220 results found
Beem LH, Cavitte MGP, Blankenship DD, et al., 2017, Ice-flow reorganization within the East Antarctic Ice Sheet deep interior, Special Publication - Geological Society of London, Vol: 461, ISSN: 0305-8719
Near the South Pole, a large subglacial lake exists beneath the East Antarctic Ice Sheet less than 10 km from where the bed temperature is inferred to be −9°C. A thermodynamic model was used to investigate the apparent contradiction of basal water existing in the vicinity of a cold bed. Model results indicate that South Pole Lake is freezing and that neither present-day geothermal flux nor ice flow is capable of producing the necessary heat to sustain basal water at this location. We hypothesize that the lake comprises relict water formed during a different configuration of ice dynamics when significant frictional heating from ice sliding was available. Additional modelling of assumed basal sliding shows frictional heating was capable of producing the necessary heat to fill South Pole Lake. Independent evidence of englacial structures measured by airborne radar revel ice-sheet flow was more dynamic in the past. Ice sliding is estimated to have ceased between 16.8 and 10.7 ka based on an ice chronology from a nearby borehole. These findings reveal major post-Last Glacial Maximum ice-dynamic change within the interior of East Antarctica, demonstrating that the present interior ice flow is different than that under full glacial conditions.
Siegert MJ, 2017, Why Should We Worry About Sea Level Change?, Frontiers for Young Minds, Vol: 5
Around 250 million people live by the coast, less than 5 m above the sea. Changes in sea level affect people through flooding, when water in rivers cannot flow into the ocean because the sea is too high and when seawater surges onto the land during storms. If the sea water finds its way to farms and reservoirs, it can harm our drinking water and our ability to grow crops. Because of this, knowledge of how and why sea level is changing is of importance to society.
Wrona T, Wolovick M, Ferraccioli F, et al., 2017, Position and variability of complex structures in the central East Antarctic Ice Sheet, Special Publication - Geological Society of London, Vol: 461, ISSN: 0305-8719
Although the flow of the East Antarctic Ice Sheet is well constrained from surface measurements and altimetry, our knowledge of the dynamic processes within the ice sheet remains limited. Recent high-resolution radar data from the Gamburtsev Subglacial Mountains in central East Antarctica reveal a series of anomalous englacial reflectors in the lower half of the ice column that cannot be explained by conventional ice flow. Expanding on previous analyses, we describe the geometrical and morphological features of 12 of these anomalous reflectors. Our description reveals a previously unacknowledged diversity in size, geometry and internal structure of these reflectors. We are able to identify four distinct morphological features: (1) fingers; (2) inclusions; (3) sheets; and (4) folds. The ‘fingers’ and ‘inclusions’ probably form by shear instabilities at the boundary between the reflectors and the surrounding meteoric ice. The ‘sheets’ highlight that basal ice can be uplifted off of the bed and above surrounding meteoric ice, and the ‘folds’ may have formed in local regions of converging flow associated with subglacial topography. The study provides key insights into the rheology, stress and deformational regimes deep within the central East Antarctic Ice Sheet.
Jeofry H, Ross N, Corr H, et al., 2017, A deep subglacial embayment adjacent to the grounding line of Institute Ice Stream, West Antarctica, Special Publication - Geological Society of London, Vol: Special Publications 461, ISSN: 0305-8719
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 bed topography in conjunction with satellite observations to fully comprehend ice-sheet processes in this region and other vulnerable locations at the grounded margin of Antarctica.
Siegert MJ, Bangbing W, Sun B, et al., 2017, Summit of the East Antarctic Ice Sheet underlain by thick ice-crystal fabric layers linked to glacial-interglacial environmental change, Special Publication - Geological Society of London, Vol: Special Publications, ISSN: 0305-8719
Ice cores in Antarctica and Greenland reveal ice-crystal fabrics that can be softer under simple shear compared with isotropic ice. Due 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 meters thick, extending over hundreds of square km. 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 revealing crystal alignment contrasts between the Eemian and the glacial episodes before and after. The anisotropy within these fabric layers has a spatial pattern determined by ice flow over subglacial topography.
