Stochastic modeling of subglacial topography exposes uncertainty in water routing at Jakobshavn Glacier

Abstract Subglacial topography is an important feature in numerous ice-sheet analyses and can drive the routing of water at the bed. Bed topography is primarily measured with ice-penetrating radar. Significant gaps, however, remain in data coverage that require interpolation. Topographic interpolations are typically made with kriging, as well as with mass conservation, where ice flow dynamics are used to constrain bed geometry. However, these techniques generate bed topography that is unrealistically smooth at small scales, which biases subglacial water flowpath models and makes it difficult to rigorously quantify uncertainty in subglacial drainage patterns. To address this challenge, we adapt a geostatistical simulation method with probabilistic modeling to stochastically simulate bed topography such that the interpolated topography retains the spatial statistics of the ice-penetrating radar data. We use this method to simulate subglacial topography using mass conservation topography as a secondary constraint. We apply a water routing model to each of these realizations. Our results show that many of the flowpaths significantly change with each topographic realization, demonstrating that geostatistical simulation can be useful for assessing confidence in subglacial flowpaths.

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RADAR-DERIVED INTERNAL LAYERING AND BASAL ROUGHNESS CHARACTERIZATION ALONG A TRAVERSE FROM ZHONGSHAN STATION TO DOME A, EAST ANTARCTICA

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xliii-b3-2020-905-2020 ◽

2020 ◽

Vol XLIII-B3-2020 ◽

pp. 905-910

Author(s):

X. Tang ◽

K. Luo ◽

J. Guo

Keyword(s):

Ice Sheet ◽

Radar Data ◽

Internal Layers ◽

Dome A ◽

Ice Flow ◽

Zhongshan Station ◽

Bed Topography ◽

New Information ◽

Flow Activity ◽

Lambert Glacier

Abstract. The internal layers of ice sheets from ice-penetrating radar (IPR) investigation preserve critical information about the englacial conditions and ice-flow field. This paper presents a new detailed analysis of the spatial distribution characteristics of internal layers and subglacial topography of East Antarctic ice sheet (EAIS) from Zhongshan station to Dome A. Taking the internal layering continuity index (ILCI) and basal roughness as indicators, it provides an opportunity to evaluate the past internal environment and dynamics of ice sheet. The radar data of 1244 km along a traverse between Zhongshan Station and Dome A of EAIS was collected during the 29th Chinese National Antarctic Research Expedition (CHINARE 29, 2012/2013). Except for the upstream of Lambert Glacier, the patterns of the folds in the internal layers are basically similar to the bed topography. The relatively flat basal topography and the decrease of ILCI with the deepening of the depth provide evidence for identifying previous rapid ice flow areas that the satellite cannot obtain, especially in the upstream of Lambert Glacier. Well continuous internal layers of Dome A almost extend to the bed, with high ILCI and high roughness characteristics. There are three kinds of basal roughness patterns in the whole traverse. The characteristics of the internal layer and basal topography of the traverse between Zhongshan Station and Dome A provide new information for understanding the ancient ice-flow activity and the historical evolution of EAIS.

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Weak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica

Journal of Glaciology ◽

10.3189/2013jog13j050 ◽

2013 ◽

Vol 59 (217) ◽

pp. 900-912 ◽

Cited By ~ 30

Author(s):

Joseph A. MacGregor ◽

Ginny A. Catania ◽

Howard Conway ◽

Dustin M. Schroeder ◽

Ian Joughin ◽

...

