scholarly journals Submarine melt as a potential trigger of the North East Greenland Ice Stream margin retreat during Marine Isotope Stage 3

2019 ◽  
Vol 13 (7) ◽  
pp. 1911-1923 ◽  
Author(s):  
Ilaria Tabone ◽  
Alexander Robinson ◽  
Jorge Alvarez-Solas ◽  
Marisa Montoya
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
High Sensitivity ◽  
Marine Isotope Stage ◽  
Atmospheric Conditions ◽  
North East ◽  
Ice Stream ◽  
Grounding Line ◽  
Oceanic Forcing ◽  
Marine Isotope Stage 3

Abstract. The Northeast Greenland Ice Stream (NEGIS) has been suffering a significant ice mass loss during the last decades. This is partly due to increasing oceanic temperatures in the subpolar North Atlantic, which enhance submarine basal melting and mass discharge. This demonstrates the high sensitivity of this region to oceanic changes. In addition, a recent study suggested that the NEGIS grounding line was 20–40 km behind its present-day location for 15 ka during Marine Isotope Stage (MIS) 3. This is in contrast with Greenland temperature records indicating cold atmospheric conditions at that time, expected to favour ice-sheet expansion. To explain this anomalous retreat a combination of atmospheric and external forcings has been invoked. Yet, as the ocean is found to be a primary driver of the ongoing retreat of the NEGIS glaciers, the effect of past oceanic changes in their paleo evolution cannot be ruled out and should be explored in detail. Here we investigate the sensitivity of the NEGIS to the oceanic forcing during the last glacial period using a three-dimensional hybrid ice-sheet–shelf model. We find that a sufficiently high oceanic forcing could account for a NEGIS ice-margin retreat of several tens of kilometres, potentially explaining the recently proposed NEGIS grounding-line retreat during Marine Isotope Stage 3.

scholarly journals The sensitivity of the Greenland Ice Sheet to glacial–interglacial oceanic forcing

2018 ◽  
Vol 14 (4) ◽  
pp. 455-472 ◽  
Author(s):  
Ilaria Tabone ◽  
Javier Blasco ◽  
Alexander Robinson ◽  
Jorge Alvarez-Solas ◽  
Marisa Montoya
Keyword(s):  
Sea Level ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Sensitivity ◽  
Glacial Cycles ◽  
The Past ◽  
Primary Driver ◽  
Oceanic Forcing ◽  
Atmospheric Variations

Abstract. Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet–shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial–interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

scholarly journals The sensitivity of the Greenland ice sheet to glacial-interglacial oceanic forcing

2017 ◽  
Author(s):  
Ilaria Tabone ◽  
Javier Blasco ◽  
Alexander Robinson ◽  
Jorge Alvarez-Solas ◽  
Marisa Montoya
Keyword(s):  
Sea Level ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Sensitivity ◽  
Glacial Cycles ◽  
The Past ◽  
Oceanic Forcing ◽  
Atmospheric Variations ◽  
Glacial Periods

Abstract. Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed acceleration of several of Greenland’s marine-terminating glaciers. Recent studies directly attribute this to increasing North Atlantic temperatures, which have triggered melting of the GrIS outlet glaciers, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break, and was thus more directly exposed to ocean changes. However, the GrIS response to paleo oceanic variations has not been investigated from a modelling perspective so far. In this work the evolution of the GrIS over the past two glacial cycles has been studied using a three-dimensional hybrid ice-sheet/ice-shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to the changing oceanic conditions. Oceanic forcing is found to be the dominant driver of the GrIS expansion in glacial times and retreat in interglacial periods. If switched off, paleo atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard in paleo ice sheet modelling.

scholarly journals Submarine melt as a potential trigger of the NEGIS margin retreat during MIS-3

2018 ◽  
Author(s):  
Ilaria Tabone ◽  
Alexander Robinson ◽  
Jorge Alvarez-Solas ◽  
Marisa Montoya
Keyword(s):  
Three Dimensional ◽  
High Sensitivity ◽  
Marine Isotopic Stage ◽  
Mis 3 ◽  
External Forcings ◽  
Grounding Line ◽  
Oceanic Forcing ◽  
Potential Trigger ◽  
Basal Melting ◽  
Mass Discharge

