201 results found
Siegert M, Kingslake J, Ross N, et al., Late Holocene Glacial History of the Weddell Sea Sector of the West Antarctic Ice Sheet, Reviews of Geophysics, ISSN: 8755-1209
Kulessa B, Key K, Thompson S, et al., 2019, Heat and groundwater transport between the Antarctic Ice Sheet and subglacial sedimentary basins from electromagnetic geophysical measurements, SEG International Exposition and 89th Annual Meeting, Publisher: Society of Exploration Geophysicists, Pages: 4819-4823, ISSN: 1949-4645
Numerical models of contemporary as well as paleo-ice sheets suggest that groundwater and heat exchanges between subglacial sedimentary basins and the ice sheet above, can be substantial and influence the flow of ice above. So far, an approach for the measurement and assessment of such heat fluxes has not been available. Here, we summarise existing evidence for groundwater and heat exchanges between contemporary and paleo ice sheets and the substrate below. We then explain the utility of electromagnetic geophysical measurements in elucidating such exchanges, and present magnetotelluric synthetic models of the deep sedimentary basin beneath the Institute Ice Stream in West Antarctica by way of illustration. Finally, we propose a simple empirical model by which heat exchanges between subglacial sedimentary basins and the overlying ice sheet can be estimated to first-order from electromagnetic data.
Siegert M, Atkinson A, Banwell A, et al., 2019, The Antarctic Peninsula under a 1.5°C global warming scenario, Frontiers in Environmental Science, Vol: 7, ISSN: 2296-665X
Warming of the Antarctic Peninsula in the latter half of the twentieth century was greater than any other terrestrial environment in the Southern Hemisphere, and clear cryospheric and biological consequences have been observed. Under a global 1.5°C scenario, warming in the Antarctic Peninsula is likely to increase the number of days above 0°C, with up to 130 of such days each year in the northern Peninsula. Ocean turbulence will increase, making the circumpolar deep water (CDW) both warmer and shallower, delivering heat to the sea surface and to coastal margins. Thinning and recession of marine margins of glaciers and ice caps is expected to accelerate to terrestrial limits, increasing iceberg production, after which glacier retreat may slow on land. Ice shelves will experience continued increase in meltwater production and consequent structural change, but not imminent regional collapses. Marine biota can respond in multiple ways to climatic changes, with effects complicated by past resource extraction activities. Southward distribution shifts have been observed in multiple taxa during the last century and these are likely to continue. Exposed (ice free) terrestrial areas will expand, providing new habitats for native and non-native organisms, but with a potential loss of genetic diversity. While native terrestrial biota are likely to benefit from modest warming, the greatest threat to native biodiversity is from non-native terrestrial species.
Wang B, Sun B, Jiaxin W, et al., Removal of ‘strip noise’ in airborne radio-echo sounding data using combined wavelet and 2D DFT filtering, Annals of Glaciology, 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.
Malard L, Šabacká M, Magiopoulos I, et al., 2019, Spatial variability in Antarctic surface snow bacterial communities, Frontiers in Microbiology, Vol: 10, ISSN: 1664-302X
It was once a long-held view that the Antarctic was a pristine environment with low biomass, low biodiversity and low rates of microbial activity. However, as the intensity of scientific investigation has increased, so these views have started to change. In particular, the role and impact of human activity toward indigenous microbial communities has started to come under more intense scrutiny. During the Subglacial Lake Ellsworth exploration campaign in December 2012, a microbiological survey was conducted to determine the extent and likelihood of exogenous input into the subglacial lake system during the hot-water drilling process. Snow was collected from the surface to represent that used for melt water production for hot-water drilling. The results of this study showed that snow used to provide melt water differed in its microbiological composition from that of the surrounding area and raised the question of how the biogeography of snow-borne microorganisms might influence the potential outcome of scientific analyses. In this study, we investigated the biogeography of microorganisms in snow around a series of Antarctic logistic hubs, where human activity was clearly apparent, and from which scientific investigations have been undertaken. A change in microbial community structure with geographical location was apparent and, notably, a decrease in alpha diversity at more remote southern latitudes. Soil-related microorganisms dominated microbial assemblages suggesting terrestrial input, most likely from long-range aeolian transport into continental Antarctica. We also observed that relic DNA was not a major issue when assessing snow samples. Overall, our observations might have profound implications for future scientific activities in Antarctica, such as the need to establish “no-go” protected areas, the need for better characterization of field sites and improved protocols for sterilization and verification of ice drilling equipment.
