and Lancaster Sound ice streams of the Late Pleistocene Laurentide Ice Sheet. A reference sediment core at 938 m water depth on the SE Baffin Slope was investigated with new oxygen isotope stratigraphy, X-ray fluorescence geochemistry, and 18 14C-AMS dates and correlated to 14 regional deep-water cores. Detrital carbonate-rich sediment layers H0-H4 were derived principally from Hudson Strait. Shortly after H2 and H3, the shelf-crossing Cumberland Sound ice stream supplied dark brown ice-proximal stratified sediments but no glacigenic debris-flow deposits. The counterparts of H3, H4, and (?)H5 events in the deep Labrador basin are 4–10 m thick units of thin-bedded carbonate-rich mud turbidites from glacigenic debris flows on the Hudson Strait slope. The behavior of the Hudson Strait ice stream changed through the last glacial cycle. The Hudson Strait ice stream remained at the shelf break in H3-H5 but retreated rapidly across the shelf in H0-H2 and did not deglaciate Hudson Bay. During this time, Cumberland Sound ice twice reached the shelf edge. In H3–H5, it remained at the shelf break long enough to supply thick turbidites. Minor supply of carbonate-rich sediment from Baffin Bay allows chronologic integration of the Baffin Bay and Labrador Sea detrital carbonate records, which is diachronous with respect to Heinrich events. The asynchrony of the carbonate events implies an open seaway through Davis Strait. Our data suggest that the maximum extent of ice streams in Hudson Strait, Cumberland Sound, and Lancaster Sound was neither synchronous.

How to cite: Rashid, H., Smith, M., Zeng, M., Wang, Y., Drapeau, J., and Piper, D.: Asynchronous instability of NE ice streams of the Laurentide Ice Sheet recorded in the marine sediments of Labrador Sea during the last glacial cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6774, https://doi.org/10.5194/egusphere-egu2020-6774, 2020

D2622 |
EGU2020-21838
Jean-Loup Rubino, Charlotte Larcher, and Julien Bourget

It is classically assume that prior to deep glacial valleys incision below large scale ice cap, often interpreted as the results of ice flow melting during tidewater period, the initial glacial topography was flat or very low angle and created during a major phase of cold glaciers advance as suggested by quaternary studies. Therefore up to now we have assume that the top of late Ordovician buried hills separating major glacial valleys was the remains of this flat surface truncating the pre-glacial Ordovician Hawaz series, later on flooded by the Lower Silurian. Surprisingly by reinterpreting 3D seismic cubes using spectral decomposition technics on the Murzuk basin in SE Libya, it appears that the top of buried hills are not at all characterized by a flat erosional surface, but it is strongly irregular and shows the development of narrow valley networks displaying the classical dendritic erosional pattern diagnostic of fluvial erosion. These small valleys are organized into a tributary network and don’t flow toward the ice margin, i.e. toward the N-NW but most of the time flow at right angle toward the adjacent main glacial valleys which are pointing toward the NW. These narrow valley networks in this context could be either glacial tunnel valleys located at the periphery of the ice cap in close relationships with glacial fronts (their common settings) or could correspond to fluvial valleys developed later on, in a subaerial setting at some distance from glacial fronts; we retain this second interpretation because in addition to the geomorphic features: (1) they flow parallel to the fronts that we have already recognized, Moreau et al. (2005), Rubino et al.  2007 and (2) they are suspended in the sense that these lateral networks do not reach the bottom of the main glacial valley but, they appear to be connected within the upper part of the glacial infill, immediately below the early Silurian post glacial flooding characterized by the well-known Rhuddanian hot shales. As a result, the incision of the valley network appears quite late in the ice cap melting history. It is why we tend to interpret these valleys erosion as the result of post glacial melting during ice retreat at some distance from the ice front and strongly enhanced by isostatic rebound. Some possible modern analogs of such valley fringing highs may exist in Artic Canadian islands.

How to cite: Rubino, J.-L., Larcher, C., and Bourget, J.: Fluvial incised networks on top of late Ordovician interglacial valley buried hills as the result of post glacial isostatic rebound; 3D seismic input, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21838, https://doi.org/10.5194/egusphere-egu2020-21838, 2020

D2623 |
EGU2020-570
Benjamin J. Stoker, Martin Margold, Duane G. Froese, and John C. Gosse

