Publications
333 results found
Siegert M, 2021, Why 2°C is too hot to handle, Financial World
Lang S, Xu B, Cui X, et al., 2021, A self-adaptive two-parameter method for characterizing roughness of multi-scale subglacial topography, Journal of Glaciology, Vol: 67, Pages: 560-568, ISSN: 0022-1430
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 the new roughness index with other methods. We show the new technique is an effective tool for quantifying bed roughness from radar data, paving the way for improved continental-wide depictions of bed roughness and incorporation of this information into ice flow models.
Lowe M, Ferraccioli F, Young D, et al., 2021, Unveiling lithosphere heterogeneity beneath the East Antarctic Ice Sheet in the Wilkes Subglacial Basin
<jats:p>&lt;p&gt;The Wilkes Subglacial Basin in East Antarctica hosts one of the largest marine-based and hence potentially more unstable sectors of the East Antarctic Ice Sheet (EAIS). Predicting the past, present and future behaviour of this key sector of the EAIS requires that we also improve our understanding of the lithospheric cradle on which it flows. This is particularly important in order to quantify geothermal heat flux heterogeneity in the region. &amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;The WSB stretches for almost 1600 km from the Southern Ocean towards South Pole. Like many intracratonic basins, it is a long-lived geological feature, which originated and evolved in different tectonic settings. A wide basin formed in the WSB in a distal back arc basin setting, likely in response to a retreating West Antarctic Paleo-Pacific active margin from Permo-Triassic times. Jurassic extension then led to the emplacement of part of a huge flood basalt province that extends from South Africa to Australia.&amp;#160; The region was then affected by relatively minor upper crustal Mesozoic to Cenozoic(?) extension and transtension, producing narrow graben-like features that were glacially overdeepened, and presently steer enhanced glacial flow of the Matusevich, Cook and Ninnis glaciers.&lt;/p&gt;&lt;p&gt;Here we present the results of our enhanced geophysical imaging and modelling in the WSB region performed within the 4D Antarctica project of ESA, which aims to help quantify the spatial variability in subglacial Antarctic geothermal heat flux (GHF), one of the least well constrained parameters of the entire continent.&lt;/p&gt;&lt;p&gt;We exploit a combination of airborne radar and aeromagnetic data compilations and crustal and lithosphere thickness estimates from both satellite and airborne gravity and independent passive seismic
Armadillo E, Rizzello D, Balbi P, et al., 2021, Some evidence for a wide fan-shaped extension of the East Antarctic plate at the Mesozoic-Cenozoic transition
<jats:p>&lt;p&gt;The Transantarctic Mountains (TAM) separate the Mesozoic to recent West Antarctic rift system (WARS) from a wide and depressed triangular sector of East Antarctica spanning from 100&amp;#176; E to 160&amp;#176; E in longitude and from the Oates, George V and Adelie coastlines to 85&amp;#176; S in latitude. The sub-ice bedrock of this sector shows a basin and range style topography comprising two major basins of continental proportions -the Wilkes Basin and the Aurora Basin complex- and many smaller basins such as the Adventure, Concordia, Aurora and Vostok trenches. Most of these basins and trenches exhibit a triangular shape with the acutest angle pointing approximatively to a single pole towards the South, giving a fan shaped pattern of significant dimensions. We name here this region as the East Antarctic Fan shaped Basin Province (EAFBP). To the West, this province is limited by the intraplate Gamburtsev Mountains (GM).&lt;/p&gt;&lt;p&gt;Origins and inter-relationships between these four fundamental Antarctic tectonic units (WARS, TAM, EAFBP, GM) are still poorly understood and strongly debated. In the EAFBP, very little is known about the mechanism generating the basins, their formation time, whether they are all coeval and if and how they relate to Australia basins before Antarctica-Australia rifting. Present genetic hypotheses for some of the basins span from continental rifting to a purely flexural origin or a combination of the two. Also, post-tectonic erosional and depositional processes may have had a significant impact on the present-day topographic configuration.&lt;/p&gt;&lt;p&gt;Here we investigate the possibility that the EAFBP is the result of a single genetic mechanism: a wide fan-shaped intra-continental extension around a pivot point at about 135&amp;#176; E, 85&amp;#176; S that occurred at the Mesozoic-Ce
Couston L-A, Siegert M, 2021, Dynamic flows create potentially habitable conditions in Antarctic subglacial lakes, SCIENCE ADVANCES, Vol: 7, ISSN: 2375-2548
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Siegert M, Hein AS, White DA, et al., 2021, Antarctic Ice Sheet changes since the Last Glacial Maximum, Antarctic Climate Evolution, Pages: 623-687, ISBN: 9780128191101
Technological advances in the study and dating of both land and marine glacial geologic features, combined with both glaciological and post-glacial isostatic rebound modelling, have developed knowledge and understanding of the Antarctic Ice Sheets at the Last Glacial Maximum (LGM) and their subsequent changes. Here, we review geological evidence for the extent and timing of the maximum advance of the East and West Antarctic Ice Sheets and the Antarctic Peninsula Ice Sheet during the most recent glacial cycle. We also discuss evidence for the rate and timing of post-LGM ice-sheet retreat. Geological data provide a very important ‘first-hand’ record of ice-sheet changes over a range of time periods. They are also useful for constraining and improving models that have the potential to both fill in the gaps where geological data are unavailable, and to make predictions about the future. In reviewing the glacial geological evidence, we provide a benchmark against which future ice-sheet modelling exercises can be assessed.
