Changes in Northwest Greenland Ice Sheet Elevation and Mass

2021 ◽  
Author(s):  
Inès Otosaka ◽  
Andrew Shepherd ◽  
Andreas Groh
Keyword(s):  
Mass Balance ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mass Change ◽  
Elevation Change ◽  
Laser Altimetry ◽  
Mass Budget ◽  
Airborne Laser ◽  
The Impact

<p>About a third of Greenland’s total ice losses come from the Northwest sector, a sector that includes a large number of marine-terminating outlet glaciers, which have all experienced widespread retreat triggered by ocean-induced melting. Here, we derive changes in surface elevation, volume and mass in the Northwest sector of the Greenland Ice Sheet using a decade of CryoSat-2 observations. We find an average elevation change rate of 18.7 ± 0.4 cm/yr, with rapid thinning at the ice sheet margins at a rate of 42.7 ± 0.9 cm/yr. We compare our CryoSat-2 rates of elevation change to airborne laser altimetry data from Operation IceBridge. Overall, there is a good agreement between the two datasets with a mean difference of 6.5 ± 0.5 cm/yr and standard deviation of 31.1 cm/yr. We further compute volume change, which we convert to mass change by testing three alternate density models and we find that the northwest sector has lost 386 ± 3.7 Gt of ice between July 2010 and July 2019. We compare our mass balance estimate to independent estimates from gravimetry and the mass budget method across different spatial scales. First, we compare the different estimates by splitting the sector into two and four regions. While our altimetry estimate is the least negative across all regions, the gravimetry and mass budget estimates alternate in recording the largest ice losses. We further compare mass changes derived from altimetry and the mass budget method in each of the 74 individual glacier basins of the Northwest sector. We find a high correlation of 0.81 between rates of mass change from altimetry and the mass budget method, with the highest differences recorded in Steenstrup-Dietrichson and Kjer Gletscher basins. Our comparisons show that the spatial pattern of the differences between mass balance estimates is complex, suggesting that discrepancies between techniques do not solely originate from one single region or technique. Finally, we explore several factors that could potentially bias our altimetry mass balance estimation, by investigating differences between satellite radar and airborne laser altimetry, the dependency on grid spatial resolution and the impact of using different density models.</p>

scholarly journals Satellite Remote Sensing of the Greenland Ice Sheet Ablation Zone: A Review

2019 ◽  
Vol 11 (20) ◽  
pp. 2405
Author(s):  
Matthew Cooper ◽  
Laurence Smith
Keyword(s):  
Remote Sensing ◽  
Mass Balance ◽  
Satellite Remote Sensing ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Zone ◽  
Elevation Change ◽  
Laser Altimetry ◽  
Surface Elevation Change ◽  
Optical Imagery

The Greenland Ice Sheet is now the largest land ice contributor to global sea level rise, largely driven by increased surface meltwater runoff from the ablation zone, i.e., areas of the ice sheet where annual mass losses exceed gains. This small but critically important area of the ice sheet has expanded in size by ~50% since the early 1960s, and satellite remote sensing is a powerful tool for monitoring the physical processes that influence its surface mass balance. This review synthesizes key remote sensing methods and scientific findings from satellite remote sensing of the Greenland Ice Sheet ablation zone, covering progress in (1) radar altimetry, (2) laser (lidar) altimetry, (3) gravimetry, (4) multispectral optical imagery, and (5) microwave and thermal imagery. Physical characteristics and quantities examined include surface elevation change, gravimetric mass balance, reflectance, albedo, and mapping of surface melt extent and glaciological facies and zones. The review concludes that future progress will benefit most from methods that combine multi-sensor, multi-wavelength, and cross-platform datasets designed to discriminate the widely varying surface processes in the ablation zone. Specific examples include fusing laser altimetry, radar altimetry, and optical stereophotogrammetry to enhance spatial measurement density, cross-validate surface elevation change, and diagnose radar elevation bias; employing dual-frequency radar, microwave scatterometry, or combining radar and laser altimetry to map seasonal snow depth; fusing optical imagery, radar imagery, and microwave scatterometry to discriminate between snow, liquid water, refrozen meltwater, and bare ice near the equilibrium line altitude; combining optical reflectance with laser altimetry to map supraglacial lake, stream, and crevasse bathymetry; and monitoring the inland migration of snowlines, surface melt extent, and supraglacial hydrologic features.

scholarly journals Satellite Remote Sensing of the Greenland Ice Sheet Ablation Zone: A Review

2019 ◽  
Author(s):  
Matthew G. Cooper ◽  
Laurence C. Smith
Keyword(s):  
Remote Sensing ◽  
Mass Balance ◽  
Satellite Remote Sensing ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Zone ◽  
Elevation Change ◽  
Laser Altimetry ◽  
Surface Elevation Change ◽  
Optical Imagery