The northwestern sector of the Laurentide Ice Sheet coalesced with the Cordilleran Ice Sheet over the southern Mackenzie Mountains, and with local montane glaciers along the eastern slopes of the Mackenzie Mountains. Recent numerical modelling studies have identified rapid ice sheet thinning in this region as a major contributor to Meltwater Pulse 1A. Despite advances in remote sensing and numerical dating methods, the configuration and chronology of the northwestern sector of the Laurentide Ice Sheet has not been reconstructed in detail. The last available studies date back to the 1990s, where field surveys and mapping from aerial imagery were used to reconstruct the Last Glacial Maximum glacier extents in the Mackenzie Mountains. Cross-cutting relationships between glacial landforms and a series of 36Cl cosmogenic nuclide dates were used to propose a deglacial model involving a significant ice readvance in the region. However, the chronological evidence supporting the readvance is uncertain because the individual ages are few and poorly clustered. Here we present an updated map of the Last Glacial Maximum glacial limits and the recessional record in the Mackenzie Mountains, based on glacial geomorphological mapping from the ArcticDEM. Sixteen new 10Be dates from four sites that were previously glaciated by the Laurentide Ice Sheet constrain the deglacial sequence across the region. These dates indicate ice sheet detachment from the eastern Mackenzie Mountains at ~16 ka as summits became ice-free. The Mackenzie Valley at ~ 65 °N became ice free at ~ 13 – 14 ka, towards the end of the Bølling-Allerød warm period. These chronological constraints on the deglaciation of the Laurentide Ice Sheet allow us to reinterpret landform relationships in the Mackenzie Mountains to reconstruct the ice sheet retreat pattern. Our updated model of the LGM extent and timing of deglaciation in the Mackenzie Mountains provides important constraints for quantifying past sea level contributions and numerical modelling studies.

How to cite: Stoker, B. J., Margold, M., Froese, D. G., and Gosse, J. C.: The deglaciation of the northwestern Laurentide Ice Sheet in the Mackenzie Mountains, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-570, https://doi.org/10.5194/egusphere-egu2020-570, 2019

D2624 |
EGU2020-9592
Andreas Born and Alexander Robinson

As layers of accumulated snow compact into ice and start to flow under its own weight, their deformations are recorded in the vertical structure of the glacier. Therefore, the isochronal stratigraphy of the Greenland ice sheet provides comprehensive dynamic constraints, which, with adequate methods, can be used to calibrate ice sheet models and greatly improve their accuracy.

We present the first three-dimensional ice sheet model that explicitly resolves isochrones. Individual layers of accumulation do not exchange mass with each other as the flow of ice deforms them, resembling the Lagrangian description of flow in the vertical dimension, while lateral flow within each layer is Eulerian. Direct comparison with dated radiostratigraphy is used to filter an ensemble of simulations of the Greenland ice sheet. The abundant information implied by the shape of the three-dimensional layering enables us to constrain a large number of degrees of freedom. The mismatch in the thickness of certain isochrones is used to calibrate the climate forcing of different periods of the last glacial cycle.

How to cite: Born, A. and Robinson, A.: Simulations of dated radiostratigraphy for the Greenland ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9592, https://doi.org/10.5194/egusphere-egu2020-9592, 2020

D2625 |
EGU2020-10033
Daniel Martin, Stephen Cornford, and Esmond Ng

The Antarctic Ice Sheet (AIS) is vulnerable to the thinning or even the collapse of its floating ice shelves, which tend to buttress ice streams. Any reduction in buttressing results in acceleration and thinning upstream and potentially the onset of Marine Ice Sheet Instability. Recent work demonstrates that West Antarctica is vulnerable to sustained disintegration in any of its major marine outlets, resulting in 2-3 m sea level rise over 1000 years. At the same time regions in East Antarctica are vulnerable only to the loss of local ice shelves. However, most of this work has used the Bedmap2 dataset as a starting point. Since the release of Bedmap2 in 2012, there has been a sustained campaign of observations, along with improved interpolation techniques based on mass conservation. The resulting datasets, including the recently released BedMachine dataset, incorporate much-improved bedrock and thickness data compared to what was available in Bedmap2. 

We reproduce our previous examination of the millennial-scale vulnerability of the AIS to the loss of its shelves to examine the effect of this improvement on projected Antarctic vulnerability, paying special attention to regions like the Aurora Basin which were under-constrained in Bedmap2.

How to cite: Martin, D., Cornford, S., and Ng, E.: Effect of Improved Bedrock Geometry on Antarctic Vulnerability to Regional Ice Shelf Collapse, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10033, https://doi.org/10.5194/egusphere-egu2020-10033, 2020

D2626 |
EGU2020-1189
Pierre-Olivier Couette, Patrick Lajeunesse, Boris Dorschel, Catalina Gebhardt, Dierk Hebbeln, Etienne Brouard, and Jean-François Ghienne