Florindo F, Siegert M, De Santis L, et al., 2021, Antarctic Climate Evolution, ISBN: 9780128191101
Antarctic Climate Evolution, Second Edition, enhances our understanding of the history of the world’s largest ice sheet, and how it responded to and influenced climate change during the Cenozoic. It includes terrestrial and marine geology, sedimentology, glacier geophysics and ship-borne geophysics, coupled with results from numerical ice sheet and climate modeling. The book’s content largely mirrors the structure of the Past Antarctic Ice Sheets (PAIS) program (www.scar.org/science/pais), formed to investigate past changes in Antarctica by supporting multidisciplinary global research. This new edition reflects recent advances and is updated with several new chapters, including those covering marine and terrestrial life changes, ice shelves, advances in numerical modeling, and increasing coverage of rates of change. The approach of the PAIS program has led to substantial improvement in our knowledge base of past Antarctic change and our understanding of the factors that have guided its evolution.
Siegert M, Alley RB, Rignot E, et al., 2020, Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures, One Earth, Vol: 3, Pages: 691-703, ISSN: 2590-3322
While twentieth century sea-level rise was dominated by thermal expansion of ocean water, mass loss from glaciers and ice sheets is now a larger annual contributor. There is uncertainty on how ice sheets will respond to further warming, however, reducing confidence in twenty-first century sea-level projections. In 2019, to address the uncertainty, the Intergovernmental Panel on Climate Change (IPCC) reported that sea-level rise from the 1950s levels would likely be within 0.61–1.10 m if warming exceeds 4°C by 2100. The IPCC acknowledged greater sea-level increases were possible through mechanisms not fully incorporated in models used in the assessment. In this perspective, we discuss challenges faced in projecting sea-level change and discuss why the IPCC's sea-level range for 2100 under strong warming is focused at the low end of possible outcomes. We argue outcomes above this range are far more probable than below it and discuss how decision makers may benefit from reframing IPCC's terminology to avoid unintentionally masking worst-case scenarios.
Napoleoni F, Jamieson SSR, Ross N, et al., 2020, Subglacial lakes and hydrology across the Ellsworth Subglacial Highlands, West Antarctica, The Cryosphere, Vol: 14, Pages: 4507-4524, ISSN: 1994-0416
Subglacial water plays an important role in ice sheet dynamics and stability. Subglacial lakes are often located at the onset of ice streams and have been hypothesised to enhance ice flow downstream by lubricating the ice–bed interface. The most recent subglacial-lake inventory of Antarctica mapped nearly 400 lakes, of which ∼ 14 % are found in West Antarctica. Despite the potential importance of subglacial water for ice dynamics, there is a lack of detailed subglacial-water characterisation in West Antarctica. Using radio-echo sounding data, we analyse the ice–bed interface to detect subglacial lakes. We report 33 previously uncharted subglacial lakes and present a systematic analysis of their physical properties. This represents a ∼ 40 % increase in subglacial lakes in West Antarctica. Additionally, a new digital elevation model of basal topography of the Ellsworth Subglacial Highlands was built and used to create a hydropotential model to simulate the subglacial hydrological network. This allows us to characterise basal hydrology, determine subglacial water catchments and assess their connectivity. We show that the simulated subglacial hydrological catchments of the Rutford Ice Stream, Pine Island Glacier and Thwaites Glacier do not correspond to their ice surface catchments.