Abstract. The Northeast Greenland Ice Stream (NEGIS) area has been suffering a significant ice mass loss during the last decades. This is partly due to increasing oceanic temperatures in the subpolar North Atlantic, which enhance submarine basal melting and mass discharge. This demonstrates the high sensitivity of this region to oceanic changes. Alongside, a recent study suggests that the NEGIS grounding line was 20–40 km behind its present-day location for 15 ka during Marine Isotopic Stage (MIS) 3, raising an important conundrum. This retreat has been attributed to a combination of atmospheric and external forcings but a modelling approach to the problem is pending. Here we investigate the sensitivity of the NEGIS to the oceanic forcing during the Last Glacial Period (LGP) using a three-dimensional hybrid ice-sheet-shelf model. We find that a sufficiently high oceanic forcing could account for a NEGIS ice-margin retreat of several tens of km, potentially explaining the recently proposed NEGIS grounding-line retreat during MIS-3.

scholarly journals Shear-margin melting causes stronger transient ice discharge than ice-stream melting according to idealized simulations

2021 ◽  
Author(s):  
Johannes Feldmann ◽  
Ronja Reese ◽  
Ricarda Winkelmann ◽  
Anders Levermann
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Ice Stream ◽  
Future Global Warming ◽  
Grounding Line ◽  
Fast Flow ◽  
Basal Melting

Abstract. Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf's 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.

scholarly journals Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation

1999 ◽  
Vol 28 ◽  
pp. 83-89 ◽  
Author(s):  
A. J. Payne ◽  
D.J. Baldwin
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Low Viscosity ◽  
Ice Stream ◽  
Scandinavian Ice Sheet ◽  
The Baltic ◽  
Stream Formation ◽  
Initial Results

AbstractThis work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.

scholarly journals The effect of the north-east ice stream on the Greenland ice sheet in changing climates

2007 ◽  
Vol 1 (1) ◽  
pp. 41-76 ◽  
Author(s):  
R. Greve ◽  
S. Otsu
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Simulation Code ◽  
North East ◽  
The North ◽  
Ice Stream ◽  
Basal Sliding ◽  
Speed Up ◽  
Fast Flow

Abstract. The north-east Greenland ice stream (NEGIS) was discovered as a large fast-flow feature of the Greenland ice sheet by synthetic aperture radar (SAR) imaginary of the ERS-1 satellite. In this study, the NEGIS is implemented in the dynamic/thermodynamic, large-scale ice-sheet model SICOPOLIS (Simulation Code for POLythermal Ice Sheets). In the first step, we simulate the evolution of the ice sheet on a 10-km grid for the period from 250 ka ago until today, driven by a climatology reconstructed from a combination of present-day observations and GCM results for the past. We assume that the NEGIS area is characterized by enhanced basal sliding compared to the "normal", slowly-flowing areas of the ice sheet, and find that the misfit between simulated and observed ice thicknesses and surface velocities is minimized for a sliding enhancement by the factor three. In the second step, the consequences of the NEGIS, and also of surface-meltwater-induced acceleration of basal sliding, for the possible decay of the Greenland ice sheet in future warming climates are investigated. It is demonstrated that the ice sheet is generally very susceptible to global warming on time-scales of centuries and that surface-meltwater-induced acceleration of basal sliding can speed up the decay significantly, whereas the NEGIS is not likely to dynamically destabilize the ice sheet as a whole.

scholarly journals Deglacial climate and ice sheet evolution of the Ross Embayment, Antarctica

2021 ◽  
Author(s):  
◽  
Daniel P. Lowry
Keyword(s):  
Spatial Pattern ◽  
Climate Models ◽  
Ice Sheet ◽  
Model Parameters ◽  
Atmospheric Conditions ◽  
Last Deglaciation ◽  
Proxy Records ◽  
External Forcings ◽  
Wide Range ◽  
Grounding Line

<p>Reconstructing past grounding-line evolution can help inform future sea level projections by constraining marine ice sheet sensitivities to changes in climate. The Ross Embayment, the largest sector of Antarctica, experienced substantial grounding-line retreat since the Last Glacial Maximum. However, different interpretations for the timing and spatial pattern of deglacial grounding-line retreat in this region persist, suggesting either very high or low sensitivity to external forcings. Complicating matters is the sparse paleoclimate record, which is limited spatially and temporally. In this thesis, I address these issues by analysing the output of two transient climate simulations in relation to Antarctic ice core and marine sediment records, and performing and analysing the largest ensemble to date of regional ice sheet model simulations of the last deglaciation in the Ross Sea. The climate models and paleoclimate proxy records exhibit key differences in the timing, magnitude and duration of millennial-scale climate change events through the deglacial period. Using this diverse set of deglacial climate trajectories as ocean and atmosphere forcings, the ice sheet model ensemble produces a wide range of ice sheet responses, supporting the view that external forcings are the main drivers of past grounding-line retreat in the region. The simulations demonstrate that atmospheric conditions early in the deglacial period can enhance or diminish ice sheet sensitivity to rising ocean temperatures, thereby controlling the initial timing and spatial pattern of grounding-line retreat. Through the Holocene, grounding-line position is more sensitive to sub-shelf melt rates as the ocean cavity below the ice shelf expands. Model parameters that control the physical properties of the bed, deformation of the continental shelf, and rheological properties of the ice strongly influence the sensitivity of ice sheets to external forcing. Basin-wide differences in these forcings, driven by oceanic and atmospheric circulation, and spatial heterogeneity of bed properties likely contribute to the asynchronous pattern of retreat in the eastern and western parts of the embayment, as indicated by marine and terrestrial proxy records.</p>

