scholarly journals Dynamic inland propagation of thinning due to ice loss at the margins of the Greenland ice sheet

2012 ◽  
Vol 58 (210) ◽  
pp. 734-740 ◽  
Author(s):  
Weili Wang ◽  
Jun Li ◽  
H. Jay Zwally
Keyword(s):  
Mass Loss ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Large Mass ◽  
Dynamic Impact ◽  
Ice Flow ◽  
Ice Cloud ◽  
Elevation Changes ◽  
Balance Analysis

AbstractMass-balance analysis of the Greenland ice sheet based on surface elevation changes observed by the European Remote-sensing Satellite (ERS) (1992-2002) and Ice, Cloud and land Elevation Satellite (ICESat) (2003-07) indicates that the strongly increased mass loss at lower elevations (<2000 m) of the ice sheet, as observed during 2003-07, appears to induce interior ice thinning at higher elevations. In this paper, we perform a perturbation experiment with a three-dimensional anisotropic ice-flow model (AIF model) to investigate this upstream propagation. Observed thinning rates in the regions below 2000 m elevation are used as perturbation inputs. The model runs with perturbation for 10 years show that the extensive mass loss at the ice-sheet margins does in fact cause interior thinning on short timescales (i.e. decadal). The modeled pattern of thinning over the ice sheet agrees with the observations, which implies that the strong mass loss since the early 2000s at low elevations has had a dynamic impact on the entire ice sheet. The modeling results also suggest that even if the large mass loss at the margins stopped, the interior ice sheet would continue thinning for 300 years and would take thousands of years for full dynamic recovery.

scholarly journals Sensitivity of ice loss to uncertainty in flow law parameters in an idealized one-dimensional geometry

2020 ◽  
Vol 14 (10) ◽  
pp. 3537-3550
Author(s):  
Maria Zeitz ◽  
Anders Levermann ◽  
Ricarda Winkelmann
Keyword(s):  
Mass Loss ◽  
Flow Line ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Surface Mass ◽  
Scientific Debate ◽  
Flow Parameters ◽  
Flow Law

Abstract. Acceleration of the flow of ice drives mass losses in both the Antarctic and the Greenland Ice Sheet. The projections of possible future sea-level rise rely on numerical ice-sheet models, which solve the physics of ice flow, melt, and calving. While major advancements have been made by the ice-sheet modeling community in addressing several of the related uncertainties, the flow law, which is at the center of most process-based ice-sheet models, is not in the focus of the current scientific debate. However, recent studies show that the flow law parameters are highly uncertain and might be different from the widely accepted standard values. Here, we use an idealized flow-line setup to investigate how these uncertainties in the flow law translate into uncertainties in flow-driven mass loss. In order to disentangle the effect of future warming on the ice flow from other effects, we perform a suite of experiments with the Parallel Ice Sheet Model (PISM), deliberately excluding changes in the surface mass balance. We find that changes in the flow parameters within the observed range can lead up to a doubling of the flow-driven mass loss within the first centuries of warming, compared to standard parameters. The spread of ice loss due to the uncertainty in flow parameters is on the same order of magnitude as the increase in mass loss due to surface warming. While this study focuses on an idealized flow-line geometry, it is likely that this uncertainty carries over to realistic three-dimensional simulations of Greenland and Antarctica.

scholarly journals Sensitivity of ice flow to uncertainty in flow law parameters in an idealized one-dimensional geometry

2020 ◽  
Author(s):  
Maria Zeitz ◽  
Anders Levermann ◽  
Ricarda Winkelmann
Keyword(s):  
Mass Loss ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Flow Parameters ◽  
Surface Temperatures ◽  
Ice Sheet Modeling ◽  
Standard Values ◽  
Flow Law