Siegert MJ, Kulessa B, Bougamont M, et al., 2017, Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow, Special Publication - Geological Society of London, Vol: Special Publications, ISSN: 0305-8719
Is groundwater abundant in Antarctica and does it modulate ice flow? Answering this question matters because ice streams flow by gliding over a wet substrate of till. Water fed to ice-stream beds thus influences ice-sheet dynamics and, potentially, sea-level rise. It is recognised that both till and the sedimentary basins from which it originates are porous and could host a reservoir of mobile groundwater that interacts with the subglacial interfacial system. According to recent numerical modelling up to half of all water available for basal lubrication, and time lags between hydrological forcing and ice-sheet response as long as millennia, may have been overlooked in models of ice flow. Here, we review evidence in support of Antarctic groundwater and propose how it can be measured to ascertain the extent to which it modulates ice flow. We present new seismoelectric soundings of subglacial till, and magnetotelluric and transient electromagnetic forward models of subglacial groundwater reservoirs. We demonstrate that multi-facetted and integrated geophysical datasets can detect, delineate and quantify the groundwater contents of subglacial sedimentary basins and, potentially, monitor groundwater exchange rates between subglacial till layers. The paper thus describes a new area of glaciological investigation and how it should progress in future.
Siegert MJ, 2017, A 60-year international history of Antarctic subglacial lake exploration, Special Publications (Geological Society London), Vol: Special Publications, ISSN: 0305-8719
In January 2013, theUS WISSARD programmemeasured and sampled Lake Whillans, a subglacial water body at the edge of West Antarctica, in a clean and environmentally sensitive manner, proving the existence of microbial life beneath this part of the ice sheet. The success of WISSARD represented benchmark in the exploration of Antarctica, made possible by a rich and diverse history of events, discoveries and discussions over the past 60 years; ranging from geophysical measurement of subglacial lakes, to the development of scientific hypotheses concerning these environments and the engineering solutions required to testthem. In this article, I provide a personal account of this history, fromthe published literature andmy own involvement in subglacial lake exploration over the last 20 years. I show that our ability to directly measure and sample subglacial water bodies in Antarctica has been made possible by a strong theme of international collaboration, at odds with the media representation of a scientific ‘race’ between nations. I also consider plans for subglacial lake explorationand discuss how such collaboration is likely to be key to success of future research in this field.
Jordan T, Cooper M, Schroeder D, et al., 2017, Self-affine subglacial roughness: consequences for radar scattering and basal thaw discrimination in northern Greenland, Cryosphere, Vol: 11, Pages: 1247-1264, ISSN: 1994-0424
Subglacial roughness can be determined at a variety of length scales from radio-echo sounding (RES) data either via statistical analysis of topography or inferred from basal radar scattering. Past studies have demonstrated that subglacial terrain exhibits self-affine (power law) roughness scaling behaviour, but existing radar scattering models do not take this into account. Here, using RES data from northern Greenland, we introduce a self-affine statistical framework that enables a consistent integration of topographic-scale roughness with the electromagnetic theory of radar scattering. We demonstrate that the degree of radar scattering, quantified using the waveform abruptness (pulse peakiness), is topographically controlled by the Hurst (roughness power law) exponent. Notably, specular bed reflections are associated with a lower Hurst exponent, with diffuse scattering associated with a higher Hurst exponent. Abrupt waveforms (specular reflections) have previously been used as a RES diagnostic for basal water, and to test this assumption we compare our radar scattering map with a recent prediction for the basal thermal state. We demonstrate that the majority of thawed regions (above pressure melting point) exhibit a diffuse scattering signature, which is in contradiction to the prior approach. Self-affine statistics provide a generalised model for subglacial terrain and can improve our understanding of the relationship between basal properties and ice-sheet dynamics.
