scholarly journals Persistent, Extensive Channelized Drainage Modeled Beneath Thwaites Glacier, West Antarctica

2021 ◽  
Author(s):  
Alexander O. Hager ◽  
Matthew J. Hoffman ◽  
Stephen F. Price ◽  
Dustin M. Schroeder
Keyword(s):  
Large Scale ◽  
High Efficiency ◽  
Effective Pressure ◽  
West Antarctica ◽  
Ice Shelf ◽  
Basal Friction ◽  
Discharge Rates ◽  
Wide Range ◽  
Grounding Line ◽  
Lateral Extent

Abstract. Subglacial hydrology is a leading control on basal friction and the dynamics of glaciers and ice sheets. At low discharge, subglacial water flows through high-pressure, sheet-like systems that lead to low effective pressures. However, at high discharge, subglacial water melts the overlying ice into localized channels that efficiently remove water from the bed, thereby increasing effective pressure and basal friction. Recent observations suggest channelized subglacial flow exists beneath Thwaites Glacier, yet it remains unclear if stable channelization is feasible in West Antarctica, where surface melting is nonexistent and water at the bed is limited. Here, we use the MPAS-Albany Land Ice model to run a suite of over 130 subglacial hydrology simulations of Thwaites Glacier across a wide range of physical parameter choices to assess the likelihood of channelization. We then narrow our range of viable simulations by comparing modeled water thicknesses to previously observed radar specularity content, which indicates flat, spatially extensive water bodies at the bed. In all of our data-compatible simulations, stable channels reliably form within 100–200 km of the grounding line, and reach individual discharge rates of 35–110 m3 s−1 at the ice-ocean boundary. While only one to two channels typically form across the 200 km width of the glacier in our simulations, their high efficiency drains water across the entire lateral extent of the glacier. No simulations resembled observed specularity content when channelization is disabled. Our results suggest channelized subglacial hydrology has two consequences for Thwaites Glacier dynamics: (i) amplifying submarine melting of the terminus and ice shelf, while (ii) simultaneously raising effective pressure within 100 km of the grounding line and increasing basal friction. The distribution of effective pressure implied from our modeling differs from parameterizations typically used in large-scale ice sheet models, suggesting the development of more process-based parameterizations may be necessary.

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 ◽  
Vol 12 (12) ◽  
pp. 3861-3876 ◽  
Author(s):  
Hongju Yu ◽  
Eric Rignot ◽  
Helene Seroussi ◽  
Mathieu Morlighem
Keyword(s):  
Sea Level ◽  
Initial Conditions ◽  
Numerical Models ◽  
West Antarctica ◽  
Ice Shelf ◽  
Flow Models ◽  
Friction Laws ◽  
Basal Friction ◽  
Grounding Line ◽  
Western Side

Abstract. Thwaites Glacier (TG), West Antarctica, has experienced rapid, potentially irreversible grounding line retreat and mass loss in response to enhanced ice shelf melting. Results from recent numerical models suggest a large spread in the evolution of the glacier in the coming decades to a century. It is therefore important to investigate how different approximations of the ice stress balance, parameterizations of basal friction and ice shelf melt parameterizations may affect projections. Here, we simulate the evolution of TG using ice sheet models of varying levels of complexity, different basal friction laws and ice shelf melt to quantify their effect on the projections. We find that the grounding line retreat and its sensitivity to ice shelf melt are enhanced when a full-Stokes model is used, a Budd friction is used and ice shelf melt is applied on partially floating elements. Initial conditions also impact the model results. Yet, all simulations suggest a rapid, sustained retreat of the glacier along the same preferred pathway. The fastest retreat rate occurs on the eastern side of the glacier, and the slowest retreat occurs across a subglacial ridge on the western side. All the simulations indicate that TG will undergo an accelerated retreat once the glacier retreats past the western subglacial ridge. Combining all the simulations, we find that the uncertainty of the projections 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 contribution to sea level depends on the model configurations, with differences up to 300 % over the next 100 years, ranging from 14 to 42 mm.