The Greenland Ice Sheet is now the largest land ice contributor to global sea level rise, largely driven by increased surface meltwater runoff from the ablation zone, i.e. areas of the ice sheet where annual mass losses exceed gains. This small but critically important area of the ice sheet has expanded in size by ~50% since the early 1960s, and satellite remote sensing is a powerful tool for monitoring the physical processes that influence its surface mass balance. This review synthesizes key remote sensing methods and scientific findings from satellite remote sensing of the Greenland Ice Sheet ablation zone, covering progress in 1) radar altimetry, 2) laser (lidar) altimetry, 3) gravimetry, 4) multispectral optical imagery and, 5) microwave and thermal imagery. Physical characteristics and quantities examined include surface elevation change, gravimetric mass balance, reflectance, albedo, and mapping of surface melt extent and glaciological facies and zones. The review concludes that future progress will benefit most from methods that combine multi-sensor, multi-wavelength, and cross-platform datasets designed to discriminate the widely varying surface processes in the ablation zone. Specific examples include fusing laser altimetry, radar altimetry, and optical stereophotogrammetry to enhance spatial measurement density, cross-validate surface elevation change, and diagnose radar elevation bias; fusing optical imagery, radar imagery, and microwave scatterometry to discriminate between snow, liquid water, refrozen meltwater, and bare ice near the equilibrium line altitude; combining optical reflectance with laser altimetry to map supraglacial lake, stream, and crevasse bathymetry; and monitoring the inland migration of snowlines, surface melt extent, and supraglacial hydrologic features.

scholarly journals Mass balance of the Greenland ice sheet (2003–2008) from ICESat data – the impact of interpolation, sampling and firn density

2011 ◽  
Vol 5 (1) ◽  
pp. 173-186 ◽  
Author(s):  
L. S. Sørensen ◽  
S. B. Simonsen ◽  
K. Nielsen ◽  
P. Lucas-Picher ◽  
G. Spada ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Mass Balance ◽  
Volume Change ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mass Change ◽  
Ice Dynamics ◽  
Elevation Changes ◽  
The Impact

Abstract. ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique dataset 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. Three different methods for deriving elevation changes from the ICESat altimetry dataset are used. This multi-method approach provides a method to assess the complexity of deriving elevation changes from this dataset. The altimetry alone can not provide an estimate of the mass balance of the Greenland ice sheet. Firn dynamics and surface densities are important factors that contribute to the mass change derived from remote-sensing altimetry. The volume change derived from ICESat data is corrected for changes in firn compaction over the observation period, vertical bedrock movement and an intercampaign elevation bias in the ICESat data. Subsequently, the corrected volume change is converted into mass change by the application of a simple surface density model, in which some of the ice dynamics are accounted for. The firn compaction and density models are driven by the HIRHAM5 regional climate model, forced by the ERA-Interim re-analysis product, at the lateral boundaries. We find annual mass loss estimates of the Greenland ice sheet in the range of 191 ± 23 Gt yr−1 to 240 ± 28 Gt yr−1 for the period October 2003 to March 2008. These results are in good agreement with several other studies of the Greenland ice sheet mass balance, based on different remote-sensing techniques.

scholarly journals Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland Ice Sheet

2018 ◽  
Vol 12 (9) ◽  
pp. 2981-2999 ◽  
Author(s):  
Jiangjun Ran ◽  
Miren Vizcaino ◽  
Pavel Ditmar ◽  
Michiel R. van den Broeke ◽  
Twila Moon ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
High Accumulation ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Meltwater Runoff

Abstract. The Greenland Ice Sheet (GrIS) is currently losing ice mass. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission Gravity Recovery and Climate Experiment (GRACE), surface mass balance (SMB) output of the Regional Atmospheric Climate Model v. 2 (RACMO2), and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. We find that the mean rate of mass variations in Greenland observed by GRACE was between −277 and −269 Gt yr−1 in 2003–2012. This estimate is consistent with the sum (i.e., -304±126 Gt yr−1) of individual contributions – surface mass balance (SMB, 216±122 Gt yr−1) and ice discharge (520±31 Gt yr−1) – and with previous studies. We further identify a seasonal mass anomaly throughout the GRACE record that peaks in July at 80–120 Gt and which we interpret to be due to a combination of englacial and subglacial water storage generated by summer surface melting. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO2.3, SNOWPACK, and MAR3.9). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast and northwest parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few gigatonnes) and does not explain the seasonal differences between the total mass and SMB signals. With the improved quantification of meltwater storage at the seasonal scale, we highlight its importance for understanding glacio-hydrological processes and their contributions to the ice sheet mass variability.