Jordan TM, Cooper MA, Schroeder DM, et al., Self-affine subglacial roughness: consequences for radar scattering and basal thaw discrimination in northern Greenland, The Cryosphere, ISSN: 1994-0416
<jats:p>&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Subglacial roughness can be determined at variety of length scales from radio-echo sounding (RES) data; either via statistical analysis of along-track topography, or inferred from basal radar scattering. Past studies have demonstrated that subglacial terrain exhibits self-affine (fractal) scaling behaviour, where vertical roughness has a power-law relationship with the horizontal length scale. A self-affine statistical framework, which enables a consistent integration of topographic roughness and radar scattering, has yet to be applied to RES. Here we do this for recent RES data from northern Greenland, and demonstrate that subglacial topography exhibits pronounced spatial variation in the Hurst (roughness power-law) exponent. A radar scattering model then enables us to explain how the Hurst exponent exerts strong topographic control upon radar scattering, which we map using the waveform abruptness (pulse peakiness) parameter. Notably, lower abruptness (associated with diffuse scattering) occurs for regions with a higher Hurst exponent, and higher abruptness (associated with specular reflections) occurs for regions with a lower Hurst exponent. Finally, we compare the RES-derived data with an independent prediction for the subglacial thermal state of northern Greenland. This analysis shows that the majority of predicted thawed regions do not have the specular RES scattering signature of deep subglacial lakes, and instead have a diffuse scattering signature.&lt;/p&gt; </jats:p>
Graham F, Roberts J, Galton-Fenzi B, et al., 2017, A high-resolution synthetic bed elevation grid of the Antarctic continent, Earth System Science Data, Vol: 9, Pages: 267-279, ISSN: 1866-3516
Digital elevation models of Antarctic bed topography are smoothed and interpolated onto low-resolution ( > 1 km) grids as current observed topography data are generally sparsely and unevenly sampled. This issue has potential implications for numerical simulations of ice-sheet dynamics, especially in regions prone to instability where detailed knowledge of the topography, including fine-scale roughness, is required. Here, we present a high-resolution (100 m) synthetic bed elevation terrain for Antarctica, encompassing the continent, continental shelf, and seas south of 60° S. Although not identically matching observations, the synthetic bed surface – denoted as HRES – preserves topographic roughness characteristics of airborne and ground-based ice-penetrating radar data measured by the ICECAP (Investigating the Cryospheric Evolution of the Central Antarctic Plate) consortium or used to create the Bedmap1 compilation. Broad-scale ( > 5 km resolution) features of the Antarctic landscape are incorporated using a low-pass filter of the Bedmap2 bed elevation data. HRES has applicability in high-resolution ice-sheet modelling studies, including investigations of the interaction between topography, ice-sheet dynamics, and hydrology, where processes are highly sensitive to bed elevations and fine-scale roughness. The data are available for download from the Australian Antarctic Data Centre (doi:10.4225/15/57464ADE22F50).
Roberts J, Galton-Fenzi B, Paolo F, et al., Ocean forced variability of Totten Glacier mass loss, Special Publication - Geological Society of London, ISSN: 0305-8719
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 the flow and surface height of floating part of TG, which buttresses the grounded component, have varied substantially over two decades (1989–2011), with variations in surface height and basal melt rates highly anti-correlated (r=0.70, p<0.05). Coupled glacier/ice-shelf simulations confirm ice flow and thickness respond to both basal melting of the ice shelf and grounding on bed obstacles. We conclude the observed variability of TG is primarily ocean-driven and enhanced ice-sheet dynamism, leading to upstream grounded ice loss, will occur from the region with ocean warming.
Willams CN, Cornford SL, Jordan TM, et al., 2017, Generating synthetic fjord bathymetry for coastal Greenland, Cryosphere, Vol: 11, Pages: 363-380, ISSN: 1994-0424
Bed topography is a critical boundary for the numerical modelling of ice sheets and ice–ocean interactions. A persistent issue with existing topography products for the bed of the Greenland Ice Sheet and surrounding sea floor is the poor representation of coastal bathymetry, especially in regions of floating ice and near the grounding line. Sparse data coverage, and the resultant coarse resolution at the ice–ocean boundary, poses issues in our ability to model ice flow advance and retreat from the present position. In addition, as fjord bathymetry is known to exert strong control on ocean circulation and ice–ocean forcing, the lack of bed data leads to an inability to model these processes adequately. Since the release of the last complete Greenland bed topography–bathymetry product, new observational bathymetry data have become available. These data can be used to constrain bathymetry, but many fjords remain completely unsampled and therefore poorly resolved. Here, as part of the development of the next generation of Greenland bed topography products, we present a new method for constraining the bathymetry of fjord systems in regions where data coverage is sparse. For these cases, we generate synthetic fjord geometries using a method conditioned by surveys of terrestrial glacial valleys as well as existing sinuous feature interpolation schemes. Our approach enables the capture of the general bathymetry profile of a fjord in north-west Greenland close to Cape York, when compared to observational data. We validate our synthetic approach by demonstrating reduced overestimation of depths compared to past attempts to constrain fjord bathymetry. We also present an analysis of the spectral characteristics of fjord centrelines using recently acquired bathymetric observations, demonstrating how a stochastic model of fjord bathymetry could be parameterised and used to create different realisations.
