Martin Siegert - Academia.edu (original) (raw)

Papers by Martin Siegert

Research paper thumbnail of Antarctic Bedmap data: FAIR sharing of 60 years of ice bed, surface and thickness data

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Research paper thumbnail of A self-adaptive two-parameter method for characterizing roughness of multi-scale subglacial topography

Journal of Glaciology

During the last few decades, bed-elevation profiles from radar sounders have been used to quantif... more During the last few decades, bed-elevation profiles from radar sounders have been used to quantify bed roughness. Various methods have been employed, such as the ‘two-parameter’ technique that considers vertical and slope irregularities in topography, but they struggle to incorporate roughness at multiple spatial scales leading to a breakdown in their depiction of bed roughness where the relief is most complex. In this article, we describe a new algorithm, analogous to wavelet transformations, to quantify the bed roughness at multiple scales. The ‘Self-Adaptive Two-Parameter’ system calculates the roughness of a bed profile using a frequency-domain method, allowing the extraction of three characteristic factors: (1) slope, (2) skewness and (3) coefficient of variation. The multi-scale roughness is derived by weighted-summing of these frequency-related factors. We use idealized bed elevations to initially validate the algorithm, and then actual bed-elevation data are used to compare ...

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Research paper thumbnail of A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude

Nature

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Research paper thumbnail of Some evidence for a wide fan-shaped extension of the East Antarctic plate at the Mesozoic-Cenozoic transition

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Research paper thumbnail of A hydrologically inspired approach to predicting fjord bedrock elevation at the ice-ocean interface of the Greenland Ice Sheet

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Research paper thumbnail of Rifting in East Antarctica: new views from the Rennick Graben and Wilkes Subglacial Basin

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Research paper thumbnail of What ancient climates tell us about high carbon dioxide concentrations in Earth’s atmosphere

During ice ages, when the sea level was around 120m lower than now and global temperature was abo... more During ice ages, when the sea level was around 120m lower than now and global temperature was about 4°C cooler, the CO 2 concentration was as little as 180 parts per million (ppm). Between ice ages, CO 2 concentration increased to around 280ppm and the world warmed to something like our familiar modern climate. The last time Earth had an ice age was 20,000 years ago. It then took 10,000 years for CO 2 to rise from 180ppm to 280ppm, and for most of the ice to melt. In other words, the world experienced significant global warming of 4°C because of an increase in CO 2 concentration of 100ppm over about 10,000 years.

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Research paper thumbnail of The roughness of grounded ice sheet beds: Case studies from high resolution radio echo sounding studies in Antarctica

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Research paper thumbnail of Supplementary material to "Optimal site selection for a high resolution ice core record in East Antarctica

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Research paper thumbnail of Automated detection and characterization of Antarctic basal units using radar sounding data: demonstration in Institute Ice Stream, West Antarctica

Annals of Glaciology, 2020

Basal units – visibly distinct englacial structures near the ice-bed interface – warrant investig... more Basal units – visibly distinct englacial structures near the ice-bed interface – warrant investigation for a number of reasons. Many are of unknown composition and origin, characteristics that could provide substantial insight into subglacial processes and ice-sheet history. Their significance, moreover, is not limited to near-bed depths; these units appear to dramatically influence the flow of surrounding ice. In order to enable improved characterization of these features, we develop and apply an algorithm that allows for the automatic detection of basal units. We use a tunable layer-optimized SAR processor to distinguish these structures from the bed, isochronous englacial layers and the ice-sheet surface, presenting a conceptual framework for the use of radio-echo character in the identification of ice-sheet features. We also outline a method by which our processor could be used to place observational constraints on basal units’ configuration, composition and provenance.

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Research paper thumbnail of RAHU Project: Assessing water security and climate change adaptation strategies in the glaciated Vilcanota-Urubamba river basin

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Research paper thumbnail of Heat and groundwater transport between the Antarctic Ice Sheet and subglacial sedimentary basins from electromagnetic geophysical measurements

SEG Technical Program Expanded Abstracts 2019, 2019

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Research paper thumbnail of Radar‐Detected Englacial Debris in the West Antarctic Ice Sheet

Geophysical Research Letters, 2019

Structural glaci‐geological processes can entrain basal sediment into ice, leading to its transpo... more Structural glaci‐geological processes can entrain basal sediment into ice, leading to its transportation and deposition downstream. Sediments potentially rich in essential nutrients, like silica and iron, can thus be transferred from continental sources to the ocean, where deposition could enhance marine primary productivity. However, a lack of data has limited our knowledge of sediment entrainment, transfer, and distribution in Antarctica, until now. We use ice‐penetrating radar to examine englacial sediments in the Weddell Sea sector of the West Antarctic Ice Sheet. Radargrams reveal englacial reflectors on the leeside of nunataks and subglacial highlands, where Mie scattering analysis of the reflectors suggests particle sizes consistent with surface moraine sediments. We hypothesize that these sediments are entrained at the thermal boundary between cold and warm‐based ice. Conservative estimates of >130 × 109 kg of englacial sediment in Horseshoe Valley alone suggest that the ...