Cooper M, Jordan T, Siegert M, et al., 2019, Surface expression of basal and englacial features, properties, and processes of the Greenland Ice Sheet, Geophysical Research Letters, Vol: 46, Pages: 783-793, ISSN: 0094-8276
Radar‐sounding surveys measuring ice thickness in Greenland have enabled an increasingly “complete” knowledge of basal topography and glaciological processes. Where such observations are spatially limited, bed elevation has been interpolated through mass conservation or kriging. Ordinary kriging fails to resolve anisotropy in bed geometry, however, leaving complex topography misrepresented in elevation models of the ice sheet bed. Here, we demonstrate the potential of new high‐resolution (≤5 m) surface topography data (ArcticDEM) to provide enhanced insight into basal and englacial geometry and processes. Notable surface features, quantified via residual surface elevation, are observed coincident with documented subglacial channels, and new, smaller‐scale tributaries (<2,000 m in width) and valley‐like structures are clearly identified. Residual surface elevation also allows the extent of basal ice units to be mapped, which in conjunction with radar data indicate that they act as “false bottoms,” likely due to a rheological contrast in the ice column.
Smith A, Woodward J, Ross N, et al., 2018, Evidence for the long-term sedimentary environment in an Antarctic subglacial lake, Earth and Planetary Science Letters, Vol: 504, Pages: 139-151, ISSN: 0012-821X
Lakes beneath the Antarctic Ice Sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments. However, no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet, and understanding of sediment pathways, processes and structure in subglacial lake environments remains uncertain. Here we present an analysis of seismic data from Subglacial Lake Ellsworth, showing that the lake bed comprises very fine-grained sediments deposited in a low energy environment, with low water- and sediment-fluxes. Minimum sediment thickness is 6 m, the result of prolonged low sedimentation rates. Based on the few available analogues, we speculate this sediment age range is a minimum of 150 ka, and possibly >1 Ma. Sediment mass movements have occurred, but they are rare and have been buried by subsequent sedimentation. We present a new conceptual model of subglacial lake sedimentation, allowing a framework for evaluating processes in subglacial lake environments, and for determining future lake access locations and interpreting subglacial lake samples.
Keen P, Saw K, Rundle N, et al., 2018, A mini corer for precision sampling of the water sediment interface of subglacial lakes and remote aqueous environments, Limnology and Oceanography: Methods, Vol: 16, Pages: 856-867, ISSN: 1541-5856
Recent interest in Antarctic subglacial lakes has seen the development of bespoke systems for sampling them. These systems are considered pristine environments potentially harboring undisturbed sedimentary sequences and ecosystems adapted to these cold oligotrophic environments in the absence of sunlight. The water/sediment interface is considered a prime location for the detection of microbial life and so is of particular interest. This article describes the development of a small corer to capture and retain a short core that includes the water/sediment interface specifically to address the question of whether life exists in these lakes. This apparatus was developed as part of the UK led project to access, measure, and sample subglacial Lake Ellsworth. In addition to addressing the constraints of coring in this difficult environment, the results of subsequent testing suggest that this corer can be applied to sampling sediments in other environments and would be particularly useful in low energy environments when the water‐sediment interface is indistinct or unconsolidated.