Williams CN, Cornford SL, Jordan TM, et al., Generating synthetic fjord bathymetry for coastal Greenland, The Cryosphere, ISSN: 1994-0416
<jats:p>&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Bed topography is a critical boundary for the numerical modelling of ice sheets and ice-ocean interactions. A persistent issue with existing topography products for the bed of the Greenland Ice Sheet and surrounding sea floor is the poor representation of coastal bathymetry, especially in regions of floating ice and near the grounding line. Sparse data coverage, and the resultant coarse resolution at the ice/ocean boundary, poses issues in our ability to model ice flow advance and retreat from the present position. In addition, as fjord bathymetry is known to exert strong control on ocean circulation and ice-ocean forcing, the lack of bed data leads to an inability to model these processes adequately. Since the release of the last complete Greenland bed topography-bathymetry product, new observational bathymetry data have become available. These data can be used to constrain bathymetry, but many fjords remain completely unsampled and therefore poorly resolved. Here, as part of the development of the next generation of Greenland bed topography products, we present a new method for constraining the bathymetry of fjord systems in regions where data coverage is sparse. For these cases, we generate synthetic fjord geometries using a method conditioned by surveys of terrestrial glacial valleys as well as existing sinuous feature interpolation schemes. Our approach enables the capture of the general bathymetry profile of a fjord in North West Greenland close to Cape York, when compared to observational data. We validate our synthetic approach by demonstrating reduced over-estimation of depths compared to past attempts to constrain fjord bathymetry. We also present an analysis of the spectral characteristics of fjord centrelines using recently acquired bathymetric observations, demonstrating how a stochastic model of fjord bathymetry could be parameterised and used
Siegert MJ, 2016, Vulnerable Antarctic ice shelves, Nature Climate Change, Vol: 7, Pages: 11-12, ISSN: 1758-6798
Standfirst: The decay of floating ice shelves around Antarctica speeds up ice flow from the continent and enhances sea-level rise. Now meltwater attributed to warm winds has been discovered on an East Antarctic ice shelf, suggesting greater vulnerability than previously thought.
Maritati A, Aitken ARA, Young DA, et al., 2016, The tectonic development and rrosion of the knox subglacial sedimentary basin, East Antarctica, Geophysical Research Letters, Vol: 43, Pages: 10728-10737, ISSN: 1944-8007
Sedimentary basins beneath the East Antarctic Ice Sheet (EAIS) have immense potential to inform models of the tectonic evolution of East Antarctica and its ice-sheet. However, even basic characteristics such as thickness and extent are often unknown. Using airborne geophysical data, we resolve the tectonic architecture of the Knox Subglacial Sedimentary Basin in western Wilkes Land. In addition, we apply an erosion restoration model to reconstruct the original basin geometry for which we resolve geometry typical of a transtensional pull-apart basin. The tectonic architecture strongly indicates formation as a consequence of the rifting of India from East Gondwana from ca. 160-130 Ma, and we suggest a spatial link with the western Mentelle Basin offshore Western Australia. The erosion restoration model shows that erosion is confined within the rift margins, suggesting that rift structure has strongly influenced the evolution of the Denman and Scott ice streams.
Kennicutt MC, Kim YD, Rogan-Finnemore M, et al., 2016, Delivering 21st century Antarctic and Southern Ocean science, Antarctic Science, Vol: 28, Pages: 407-423, ISSN: 1365-2079
The Antarctic Roadmap Challenges (ARC) project identified critical requirements to deliver high priority Antarctic research in the 21st century. The ARC project addressed the challenges of enabling technologies, facilitating access, providing logistics and infrastructure, and capitalizing on international co-operation. Technological requirements include: i) innovative automated in situ observing systems, sensors and interoperable platforms (including power demands), ii) realistic and holistic numerical models, iii) enhanced remote sensing and sensors, iv) expanded sample collection and retrieval technologies, and v) greater cyber-infrastructure to process ‘big data’ collection, transmission and analyses while promoting data accessibility. These technologies must be widely available, performance and reliability must be improved and technologies used elsewhere must be applied to the Antarctic. Considerable Antarctic research is field-based, making access to vital geographical targets essential. Future research will require continent- and ocean-wide environmentally responsible access to coastal and interior Antarctica and the Southern Ocean. Year-round access is indispensable. The cost of future Antarctic science is great but there are opportunities for all to participate commensurate with national resources, expertise and interests. The scope of future Antarctic research will necessitate enhanced and inventive interdisciplinary and international collaborations. The full promise of Antarctic science will only be realized if nations act together.