scholarly journals Surface roughness over the northern half of the Greenland Ice Sheet from airborne laser altimetry

2009 ◽  
Vol 114 (F1) ◽  
Author(s):  
C. J. van der Veen ◽  
Y. Ahn ◽  
B. M. Csatho ◽  
E. Mosley-Thompson ◽  
W. B. Krabill
Keyword(s):  
Surface Roughness ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Laser Altimetry ◽  
Airborne Laser ◽  
Northern Half

scholarly journals Modeling of firn compaction for estimating ice-sheet mass change from observed ice-sheet elevation change

2011 ◽  
Vol 52 (59) ◽  
pp. 1-7 ◽  
Author(s):  
Jun Li ◽  
H. Jay Zwally
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temporal Variations ◽  
Mass Change ◽  
Surface Elevation ◽  
Effective Density ◽  
Elevation Change ◽  
Surface Elevation Change ◽  
Elevation Changes

AbstractChanges in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kgm–3, which along with 900 kgm–3 for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kgm–3. We show that using an average (or ‘effective’) density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

scholarly journals Elevation change of the Greenland Ice Sheet due to surface mass balance and firn processes, 1960–2014

2015 ◽  
Vol 9 (6) ◽  
pp. 2009-2025 ◽  
Author(s):  
P. Kuipers Munneke ◽  
S. R. M. Ligtenberg ◽  
B. P. Y. Noël ◽  
I. M. Howat ◽  
J. E. Box ◽  
...  
Keyword(s):  
Mass Balance ◽  
Volume Change ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Elevation ◽  
Surface Mass Balance ◽  
Elevation Change ◽  
Ice Dynamics ◽  
Surface Mass

Abstract. Observed changes in the surface elevation of the Greenland Ice Sheet are caused by ice dynamics, basal elevation change, basal melt, surface mass balance (SMB) variability, and by compaction of the overlying firn. The last two contributions are quantified here using a firn model that includes compaction, meltwater percolation, and refreezing. The model is forced with surface mass fluxes and temperature from a regional climate model for the period 1960–2014. The model results agree with observations of surface density, density profiles from 62 firn cores, and altimetric observations from regions where ice-dynamical surface height changes are likely small. In areas with strong surface melt, the firn model overestimates density. We find that the firn layer in the high interior is generally thickening slowly (1–5 cm yr−1). In the percolation and ablation areas, firn and SMB processes account for a surface elevation lowering of up to 20–50 cm yr−1. Most of this firn-induced marginal thinning is caused by an increase in melt since the mid-1990s and partly compensated by an increase in the accumulation of fresh snow around most of the ice sheet. The total firn and ice volume change between 1980 and 2014 is estimated at −3295 ± 1030 km3 due to firn and SMB changes, corresponding to an ice-sheet average thinning of 1.96 ± 0.61 m. Most of this volume decrease occurred after 1995. The computed changes in surface elevation can be used to partition altimetrically observed volume change into surface mass balance and ice-dynamically related mass changes.

scholarly journals Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland ice sheet

2018 ◽  
Author(s):  
Jiangjun Ran ◽  
Miren Vizcaino ◽  
Pavel Ditmar ◽  
Michiel R. van den Broeke ◽  
Twila Moon ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
Climate Model ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
High Accumulation ◽  
Outlet Glacier ◽  
Surface Mass

Abstract. The Greenland Ice Sheet (GrIS) is currently losing ice mass as the result of changes in the complex ice-climate interactions that have been driven by global climate change. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission GRACE, surface mass balance (SMB) output of RACMO 2.3, and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. Firstly, in agreement with previous estimates, we find that the rate of mass loss from Greenland observed by GRACE was between −277 and −269 Gt/yr in 2003–2012. This estimate is consistent with the sum of individual contributions: surface mass balance (SMB, around 216 ± 122 Gt/yr) and ice discharge (520 ± 31 Gt/yr), indicating a good performance of the regional climate model. Secondly, we examine the average accelerations of mass anomalies in Greenland over 2003–2012, suggesting that the SMB (−23.3 ± 2.7 Gt/yr2) contributes 75 % to the total acceleration observed by GRACE. The remaining contributions to the mass loss acceleration for entire Greenland are statistically insignificant. Finally and most importantly, this study suggests the existence of a substantial meltwater storage during summer, with a peak value of 80–120 Gt in July. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO 2.3 and SNOWPACK). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast (SE) and northwest (NW) parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few Gt) and does not explain the intra-annual differences between the total mass and SMB signals.