Jordan T, Martin C, Ferraccioli F, et al., 2018, Anomalously high geothermal flux near the South Pole, Scientific Reports, Vol: 8, ISSN: 2045-2322
Melting at the base of the Antarctic Ice Sheet influences ice dynamics and our ability to recover ancient climatic records from deep ice cores. Basal melt rates are affected by geothermal flux, one of the least constrained properties of the Antarctic continent. Estimates of Antarctic geothermal flux are typically regional in nature, derived from geological, magnetic or seismic data, or from sparse point measurements at ice core sites. We analyse ice-penetrating radar data upstream of South Pole revealing a ~100 km long and 50 km wide area where internal ice sheet layers converge with the bed. Ice sheet modelling shows that this englacial layer configuration requires basal melting of up to 6 ± 1 mm a−1 and a geothermal flux of 120 ± 20 mW m−2, more than double the values expected for this cratonic sector of East Antarctica. We suggest high heat producing Precambrian basement rocks and hydrothermal circulation along a major fault system cause this anomaly. We conclude that local geothermal flux anomalies could be more widespread in East Antarctica. Assessing their influence on subglacial hydrology and ice sheet dynamics requires new detailed geophysical observations, especially in candidate areas for deep ice core drilling and at the onset of major ice streams.
Jeofry H, Ross N, Le Brocq A, et al., 2018, Hard rock landforms generate 130 km ice shelf channels through water focusing in basal corrugations, Nature Communications, Vol: 9, ISSN: 2041-1723
Satellite imagery reveals flowstripes on Foundation Ice Stream parallel to ice flow, and meandering features on the ice-shelf that cross-cut ice flow and are thought to be formed by water exiting a well-organised subglacial system. Here, ice-penetrating radar data show flow-parallel hard-bed landforms beneath the grounded ice, and channels incised upwards into the ice shelf beneath meandering surface channels. As the ice transitions to flotation, the ice shelf incorporates a corrugation resulting from the landforms. Radar reveals the presence of subglacial water alongside the landforms, indicating a well-organised drainage system in which water exits the ice sheet as a point source, mixes with cavity water and incises upwards into a corrugation peak, accentuating the corrugation downstream. Hard-bedded landforms influence both subglacial hydrology and ice-shelf structure and, as they are known to be widespread on formerly glaciated terrain, their influence on the ice-sheet-shelf transition could be more widespread than thought previously.
Rintoul SR, Chown SL, DeConto RM, et al., 2018, Choosing the future of Antarctica (vol 558, 233, 2018), NATURE, Vol: 562, Pages: E5-E5, ISSN: 0028-0836
Siegert MJ, Kennicutt MC, 2018, Governance of the exploration of subglacial Antarctica, Frontiers in Environmental Science, Vol: 6, ISSN: 2296-665X
Subglacial lakes, and their surrounding aqueous environments, are known to be viable yet extreme habitats for microbial life that may hold records of climate change spanning hundreds of thousands of years. Since the detection of Lake Vostok in 1996 plans have been developed to access, sample, and monitor these unique environments. Critical to these plans is assurance that contamination and disturbance is minimized in all aspects of the activity. Precisely how this is achieved has been a matter of international debate for many years culminating in the formulation of a “Code of Conduct” to guide responsible scientific exploration and stewardship of these pristine systems by the Scientific Committee on Antarctic research. The Code of Conduct was first introduced to the Antarctic Treaty Consultative Meeting in 2011, influencing planning for three exploration programs. In May 2018, following several recent and operational advances, Antarctic Treaty Parties agreed to its use and dissemination, ensuring that subglacial lakes exploration and access is undertaken in a responsible, defensible, and fact-based manner. As our knowledge of subglacial lakes improves, so too will our appreciation of their scientific value and potential vulnerability. In other regions of Antarctica where value and vulnerabilities are high, Antarctic Specially Protected Areas and Antarctic Specially Managed Areas ensure long-term protection whilst allowing scientific access and study. Such governance models will be applicable to the conservation and protection of subglacial lake systems as scientific understanding of their form and functioning advances.