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.

scholarly journals Drivers of Pine Island Glacier speed-up between 1996 and 2016

2021 ◽  
Vol 15 (1) ◽  
pp. 113-132
Author(s):  
Jan De Rydt ◽  
Ronja Reese ◽  
Fernando S. Paolo ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Large Scale ◽  
Contemporary Evolution ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Flow ◽  
Future Evolution ◽  
The Past ◽  
Grounding Line ◽  
Speed Up ◽  
Spatially Varying

Abstract. Pine Island Glacier in West Antarctica is among the fastest changing glaciers worldwide. Over the last 2 decades, the glacier has lost in excess of a trillion tons of ice, or the equivalent of 3 mm of sea level rise. The ongoing changes are thought to have been triggered by ocean-induced thinning of its floating ice shelf, grounding line retreat, and the associated reduction in buttressing forces. However, other drivers of change, such as large-scale calving and changes in ice rheology and basal slipperiness, could play a vital, yet unquantified, role in controlling the ongoing and future evolution of the glacier. In addition, recent studies have shown that mechanical properties of the bed are key to explaining the observed speed-up. Here we used a combination of the latest remote sensing datasets between 1996 and 2016, data assimilation tools, and numerical perturbation experiments to quantify the relative importance of all processes in driving the recent changes in Pine Island Glacier dynamics. We show that (1) calving and ice shelf thinning have caused a comparable reduction in ice shelf buttressing over the past 2 decades; that (2) simulated changes in ice flow over a viscously deforming bed are only compatible with observations if large and widespread changes in ice viscosity and/or basal slipperiness are taken into account; and that (3) a spatially varying, predominantly plastic bed rheology can closely reproduce observed changes in flow without marked variations in ice-internal and basal properties. Our results demonstrate that, in addition to its evolving ice thickness, calving processes and a heterogeneous bed rheology play a key role in the contemporary evolution of Pine Island Glacier.

scholarly journals Sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions: a model study

2002 ◽  
Vol 48 (163) ◽  
pp. 552-558 ◽  
Author(s):  
Marjorie Schmeltz ◽  
Eric Rignot ◽  
Todd K. Dupont ◽  
Douglas R. MacAyeal
Keyword(s):  
Shear Stress ◽  
Element Model ◽  
Shelf Area ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Stream ◽  
Model Study ◽  
Grounding Line ◽  
Glacier Velocity ◽  
Basal Shear

AbstractWe use a finite-element model of coupled ice-stream/ice-shelf flow to study the sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions. By tuning a softening coefficient of the ice along the glacier margins, and a basal friction coefficient controlling the distribution of basal shear stress underneath the ice stream, we are able to match model velocity to that observed with interferometric synthetic aperture radar (InSAR). We use the model to investigate the effect of small perturbations on ice flow. We find that a 5.5–13% reduction in our initial ice-shelf area increases the glacier velocity by 3.5–10% at the grounding line. The removal of the entire ice shelf increases the grounding-line velocity by > 70%. The changes in velocity associated with ice-shelf reduction are felt several tens of km inland. Alternatively, a 5% reduction in basal shear stress increases the glacier velocity by 13% at the grounding line. By contrast, softening of the glacier side margins would have to be increased a lot more to produce a comparable change in ice velocity. Hence, both the ice-shelf buttressing and the basal shear stress contribute significant resistance to the flow of Pine Island Glacier.

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 Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment

2020 ◽  
Vol 117 (40) ◽  
pp. 24735-24741 ◽  
Author(s):  
Stef Lhermitte ◽  
Sainan Sun ◽  
Christopher Shuman ◽  
Bert Wouters ◽  
Frank Pattyn ◽  
...  
Keyword(s):  
Sea Level ◽  
Rapid Development ◽  
Shear Zones ◽  
West Antarctica ◽  
Ice Shelf ◽  
Damage Development ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Grounding Line ◽  
Global Sea Level

Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in West Antarctica with large consequences for global sea level. Yet, assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood. Here, we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of Pine Island and Thwaites ice shelves. These damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade. Idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones, which results in further speedup, shearing, and weakening, hence promoting additional damage development. This damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat. The results of this study suggest that damage feedback processes are key to future ice shelf stability, grounding line retreat, and sea level contributions from Antarctica. Moreover, they underline the need for incorporating these feedback processes, which are currently not accounted for in most ice sheet models, to improve sea level rise projections.

scholarly journals Modelled fracture and calving on the Totten Ice Shelf

2018 ◽  
Vol 12 (7) ◽  
pp. 2401-2411 ◽  
Author(s):  
Sue Cook ◽  
Jan Åström ◽  
Thomas Zwinger ◽  
Benjamin Keith Galton-Fenzi ◽  
Jamin Stevens Greenbaum ◽  
...  
Keyword(s):  
Sea Level ◽  
Drainage Basin ◽  
Element Model ◽  
Fracture Pattern ◽  
Current Position ◽  
Ice Shelf ◽  
Wide Range ◽  
Grounding Line ◽  
Flow Features ◽  
Calving Rate

