The effect of Antarctic ice-shelf extent on ice discharge

2021 ◽  
Author(s):  
Jim Jordan ◽  
HIlmar Gudmundsson ◽  
Adrian Jenkins ◽  
Chris Stokes ◽  
Stewart Jamiesson ◽  
...  
Keyword(s):  
Mass Loss ◽  
Recent Work ◽  
Flow Model ◽  
Ice Shelf ◽  
Geophysical Research ◽  
Ice Flow ◽  
Ice Shelves ◽  
Grounding Line ◽  
Natural Variance ◽  
Observational Record

<div>The buttressing strength of Antarctic ice shelves directly effects the amount of ice discharge across the grounding line, with buttressing strength affected by both the thickness and extent of an ice shelf. Recent work has shown that a reduction in ice-shelf buttressing due to ocean induced ice-shelf thinning is responsible for a significant portion of increased Antarctic ice discharge (Gudmundsson et al., 2019, but few studies have attempted to show the effect of variability in ice-shelf extent on ice discharge. This variability arises due to ice-shelf calving following a cycle of long periods of slow, continuous calving interposed with calving of large, discrete sections.  These discrete calving events tend to occur on a comparative timeframe to that of the observational record. As such, when determining observed changes in ice discharge it is crucial that this natural variability is separated from any observed trends.  </div><div> </div><div>In this work we use the numerical ice-flow model Úa in combination with observations of ice shelf extent to diagnostically calculate Antarctic ice discharge. These observations primarily date back to the 1970s, though for some ice shelves records exist back to the 1940s. We assemble an Antarctic wide model for two scenarios: 1) with ice shelves at their maximum observed extent and 2) with ice shelves at their minimum observed extent. We then compare these two scenarios to differences in the observed changes in Antarctic ice-discharge to determine how much can be attributed to natural variance .</div><p> </p><p><span>Gudmundsson, G. H.</span><span>, Paolo, F. S., Adusumilli, S., & Fricker, H. A. (2019). </span>Instantaneous Antarctic ice‐ sheet mass loss driven by thinning ice shelves. <em>Geophysical Research Letters</em>, 46, 13903– 13909. </p>

scholarly journals Simulated retreat of Jakobshavn Isbræ during the 21st century

2019 ◽  
Vol 13 (11) ◽  
pp. 3139-3153 ◽  
Author(s):  
Xiaoran Guo ◽  
Liyun Zhao ◽  
Rupert M. Gladstone ◽  
Sainan Sun ◽  
John C. Moore
Keyword(s):  
Mass Loss ◽  
21St Century ◽  
Three Dimensional ◽  
Climate Scenario ◽  
Ice Shelf ◽  
Ice Flow ◽  
Early 21St Century ◽  
Total Mass Loss ◽  
Grounding Line ◽  
Earth System Models

Abstract. The early 21st century retreat of Jakobshavn Isbræ into its overdeepened bedrock trough was accompanied by acceleration to unprecedented ice stream speeds. Such dramatic changes suggested the possibility of substantial mass loss over the rest of this century. Here we use a three-dimensional ice sheet model with parameterizations to represent the effects of ice mélange buttressing, crevasse-depth-based calving and submarine melting to adequately reproduce its recent evolution. We are the first study on Jakobshavn Isbræ that solves for three-dimensional ice flow coupled with representations of hydro-fracturing-induced calving and mélange buttressing. Additionally, the model can accurately replicate interannual variations in grounding line and terminus position, including seasonal fluctuations that emerged after arriving at the overdeepened basin and the disappearance of its floating ice shelf. Our simulated ice viscosity variability due to shear margin evolution is particularly important in reproducing the large observed interannual changes in terminus velocity. We use this model to project Jakobshavn's evolution over this century, forced by ocean temperatures from seven Earth system models and surface runoff derived from RACMO, all under the IPCC RCP4.5 climate scenario. In our simulations, Jakobshavn's grounding line continues to retreat ∼18.5 km by the end of this century, leading to a total mass loss of ∼2068 Gt (5.7 mm sea level rise equivalent). Despite the relative success of the model in simulating the recent behavior of the glacier, the model does not simulate winter calving events that have become relatively more important.

scholarly journals Numerical simulations of the ice flow dynamics of George VI Ice Shelf, Antarctica

2007 ◽  
Vol 53 (183) ◽  
pp. 659-664 ◽  
Author(s):  
Angelika Humbert
Keyword(s):  
High Spatial Resolution ◽  
Thickness Distribution ◽  
Satellite System ◽  
Flow Dynamics ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Geometry ◽  
Grounding Line