Keyword(s):

Flow Pattern ◽

Radar Data ◽

Geophysical Survey ◽

Clear Relationship ◽

West Antarctica ◽

Amundsen Sea ◽

Ice Flow ◽

Bed Topography ◽

Bed Roughness

AbstractRecent acceleration and thinning of Thwaites Glacier, West Antarctica, motivates investigation of the controls upon, and stability of, its present ice-flow pattern. Its eastern shear margin separates Thwaites Glacier from slower-flowing ice and the southern tributaries of Pine Island Glacier. Troughs in Thwaites Glacier’s bed topography bound nearly all of its tributaries, except along this eastern shear margin, which has no clear relationship with regional bed topography along most of its length. Here we use airborne ice-penetrating radar data from the Airborne Geophysical Survey of the Amundsen Sea Embayment, Antarctica (AGASEA) to investigate the nature of the bed across this margin. Radar data reveal slightly higher and rougher bed topography on the slower-flowing side of the margin, along with lower bed reflectivity. However, the change in bed reflectivity across the margin is partially explained by a change in bed roughness. From these observations, we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties. Given the potential for future increases in ice flux farther downstream, the eastern shear margin may be vulnerable to migration. However, there is no evidence that this margin is migrating presently, despite ongoing changes farther downstream.

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Inverting ice surface elevation and velocity for bed topography and slipperiness beneath Thwaites Glacier

10.5194/tc-2021-287 ◽

2021 ◽

Author(s):

Helen Ockenden ◽

Robert G. Bingham ◽

Andrew Curtis ◽

Daniel Goldberg

Keyword(s):

High Resolution ◽

Ice Sheets ◽

Mass Conservation ◽

Radar Data ◽

Surface Flow ◽

Surface Elevation ◽

Linear Perturbation ◽

Detailed Knowledge ◽

Bed Topography ◽

Ice Stream

Abstract. There is significant uncertainty over how ice sheets and glaciers will respond to rising global temperatures. Limited knowledge of the topography and rheology of ice-bed interface is a key cause of this uncertainty, as models show that small changes in the bed can have a large influence on predicted rates of ice loss. Most of our detailed knowledge of bed topography comes from airborne and ground-penetrating radar observations. However, these direct observations are not spaced closely enough to meet the requirements of ice-sheet models, so interpolation and inversion methods are used to fill in the gaps. Here we present the results of a new inversion of surface-elevation and velocity data over Thwaites Glacier, West Antarctica, for bed topography and slipperiness (i.e. the degree of basal slip for a given level of drag). The inversion is based on a steady-state linear perturbation analysis of the shallow-ice-stream equations. The method works by identifying disturbances to surface flow which are caused by obstacles or sticky patches in the bed, and can therefore be applied wherever the shallow-ice-stream equations hold and where surface data are available, even where the ice thickness is not well known. We assess the performance of the inversion for topography with the available radar data. Although the topographic output from the inversion is less successful where the bed slopes steeply, it compares well with radar data from the central trunk of the glacier. This method could therefore be useful as either an independent test of other interpolation methods such as mass conservation and kriging, or as a complementary technique in regions where those techniques fail. We do not have data to allow us to assess the success of the slipperiness results from our inversions, but we provide maps that may guide future seismic data collection across Thwaites Glacier. The methods presented here show significant promise for using high-resolution satellite datasets, calibrated by the sparser field datasets, to generate high resolution bed topography products across the ice sheets, and therefore contribute to reduced uncertainty in predictions of future sea-level rise.

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Bedrock topography and wind erosion sites in East Antarctica: observations from the 2002 US-ITASE traverse

Annals of Glaciology ◽

10.3189/172756405781813258 ◽

2005 ◽

Vol 41 ◽

pp. 92-96 ◽

Cited By ~ 12

Author(s):

Brian C. Welch ◽

Robert W. Jacobel

Keyword(s):