Abstract. The Totten Ice Shelf (IS) has a large drainage basin, much of which is grounded below sea level, leaving the glacier vulnerable to retreat through the marine ice sheet instability mechanism. The ice shelf has also been shown to be sensitive to changes in calving rate, as a very small retreat of the calving front from its current position is predicted to cause a change in flow at the grounding line. Therefore understanding the processes behind calving on the Totten IS is key to predicting its future sea level rise contribution. Here we use the Helsinki Discrete Element Model (HiDEM) to show that not all of the fractures visible at the front of the Totten IS are produced locally, but that the across-flow basal crevasses, which are part of the distinctive cross-cutting fracture pattern, are advected into the calving front area from upstream. A separate simulation of the grounding line shows that re-grounding points may be key areas of basal crevasse production, and can produce basal crevasses in both an along- and across-flow orientation. The along-flow basal crevasses at the grounding line may be a possible precursor to basal channels, while we suggest the across-flow grounding-line fractures are the source of the across-flow features observed at the calving front. We use two additional models to simulate the evolution of basal fractures as they advect downstream, demonstrating that both strain and ocean melt have the potential to deform narrow fractures into the broad basal features observed near the calving front. The wide range of factors which influence fracture patterns and calving on this glacier will be a challenge for predicting its future mass loss.

scholarly journals Stopping the Flood: Could We Use Targeted Geoengineering to Mitigate Sea Level Rise?

2018 ◽  
Author(s):  
Michael J. Wolovick ◽  
John C. Moore
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Dynamic Feedback ◽  
West Antarctica ◽  
Ice Shelf ◽  
Long Run ◽  
Grounding Line ◽  
Individual Source ◽  
Engineering Projects

Abstract. The Marine Ice Sheet Instability (MISI) is a dynamic feedback that can cause an ice sheet to enter a runaway collapse. Thwaites Glacier, West Antarctica, is the largest individual source of future sea level rise and may have already entered the MISI. Here, we use a suite of coupled ice–ocean flowband simulations to explore whether targeted geoengineering using an artificial sill or artificial ice rises could counter a collapse. Successful interventions occur when the floating ice shelf regrounds on the pinning points, increasing buttressing and reducing ice flux across the grounding line. Regrounding is more likely with a continuous sill that is able to block warm water transport to the grounding line. The smallest design we consider is comparable in scale to existing civil engineering projects but has only a 30 % success rate, while larger designs are more effective. There are multiple possible routes forward to improve upon the designs that we considered, and with decades or more to research designs it is plausible that the scientific community could come up with a plan that was both effective and achievable. While reducing emissions remains the short-term priority for minimizing the effects of climate change, in the long run humanity may need to develop contingency plans to deal with an ice sheet collapse.

scholarly journals Research on the Principle and Cooperative Processing Method of MRS Multisystem Joint Detection

Sensors ◽  
2021 ◽  
Vol 21 (20) ◽  
pp. 6725
Author(s):  
Cong Li ◽  
Zhaofa Zeng ◽  
Zhuo Wang ◽  
Xiaofeng Yi
Keyword(s):  
Large Scale ◽  
High Efficiency ◽  
Joint Detection ◽  
Multiple Systems ◽  
Work Area ◽  
Magnetic Resonance Sounding ◽  
Wide Range ◽  
Working Together ◽  
Working Distance ◽  
Measurement Efficiency

Magnetic resonance sounding (MRS) technology is the only geophysical means to directly and quantitatively detect groundwater and has achieved good results in hydrogeological prospecting applications. In recent years, researchers have conducted considerable research on the efficiency of a single instrument, yielding certain results. However, the overall work efficiency of this method has not been effectively determined in its application to a large-scale survey. Hence, we propose both a joint detection method for MRS that determines the minimum working distance when multiple systems operate simultaneously and a collaborative measurement method of dual systems operating simultaneously in a fixed range of work areas. The cooperative working mode of the instruments is tested in the detection area, and the working mode proposed in this paper is shown to effectively avoid measurement interference between systems. Compared with the working mode of a single set of instruments, the measurement efficiency is more than doubled. Through this research, the feasibility of multiple MRS instruments working together in the same work area is verified, which provides effective technical support for the rapid and high-efficiency utilization of MRS over a wide range of measurement areas.

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.

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