Abstract. The flow of ice drives mass losses in both, the Antarctic and the Greenland Ice Sheet. The projections of possible future sea-level rise rely on numerical ice-sheet models, which solve the physics of ice flow and melt. While a number of important uncertainties have been addressed by the ice-sheet modeling community, the flow law, which is at the center of most process-based ice-sheet models, has so far been assumed certain. Unfortunately, recent studies show that the parameters in the flow law might be uncertain and different from the widely accepted standard values. Here, we use an idealized flowline setup to investigate how uncertainties in the flow law translate into uncertainties in flow-driven mass loss given a step-wise increase of surface temperatures. We find that the measured range of flow parameters can double the flow-driven mass loss within the first centuries of warming, compared to a setting with standard parameters. The spread of ice loss due to an uncertainty in flow parameters is of the same order as the increase in mass loss due to increasing surface temperatures. While this study focuses on an idealized setting in order to disentangle the effect of the flow law from other effects, it is likely that this uncertainty carries over to realistic three-dimensional simulations of Greenland and Antarctica.

scholarly journals Hindcasting to measure ice sheet model sensitivity to initial states

2012 ◽  
Vol 6 (6) ◽  
pp. 5069-5094 ◽  
Author(s):  
A. Aschwanden ◽  
G. Aðalgeirsdóttir ◽  
C. Khroulev
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Initial State ◽  
Multiple Observations ◽  
Elevation Changes ◽  
Initial States ◽  
Global Mean Sea Level ◽  
Good Agreement

Abstract. Recent observations of the Greenland ice sheet indicate rapid mass loss at an accelerating rate with an increasing contribution to global mean sea level. Ice sheet models are used for projections of such future contributions of ice sheets to sea level, but the quality of projections is difficult to measure directly. Realistic initial states are crucial for accurate simulations. To test initial states we use hindcasting, i.e. forcing a model with known or closely-estimated inputs for past events to see how well the output matches observations. By simulating the recent past of Greenland, and comparing to observations of ice thickness, ice discharge, surface speeds, mass loss and surface elevation changes for validation, we find that the short term model response is strongly influenced by the initial state. We show that the dynamical state can be mis-represented despite a good agreement with some observations, stressing the importance of using multiple observations. Some initial states generate good agreement with measured mass time series in the hindcast period, and good agreement with present-day kinematic fields. We suggest hindcasting as a methodology for careful validation of initial states that can be done before making projections on decadal to century time-scales.

scholarly journals Mass balance of the Greenland ice sheet – a study of ICESat data, surface density and firn compaction modelling

2010 ◽  
Vol 4 (4) ◽  
pp. 2103-2141 ◽  
Author(s):  
L. S. Sørensen ◽  
S. B. Simonsen ◽  
K. Nielsen ◽  
P. Lucas-Picher ◽  
G. Spada ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Mass Loss ◽  
Mass Balance ◽  
Volume Change ◽  
Surface Density ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Altimetry Data ◽  
Data Set ◽  
Elevation Changes

Abstract. ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique data set for monitoring the changes of the cryosphere. Here we present a novel method for determining the mass balance of the Greenland ice sheet derived from ICESat altimetry data. Four different methods for deriving the elevation changes from the ICESat altimetry data set are used. This multi method approach gives an understanding of the complexity associated with deriving elevation changes from the ICESat altimetry data set. The altimetry can not stand alone in estimating the mass balance of the Greenland ice sheet. We find firn dynamics and surface densities to be important factors in deriving the mass loss from remote sensing altimetry. The volume change derived from ICESat data is corrected for firn compaction, vertical bedrock movement and an intercampaign elevation bias in the ICESat data. Subsequently, the corrected volume change is converted into mass change by surface density modelling. The firn compaction and density models are driven by a dynamically downscaled simulation of the HIRHAM5 regional climate model using ERA-Interim reanalysis lateral boundary conditions. We find an annual mass loss of the Greenland ice sheet of 210 ± 21 Gt yr−1 in the period from October 2003 to March 2008. This result is in good agreement with other studies of the Greenland ice sheet mass balance, based on different remote sensing techniques.

scholarly journals Sliding dominates slow-flowing margin regions, Greenland Ice Sheet

2019 ◽  
Vol 5 (7) ◽  
pp. eaaw5406 ◽  
Author(s):  
Nathan Maier ◽  
Neil Humphrey ◽  
Joel Harper ◽  
Toby Meierbachtol
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Zone ◽  
Ice Flow ◽  
Dimensional Array ◽  
Theoretical Maximum ◽  
Resistance To Sliding ◽  
Lower Elevation ◽  
Tilt Sensors