A diagnostic, dynamic/thermodynamic ice-shelf model is applied to the George VI Ice Shelf, situated in the Bellinghausen Sea, Antarctica. The George VI Ice Shelf has a peculiar flow geometry which sets it apart from other ice shelves. Inflow occurs along the two longest, and almost parallel, sides, whereas outflow occurs on the two ice fronts that are relatively short and situated at opposite ends of the ice shelf. Two data sources were used to derive the ice thickness distribution: conventional radioecho sounding from the British Antarctic Survey was combined with thickness inferred from surface elevation obtained by the NASA GLAS satellite system assuming hydrostatic equilibrium. We simulate the present ice flow over the ice shelf that results from the ice thickness distribution, the inflow at the grounding line and the flow rate factor. The high spatial resolution of the ice thickness distribution leads to very detailed simulations. The flow field has some extraordinary elements (e.g. the stagnation point characteristics resulting from the unusual ice-shelf geometry).

scholarly journals Channelization of plumes beneath ice shelves

2015 ◽  
Vol 785 ◽  
pp. 109-134 ◽  
Author(s):  
M. C. Dallaston ◽  
I. J. Hewitt ◽  
A. J. Wells
Keyword(s):  
Turbulent Mixing ◽  
Simplified Model ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Narrow Channels ◽  
One Dimensional ◽  
Grounding Line ◽  
The One

We study a simplified model of ice–ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one-dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

scholarly journals Grounding-zone flow variability of Priestley Glacier, Antarctica, in a diurnal tidal regime

2021 ◽  
Author(s):  
Reinhard Drews ◽  
Christian Wild ◽  
Oliver Marsh ◽  
Wolfgang Rack ◽  
Todd Ehlers ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line ◽  
Temporal And Spatial ◽  
Gnss Measurements ◽  
Natural Laboratory

<p>Dynamics of polar outlet glaciers vary with ocean tides, providing a natural laboratory to understand basal processes beneath ice streams, ice rheology and ice-shelf buttressing. We apply Terrestrial Radar Interferometry to close the spatiotemporal gap between localized, temporally well-resolved GNSS and area-wide but sparse satellite observations. Three-hour flowfields collected over an eight day period at Priestley Glacier, Antarctica, validate and provide the spatial context for concurrent GNSS measurements. Ice flow is fastest during falling tides and slowest during rising tides. Principal components of the timeseries prove upstream propagation of tidal signatures $>$ 10 km away from the grounding line. Hourly, cm-scale horizontal and vertical flexure patterns occur $>$6 km upstream of the grounding line. Vertical uplift upstream of the grounding line is consistent with ephemeral re-grounding during low-tide impacting grounding-zone stability. On the freely floating ice shelves, we find velocity peaks both during high- and low-tide suggesting that ice-shelf buttressing varies temporally as a function of flexural bending from tidal displacement. Taken together, these observations identify tidal imprints on ice-stream dynamics on new temporal and spatial scales providing constraints for models designed to isolate dominating processes in ice-stream and ice-shelf mechanics.</p>

scholarly journals Assessing Controls on Ice Dynamics at Crane Glacier, Antarctic Peninsula Using a Numerical Ice Flow Model

2021 ◽  
Author(s):  
Rainey Aberle
Keyword(s):  
Antarctic Peninsula ◽  
Flow Model ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Surface Mass ◽  
Climate Conditions ◽  
Ice Shelves ◽  
Tidewater Glacier ◽  
Mass Discharge

The widespread retreat of glaciers and the collapse of ice shelves along the Antarctic Peninsula has been attributed to atmospheric and oceanic warming, which promotes mass loss. However, several glaciers on the eastern peninsula that were buttressed by the Larsen A and B ice shelves prior to collapse in 1995 and 2002, respectively, have been advancing in recent years. This asymmetric pattern of rapid retreat and long-term re-advance is similar to the tidewater glacier cycle, which can occur largely independent of climate forcing. Here, I use a width- and depth-integrated numerical ice flow model to investigate glacier response to ice shelf collapse and the influence of changing climate conditions at Crane Glacier, formerly a tributary of the Larsen B ice shelf, over the last ~10 years. Sensitivity tests to explore the influence of perturbations in surface mass balance and submarine melt (up to 10 m a-1) and fresh water impounded in crevasses (up to 10 m) on glacier dynamics reveal that by 2100, the modeled mass discharge ranges from 0.53-98 Gt a-1, with the most substantial changes due to surface melt-induced thinning. My findings suggest that the growth of a floating ice tongue can hinder enhanced flow, allowing the grounding zone to remain steady for many decades, analogous to the advancing stage of the tidewater glacier cycle. Additionally, former tributary glaciers can take several decades to geometrically adjust to ice shelf collapse at their terminal boundary while elevated glacier discharge persists.