Wind Erosion ◽

Flow Direction ◽

Surface Wind ◽

Ice Cores ◽

Radar Data ◽

Small Range ◽

Local Correlation ◽

Ice Flow ◽

Bedrock Topography ◽

Subglacial Topography

AbstractIce stratigraphy from deep-penetrating radar data collected during the 2002 US International Trans-Antarctic Scientific Expedition (US-ITASE) traverse shows evidence of a significant erosion surface and drift-filled basin related to a previously undiscovered 1400m subglacial mountain between Hercules Dome (87˚420 S, 108˚ W) and South Pole. The 3MHz radar profile crosses three subglacial mountains at approximately 458 to the ice-flow direction. Cross-cutting reflectors in the top 500m of ice stratigraphy are interpreted as angular unconformities resulting from wind erosion as the ice deforms over the mountain tops. The unconformities correlate locally with zones of high RADARSAT reflectivity. Several nearby sites with similar relatively high RADARSAT reflectivity adjacent to the traverse indicate that active wind erosion may be taking place at these locations as well. Based on the local correlation between surface wind scour and subglacial topography, we interpret the nearby cluster of bright RADARSAT reflectivity to indicate the presence of a small range of subglacial mountains. The ability to trace isochronal stratigraphy, associated with scour sites using shallow and deep radar, to nearby dated ice cores presents the possibility of exploiting wind-scour zones to access well-dated older ice with shallow-coring equipment.

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High-resolution bed topography mapping of Russell Glacier, Greenland, inferred from Operation IceBridge data

Journal of Glaciology ◽

10.3189/2013jog12j235 ◽

2013 ◽

Vol 59 (218) ◽

pp. 1015-1023 ◽

Cited By ~ 38

Author(s):

M. Morlighem ◽

E. Rignot ◽

J. Mouginot ◽

X. Wu ◽

H. Seroussi ◽

...

Keyword(s):

Mass Conservation ◽

Radar Data ◽

Airborne Radar ◽

Ice Thickness ◽

Flux Divergence ◽

Motion Data ◽

Bed Topography ◽

Bed Elevation ◽

Comparable Performance ◽

Mapping Techniques

AbstractDetailed maps of bed elevation and ice thickness are essential for understanding and projecting the evolution of the ice sheets. Such maps are traditionally obtained using airborne radar-sounding profiler data interpolated onto regular grids using geostatistical tools such as kriging. Here we compare three mapping techniques applied to a dense radar survey of Russell Glacier, West Greenland, by NASA Operation IceBridge: (1) radar tomography (RT) processing of the radar data to map the bed elevation, (2) interpolation of radar-derived thickness by ordinary kriging (KR) and (3) reconstruction of ice thickness based on the principles of mass conservation (MC) combining radar-sounding profiler and ice motion data. RT eliminates ambiguities caused by off-nadir reflections, but is spatially limited. KR yields a standard error in bed elevation of 35 m, but large errors (>300 m a−1) in flux divergence when combined with ice motion data. MC yields a comparable performance in bed elevation mapping, and errors smaller than 1 m a−1 in flux divergence. When the number of radar-sounding tracks is reduced, the performance of KR decreases more rapidly than for MC. Our study site shows that MC is capable of maintaining precision levels of 60 m at 400 m posting with flight tracks separated by 5 km.

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Radar-Derived Internal Structure and Basal Roughness Characterization along a Traverse from Zhongshan Station to Dome A, East Antarctica

Remote Sensing ◽

10.3390/rs12071079 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1079

Author(s):

Kun Luo ◽

Sixin Liu ◽

Jingxue Guo ◽

Tiantian Wang ◽

Lin Li ◽

...

Keyword(s):