Roberts J, Curran M, Poynter S, et al., 2016, Correlation confidence limits for unevenly sampled data, Computers & Geosciences, Vol: 104, Pages: 120-124, ISSN: 0098-3004
Estimation of correlation with appropriate uncertainty limits for scientific data that are potentially serially correlated is a common problem made seriously challenging especially when data are sampled unevenly in space and/or time. Here we present a new, robust method for estimating correlation with uncertainty limits between autocorrelated series that does not require either resampling or interpolation. The technique employs the Gaussian kernel method with a bootstrapping resampling approach to derive the probability density function and resulting uncertainties. The method is validated using an example from radar geophysics. Autocorrelation and error bounds are estimated for an airborne radio-echo profile of ice sheet thickness. The computed limits are robust when withholding 10%, 20%, and 50% of data. As a further example, the method is applied to two time-series of methanesulphonic acid in Antarctic ice cores from different sites. We show how the method allows evaluation of the significance of correlation where the signal-to-noise ratio is low and reveals that the two ice cores exhibit a significant common signal.
Jordan T, Bamber J, Williams C, et al., 2016, An ice sheet wide framework for radar-inference of englacial attenuation and basal reflection with application to Greenland, Cryosphere, Vol: 10, Pages: 1547-1570, ISSN: 1994-0424
Radar inference of the bulk properties of glacierbeds, most notably identifying basal melting, is, in general,derived from the basal reflection coefficient. On the scale ofan ice sheet, unambiguous determination of basal reflectionis primarily limited by uncertainty in the englacial attenuationof the radio wave, which is an Arrhenius function oftemperature. Existing bed-returned power algorithms for derivingattenuation assume that the attenuation rate is regionallyconstant, which is not feasible at an ice-sheet-wide scale.Here we introduce a new semi-empirical framework for derivingenglacial attenuation, and, to demonstrate its efficacy,we apply it to the Greenland Ice Sheet. A central featureis the use of a prior Arrhenius temperature model to estimatethe spatial variation in englacial attenuation as a firstguess input for the radar algorithm. We demonstrate regionsof solution convergence for two input temperature fields andfor independently analysed field campaigns. The coverageachieved is a trade-off with uncertainty and we propose thatthe algorithm can be “tuned” for discrimination of basal melt(attenuation loss uncertainty ∼ 5 dB). This is supported byour physically realistic (∼ 20 dB) range for the basal reflectioncoefficient. Finally, we show that the attenuation solutioncan be used to predict the temperature bias of thermomechanicalice sheet models and is in agreement with known modeltemperature biases at the Dye 3 ice core.
Cooper MA, Michaelides K, Siegert MJ, et al., 2016, Paleofluvial landscape inheritance for Jakobshavn Isbræ catchment, Greenland, Geophysical Research Letters, Vol: 43, Pages: 6350-6357, ISSN: 1944-8007
Subglacial topography exerts strong controls on glacier dynamics, influencing the orientation and velocity of ice flow, as well as modulating the distribution of basal waters and sediment. Bed geometry can also provide a long-term record of geomorphic processes, allowing insight into landscape evolution, the origin of which may predate ice sheet inception. Here we present evidence from ice-penetrating radar data for a large dendritic drainage network, radiating inland from Jakobshavn Isbræ, Greenland's largest outlet glacier. The size of the drainage basin is ∼450,000 km2 and accounts for about 20% of the total land area of Greenland. Topographic and basin morphometric analyses of an isostatically uplifted (ice-free) bedrock topography suggests that this catchment predates ice sheet initiation and has likely been instrumental in controlling the location and form of the Jakobshavn ice stream, and ice flow from the deep interior to the margin, now and over several glacial cycles.