scholarly journals Impact of ice-shelf basal melting on inland ice-sheet thickness: a model study

2012 ◽  
Vol 53 (60) ◽  
pp. 129-135 ◽  
Author(s):  
Jürgen Determann ◽  
Malte Thoma ◽  
Klaus Grosfeld ◽  
Sylvia Massmann
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Volume ◽  
Basal Melting ◽  
The Impact

AbstractIce flow from the ice sheets to the ocean contains the maximum potential contributing to future eustatic sea-level rise. In Antarctica most mass fluxes occur via the extended ice-shelf regions covering more than half the Antarctic coastline. The most extended ice shelves are the Filchner–Ronne and Ross Ice Shelves, which contribute ~30% to the total mass loss caused by basal melting. Basal melt rates here show small to moderate average amplitudes of <0.5ma–1. By comparison, the smaller but most vulnerable ice shelves in the Amundsen and Bellinghausen Seas show much higher melt rates (up to 30 ma–1), but overall basal mass loss is comparably small due to the small size of the ice shelves. The pivotal question for both characteristic ice-shelf regions, however, is the impact of ocean melting, and, coevally, change in ice-shelf thickness, on the flow dynamics of the hinterland ice masses. In theory, ice-shelf back-pressure acts to stabilize the ice sheet, and thus the ice volume stored above sea level. We use the three-dimensional (3-D) thermomechanical ice-flow model RIMBAY to investigate the ice flow in a regularly shaped model domain, including ice-sheet, ice-shelf and open-ocean regions. By using melting scenarios for perturbation studies, we find a hysteresis-like behaviour. The experiments show that the system regains its initial state when perturbations are switched off. Average basal melt rates of up to 2 ma–1 as well as spatially variable melting calculated by our 3-D ocean model ROMBAX act as basal boundary conditions in time-dependent model studies. Changes in ice volume and grounding-line position are monitored after 1000 years of modelling and reveal mass losses of up to 40 Gt a–1.

scholarly journals Diagnosing the sensitivity of grounding line flux to changes in sub-ice shelf melting

2020 ◽  
Author(s):  
Tong Zhang ◽  
Stephen F. Price ◽  
Matthew J. Hoffman ◽  
Mauro Perego ◽  
Xylar Asay-Davis
Keyword(s):  
Principal Stress ◽  
Flow Model ◽  
Ice Thickness ◽  
Diagnostic Model ◽  
Line Flux ◽  
Ice Shelf ◽  
Ice Flow ◽  
Causal Connections ◽  
Alternative Approach ◽  
Grounding Line

Abstract. We seek to understand causal connections between changes in sub-ice shelf melting, ice shelf buttressing, and grounding-line flux. Using a numerical ice flow model, we study changes in ice shelf buttressing and grounding line flux due to localized ice thickness perturbations – a proxy for changes in sub-ice shelf melting – applied to idealized (MISMIP+) and realistic (Larsen C) domains. From our experiments, we identify a correlation between a locally derived buttressing number on the ice shelf, based on the first principal stress, and changes in the integrated grounding line flux. The origin of this correlation, however, remains elusive from a physical perspective; while local thickness perturbations on the ice shelf (thinning) generally correspond to local increases in buttressing, their integrated impact on changes at the grounding line are exactly the opposite (buttressing at the grounding line decreases and ice flux at the grounding line increases). This and additional complications encountered when examining realistic domains motivates us to seek an alternative approach, an adjoint-based method for calculating the sensitivity of the integrated grounding line flux to local changes in ice shelf geometry. We show that the adjoint-based sensitivity is identical to that deduced from pointwise, diagnostic model perturbation experiments. Based on its much wider applicability and the significant computational savings, we propose that the adjoint-based method is ideally suited for assessing grounding line flux sensitivity to changes in sub-ice shelf melting.

scholarly journals Diagnosing the sensitivity of grounding-line flux to changes in sub-ice-shelf melting

2020 ◽  
Vol 14 (10) ◽  
pp. 3407-3424
Author(s):  
Tong Zhang ◽  
Stephen F. Price ◽  
Matthew J. Hoffman ◽  
Mauro Perego ◽  
Xylar Asay-Davis
Keyword(s):  
Principal Stress ◽  
Flow Model ◽  
Ice Thickness ◽  
Diagnostic Model ◽  
Line Flux ◽  
Ice Shelf ◽  
Ice Flow ◽  
Alternative Approach ◽  
Grounding Line ◽  
Physically Based