Ice Sheet ◽

Radar Data ◽

Frequency Variation ◽

Internal Layers ◽

Dome A ◽

Ice Flow ◽

Zhongshan Station ◽

Bed Topography ◽

Flow Activity ◽

Lambert Glacier

The internal layers of ice sheets from ice-penetrating radar (IPR) investigation preserve critical information about the ice-flow field and englacial conditions. This paper presents a new detailed analysis of spatial distribution characteristics of internal layers and subglacial topography of the East Antarctic ice sheet (EAIS) from Zhongshan Station to Dome A. The radar data of 1244 km along a traverse between Zhongshan Station and Dome A of EAIS were collected during the 29th Chinese National Antarctic Research Expedition (CHINARE 29, 2012/2013). In this study, the Internal Layering Continuity Index (ILCI) and basal roughness were taken as indicators to provide an opportunity to evaluate the past internal environment and dynamics of the ice sheet. Except for the upstream of Lambert Glacier, the fold patterns of internal layers are basically similar to that of the bed topography. The relatively flat basal topography and the decrease of ILCI with increasing depth provide evidence for identifying previous rapid ice flow areas that are unavailable to satellites, especially in the upstream of Lambert Glacier. Continuous internal layers of Dome A, recording the spatial change of past ice accumulation and ice-flow history over 160 ka, almost extend to the bed, with high ILCI and high basal roughness of the corresponding bed topography. There are three kinds of basal roughness patterns along the traverse, that is, “low ξt low η”, “low ξt high η”, and “high ξt high η”, where ξt represents the amplitude of the undulations, and quantifies the vertical variation of the bedrock, and η measures the frequency variation of fluctuations and the horizontal irregularity of the profile. The characteristics of internal layers and basal topography of the traverse between Zhongshan Station and Dome A provide new information for understanding the ancient ice-flow activity and the historical evolution of EAIS.

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Mapping high-resolution basal topography of West Antarctica from radar data using non-stationary multiple-point geostatistics (MPS-BedMappingV1)

10.5194/gmd-2021-297 ◽

2021 ◽

Author(s):

Zhen Yin ◽

Chen Zuo ◽

Emma J. MacKie ◽

Jef Caers

Keyword(s):

High Resolution ◽

Radar Data ◽

Spatial Uncertainty ◽

Geostatistical Simulation ◽

The Arctic ◽

Multiple Point ◽

Amundsen Sea ◽

Bed Topography ◽

Training Images ◽

The Impact

Abstract. The subglacial bed topography is critical for modeling the evolution of Thwaites Glacier in the Amundsen Sea Embayment (ASE), where rapid ice loss threatens the stability of the West Antarctic Ice Sheet. However, mapping of subglacial topography is subject to high uncertainty. This is mainly because the bed topography is measured by airborne ice-penetrating radar along flight lines with large gaps up to tens of kilometers. Deterministic interpolation approaches do not reflect such spatial uncertainty. While traditional geostatistical simulation can model such uncertainty, it may be difficult to apply because of the significant non-stationary spatial variation of topography over such large surface area. In this study, we develop a non-stationary multiple-point geostatistical approach to interpolate large areas with irregular geophysical data and apply it to model the spatial uncertainty of entire ASE basal topography. We collect 166 high-resolution topographic training images (TIs) to train the gap-filling of radar data gaps, thereby simulating realistic topography maps. The TIs are extensively sampled from deglaciated regions in the Arctic as well as Antarctica. To address the non-stationarity in topographic modeling, we introduce a Bayesian framework that models the posterior distribution of non-stationary training images to the local modeling domain. Sampling from this distribution then provide candidate training images for local topographic modeling with uncertainty, constrained to radar flight line data. Compared to traditional MPS approaches without considering TI sampling, our approach demonstrates significant improvement in the topographic modeling quality and efficiency of the simulation algorithm. Finally, we simulate multiple realizations of high-resolution ASE topographic maps. We use the multiple realizations to investigate the impact of basal topography uncertainty on subglacial hydrological flow patterns.

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Ice thickness distribution of all Swiss glaciers based on extended ground-penetrating radar data and glaciological modeling

Journal of Glaciology ◽

10.1017/jog.2021.55 ◽

2021 ◽

pp. 1-19

Author(s):

Melchior Grab ◽

Enrico Mattea ◽

Andreas Bauder ◽

Matthias Huss ◽

Lasse Rabenstein ◽

...

