scholarly journals On the evolution of an ice shelf melt channel at the base of Filchner Ice Shelf, from observations and viscoelastic modeling

2021 ◽  
Author(s):  
Angelika Humbert ◽  
Julia Christmann ◽  
Hugh F. J. Corr ◽  
Veit Helm ◽  
Lea-Sophie Höyns ◽  
...  
Keyword(s):  
Ice Shelf ◽  
Climate Conditions ◽  
Ice Shelves ◽  
Grounding Line ◽  
The Stability ◽  
Viscoelastic Modeling ◽  
Basal Melting ◽  
The Antarctic ◽  
Measurement Period

Abstract. Ice shelves play a key role in the stability of the Antarctic Ice Sheet due to their buttressing effect. A loss of buttressing as a result of increased basal melting or ice shelf disintegration will lead to increased ice discharge. Some ice shelves exhibit channels at the base that are not yet fully understood. In this study, we present in-situ melt rates of a channel which is up to 330 m high and located at the southern Filchner Ice Shelf. Maximum observed melt rates are 2.3 m a−1. Melt rates decline inside the channel along flow and turn into freezing 55 km downstream of the grounding line. While closer to the grounding line melt rates are higher within the channel than outside, this reverses further downstream. Comparing the evolution of this channel under present-day climate conditions over 250 years with its present geometry reveals a mismatch. This mismatch indicates melt rates two times higher were necessary over the past 250 years to form today's channel geometry. In contrast, forcing the model with present-day melt rates results in a closure of the channel, which contradicts observations. Time series of melt rate measurements show strong tidally-induced variability in vertical strain-rates. We found no evidence of seasonality, but discrete pulses of increased melting occurred throughout the measurement period. The type of melt channel in this study diminishes with distance from the grounding line and are hence not a destabilizing factor for ice shelves.

scholarly journals Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

2017 ◽  
Author(s):  
Werner M. J. Lazeroms ◽  
Adrian Jenkins ◽  
G. Hilmar Gudmundsson ◽  
Roderik S. W. van de Wal
Keyword(s):  
Temperature Field ◽  
Ice Sheet ◽  
Detailed Knowledge ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Grounding Line ◽  
Basal Melting ◽  
The Antarctic

Abstract. Basal melting below ice shelves is a major factor in the decline of the Antarctic ice sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a nonlinear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth zgl and the local slope α of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for zgl and α for any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and flow patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. The result is a realistic map of basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field are therefore promising tools for future simulations of the Antarctic ice sheet.

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

scholarly journals Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

2017 ◽  
Vol 63 (240) ◽  
pp. 731-744 ◽  
Author(s):  
JORGE BERNALES ◽  
IRINA ROGOZHINA ◽  
MAIK THOMAS
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Model Parameters ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Model Set ◽  
Set Up ◽  
Basal Melting ◽  
The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input datasets.

scholarly journals Modelling the long-term response of the Antarctic ice sheet to global warming

1998 ◽  
Vol 27 ◽  
pp. 161-168 ◽  
Author(s):  
Roland C. Warner ◽  
W.Κ. Budd
Keyword(s):  
Global Warming ◽  
Mass Loss ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Antarctic ◽  
Term Response

The primary effects of global warming on the Antarctic ice sheet can involve increases in surface melt for limited areas at lower elevations, increases in net accumulation, and increased basal melting under floating ice. For moderate global wanning, resulting in ocean temperature increases of a few °C, the large- increase in basal melting can become the dominant factor in the long-term response of the ice sheet. The results from ice-sheet modelling show that the increased basal melt rates lead to a reduction of the ice shelves, increased strain rates and flow at the grounding lines, then thinning and floating of the marine ice sheets, with consequential further basal melting. The mass loss from basal melting is counteracted to some extent by the increased accumulation, but in the long term the area of ice cover decreases, particularly in West Antarctica, and the mass loss can dominate. The ice-sheet ice-shelf model of Budd and others (1994) with 20 km resolution has been modified and used to carry out a number of sensitivity studies of the long-term response of the ice sheet to prescribed amounts of global warming. The changes in the ice sheet are computed out to near-equilibrium, but most of the changes take place with in the first lew thousand years. For a global mean temperature increase of 3°C with an ice-shelf basal melt rate of 5 m a−1 the ice shelves disappear with in the first few hundred years, and the marine-based parts of the ice sheet thin and retreat. By 2000 years the West Antarctic region is reduced to a number of small, isolated ice caps based on the bedrock regions which are near or above sea level. This allows the warmer surface ocean water to circulate through the archipelago in summer, causing a large change to the local climate of the region.

scholarly journals Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice shelf geometry

2019 ◽  
Vol 13 (10) ◽  
pp. 2771-2787 ◽  
Author(s):  
Jan De Rydt ◽  
Gudmundur Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite
Keyword(s):  
Large Scale ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
Speed Up ◽  
The Antarctic ◽  
Detrimental Impact ◽  
Natural Laboratory

Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use 2 decades of in situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration, are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

scholarly journals Viscous and elastic buoyancy stresses as drivers of ice-shelf calving