Aitken ARA, Roberts JL, van Ommen TD, et al., 2016, Repeated large-scale retreat and advance of Totten Glacier indicated by inland bed erosion, Nature, Vol: 533, Pages: 385-389, ISSN: 0028-0836
Siegert MJ, Ross N, Li J, et al., 2016, Subglacial controls on the flow of Institute Ice Stream, West Antarctica, Annals of Glaciology, Vol: 57, Pages: 19-24, ISSN: 1727-5644
The Institute Ice Stream (IIS) rests on a reverse-sloping bed, extending >150 km upstream into the ~1.8 km deep Robin Subglacial Basin, placing it at the threshold of marine ice-sheet instability. Understanding IIS vulnerability has focused on the effect of grounding-line melting, which is forecast to increase significantly this century. Changes to ice-flow dynamics are also important to IIS stability, yet little is known about them. Here we reveal the trunk of the IIS occurs downstream of the intersection of three discrete subglacial features; a large ‘active’ subglacial lake, a newly-discovered sharp transition to a zone of weak basal sediments, and a major tectonic rift. The border of IIS trunk flow is confined by the sediment on one side, and by a transition between basal melting and freezing at the border with the Bungenstock Ice Rise. By showing how basal sediment and water dictate present-day flow of IIS, we reveal that ice-sheet stability here is dependent on this unusual arrangement.
Siegert MJ, Frederick BC, Young DA, et al., 2016, Distribution of subglacial sediments across the Wilkes Subglacial Basin, East Antarctica, Journal of Geophysical Research. Earth Surface, Vol: 121, Pages: 790-813, ISSN: 2169-9003
Topography, sediment distribution, and heat flux are all key boundary conditions governing the dynamics of the East Antarctic Ice Sheet (EAIS). EAIS stability is most at risk in Wilkes Land across vast expanses of marine-based catchments including the 1400 km × 600 km expanse of the Wilkes Subglacial Basin (WSB) region. Data from a recent regional aerogeophysical survey (Investigating the Cryospheric Evolution of the Central Antarctic Plate (ICECAP)/IceBridge) are combined with two historical surveys (Wilkes basin/Transantarctic Mountains System Exploration-Ice-house Earth: Stability or DYNamism? (WISE-ISODYN) and Wilkes Land Transect (WLK)) to improve our understanding of the vast subglacial sedimentary basins impacting WSB ice flow and geomorphology across geologic time. Analyzing a combination of gravity, magnetic and ice-penetrating radar data, we present the first detailed subglacial sedimentary basin model for the WSB that defines distinct northern and southern subbasin isopachs with average sedimentary basin thicknesses of 1144 m ± 179 m and 1623 m ± 254 m, respectively. Notably, more substantial southern subbasin sedimentary deposition in the WSB interior supports a regional Wilkes Land hypothesis that basin-scale ice flow and associated glacial erosion is dictated by tectonic basement structure and the inherited geomorphology of preglacial fluvial networks. Orbital, temperate/polythermal glacial cycles emanating from adjacent alpine highlands during the early Miocene to late Oligocene likely preserved critical paleoclimatic data in subglacial sedimentary strata. Substantially thinner northern WSB subglacial sedimentary deposits are generally restricted to fault-controlled, channelized basins leading to prominent outlet glacier catchments suggesting a more dynamic EAIS during the Pliocene.
Siegert MJ, 2016, A wide variety of unique environments beneath the Antarcticice sheet, Geology, Vol: 44, Pages: 399-400, ISSN: 0091-7613
It is 20 years since subglacial Lake Vostok in central East Antarcticawas found to be one of the world’s largest freshwater bodies (Kapitsa et al.,1996). It was hypothesized to be both an ancient, extreme yet viable environmentfor microbial life, and a recorder of past climate change. Testingthese hypotheses is possible with direct measurement and sampling, butin-situ examination is challenging because of the thick ice to drill through,the necessary cleanliness required of the experiment, and the extremepolar conditions in which to operate. In this issue of Geology, Michaudet al. (2016, p. 347) report on water and sedimentary material collectedin January 2013 from Lake Whillans, a component of the hydrologicalsystem beneath Whillans ice stream in West Antarctica. They reveal thewater comprises melted basal ice and a small proportion of seawater, theconcentration of which increases with sediment depth, making it uniqueamong known subglacial environments within and outside of Antarctica.Here, to place the Lake Whillans work in context, I discuss the range ofAntarctic subglacial lake environments, showing the continent to containan assortment of systems in which novel physical, chemical, and biologicalprocesses may take place.