Keyword(s):

Ground Penetrating Radar ◽

Thickness Distribution ◽

Radar Data ◽

Tourism Industry ◽

Swiss Alps ◽

Ice Thickness ◽

Hazard Management ◽

Bed Topography ◽

Ice Volume ◽

Ground Penetrating

Abstract Accurate knowledge of the ice thickness distribution and glacier bed topography is essential for predicting dynamic glacier changes and the future developments of downstream hydrology, which are impacting the energy sector, tourism industry and natural hazard management. Using AIR-ETH, a new helicopter-borne ground-penetrating radar (GPR) platform, we measured the ice thickness of all large and most medium-sized glaciers in the Swiss Alps during the years 2016–20. Most of these had either never or only partially been surveyed before. With this new dataset, 251 glaciers – making up 81% of the glacierized area – are now covered by GPR surveys. For obtaining a comprehensive estimate of the overall glacier ice volume, ice thickness distribution and glacier bed topography, we combined this large amount of data with two independent modeling algorithms. This resulted in new maps of the glacier bed topography with unprecedented accuracy. The total glacier volume in the Swiss Alps was determined to be 58.7 ± 2.5 km3 in the year 2016. By projecting these results based on mass-balance data, we estimated a total ice volume of 52.9 ± 2.7 km3 for the year 2020. Data and modeling results are accessible in the form of the SwissGlacierThickness-R2020 data package.

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Ice thickness estimates of Lemon Creek Glacier, Alaska, from active-source seismic imaging

Journal of Glaciology ◽

10.1017/jog.2021.32 ◽

2021 ◽

pp. 1-9

Author(s):

Stephen A. Veitch ◽

Marianne Karplus ◽

Galen Kaip ◽

Lucia F. Gonzalez ◽

Jason M. Amundson ◽

...

Keyword(s):

Ice Thickness ◽

Equilibrium Line Altitude ◽

Seismic Line ◽

Ice Flow ◽

Southeast Alaska ◽

Velocity Modeling ◽

Active Source ◽

Valley Glacier ◽

Subglacial Topography ◽

The Impact

Abstract Lemon Creek Glacier, a temperate valley glacier in the Juneau Icefield of Southeast Alaska, is the site of long running (>60 years) glaciological studies. However, the most recent published estimates of its thickness and subglacial topography come from two ~50 years old sources that are not in agreement and do not account for the effects of years of negative mass balance. We collected a 1-km long active-source seismic line on the upper section of the glacier parallel and near to the centerline of the glacier, roughly straddling the equilibrium-line altitude. We used these data to perform joint reflection-refraction velocity modeling and reflection imaging of the glacier bed. We find that this upper section of Lemon Creek Glacier is as much as 150 m (~65%) thicker than previously suggested with a large overdeepening in an area previously believed to have a uniform thickness. Our results lead us to reinterpret the impact of basal motion on ice flow and have a significant impact on expectations of subglacial hydrology. We suggest that further efforts to develop a whole-glacier model of subglacial topography are necessary to support studies that require accurate models of ice thickness and subglacial topography.

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A new bedrock and surface elevation dataset for modelling the Greenland ice sheet

Annals of Glaciology ◽

10.3189/172756403781815456 ◽

2003 ◽

Vol 37 ◽

pp. 351-356 ◽

Cited By ~ 15

Author(s):

Jonathan L. Bamber ◽

Duncan J. Baldwin ◽

S. Prasad Gogineni

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Detailed Comparison ◽

Radar Data ◽

The Arctic ◽

Small Scale ◽

Surface Model ◽

Rock Outcrops ◽

Bed Topography ◽

Elevation Model

AbstractA new digital elevation model of the surface of the Greenland ice sheet and surrounding rock outcrops has been produced from a comprehensive suite of satellite and airborne remote-sensing and cartographic datasets. The surface model has been regridded to a resolution of 5 km, and combined with a new ice-thickness grid derived from ice-penetrating radar data collected in the 1970s and 1990s. A further dataset, the International Bathymetric Chart of the Arctic Ocean, was used to extend the bed elevations to include the continental shelf. The new bed topography was compared with a previous version used for ice-sheet modelling. Near the margins of the ice sheet and, in particular, in the vicinity of small-scale features associated with outlet glaciers and rapid ice motion, significant differences were noted. This was highlighted by a detailed comparison of the bed topography around the northeast Greenland ice stream.

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