scholarly journals Modeling the Antarctic ice sheet

1997 ◽  
Vol 25 ◽  
pp. 259-268 ◽  
Author(s):  
Mikhail Verbitsky ◽  
Barry Saltzman
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Antarctic Ice Sheet ◽  
Thermodynamic Equation ◽  
Last Glacial ◽  
Ice Stream ◽  
Basal Melting ◽  
The Antarctic ◽  
The Last Glacial

A three-dimensional (3-D), high-resolution, non-linearly viscous, non-isothermal ice-sheet model is employed to calculate the “present-day” equilibrium regime of the Antarctic ice sheet and its evolution during the last glacial cycle. The model is augmented by an approximate formula for ice-sheet basal temperature, based on a scaling of the thermodynamic equation for the ice flow. Steady-state solutions for both the shape and extent of the areas of basal melting (or freezing) are shown to be in good agreement with those obtained from the solution of the full 3-D thermodynamic equation. The solution for the basal temperature field of the West Antaretie Siple Coast produces areas at the pressure-melting point separated by strips of frozen-to-bed ice, the structure of which is reminiscent of Ice Streams A–E. This configuration appears to be robust, preserving its features in spite of climatic changes during the last glacial cycle. Ice Stream C seems to be more vulnerable to stagnation, switching to a passive mode at least once during the penultimate interglacial. We conjecture that the peculiarities of local topography determine the unique behavior of Ice Stream C: reduced basal stress and, consequently, relatively weak warming due to internal friction and basal sliding is not able to counteract the advective cooling during the periods of increased snowfall rate.

scholarly journals Was the Laurentide Ice Sheet significantly reduced during Marine Isotope Stage 3?

Geology ◽  
2019 ◽  
Vol 47 (2) ◽  
pp. 111-114 ◽  
Author(s):  
April S. Dalton ◽  
Sarah A. Finkelstein ◽  
Steven L. Forman ◽  
Peter J. Barnett ◽  
Tamara Pico ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Marine Isotope Stage ◽  
Laurentide Ice Sheet ◽  
Marine Isotope Stage 3

scholarly journals Modeling the elastic transmission of tidal stresses to great distances inland in channelized ice streams

2014 ◽  
Vol 8 (6) ◽  
pp. 2007-2029 ◽  
Author(s):  
J. Thompson ◽  
M. Simons ◽  
V. C. Tsai
Keyword(s):  
Three Dimensional ◽  
Hydrologic Model ◽  
Ice Streams ◽  
Ice Stream ◽  
Nonlinear Viscoelastic ◽  
Grounding Line ◽  
Dimensional Finite Element ◽  
Order Of Magnitude ◽  
Three Dimensional Finite Element ◽  
The Impact

Abstract. Geodetic surveys suggest that ocean tides can modulate the motion of Antarctic ice streams, even at stations many tens of kilometers inland from the grounding line. These surveys suggest that ocean tidal stresses can perturb ice stream motion at distances about an order of magnitude farther inland than tidal flexure of the ice stream alone. Recent models exploring the role of tidal perturbations in basal shear stress are primarily one- or two-dimensional, with the impact of the ice stream margins either ignored or parameterized. Here, we use two- and three-dimensional finite-element modeling to investigate transmission of tidal stresses in ice streams and the impact of considering more realistic, three-dimensional ice stream geometries. Using Rutford Ice Stream as a real-world comparison, we demonstrate that the assumption that elastic tidal stresses in ice streams propagate large distances inland fails for channelized glaciers due to an intrinsic, exponential decay in the stress caused by resistance at the ice stream margins. This behavior is independent of basal conditions beneath the ice stream and cannot be fit to observations using either elastic or nonlinear viscoelastic rheologies without nearly complete decoupling of the ice stream from its lateral margins. Our results suggest that a mechanism external to the ice stream is necessary to explain the tidal modulation of stresses far upstream of the grounding line for narrow ice streams. We propose a hydrologic model based on time-dependent variability in till strength to explain transmission of tidal stresses inland of the grounding line. This conceptual model can reproduce observations from Rutford Ice Stream.

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