Cui X, Jeofry H, Greenbaum J, et al., 2020, Bed topography of Princess Elizabeth Land in East Antarctica, Earth System Science Data, Vol: 12, Pages: 2765-2774, ISSN: 1866-3508
We present a topographic digital elevation model (DEM) for Princess Elizabeth Land (PEL), East Antarctica. The DEM covers an area of ∼900 000 km2 and was built from radio-echo sounding data collected during four campaigns since 2015. Previously, to generate the Bedmap2 topographic product, PEL's bed was characterized from low-resolution satellite gravity data across an otherwise large (>200 km wide) data-free zone. We use the mass conservation (MC) method to produce an ice thickness grid across faster flowing (>30 m yr−1) regions of the ice sheet and streamline diffusion in slower flowing areas. The resulting ice thickness model is integrated with an ice surface model to build the bed DEM. Together with BedMachine Antarctica and Bedmap2, this new bed DEM completes the first-order measurement of subglacial continental Antarctica – an international mission that began around 70 years ago. The ice thickness data and bed DEMs of PEL (resolved horizontally at 500 m relative to ice surface elevations obtained from the Reference Elevation Model of Antarctica – REMA) are accessible from https://doi.org/10.5281/zenodo.4023343 (Cui et al., 2020a) and https://doi.org/10.5281/zenodo.4023393 (Cui et al., 2020b).
Siegert M, 2020, Mitigating future disasters, FRONTIERS IN PUBLIC HEALTH, Vol: 8, Pages: 42-48
Roberts JL, Jong LM, McCormack FS, et al., 2020, Integral correlation for uneven and differently sampled data, and its application to the Law Dome Antarctic climate record., Scientific Reports, Vol: 10, Pages: 17477-17477, ISSN: 2045-2322
We present a new simple and efficient method for correlation of unevenly and differently sampled data. This new method overcomes problems with other methods for correlation with non-uniform sampling and is an easy modification to existing correlation based codes. To demonstrate the usefulness of this new method to real-world examples, we apply the method with good success to two glaciological examples to map the ages from a well-dated ice core to a nearby core, and by tracing isochronous layers within the ice sheet measured from ice-penetrating radar between the two ice core sites.
Arora D, Pant N, Pandey M, et al., 2020, Insights into geological evolution of Princess Elizabeth Land, East Antarctica-clues for continental suturing and breakup since Rodinian time, Gondwana Research, Vol: 84, Pages: 260-283, ISSN: 1342-937X
Svenner Islands-Brattstrand Bluffs-Larsemann Hills constitutes ~70 km long coastal outcrops of Princess Elizabeth Land (PEL), comprising complexly deformed metapelites and orthogneisses. Pelitic granulites from these outcrops are investigated in this work. Conventional geothermobarometric estimations and Pseudosection modelling consistently indicate that the peak metamorphic grade throughout the area is high to ultra-high temperature (800–950 °C) at low to medium pressure (2–5 kbar). A high pressure (~10 kbar) relict metamorphic event and a substantial decompression component of ~5 kbar, corresponding to >15 km uplift, are inferred through petrographic as well as pseudosection analysis. Two set of ages are estimated (~800 Ma and ~500 Ma), corresponding to Tonian and Pan-African metamorphic events, respectively. Field data, petrographic studies and ages estimated from orthogneisses from the Brattstrand Bluffs and the Grovnes Peninsula suggest that this unit is a product of in-situ melting of the pelitic granulites.Pelitic granulites of PEL possess similarities with those exposed in the Eastern Ghat Mobile Belt of India. We propose that these sectors represent a contiguous terrane with two major orogenic imprints, reflecting Rodinia and Gondwana amalgamations. An attempt is made to mark out paleo-orogenic belt axes, supported by both field as well as recent aero-magnetic signatures in interior PEL. We support that the parent sediments of the pelitic granulites were deposited during Stenian period, which underwent compressional UHT-HP(?) metamorphism at ~800 Ma. Another extensive basin is proposed at ~600 Ma prior to the Pan-African orogenic event. We propose that the Pan-African orogeny marked the collision of Indo-Australo-Africo-Antarctic cratons and stitched the East Gondwana. We also propose a thinned lithosphere along the system of subglacial lakes-canyons confirmed by ICECAP data. Analog modelling is used to demonstrate the influence of pervas
Waring B, Neumann M, Prentice IC, et al., 2020, What role can forests play in tackling climate change?, What role can forests play in tackling climate change?, www.imperial.ac.uk/grantham, Publisher: Grantham Institute, Discussion paper 6
This discussion paper consolidates knowledge on the potential environmental, economic and societal benefits of using trees to reduce the concentration of carbon dioxide in the atmosphere. It highlights areas for further research and defines the limits of trees’ ability to halt the progress of climate change.