Jordan T, Williams C, Schroeder D, et al., 2018, A constraint upon the basal water distribution and thermal state of the Greenland Ice Sheet from radar bed echoes, The Cryosphere, Vol: 12, Pages: 2831-2854, ISSN: 1994-0416
There is widespread, but often indirect, evidence that a significant fraction of the bed beneath the Greenland Ice Sheet is thawed (at or above the pressure melting point for ice). This includes the beds of major outlet glaciers and their tributaries and a large area around the NorthGRIP borehole in the ice-sheet interior. The ice-sheet-scale distribution of basal water is, however, poorly constrained by existing observations. In principle, airborne radio-echo sounding (RES) enables the detection of basal water from bed-echo reflectivity, but unambiguous mapping is limited by uncertainty in signal attenuation within the ice. Here we introduce a new, RES diagnostic for basal water that is associated with wet–dry transitions in bed material: bed-echo reflectivity variability. This technique acts as a form of edge detector and is a sufficient, but not necessary, criteria for basal water. However, the technique has the advantage of being attenuation insensitive and suited to combined analysis of over a decade of Operation IceBridge survey data.The basal water predictions are compared with existing analyses of the basal thermal state (frozen and thawed beds) and geothermal heat flux. In addition to the outlet glaciers, we demonstrate widespread water storage in the northern and eastern interior. Notably, we observe a quasilinear corridor of basal water extending from NorthGRIP to Petermann Glacier that spatially correlates with elevated heat flux predicted by a recent magnetic model. Finally, with a general aim to stimulate regional- and process-specific investigations, the basal water predictions are compared with bed topography, subglacial flow paths and ice-sheet motion. The basal water distribution, and its relationship with the thermal state, provides a new constraint for numerical models.
Colleoni F, De Santis L, Siddoway CS, et al., 2018, Publisher correction: Spatio-temporal variability of processes across Antarctic ice-bed-ocean interfaces (vol 9, 2289, 2018), Nature Communications, Vol: 9, ISSN: 2041-1723
Colleoni F, De Santis L, Siddoway CS, et al., 2018, Spatio-temporal variability of processes across Antarctic ice-bed–ocean interfaces, Nature Communications, Vol: 9, ISSN: 2041-1723
Understanding how the Antarctic ice sheet will respond to global warming relies on knowledge of how it has behaved in the past. The use of numerical models, the only means to quantitatively predict the future, is hindered by limitations to topographic data both now and in the past, and in knowledge of how subsurface oceanic, glaciological and hydrological processes interact. Incorporating the variety and interplay of such processes, operating at multiple spatio-temporal scales, is critical to modeling the Antarctic’s system evolution and requires direct observations in challenging locations. As these processes do not observe disciplinary boundaries neither should our future research.
We present two narratives on the future of Antarctica and the Southern Ocean, from the perspective of an observer looking back from 2070. In the first scenario, greenhouse gas emissions remained unchecked, the climate continued to warm, and the policy response was ineffective; this had large ramifications in Antarctica and the Southern Ocean, with worldwide impacts. In the second scenario, ambitious action was taken to limit greenhouse gas emissions and to establish policies that reduced anthropogenic pressure on the environment, slowing the rate of change in Antarctica. Choices made in the next decade will determine what trajectory is realized.
Jeofry H, Ross N, Corr HFJ, et al., 2018, A new bed elevation model for the Weddell Sea sector of the West Antarctic Ice Sheet, Earth System Science Data, Vol: 10, Pages: 711-725, ISSN: 1866-3508
We present a new digital elevation model (DEM) of the bed, with a 1 km gridding, of the Weddell Sea (WS) sector of the West Antarctic Ice Sheet (WAIS). The DEM has a total area of ∼ 125 000 km2 covering the Institute, Möller and Foundation ice streams, as well as the Bungenstock ice rise. In comparison with the Bedmap2 product, our DEM includes new aerogeophysical datasets acquired by the Center for Remote Sensing of Ice Sheets (CReSIS) through the NASA Operation IceBridge (OIB) program in 2012, 2014 and 2016. We also improve bed elevation information from the single largest existing dataset in the region, collected by the British Antarctic Survey (BAS) Polarimetric radar Airborne Science Instrument (PASIN) in 2010–2011, from the relatively crude measurements determined in the field for quality control purposes used in Bedmap2. While the gross form of the new DEM is similar to Bedmap2, there are some notable differences. For example, the position and size of a deep subglacial trough (∼ 2 km below sea level) between the ice-sheet interior and the grounding line of the Foundation Ice Stream have been redefined. From the revised DEM, we are able to better derive the expected routing of basal water and, by comparison with that calculated using Bedmap2, we are able to assess regions where hydraulic flow is sensitive to change. Given the potential vulnerability of this sector to ocean-induced melting at the grounding line, especially in light of the improved definition of the Foundation Ice Stream trough, our revised DEM will be of value to ice-sheet modelling in efforts to quantify future glaciological changes in the region and, from this, the potential impact on global sea level. The new 1 km bed elevation product of the WS sector can be found at https://doi.org/10.5281/zenodo.1035488.