scholarly journals Application of GRACE to the assessment of model-based estimates of monthly Greenland Ice Sheet mass balance (2003–2012)

2016 ◽  
Vol 10 (5) ◽  
pp. 1965-1989 ◽  
Author(s):  
Nicole-Jeanne Schlegel ◽  
David N. Wiese ◽  
Eric Y. Larour ◽  
Michael M. Watkins ◽  
Jason E. Box ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Models ◽  
Spatial Scales ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Regional Climate Models ◽  
Surface Mass ◽  
Model Based ◽  
Ice Sheet Mass Balance

Abstract. Quantifying the Greenland Ice Sheet's future contribution to sea level rise is a challenging task that requires accurate estimates of ice sheet sensitivity to climate change. Forward ice sheet models are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is challenging due to the scarcity of continental-wide data for model evaluation. Recent advancements in processing of Gravity Recovery and Climate Experiment (GRACE) data using Bayesian-constrained mass concentration ("mascon") functions have led to improvements in spatial resolution and noise reduction of monthly global gravity fields. Specifically, the Jet Propulsion Laboratory's JPL RL05M GRACE mascon solution (GRACE_JPL) offers an opportunity for the assessment of model-based estimates of ice sheet mass balance (MB) at ∼ 300 km spatial scales. Here, we quantify the differences between Greenland monthly observed MB (GRACE_JPL) and that estimated by state-of-the-art, high-resolution models, with respect to GRACE_JPL and model uncertainties. To simulate the years 2003–2012, we force the Ice Sheet System Model (ISSM) with anomalies from three different surface mass balance (SMB) products derived from regional climate models. Resulting MB is compared against GRACE_JPL within individual mascons. Overall, we find agreement in the northeast and southwest where MB is assumed to be primarily controlled by SMB. In the interior, we find a discrepancy in trend, which we presume to be related to millennial-scale dynamic thickening not considered by our model. In the northwest, seasonal amplitudes agree, but modeled mass trends are muted relative to GRACE_JPL. Here, discrepancies are likely controlled by temporal variability in ice discharge and other related processes not represented by our model simulations, i.e., hydrological processes and ice–ocean interaction. In the southeast, GRACE_JPL exhibits larger seasonal amplitude than predicted by the models while simultaneously having more pronounced trends; thus, discrepancies are likely controlled by a combination of missing processes and errors in both the SMB products and ISSM. At the margins, we find evidence of consistent intra-annual variations in regional MB that deviate distinctively from the SMB annual cycle. Ultimately, these monthly-scale variations, likely associated with hydrology or ice–ocean interaction, contribute to steeper negative mass trends observed by GRACE_JPL. Thus, models should consider such processes at relatively high (monthly-to-seasonal) temporal resolutions to achieve accurate estimates of Greenland MB.

scholarly journals Improved GRACE regional mass balance estimates of the Greenland ice sheet cross-validated with the input–output method

2016 ◽  
Vol 10 (2) ◽  
pp. 895-912 ◽  
Author(s):  
Zheng Xu ◽  
Ernst J. O. Schrama ◽  
Wouter van der Wal ◽  
Michiel van den Broeke ◽  
Ellyn M. Enderlin
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mass Change ◽  
Input Output ◽  
Surface Mass ◽  
Ice Cloud ◽  
The Difference ◽  
Gravity Recovery

Abstract. In this study, we use satellite gravimetry data from the Gravity Recovery and Climate Experiment (GRACE) to estimate regional mass change of the Greenland ice sheet (GrIS) and neighboring glaciated regions using a least squares inversion approach. We also consider results from the input–output method (IOM). The IOM quantifies the difference between the mass input and output of the GrIS by studying the surface mass balance (SMB) and the ice discharge (D). We use the Regional Atmospheric Climate Model version 2.3 (RACMO2.3) to model the SMB and derive the ice discharge from 12 years of high-precision ice velocity and thickness surveys. We use a simulation model to quantify and correct for GRACE approximation errors in mass change between different subregions of the GrIS, and investigate the reliability of pre-1990s ice discharge estimates, which are based on the modeled runoff. We find that the difference between the IOM and our improved GRACE mass change estimates is reduced in terms of the long-term mass change when using a reference discharge derived from runoff estimates in several subareas. In most regions our GRACE and IOM solutions are consistent with other studies, but differences remain in the northwestern GrIS. We validate the GRACE mass balance in that region by considering several different GIA models and mass change estimates derived from data obtained by the Ice, Cloud and land Elevation Satellite (ICESat). We conclude that the approximated mass balance between GRACE and IOM is consistent in most GrIS regions. The difference in the northwest is likely due to underestimated uncertainties in the IOM solutions.

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