Li Y, Lu Y, Siegert MJ, 2020, Radar sounding confirms a hydrologically active deep-water subglacial lake in East Antarctica, Frontiers in Earth Science, Vol: 8, Pages: 1-9, ISSN: 2296-6463
Lake CookE2, upstream of Cook Glacier in East Antarctica, is an “active” subglacial lake that experiences episodic discharge and recharge of basal water. Although around 130 active lakes are known to exist, the majority are not able to be identified by ice-sounding radar techniques, suggesting they are ephemeral and/or distributed stores of small amounts of water rather than permanent significant singular features. However, airborne radar data from Lake CookE2 reveal a bright and flat ice-bed interface, providing clear evidence of deep (>10 m) water surrounded by elevated topography. The data show the lake area is ∼46 km2; three times less than a previous estimate (145 km2) from Ice, Cloud and land Elevation Satellite (ICESat) satellite altimetry, suggesting a bias in identifying subglacial lake area from surface depressions. Using time-series altimetry from ICESat, Cryosat-2, and the Reference Elevation Model of Antarctica, we re-estimate the lake discharged ∼2.73 km3 of water (or ∼59.6 m in lake level) between February 2006 and October 2008. Subsequently, the ice surface over the lake rose steadily and experienced a mean uplift of ∼9 m between January 2011 and November 2016, indicating continuous recharge with total volume increase of ∼0.42 km3. The lake is recharging at a rate of ∼1.1 m/year, which means it could take another ∼39 years to reach the lake level that triggered the previous discharge.
Ross N, Corr H, Siegert M, 2020, Large-scale englacial folding and deep-ice stratigraphy within the West Antarctic Ice Sheet, The Cryosphere, Vol: 14, Pages: 2103-2114, ISSN: 1994-0416
It has been hypothesized that complex englacial structures identified within the East Antarctic and Greenland ice sheets are generated by (i) water freezing to the ice sheet base and evolving under ice flow, (ii) deformation of ice of varying rheology, or (iii) entrainment of basal material. Using ice-penetrating radar, we identify a widespread complex of deep-ice facies in West Antarctica that exist in the absence of basal water. These deep-ice units are extensive, thick (>500 m), and incorporate multiple highly reflective englacial layers. At the lateral margin of an enhanced flow tributary of the Institute Ice Stream, these units are heavily deformed and folded by the action of lateral flow convergence. Radar reflectivity analysis demonstrates that the uppermost reflector of the deep-ice package is highly anisotropic, due to abrupt alternations in crystal orientation fabric, and consequently will have a different rheology to the ice above and below it. Deformation and folding of the deep-ice package is an englacial response to the combination of laterally-convergent ice flow and the physical properties of the ice column.
Siegert M, Bacon S, Barnes D, et al., 2020, The Arctic and the UK: climate, research and engagement, The Arctic and the UK: climate, research and engagement, www.imperial.ac.uk/grantham, Publisher: The Grantham Institute, Discussion Paper 7
This discussion paper explains how the UK’s climate is linked to conditions in the Arctic, and why a UK Arctic science strategy is integral to understanding how global warming will change the Arctic and affect the UK.
Siegert M, Haywood A, Lunt D, et al., 2020, What ancient climates tell us about high carbon dioxide concentrations in Earth’s atmosphere, What ancient climates tell us about high carbon dioxide concentrations in Earth’s atmosphere, http://www.imperial.ac.uk/grantham, Publisher: The Grantham Institute, Briefing note 13
This briefing discusses the last time our planet had the same levels of carbon dioxide in the atmosphere as it does today, and what environmental conditions were like then. Studying the geology from this and earlier periods tells us that global temperatures may rise by over 10°C if we keep emitting carbon dioxide as forecast for the next 80 years. The paper explains how, to avoid this catastrophic climate, the world must cut greenhouse gas emissions to net zero by 2050 at the latest.
Yazdanpanah V, Mehryar S, Jennings NR, et al., 2020, Multiagent climate change research, AAMAS 2020, Publisher: IFAAMAS, Pages: 1726-1731, ISSN: 1548-8403
We call for attention to climate change research as a domain of application for multiagent technologies. The multiagent nature of climate change challenges and successful application of multiagent methods in decentralized power grid systems, market organization, and industrial engineering, could improve our ability to address decarbonization (climate change mitigation) and to deal with some unavoidable consequences of global warming (climate change adaptation). We review major challenges to which the community of multiagent systems can contribute, highlight open research problems and argue for the application of multiagent models and solution concepts in a variety of issues related to this global challenge.