On the Greenland Ice Sheet (GrIS), ice flow due to deformation and sliding across the bed delivers ice to lower-elevation marginal regions where it can melt. We measured the two mechanisms of motion using a three-dimensional array of 212 tilt sensors installed within a network of boreholes drilled to the bed in the ablation zone of GrIS. Unexpectedly, sliding completely dominates ice motion all winter, despite a hard bedrock substrate and no concurrent surface meltwater forcing. Modeling constrained by detailed tilt observations made along the basal interface suggests that the high sliding is due to a slippery bed, where sparsely spaced bedrock bumps provide the limited resistance to sliding. The conditions at the site are characterized as typical of ice sheet margins; thus, most ice flow near the margins of GrIS is mainly from sliding, and marginal ice fluxes are near their theoretical maximum for observed surface speeds.

scholarly journals Melting of Northern Greenland during the last interglaciation

2012 ◽  
Vol 6 (6) ◽  
pp. 1239-1250 ◽  
Author(s):  
A. Born ◽  
K. H. Nisancioglu
Keyword(s):  
Climate Model ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Large Mass ◽  
Climate Data ◽  
Coupled Climate Model ◽  
The South ◽  
High Accumulation ◽  
Positive Feedbacks

Abstract. Using simulated climate data from the comprehensive coupled climate model IPSL CM4, we simulate the Greenland ice sheet (GrIS) during the Eemian interglaciation with the three-dimensional ice sheet model SICOPOLIS. The Eemian is a period 126 000 yr before present (126 ka) with Arctic temperatures comparable to projections for the end of this century. In our simulation, the northeastern part of the GrIS is unstable and retreats significantly, despite moderate melt rates. This result is found to be robust to perturbations within a wide parameter space of key parameters of the ice sheet model, the choice of initial ice temperature, and has been reproduced with climate forcing from a second coupled climate model, the CCSM3. It is shown that the northeast GrIS is the most vulnerable. Even a small increase in melt removes many years of ice accumulation, giving a large mass imbalance and triggering the strong ice-elevation feedback. Unlike the south and west, melting in the northeast is not compensated by high accumulation. The analogy with modern warming suggests that in coming decades, positive feedbacks could increase the rate of mass loss of the northeastern GrIS, exceeding the recent observed thinning rates in the south.

scholarly journals <i>Brief Communication</i> "Expansion of meltwater lakes on the Greenland ice sheet"

2012 ◽  
Vol 6 (5) ◽  
pp. 4447-4454 ◽  
Author(s):  
I. M. Howat ◽  
S. de la Peña ◽  
J. H. van Angelen ◽  
J. T. M. Lenaerts ◽  
M. R. van den Broeke
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
Satellite Imagery ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Equilibrium Line ◽  
Ice Flow ◽  
West Greenland ◽  
Physical Limit

Abstract. Forty years of satellite imagery reveal that meltwater lakes on the margin of the Greenland Ice Sheet have expanded substantially inland to higher elevations with warming. These lakes are important because they provide a mechanism for bringing water to the ice bed, warming the ice and causing sliding. Inland expansion of lakes could accelerate ice flow by bringing water to previously frozen bed, potentially increasing future rates of mass loss. Increasing lake elevations in West Greenland closely follow the rise of the mass balance equilibrium line, suggesting no physical limit on lake expansion there. This is not included in ice sheet models.

scholarly journals Circum-Greenland, ice-thickness measurements collected during PROMICE airborne surveys in 2007, 2011 and 2015

2018 ◽  
pp. 79-82 ◽  
Author(s):  
Louise Sandberg Sørensen ◽  
Sebastian B. Simonsen ◽  
René Forsberg ◽  
Lars Stenseng ◽  
Henriette Skourup ◽  
...  
Keyword(s):  
Mass Loss ◽  
Laser Scanning ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Thickness ◽  
Average Mass ◽  
Airborne Laser ◽  
Elevation Changes ◽  
Ice Velocity ◽  
Thickness Measurements