2020 ◽  
Vol 66 (258) ◽  
pp. 643-657 ◽  
Author(s):  
Cyrille Mosbeux ◽  
Till J. W. Wagner ◽  
Maya K. Becker ◽  
Helen A. Fricker
Keyword(s):  
Ice Sheet ◽  
Elastic Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Bending Stresses ◽  
Iceberg Calving ◽  
Basal Melting ◽  
The Antarctic ◽  
The Impact ◽  
Maximum Stresses

AbstractThe Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical frameworks to model the ‘footloose’ calving mechanism. This mechanism is triggered by submerged ice protrusions at the ice front, which induce unbalanced buoyancy forces that can lead to fracturing. We compare the results to identify the different roles that viscous and elastic deformations play in setting the rate and magnitude of calving events. Our results show that, although the bending stresses in both frameworks share some characteristics, their differences have important implications for modeling the calving process. In particular, the elastic model predicts that maximum stresses arise farther from the ice front than in the viscous model, leading to larger calving events. We also find that the elastic model would likely lead to more frequent events than the viscous one. Our work provides a theoretical framework for the development of a better understanding of the physical processes that govern glacier and ice-shelf calving cycles.

scholarly journals Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

2018 ◽  
Vol 12 (1) ◽  
pp. 49-70 ◽  
Author(s):  
Werner M. J. Lazeroms ◽  
Adrian Jenkins ◽  
G. Hilmar Gudmundsson ◽  
Roderik S. W. van de Wal
Keyword(s):  
Temperature Field ◽  
Ice Sheet ◽  
Detailed Knowledge ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Grounding Line ◽  
The Antarctic ◽  
Line Depth

Abstract. Basal melting below ice shelves is a major factor in mass loss from the Antarctic Ice Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and circulation patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic Ice Sheet requiring a more realistic oceanic forcing.

scholarly journals Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice-shelf geometry

2019 ◽  
Author(s):  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite
Keyword(s):  
Large Scale ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
Speed Up ◽  
The Antarctic ◽  
Detrimental Impact ◽  
Natural Laboratory

Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use a unique 50-years' time series of in-situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

scholarly journals On the coupled response to ice-shelf basal melting

2012 ◽  
Vol 58 (208) ◽  
pp. 203-215 ◽  
Author(s):  
Christopher M. Little ◽  
Daniel Goldberg ◽  
Anand Gnanadesikan ◽  
Michael Oppenheimer
Keyword(s):  
Temporal Evolution ◽  
Closed Form Solution ◽  
Form Solution ◽  
Ice Shelf ◽  
Ice Streams ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Grounding Line ◽  
Tightly Coupled ◽  
Basal Melting

AbstractIce-shelf basal melting is tightly coupled to ice-shelf morphology. Ice shelves, in turn, are coupled to grounded ice via their influence on compressive stress at the grounding line (‘ice-shelf buttressing’). Here, we examine this interaction using a local parameterization that relates the basal melt rate to the ice-shelf thickness gradient. This formulation permits a closed-form solution for a steady-state ice tongue. Time-dependent numerical simulations reveal the spatial and temporal evolution of ice-shelf/ice-stream systems in response to changes in ocean temperature, and the influence of morphology-dependent melting on grounding-line retreat. We find that a rapid (<1 year) re-equilibration in upstream regions of ice shelves establishes a spatial pattern of basal melt rates (relative to the grounding line) that persists over centuries. Coupling melting to ice-shelf shape generally, but not always, increases grounding-line retreat rates relative to a uniform distribution with the same area- average melt rate. Because upstream ice-shelf thickness gradients and retreat rates increase nonlinearly with thermal forcing, morphology-dependent melting is more important to the response of weakly buttressed, strongly forced ice streams grounded on beds that slope upwards towards the ocean (e.g. those in the Amundsen Sea).

Response of a Marine Ice Sheet to Changes at the Grounding Line

1985 ◽  
Vol 24 (3) ◽  
pp. 257-267 ◽  
Author(s):  
C. J. Van der Veen
Keyword(s):  
Ice Sheet ◽  
Ice Shelf ◽  
West Antarctic Ice Sheet ◽  
Ice Shelves ◽  
West Antarctic ◽  
Grounding Line ◽  
Measured Profile ◽  
The Stability ◽  
Near Future ◽  
Basic Experiments

A numerical model was designed to study the stability of a marine ice sheet, and used to do some basic experiments. The ice-shelf/ice-sheet interaction enters through the flow law in which the longitudinal stress is also taken into account. Instead of applying the model to some (measured) profile and showing that this is unstable (as is common practice in other studies), an attempt is made to simulate a whole cycle of growth and retreat of a marine ice sheet, although none of the model sheets is particularly sensitive to changes in environmental conditions. The question as to what might happen to the West Antarctic Ice Sheet in the near future when a climatic warming can be expecied as a result of the CO2 effect, seems to be open for discussion again. From the results presented in this paper one can infer that a collapse, caused by increased melting on the ice shelves, is not very likely.

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