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 Simulated retreat of Jakobshavn Isbræ during the 21st century

2019 ◽  
Author(s):  
Xiaoran Guo ◽  
Liyun Zhao ◽  
Rupert Gladstone ◽  
Sainan Sun ◽  
John C. Moore
Keyword(s):  
Mass Loss ◽  
21St Century ◽  
Three Dimensional ◽  
Climate Scenario ◽  
Seasonal Fluctuations ◽  
Ice Shelf ◽  
Annual Variations ◽  
Total Mass Loss ◽  
Grounding Line ◽  
Earth System Models

Abstract. The early in the 21st century retreat of Jakobshavn Isbræ, one of Greenland's largest outlet glaciers, into its over-deepened 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. Using a three-dimensional ice-sheet model with parameterizations to represent the effects of ice mélange buttressing, crevasse-depth-based calving and submarine melting, we can reproduce its recent evolution. The model can accurately replicate its inter-annual variations in grounding line and terminus position, including new modes of seasonal fluctuations that emerged after arriving at the over-deepened basin and the disappearance of a persistent floating ice shelf. The shear margin induced decreases in ice viscosity we simulate are particularly important in reproducing the large observed inter-annual changes in terminus velocity. We use this model to project Jakobshavn's evolution over this century when forced by the IPCC RCP4.5 climate scenario and simulated by ocean temperatures from 7 Earth System Models along with surface runoff derived from RACMO. In our simulations, Jakobshavn's grounding line continues to retreat ~ 18.5 km by the end of this century with total mass loss of ~ 2030 Gt (5.6 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.

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 Sensitivity of the dynamics of Pine Island Glacier, West Antarctica, to climate forcing for the next 50 years

2014 ◽  
Vol 8 (5) ◽  
pp. 1699-1710 ◽  
Author(s):  
H. Seroussi ◽  
M. Morlighem ◽  
E. Rignot ◽  
J. Mouginot ◽  
E. Larour ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Three Dimensional ◽  
Major Contributor ◽  
West Antarctica ◽  
Climatic Impact ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Grounding Line

Abstract. Pine Island Glacier, a major contributor to sea level rise in West Antarctica, has been undergoing significant changes over the last few decades. Here, we employ a three-dimensional, higher-order model to simulate its evolution over the next 50 yr in response to changes in its surface mass balance, the position of its calving front and ocean-induced ice shelf melting. Simulations show that the largest climatic impact on ice dynamics is the rate of ice shelf melting, which rapidly affects the glacier speed over several hundreds of kilometers upstream of the grounding line. Our simulations show that the speedup observed in the 1990s and 2000s is consistent with an increase in sub-ice-shelf melting. According to our modeling results, even if the grounding line stabilizes for a few decades, we find that the glacier reaction can continue for several decades longer. Furthermore, Pine Island Glacier will continue to change rapidly over the coming decades and remain a major contributor to sea level rise, even if ocean-induced melting is reduced.

scholarly journals Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012

2014 ◽  
Vol 60 (221) ◽  
pp. 489-499 ◽  
Author(s):  
Andreas Münchow ◽  
Laurie Padman ◽  
Helen A. Fricker
Keyword(s):  
Mass Loss ◽  
Three Dimensional ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Ice Shelf ◽  
Laser Altimetry ◽  
Laser Altimeter ◽  
Airborne Laser ◽  
Tracking Surface ◽  
Basal Melting

AbstractPetermann Gletscher, northwest Greenland, drains 4% of the Greenland ice sheet into Nares Strait. Its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012. We document changes in the three-dimensional ice-shelf structure from 2000 to 2012, using repeated tracks of airborne laser altimetry and ice radio-echo sounding, ICESat laser altimetry and MODIS visible imagery. The recent ice-shelf velocity, measured by tracking surface features between flights in 2010 and 2011, is ~1.25 km a−1, ~15–30% faster than estimates made before 2010. The steady- state along-flow ice divergence represents 6.3 Gta−1 mass loss through basal melting (~5Gta−1) and surface melting and sublimation (~1.0Gta−1). Airborne laser altimeter data reveal thinning, both along a thin central channel and on the thicker ambient ice shelf. From 2007 to 2010 the ice shelf thinned by ~5 m a−1, which represents a non-steady mass loss of ~4.1 Gta−1. We suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events.