The Greenland ice sheet has experienced an average mass loss of 142 ± 49 Gt/yr from 1992 to 2011 (Shepherd et al. 2012), making it a significant contributor to sea-level rise. Part of the ice- sheet mass loss is the result of increased dynamic response of outlet glaciers (Rignot et al. 2011). The ice discharge from outlet glaciers can be quantified by coincident measurements of ice velocity and ice thickness (Thomas et al. 2000; van den Broeke et al. 2016). As part of the Programme for monitoring of the Greenland Ice Sheet (PROMICE; Ahlstrøm et al. 2008), three airborne surveys were carried out in 2007, 2011 and 2015, with the aim of measuring the changes in Greenland ice-sheet thicknesses. The purpose of the airborne surveys was to collect data to assess the dynamic mass loss of the Greenland ice sheet (Andersen et al. 2015). Here, we present these datasets of observations from ice-penetrating radar and airborne laser scanning, which, in combination, make us able to determine the ice thickness precisely. Surface-elevation changes between surveys are also presented, although we do not provide an in-depth scientific interpretation of these.

scholarly journals Improved retrieval of land ice topography from CryoSat-­2 data and its impact for volume change estimation of the Greenland Ice Sheet

2016 ◽  
Author(s):  
Johan Nilsson ◽  
Alex Gardner ◽  
Louise Sandberg Sørensen ◽  
Rene Forsberg
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lower Sensitivity ◽  
Volume Changes ◽  
Near Surface ◽  
Ice Cloud ◽  
Ice Surface ◽  
Airborne Laser ◽  
Elevation Changes ◽  
New Processing

Abstract. A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publically available Cryosat-2 elevation product (L2 Baseline-B). This when compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in Interferometric Synthetic Aperture mode over the high relief regions of the Greenland ice sheet we find an improvement in the root-mean-square-error (RMSE) of 27 % and 40 % compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in Low Resolution Mode, we find an improvement in the RMSE of 68 % and 55 % in the derived elevation and elevation changes, respectively. There is also an 86 % improvement in the magnitude of the seasonal amplitudes when compared to amplitudes derived from ICESat data. These results indicate that the new methodology provides improved tracking of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes and total volume changes from Cryosat-2 data for Greenland Ice Sheet during the period Jan-2011 to Jan-2015. We find that the Greenland Ice Sheet decreased in volume at rate of 289 &amp;pm; 16 km3 a−1, with high inter-annual variability and spatial heterogeneity in rates of loss. This rate is 65 km3 a−1 more negative than rates determined from ESA's L2 product, highlighting the importance of Cryosat-2 processing methodologies.

scholarly journals Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet

2016 ◽  
Vol 10 (6) ◽  
pp. 2953-2969 ◽  
Author(s):  
Johan Nilsson ◽  
Alex Gardner ◽  
Louise Sandberg Sørensen ◽  
Rene Forsberg
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lower Sensitivity ◽  
Volume Changes ◽  
Near Surface ◽  
Ice Cloud ◽  
Ice Surface ◽  
Airborne Laser ◽  
Elevation Changes ◽  
New Processing

Abstract. A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publicly available CryoSat-2 elevation product (L2 Baseline-B). The results are compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in interferometric synthetic aperture mode (SIN) over the high-relief regions of the Greenland Ice Sheet we find an improvement in the root-mean-square error (RMSE) of 27 and 40 % compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in low-resolution mode (LRM), we find an improvement in the RMSE of 68 and 55 % in the derived elevation and elevation changes, respectively. There is also an 86 % improvement in the magnitude of the seasonal amplitudes when compared to amplitudes derived from ICESat data. These results indicate that the new methodology provides improved tracking of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes, and total volume changes from CryoSat-2 data for the Greenland Ice Sheet during the period January 2011 to January 2015. We find that the Greenland Ice Sheet decreased in volume at a rate of 289 ± 20 km3a−1, with high interannual variability and spatial heterogeneity in rates of loss. This rate is 65 km3a−1 more negative than rates determined from ESA's L2 product, highlighting the importance of CryoSat-2 processing methodologies.

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