The maximal extent and subsequent deglaciation of the Laurentide Ice Sheet (LIS) across eastern Baffin Island during the last glacial cycle (MIS-2) has been widely debated during the last decades as different palaeo-glaciological models have been proposed. Spatial and temporal variability of ice sheets extension during Quaternary glaciations complicate the establishment of a reliable reconstruction of the ice dynamics in the area. Furthermore, the lack of geophysical data in most of the fjords, and seaward, makes it difficult to reconcile the proposed terrestrial and marine glacial margins. High-resolution swath-bathymetric data, collected between 2003 and 2017, display a diversity of glacial bedforms in the Clyde Inlet fjord-cross-shelf-trough system (Eastern Baffin Island, Arctic Canada). These bedforms reveal a potential position of the LIS margin during the Last Glacial Maximum (LGM) near the shelf break. Early deglaciation of the Clyde Trough was marked by an initial break up of the ice sheet. This rapid retreat of the ice margin was punctuated by episodic stabilizations forming GZWs. This retreat was followed by a readvance and subsequent slow retreat of the LIS, as indicated by the presence of recessional moraines. Long-term stabilizations within the trough possibly coincided with major climatic cooling episodes, such as the end of Heinrich event 1 (H1) and the Younger Dryas. However, these stabilizations appear to have been influenced by topography, as GZWs can be found at pinning points in the trough. Deglaciation of the fjord occurred during the early Holocene and was faster, probably due to increased water depths. The presence of multiple moraine systems however indicate that deglaciation of Clyde Inlet was marked by stages of ice margin stabilization.

How to cite: Couette, P.-O., Lajeunesse, P., Dorschel, B., Gebhardt, C., Hebbeln, D., Brouard, E., and Ghienne, J.-F.: Morphology reveals deglaciation patterns of the Laurentide Ice Sheet in the Clyde Inlet fjord-cross-shelf trough system, eastern Baffin Island (Arctic Canada), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1189, https://doi.org/10.5194/egusphere-egu2020-1189, 2019

D2627 |
EGU2020-2384
Tancrede P.M Leger, Andrew S. Hein, Angel Rodes, Robert G. Bingham, and Derek Fabel

The former Patagonian Ice Sheet was the most extensive Quaternary ice sheet of the southern hemisphere outside of Antarctica. Against a background of Northern Hemisphere-dominated ice volumes, it is essential to document how the Patagonian Ice Sheet and its outlet glaciers fluctuated throughout the Quaternary. This information can help us investigate the climate forcing mechanisms responsible for ice sheet fluctuations and provide insight on the causes of Quaternary glacial cycles at the southern mid-latitudes. Moreover, Patagonia is part of the only continental landmass that fully intersects the precipitation-bearing southern westerly winds and is thus uniquely positioned to study past climatic fluctuations in the southern mid-latitudes. While Patagonian palaeoglaciological investigations have increased, there remains few published studies investigating glacial deposits from the north-eastern sector of the former ice sheet, between latitudes 41°S and 46°S. Palaeoglaciological reconstructions from this region are required to understand the timing of late-Pleistocene glacial expansion and retreat, and to understand the causes behind potential latitudinal asynchronies in the glacial records throughout Patagonia. Here, we reconstruct the glacial history and chronology of a previously unstudied region of north-eastern Patagonia that formerly hosted the Rio Huemul and Rio Corcovado (43°S, 71°W) palaeo ice-lobes. We present the first detailed glacial geomorphological map of the valley enabling interpretations of the region’s late Quaternary glacial history. Moreover, we present new cosmogenic 10Be exposure ages from moraine boulders, palaeolake shoreline surface cobbles and ice-moulded bedrock. This new dataset establishes a high-resolution reconstruction of the local LGM through robust dating of five distinct moraines limits of the Rio Corcovado palaeo-glacier. Our results demonstrate that, in its north-eastern sector, the Patagonian Ice Sheet reached its last maximum extent during MIS 2, thus contrasting with the MIS 3 maxima found for the southern parts of the ice sheet. We also present geomorphological evidence along with chronological data for the formation of two ice-dammed proglacial lake phases in the valley caused by LGM ice-extent fluctuations and final glacial recession. Furthermore, this dataset allows us to determine the timing and onset of glacial termination 1 in the region. Finally, our findings include the reconstruction of a proglacial lake drainage and Atlantic/Pacific drainage reversal event caused by ice sheet break-up in western Patagonia. Such findings have significant implications for climate fluctuations at the southern mid-latitudes, former Southern Westerly Winds behaviour and interhemispheric climate linkages during and following the local LGM. They provide further evidence supporting the proposed latitudinal asynchrony in the timing of expansion of the Patagonian Ice Sheet during the last glacial cycle and enable glacio-geomorphological interpretations for the studied region.

How to cite: Leger, T. P. M., Hein, A. S., Rodes, A., Bingham, R. G., and Fabel, D.: Late-Pleistocene geomorphological and geochronological history of the former Patagonian Ice Sheet in north-eastern Patagonia (43°S), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2384, https://doi.org/10.5194/egusphere-egu2020-2384, 2020