Cavitte M, Blankenship D, Young D, et al., 2016, Deep radiostratigraphy of the East Antarctic plateau: connectingthe Dome C and Vostok ice core sites, Journal of Glaciology, Vol: 62, Pages: 323-334, ISSN: 1727-5652
Several airborne radar-sounding surveys are used to trace internal reflections around theEuropean Project for Ice Coring in Antarctica Dome C and Vostok ice core sites. Thirteen reflections,spanning the last two glacial cycles, are traced within 200 km of Dome C, a promising region formillion-year-old ice, using the University of Texas Institute for Geophysics High-Capacity RadarSounder. This provides a dated stratigraphy to 2318 m depth at Dome C. Reflection age uncertaintiesare calculated from the radar range precision and signal-to-noise ratio of the internal reflections. Theradar stratigraphy matches well with the Multichannel Coherent Radar Depth Sounder (MCoRDS)radar stratigraphy obtained independently. We show that radar sounding enables the extension of icecore ages through the ice sheet with an additional radar-related age uncertainty of ∼1/3–1/2 that ofthe ice cores. Reflections are extended along the Byrd-Totten Glacier divide, using University ofTexas/Technical University of Denmark and MCoRDS surveys. However, core-to-core connection isimpeded by pervasive aeolian terranes, and Lake Vostok’s influence on reflection geometry. Poorradar connection of the two ice cores is attributed to these effects and suboptimal survey design inaffected areas. We demonstrate that, while ice sheet internal radar reflections are generally isochronaland can be mapped over large distances, careful survey planning is necessary to extend ice core chronologiesto distant regions of the East Antarctic ice sheet.
Siegert MJ, 2016, Environmental Sciences in the Twenty-First Century, Frontiers in Environmental Science, Vol: 4, ISSN: 2296-665X
Vance T, Roberts J, Moy A, et al., 2016, Optimal site selection for a high-resolution ice core record in East Antarctica, Climate of the Past, Vol: 12, Pages: 595-610, ISSN: 1814-9332
Ice cores provide some of the best-dated and most comprehensive proxy records, as they yield a vast and growing array of proxy indicators. Selecting a site for ice core drilling is nonetheless challenging, as the assessment of potential new sites needs to consider a variety of factors. Here, we demonstrate a systematic approach to site selection for a new East Antarctic high-resolution ice core record. Specifically, seven criteria are considered: (1) 2000-year-old ice at 300 m depth; (2) above 1000 m elevation; (3) a minimum accumulation rate of 250 mm years−1 IE (ice equivalent); (4) minimal surface reworking to preserve the deposited climate signal; (5) a site with minimal displacement or elevation change in ice at 300 m depth; (6) a strong teleconnection to midlatitude climate; and (7) an appropriately complementary relationship to the existing Law Dome record (a high-resolution record in East Antarctica). Once assessment of these physical characteristics identified promising regions, logistical considerations (for site access and ice core retrieval) were briefly considered. We use Antarctic surface mass balance syntheses, along with ground-truthing of satellite data by airborne radar surveys to produce all-of-Antarctica maps of surface roughness, age at specified depth, elevation and displacement change, and surface air temperature correlations to pinpoint promising locations. We also use the European Centre for Medium-Range Weather Forecast ERA 20th Century reanalysis (ERA-20C) to ensure that a site complementary to the Law Dome record is selected. We find three promising sites in the Indian Ocean sector of East Antarctica in the coastal zone from Enderby Land to the Ingrid Christensen Coast (50–100° E). Although we focus on East Antarctica for a new ice core site, the methodology is more generally applicable, and we include key parameters for all of Antarctica which may be useful for ice core site selection elsewhere and/or for other purposes.