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Research paper thumbnail of A mini‐corer for precision sampling of the water‐sediment interface in subglacial lakes and other remote aqueous environments

Limnology and Oceanography: Methods, 2018

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Research paper thumbnail of Publisher Correction: Spatio-temporal variability of processes across Antarctic ice-bed-ocean interfaces

Nature communications, Jan 11, 2018

The original version of this Article contained an error in the spelling of the author Florence Co... more The original version of this Article contained an error in the spelling of the author Florence Colleoni, which was incorrectly given as Florence Colloni. This has been corrected in both the PDF and HTML versions of the Article.

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Research paper thumbnail of Why Should We Worry About Sea Level Change?

Frontiers for Young Minds, 2017

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Research paper thumbnail of A deep subglacial embayment adjacent to the grounding line of Institute Ice Stream, West Antarctica

Geological Society, London, Special Publications, 2017

The Institute Ice Stream (IIS) in West Antarctica may be increasingly vulnerable to melting at th... more The Institute Ice Stream (IIS) in West Antarctica may be increasingly vulnerable to melting at the grounding line through modifications in ocean circulation. Understanding such change requires knowledge of grounding-line boundary conditions, including the topography on which it rests. Here, we discuss evidence from new radio-echo sounding (RES) data on the subglacial topography adjacent to the grounding line of the IIS. In doing so, we reveal a previously unknown subglacial embayment immediately inland of the IIS grounding zone which is not represented in the Bedmap2 compilation. We discuss whether there is an open-water connection between the embayment and the ice-shelf cavity. The exact location of the grounding line over the embayment has been the subject of considerable uncertainty, with several positions being proposed recently. From our compilation of data, we are able to explain which of these grounding lines is most likely and, in doing so, highlight the need for accurate be...

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Research paper thumbnail of Summit of the East Antarctic Ice Sheet underlain by thick ice-crystal fabric layers linked to glacial–interglacial environmental change

Geological Society, London, Special Publications, 2017

Ice cores in Antarctica and Greenland reveal ice-crystal fabrics that can be softer under simple ... more Ice cores in Antarctica and Greenland reveal ice-crystal fabrics that can be softer under simple shear compared with isotropic ice. Owing to the sparseness of ice cores in regions away from the ice divide, we currently lack information about the spatial distribution of ice fabrics and its association with ice flow. Radio-wave reflections are influenced by ice-crystal alignments, allowing them to be tracked provided reflections are recorded simultaneously in orthogonal orientations (polarimetric measurements). Here, we image spatial variations in the thickness and extent of ice fabric across Dome A in East Antarctica, by interpreting polarimetric radar data. We identify four prominent fabric units, each several hundred metres thick, extending over hundreds of square kilometres. By tracing internal ice-sheet layering to the Vostok ice core, we are able to determine the approximate depth–age profile at Dome A. The fabric units correlate with glacial–interglacial cycles, most noticeably...

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Research paper thumbnail of Ocean forced variability of Totten Glacier mass loss

Geological Society, London, Special Publications, 2017

A large volume of the East Antarctic Ice Sheet drains through the Totten Glacier (TG) and is thou... more A large volume of the East Antarctic Ice Sheet drains through the Totten Glacier (TG) and is thought to be a potential source of substantial global sea-level rise over the coming centuries. We show that the surface velocity and height of the floating part of the TG, which buttresses the grounded component, have varied substantially over two decades (1989–2011), with variations in surface height strongly anti-correlated with simulated basal melt rates (r = 0.70, p < 0.05). Coupled glacier–ice shelf simulations confirm that ice flow and thickness respond to both basal melting of the ice shelf and grounding on bed obstacles. We conclude the observed variability of the TG is primarily ocean-driven. Ocean warming in this region will lead to enhanced ice-sheet dynamism and loss of upstream grounded ice.