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 ХУДОЖНЬО-КОМПОЗИЦІЙНІ ОСОБЛИВОСТІ ДИТЯЧОГО КОСТЮМУ У КОЛЕКЦІЯХ ВИСОКОЇ МОДИ ХХ – ПОЧАТКУ ХХІ СТ.

2020 ◽  
pp. 21-33
Author(s):  
О. Д. Герасименко ◽  
К. Л. Пашкевич ◽  
Г. В. Омельченко ◽  
Б. П. Загрійчук ◽  
О. М. Колосниченко
Keyword(s):  
21St Century ◽  
Three Dimensional ◽  
Practical Significance ◽  
Historical Study ◽  
Structural Elements ◽  
Early 21St Century ◽  
Haute Couture ◽  
Dimensional Shape ◽  
Color Scheme ◽  
Three Dimensional Shape

The purpose of the work is to study the artistic and compositional features in children's collections of haute couture houses and determine the patterns of their repetition in the design of children's costumes in the 20th and early 21st century. To achieve this goal, a historical study of materials, a visual-analytical method, morphological and compositional-structural analysis were applied. The evolution of children's costume in the high fashion collections in the and early 21st century is investigated and the main trends in children's fashion for a given period of time are analyzed. The artistic and compositional features of the children's costume are identified, the most characteristic artistic and structural elements of children's clothing are identified: three-dimensional shape, color scheme and fabric pattern, structural and decorative elements and decoration. The regularity of repeating the pattern of fabric in the collections of children's clothing of the Fashion houses in the 20th and early 21st century is established. The collected materials and their analysis made it possible to establish regularity of repeating of artistic and compositional features in a children's costume, such as a fabric pattern and decoration in different years in models of children's clothing of High Fashion Houses. Practical significance lies in the generalization of artistic compositional features and the identification of leading trends in the artistic compositional solution of children's costumes in the high fashion collections in the 20th and early 21st century. The results will make it possible to predict trends in children's fashion, design actual models of clothing for children and can be used in further research on the design of children's clothing.

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 Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica

2016 ◽  
Author(s):  
Hongju Yu ◽  
Eric Rignot ◽  
Mathieu Morlighem ◽  
Helene Seroussi
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Melt ◽  
Linear Elastic ◽  
Grounding Line ◽  
Iceberg Calving ◽  
Elastic Fracture ◽  
The Difference ◽  
The Impact

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and iceberg calving.

scholarly journals Retreat of Thwaites Glacier, West Antarctica, over the next 100 years using various ice flow models, ice shelf melt scenarios and basal friction laws

2018 ◽  
Author(s):  
Hongju Yu ◽  
Eric Rignot ◽  
Helene Seroussi ◽  
Mathieu Morlighem
Keyword(s):  
Mass Loss ◽  
Initial Conditions ◽  
Numerical Models ◽  
West Antarctica ◽  
Ice Shelf ◽  
Flow Models ◽  
Friction Laws ◽  
Basal Friction ◽  
Grounding Line ◽  
Western Side

Abstract. Thwaites Glacier (TG), West Antarctica, experiences rapid, potentially irreversible grounding line retreat and mass loss in response to enhanced ice shelf melting. Several numerical models of TG have been developed recently, showing a large spread in the evolution of the glacier in the coming decades to a century. It is, however, not clear how different parameterizations of basal friction and ice shelf melt or different approximations in ice stress balance affect projections.Here, we simulate the evolution of TG using different ice shelf melt, basal friction laws and ice sheet models of varying levels of complexity to quantify the effect of these model configurations on the results. We find that the grounding line retreat and its sensitivity to ocean forcing is enhanced when a full-Stokes model is used, ice shelf melt is applied on partially floating elements, and a Budd friction is used. Initial conditions also impact the model results. Yet, all simulations suggest a rapid, sustained retreat along the same preferred pathway. The highest retreat rate occurs on the eastern side of the glacier and the lowest rate on a subglacial ridge on the western side. All the simulations indicate that TG will undergo an accelerated retreat once it retreats past the western ridge. Combining the results, we find the uncertainty is small in the first 30 years, with a cumulative contribution to sea level rise of 5 mm, similar to the current rate. After 30 years, the mass loss depends on the model configurations, with a 300 % difference over the next 100 years, ranging from 14 to 42 mm.

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