Aitken ARA, Betts PG, Young DA, et al., 2016, The Australo-Antarctic Columbia to Gondwana transition, Gondwana Research, Vol: 29, Pages: 136-152, ISSN: 1342-937X
From the Mesoproterozoic to Cambrian, Australo-Antarctica was characterised by tectonic reconfiguration as part of the supercontinents Columbia, Rodinia and Gondwana. New tectonic knowledge of the Wilkes Land region of Antarctica allows Australo-Antarctic tectonic linkages to be resolved through reconstruction into ca. 160 Ma Gondwana. We also resolve 330 ± 30 km of sinistral strike-slip offset on the > 3000 km long Mundrabilla-Frost Shear Zone and 260 ± 20 km of dextral offset on the > 1000 km long Aurora Fault to reconstruct the ca. 1150 Ma geometry of Australo-Antarctica. Using this revised geometry, we derive the first model of the Columbia to Gondwana reconfiguration process that is geometrically constrained to ~ 100 km scale. In this model, early Mesoproterozoic tectonics is driven by two opposing subduction systems. A dominantly west-dipping subduction zone existed at the eastern margin of Australo-Antarctica until ca. 1.55–1.50 Ga. A predominantly east-dipping subduction zone operated at the western margin of the Mawson Craton from ca. 1.70 Ga to ca. 1.42 Ga. The latter caused gradual westwards motion and clockwise rotation of the Mawson Craton relative to the West and North Australian Craton and the accretion of a series of continental ribbons now preserved in the Musgrave Province and its southern extensions. A mid-Mesoproterozoic switch to predominantly west-dipping subduction beneath the West Australian Craton brought about the final closure of the Mawson Craton with the North and West Australian Craton along the Rodona-Totten Shear Zone. Convergence was achieved prior to 1.31 Ga, but final collision may not have occurred until ca. 1.29 Ga. Post-1.29 Ga intraplate activity involved prolonged high-temperature orogenesis from 1.22 to 1.12 Ga, and significant movement on the Mundrabilla-Frost Shear Zone between 1.13 and 1.09 Ga, perhaps in response to the assembly of Rodinia at ca. 1.1 Ga. The Australo-Antarctic Craton was amalgama
Jamieson SSR, Ross N, Greenbaum JS, et al., 2015, An extensive subglacial lake and canyon system in Princess Elizabeth Land, East Antarctica, Geology, Vol: 44, Pages: 87-90, ISSN: 1943-2682
The subglacial landscape of Princess Elizabeth Land (PEL) in East Antarctica is poorly known due to a paucity of ice thickness measurements. This is problematic given its importance for understanding ice sheet dynamics and landscape and climate evolution. To address this issue, we describe the topography beneath the ice sheet by assuming that ice surface expressions in satellite imagery relate to large-scale subglacial features. We find evidence that a large, previously undiscovered subglacial drainage network is hidden beneath the ice sheet in PEL. We interpret a discrete feature that is 140 × 20 km in plan form, and multiple narrow sinuous features that extend over a distance of ∼1100 km. We hypothesize that these are tectonically controlled and relate to a large subglacial basin containing a deep-water lake in the interior of PEL linked to a series of long, deep canyons. The presence of 1-km-deep canyons is confirmed at a few localities by radio-echo sounding data, and drainage analysis suggests that these canyons will direct subglacial meltwater to the coast between the Vestfold Hills and the West Ice Shelf.
Ross N, Le Brocq AM, Siegert MJ, 2015, Recent advances in understanding Antarctic subglacial lakes and hydrology, Journal: Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 374, ISSN: 1471-2962
It is now well documented that over 400 subglacial lakes exist across the bed of the Antarctic Ice Sheet. They comprise a variety of sizes and volumes (from the approx. 250 km long Lake Vostok to bodies of water less than 1 km in length), relate to a number of discrete topographic settings (from those contained within valleys to lakes that reside in broad flat terrain) and exhibit a range of dynamic behaviours (from ‘active’ lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years). Here we critique recent advances in our understanding of subglacial lakes, in particular since the last inventory in 2012. We show that within 3 years our knowledge of the hydrological processes at the ice-sheet base has advanced considerably. We describe evidence for further ‘active’ subglacial lakes, based on satellite observation of ice-surface changes, and discuss why detection of many ‘active’ lakes is not resolved in traditional radio-echo sounding methods. We go on to review evidence for large-scale subglacial water flow in Antarctica, including the discovery of ancient channels developed by former hydrological processes. We end by predicting areas where future discoveries may be possible, including the detection, measurement and significance of groundwater (i.e. water held beneath the ice-bed interface).
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