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Research paper thumbnail of A high-resolution synthetic bed elevation grid of the Antarctic continent

Earth System Science Data Discussions, 2016

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Research paper thumbnail of Antarctic Bedmap data: FAIR sharing of 60 years of ice bed, surface and thickness data

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A self-adaptive two-parameter method for characterizing roughness of multi-scale subglacial topography

Journal of Glaciology

During the last few decades, bed-elevation profiles from radar sounders have been used to quantif... more During the last few decades, bed-elevation profiles from radar sounders have been used to quantify bed roughness. Various methods have been employed, such as the ‘two-parameter’ technique that considers vertical and slope irregularities in topography, but they struggle to incorporate roughness at multiple spatial scales leading to a breakdown in their depiction of bed roughness where the relief is most complex. In this article, we describe a new algorithm, analogous to wavelet transformations, to quantify the bed roughness at multiple scales. The ‘Self-Adaptive Two-Parameter’ system calculates the roughness of a bed profile using a frequency-domain method, allowing the extraction of three characteristic factors: (1) slope, (2) skewness and (3) coefficient of variation. The multi-scale roughness is derived by weighted-summing of these frequency-related factors. We use idealized bed elevations to initially validate the algorithm, and then actual bed-elevation data are used to compare ...

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Research paper thumbnail of A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude

Nature

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Research paper thumbnail of Some evidence for a wide fan-shaped extension of the East Antarctic plate at the Mesozoic-Cenozoic transition

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A hydrologically inspired approach to predicting fjord bedrock elevation at the ice-ocean interface of the Greenland Ice Sheet

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Rifting in East Antarctica: new views from the Rennick Graben and Wilkes Subglacial Basin

Bookmarks Related papers MentionsView impact

Research paper thumbnail of What ancient climates tell us about high carbon dioxide concentrations in Earth’s atmosphere

During ice ages, when the sea level was around 120m lower than now and global temperature was abo... more During ice ages, when the sea level was around 120m lower than now and global temperature was about 4°C cooler, the CO 2 concentration was as little as 180 parts per million (ppm). Between ice ages, CO 2 concentration increased to around 280ppm and the world warmed to something like our familiar modern climate. The last time Earth had an ice age was 20,000 years ago. It then took 10,000 years for CO 2 to rise from 180ppm to 280ppm, and for most of the ice to melt. In other words, the world experienced significant global warming of 4°C because of an increase in CO 2 concentration of 100ppm over about 10,000 years.

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Research paper thumbnail of The roughness of grounded ice sheet beds: Case studies from high resolution radio echo sounding studies in Antarctica

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Supplementary material to "Optimal site selection for a high resolution ice core record in East Antarctica

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Automated detection and characterization of Antarctic basal units using radar sounding data: demonstration in Institute Ice Stream, West Antarctica

Annals of Glaciology, 2020

Basal units – visibly distinct englacial structures near the ice-bed interface – warrant investig... more Basal units – visibly distinct englacial structures near the ice-bed interface – warrant investigation for a number of reasons. Many are of unknown composition and origin, characteristics that could provide substantial insight into subglacial processes and ice-sheet history. Their significance, moreover, is not limited to near-bed depths; these units appear to dramatically influence the flow of surrounding ice. In order to enable improved characterization of these features, we develop and apply an algorithm that allows for the automatic detection of basal units. We use a tunable layer-optimized SAR processor to distinguish these structures from the bed, isochronous englacial layers and the ice-sheet surface, presenting a conceptual framework for the use of radio-echo character in the identification of ice-sheet features. We also outline a method by which our processor could be used to place observational constraints on basal units’ configuration, composition and provenance.

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Research paper thumbnail of RAHU Project: Assessing water security and climate change adaptation strategies in the glaciated Vilcanota-Urubamba river basin

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Heat and groundwater transport between the Antarctic Ice Sheet and subglacial sedimentary basins from electromagnetic geophysical measurements

SEG Technical Program Expanded Abstracts 2019, 2019

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Radar‐Detected Englacial Debris in the West Antarctic Ice Sheet

Geophysical Research Letters, 2019

Structural glaci‐geological processes can entrain basal sediment into ice, leading to its transpo... more Structural glaci‐geological processes can entrain basal sediment into ice, leading to its transportation and deposition downstream. Sediments potentially rich in essential nutrients, like silica and iron, can thus be transferred from continental sources to the ocean, where deposition could enhance marine primary productivity. However, a lack of data has limited our knowledge of sediment entrainment, transfer, and distribution in Antarctica, until now. We use ice‐penetrating radar to examine englacial sediments in the Weddell Sea sector of the West Antarctic Ice Sheet. Radargrams reveal englacial reflectors on the leeside of nunataks and subglacial highlands, where Mie scattering analysis of the reflectors suggests particle sizes consistent with surface moraine sediments. We hypothesize that these sediments are entrained at the thermal boundary between cold and warm‐based ice. Conservative estimates of >130 × 109 kg of englacial sediment in Horseshoe Valley alone suggest that the ...