Waring B, Neumann M, Prentice IC, et al., 2020, Forests and decarbonization: roles of natural and planted forests, Frontiers in Forests and Global Change, Vol: 3, ISSN: 2624-893X
The severe consequences of human disruptions to the global carbon cycle have prompted intense interest in strategies to reduce atmospheric CO2 concentrations. Because growing forests capture CO2 in their biomass and soils, large-scale tree planting efforts have been advertised as a viable way to counteract anthropogenic emissions as part of net-zero emission strategies. Here, we assess the potential impact of reforestation and afforestation on the global climate system, and identify ecological, economic, and societal implications of such efforts.
Goldberg M, Schroeder D, Castelletti D, et al., 2020, Automated detection and characterization of Antarctic basal units using radar sounding data: demonstration in Institute Ice Stream, West Antarctica, Annals of Glaciology, Vol: 61, Pages: 242-248, ISSN: 0260-3055
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.
Wang B, Sun B, Jiaxin W, et al., 2020, Removal of ‘strip noise’ in airborne radio-echo sounding data using combined wavelet and 2D DFT filtering, Annals of Glaciology, Vol: 61, Pages: 124-134, ISSN: 0260-3055
Radio-echo sounding (RES) can be used to understand ice-sheet processes, englacial flow structures and bed properties, making it one of the most popular tools in glaciological exploration. However, RES data are often subject to ‘strip noise’, caused by internal instrument noise and interference, and/or external environmental interference, which can hamper measurementand interpretation. For example, strip noise can result in reduced power from the bed, affecting the quality of ice thickness measurements and the characterization of subglacial conditions. Here, we present a method for removing strip noise based on combined wavelet and 2D Fourier filtering. First, we implement discrete wavelet decomposition on RES data to obtain multi-scale wavelet components. Then, 2D DFT spectral analysis is performed on components containing the noise. In the Fourier domain, the 2D DFT spectrum of strip noise keeps its linear features and can be removed with a ‘targeted masking’ operation. Finally, inverse wavelet transforms are performed on all wavelet components, including strip-removed components, to restore the data with enhanced fidelity. Model tests and field-data processing demonstrate the method removes strip noise well and, incidentally, can remove the strong first reflector from the ice surface, thus drastically improving the general quality of radar data.
Jeofry H, Ross N, Siegert M, 2020, Comparing numerical ice-sheet model output with radio-echo sounding measurements in the Weddell Sea sector of West Antarctica, Annals of Glaciology, Vol: 61, Pages: 188-197, ISSN: 0260-3055
Numerical ice-sheet models are commonly matched to surface ice velocities from InSAR measurements by modifying basal drag, allowing the flow and form of the ice sheet to be simulated. Geophysical measurements of the bed are rarely used to examine if this modification is realistic, however. Here, we examine radio-echo sounding (RES) data from the Weddell Sea (WS) sector of West Antarctica to investigate how output from a well-established ice-sheet model compares with measurements of the basal environment. We know the WS sector contains the Institute, Möller and Foundation ice streams, each with distinct basal characteristics: Institute Ice Stream lies partly over wet unconsolidated sediments, where basal drag is very low; Möller Ice Stream lies on relatively rough bed, where basal drag is likely larger; and Foundation Ice Stream is controlled by a deep subglacial trough with flow-aligned bedrock landforms and smooth unconsolidated sediments. In general, the ice-sheet model represents each ice-stream system well. We also find that ice velocities do not match perfectly in some locations, and that adjustment of the boundaries of low basal drag, to reflect RES evidence, should improve model performance. Our work showcases the usefulness of RES in calibrating ice-sheet model results with observations of the bed.
Schroeder DM, Bingham RG, Blankenship DD, et al., 2020, Five decades of radioglaciology, Annals of Glaciology, Vol: 61, Pages: 1-13, ISSN: 0260-3055
Radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of the Annals of Glaciology on ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciological Annals of Glaciology issue of 2014, the context of their history and future prospects.
Ross N, Siegert M, 2020, Basal melting over Subglacial Lake Ellsworth and its catchment: insights from englacial layering, ANNALS OF GLACIOLOGY, Vol: 61, Pages: 198-205, ISSN: 0260-3055
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Shoemaker IM, Kusenko A, Kuipers Munneke P, et al., 2020, Reflections on the anomalous ANITA events: the Antarctic subsurface as a possible explanation, ANNALS OF GLACIOLOGY, Vol: 61, Pages: 92-98, ISSN: 0260-3055
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- Citations: 15
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