Jeofry H, Ross N, Corr HFJ, et al., A new bed elevation model for the Weddell Sea sector of the West Antarctic Ice Sheet, Earth System Science Data, ISSN: 1866-3508
Parrenin F, Cavitte MGP, Blankenship DD, et al., 2017, Is there 1.5 million-year old ice near Dome C, Antarctica?, The Cryosphere, Vol: 11, Pages: 2427-2437, ISSN: 1994-0416
Ice sheets provide exceptional archives of past changes in polar climate, regional environment and global atmospheric composition. The oldest dated deep ice core drilled in Antarctica has been retrieved at EPICA Dome C (EDC), reaching ∼ 800 000 years. Obtaining an older paleoclimatic record from Antarctica is one of the greatest challenges of the ice core community. Here, we use internal isochrones, identified from airborne radar coupled to ice-flow modelling to estimate the age of basal ice along transects in the Dome C area. Three glaciological properties are inferred from isochrones: surface accumulation rate, geothermal flux and the exponent of the Lliboutry velocity profile. We find that old ice (> 1.5 Myr, 1.5 million years) likely exists in two regions: one ∼ 40 km south-west of Dome C along the ice divide to Vostok, close to a secondary dome that we name Little Dome C (LDC), and a second region named North Patch (NP) located 10–30 km north-east of Dome C, in a region where the geothermal flux is apparently relatively low. Our work demonstrates the value of combining radar observations with ice flow modelling to accurately represent the true nature of ice flow, and understand the formation of ice-sheet architecture, in the centre of large ice sheets.
Siegert MJ, Jamieson SSR, White D, 2017, Exploration of subsurface Antarctica: uncovering past changes and modern processes, Geological Society Special Publications, Vol: Special Publications, ISSN: 0305-8719
The Antarctic continent, which contains enough ice to raise sea level globally by around 60 m, is the last major scientific frontier on our planet. We know far more about the surfaces of the Moon, Mars and around half of Pluto than we do about the underside of the Antarctic ice sheet. Geophysical exploration is the key route to measuring the ice sheet's internal structure and the land on which the ice rests. From such measurements, we are able to reveal how the ice sheet flows, and how it responds to atmospheric and ocean warming. By examining landscapes that have been moulded by former ice flow, we are able to identify how the ice sheet behaved in the past. Geophysics is therefore critical to understanding change in Antarctica.
Morlighem M, Williams C, Rignot E, et al., 2017, BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multi-beam radar sounding combined with mass conservation, Geophysical Research Letters, Vol: 44, Pages: 11,051-11,061, ISSN: 0094-8276
Greenland’s bed topography is a primary control on ice flow, grounding line migration,calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warmAtlantic water (AW) that rapidly melts and undercuts Greenland’s marine-terminating glaciers. Here wepresent a new compilation of Greenland bed topography that assimilates seafloor bathymetry and icethickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yieldingmajor improvements over previous data sets, particularly in the marine-terminating sectors of northwestand southeast Greenland. Our map reveals that the total sea level potential of the Greenland ice sheetis 7.42 ± 0.05 m, which is 7 cm greater than previous estimates. Furthermore, it explains recent calvingfront response of numerous outlet glaciers and reveals new pathways by which AW can access glacierswith marine-based basins, thereby highlighting sectors of Greenland that are most vulnerable to futureoceanic forcing.
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.
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).
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