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Research paper thumbnail of A mini‐corer for precision sampling of the water‐sediment interface in subglacial lakes and other remote aqueous environments

Limnology and Oceanography: Methods, 2018

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Publisher Correction: Spatio-temporal variability of processes across Antarctic ice-bed-ocean interfaces

Nature communications, Jan 11, 2018

The original version of this Article contained an error in the spelling of the author Florence Co... more The original version of this Article contained an error in the spelling of the author Florence Colleoni, which was incorrectly given as Florence Colloni. This has been corrected in both the PDF and HTML versions of the Article.

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Research paper thumbnail of Why Should We Worry About Sea Level Change?

Frontiers for Young Minds, 2017

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Research paper thumbnail of A deep subglacial embayment adjacent to the grounding line of Institute Ice Stream, West Antarctica

Geological Society, London, Special Publications, 2017

The Institute Ice Stream (IIS) in West Antarctica may be increasingly vulnerable to melting at th... more The Institute Ice Stream (IIS) in West Antarctica may be increasingly vulnerable to melting at the grounding line through modifications in ocean circulation. Understanding such change requires knowledge of grounding-line boundary conditions, including the topography on which it rests. Here, we discuss evidence from new radio-echo sounding (RES) data on the subglacial topography adjacent to the grounding line of the IIS. In doing so, we reveal a previously unknown subglacial embayment immediately inland of the IIS grounding zone which is not represented in the Bedmap2 compilation. We discuss whether there is an open-water connection between the embayment and the ice-shelf cavity. The exact location of the grounding line over the embayment has been the subject of considerable uncertainty, with several positions being proposed recently. From our compilation of data, we are able to explain which of these grounding lines is most likely and, in doing so, highlight the need for accurate be...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Summit of the East Antarctic Ice Sheet underlain by thick ice-crystal fabric layers linked to glacial–interglacial environmental change

Geological Society, London, Special Publications, 2017

Ice cores in Antarctica and Greenland reveal ice-crystal fabrics that can be softer under simple ... more Ice cores in Antarctica and Greenland reveal ice-crystal fabrics that can be softer under simple shear compared with isotropic ice. Owing to the sparseness of ice cores in regions away from the ice divide, we currently lack information about the spatial distribution of ice fabrics and its association with ice flow. Radio-wave reflections are influenced by ice-crystal alignments, allowing them to be tracked provided reflections are recorded simultaneously in orthogonal orientations (polarimetric measurements). Here, we image spatial variations in the thickness and extent of ice fabric across Dome A in East Antarctica, by interpreting polarimetric radar data. We identify four prominent fabric units, each several hundred metres thick, extending over hundreds of square kilometres. By tracing internal ice-sheet layering to the Vostok ice core, we are able to determine the approximate depth–age profile at Dome A. The fabric units correlate with glacial–interglacial cycles, most noticeably...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Ocean forced variability of Totten Glacier mass loss

Geological Society, London, Special Publications, 2017

A large volume of the East Antarctic Ice Sheet drains through the Totten Glacier (TG) and is thou... more A large volume of the East Antarctic Ice Sheet drains through the Totten Glacier (TG) and is thought to be a potential source of substantial global sea-level rise over the coming centuries. We show that the surface velocity and height of the floating part of the TG, which buttresses the grounded component, have varied substantially over two decades (1989–2011), with variations in surface height strongly anti-correlated with simulated basal melt rates (r = 0.70, p < 0.05). Coupled glacier–ice shelf simulations confirm that ice flow and thickness respond to both basal melting of the ice shelf and grounding on bed obstacles. We conclude the observed variability of the TG is primarily ocean-driven. Ocean warming in this region will lead to enhanced ice-sheet dynamism and loss of upstream grounded ice.

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Research paper thumbnail of A high-resolution synthetic bed elevation grid of the Antarctic continent

Earth System Science Data Discussions, 2016

Bookmarks Related papers MentionsView impact