Abstract. Using a numerical ice flow model, we study changes in ice shelf buttressing and grounding-line flux due to localized ice thickness perturbations, a proxy for localized changes in sub-ice-shelf melting. From our experiments, applied to idealized (MISMIP+) and realistic (Larsen C) ice shelf domains, we identify a correlation between a locally derived buttressing number on the ice shelf, based on the first principal stress, and changes in the integrated grounding-line flux. The origin of this correlation, however, remains elusive from the perspective of a theoretical or physically based understanding. This and the fact that the correlation is generally much poorer when applied to realistic ice shelf domains motivate us to seek an alternative approach for predicting changes in grounding-line flux. We therefore propose an adjoint-based method for calculating the sensitivity of the integrated grounding-line flux to local changes in ice shelf geometry. We show that the adjoint-based sensitivity is identical to that deduced from pointwise, diagnostic model perturbation experiments. Based on its much wider applicability and the significant computational savings, we propose that the adjoint-based method is ideally suited for assessing grounding-line flux sensitivity to changes in sub-ice-shelf melting.

scholarly journals Sensitivity of the ice-shelf/ocean system to the sub-ice-shelf cavity shape measured by NASA IceBridge in Pine Island Glacier, West Antarctica

2012 ◽  
Vol 53 (60) ◽  
pp. 156-162 ◽  
Author(s):  
Michael P. Schodlok ◽  
Dimitris Menemenlis ◽  
Eric Rignot ◽  
Michael Studinger
Keyword(s):  
Mass Loss ◽  
Temporal Evolution ◽  
West Antarctica ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Cavity Shape ◽  
Grounding Line ◽  
The Mean

AbstractTwo high-resolution (1 km grid) numerical model simulations of the Amundsen Sea, West Antarctica, are used to study the role of the ocean in the mass loss and grounding line retreat of Pine Island Glacier. The first simulation uses BEDMAP bathymetry under the Pine Island ice shelf, and the second simulation uses NASA IceBridge-derived bathymetry. The IceBridge data reveal the existence of a trough from the ice-shelf edge to the grounding line, enabling warm Circumpolar Deep Water to penetrate to the grounding line, leading to higher melt rates than previously estimated. The mean melt rate for the simulation with NASA IceBridge data is 28 ma–1, much higher than previous model estimates but closer to estimates from remote sensing. Although the mean melt rate is 25% higher than in the simulation with BEDMAP bathymetry, the temporal evolution remains unchanged between the two simulations. This indicates that temporal variability of melting is mostly driven by processes outside the cavity. Spatial melt rate patterns of BEDMAP and IceBridge simulations differ significantly, with the latter in closer agreement with satellite-derived melt rate estimates of ~50ma–1 near the grounding line. Our simulations confirm that knowledge of the cavity shape and its time evolution are essential to accurately capture basal mass loss of Antarctic ice shelves.

scholarly journals The sensitivity of Cook Glacier, East Antarctica, to changes in ice-shelf extent and grounding-line position

2021 ◽  
pp. 1-13
Author(s):  
James R. Jordan ◽  
G. Hilmar Gudmundsson ◽  
Adrian Jenkins ◽  
Chris R. Stokes ◽  
Bertie W. J. Miles ◽  
...  
Keyword(s):  
Flow Model ◽  
East Antarctica ◽  
Line Position ◽  
Ice Shelf ◽  
Ice Flow ◽  
Mean Sea Level ◽  
Front Position ◽  
Grounding Line ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract The Wilkes Subglacial Basin in East Antarctica contains ice equivalent to 3–4 m of global mean sea level rise and is primarily drained by Cook Glacier. Of concern is that recent observations (since the 1970s) show an acceleration in ice speed over the grounding line of both the Eastern and Western portions of Cook Glacier. Here, we use a numerical ice-flow model (Úa) to simulate the instantaneous effects of observed changes at the terminus of Cook Glacier in order to understand the link between these changes and recently observed ice acceleration. Simulations suggest that the acceleration of Cook West was caused by a retreat in calving-front position in the 1970s, potentially enhanced by grounding-line retreat, while acceleration of Cook East was likely caused by ice-shelf thinning and grounding-line retreat in the mid-1990s. Moreover, we show that the instantaneous ice discharge at Cook East would increase by up to 85% if the whole ice shelf is removed and it ungrounds from a pinning point; and that the discharge at Cook West could increase by ~300% if its grounding line retreated by 10 km.

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