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The future contributions of the Antarctic Ice Sheet to sea level rise will depend on the evolution of its surface mass balance (SMB), which could amplify/dampen mass losses increasingly observed at the ice sheet's edge. In situ constraints of SMB over annual-to-decadal timescales consist mostly of firn/ice cores that have a surface footprint cm. SMB constraints also come from climate models, which have a higher temporal resolution but a larger surface footprint of several km. We use ice-penetrating radar data to obtain an intermediate spatial and temporal resolution SMB record over three ice rises along the Princess Ragnhild Coast. The co-located ice cores allow us to obtain absolute radar-derived SMB rates at a multi-annual-to-decadal temporal resolution. By comparing the ice core SMB measurements and the radar-derived SMB records, we determine that pointwise measurements of SMB are representative of a small surface area, m radius extending from the ice core drill site for the ice rises studied here, and that the pointwise measurements are systematically 7–15 cm w.e. a lower than the mean SMB value calculated for the whole ice rises. However, ice core records are representative of an entire ice rise's temporal variability at the temporal resolution examined.

The future contributions of the Antarctic Ice Sheet to sea level rise will depend on the evolution of its surface mass balance (SMB), which could amplify/dampen mass losses increasingly observed at the ice sheet's edge. In situ constraints of SMB over annual-to-decadal timescales consist mostly of firn/ice cores that have a surface footprint $sim$ cm $^{2}$ .SMB constraints also come from climate models, which have a higher temporal resolution but a larger surface footprint of several km $^{2}$ .We use ice-penetrating radar data to obtain an intermediate spatial and temporal resolution SMB record over three ice rises along the Princess Ragnhild Coast. The co-located ice cores allow us to obtain absolute radar-derived SMB rates at a multi-annual-to-decadal temporal resolution. By comparing the ice core SMB measurements and the radar-derived SMB records, we determine that pointwise measurements of SMB are representative of a small surface area, $sim 200-500$ m radius extending from the ice core drill site for the ice rises studied here, and that the pointwise measurements are systematically 7–15 cm w.e. a $^{-1}$ lower than the mean SMB value calculated for the whole ice rises. However, ice core records are representative of an entire ice rise's temporal variability at the temporal resolution examined., SCOPUS: ar.j, info:eu-repo/semantics/published

The future contributions of the Antarctic Ice Sheet to sea level rise will depend on the evolution of its surface mass balance (SMB), which could amplify/dampen mass losses increasingly observed at the ice sheet's edge. In situ constraints of SMB over annual-to-decadal timescales consist mostly of firn/ice cores that have a surface footprint cm. SMB constraints also come from climate models, which have a higher temporal resolution but a larger surface footprint of several km. We use ice-penetrating radar data to obtain an intermediate spatial and temporal resolution SMB record over three ice rises along the Princess Ragnhild Coast. The co-located ice cores allow us to obtain absolute radar-derived SMB rates at a multi-annual-to-decadal temporal resolution. By comparing the ice core SMB measurements and the radar-derived SMB records, we determine that pointwise measurements of SMB are representative of a small surface area, m radius extending from the ice core drill site for the ice rises studied here, and that the pointwise measurements are systematically 7–15 cm w.e. a lower than the mean SMB value calculated for the whole ice rises. However, ice core records are representative of an entire ice rise's temporal variability at the temporal resolution examined., Mathematical Geodesy and Positioning

Quantarctica (https://www.npolar.no/quantarctica) is a geospatial data package, analysis environment, and visualization platform for the Antarctic Continent, Southern Ocean (>40oS), and sub-Antarctic islands. Quantarctica works with the free, cross-platform Geographical Information System (GIS) software QGIS and can run without an Internet connection, making it a viable tool for fieldwork in remote areas. The data package includes basemaps, satellite imagery, terrain models, and scientific data in nine disciplines, including physical and biological sciences, environmental management, and social science. To provide a clear and responsive user experience, cartography and rendering settings are carefully prepared using colour sets that work well for typical data combinations and with consideration of users with common colour vision deficiencies. Metadata included in each dataset provides brief abstracts for non-specialists and references to the original data sources. Thus, Quantarctica provides an integrated environment to view and analyse multiple Antarctic datasets together conveniently and with a low entry barrier.

The limited number of surface mass balance (SMB) observations in the Antarctic inland hampers estimates of ice-sheet contribution to global sea level and locations with million-year-old ice. We present finely resolved SMB over the past three centuries in a low-accumulation region with significant depth hoar formation on Dome Fuji derived from ∼1,100 km of microwave radar stratigraphy dated with a firn core. The regional-mean SMB over the past 264 years is estimated to ∼22.5 ± 3.3 kg m−2 a−1, but with large local variability of up to 30%. We found that local SMB is negatively correlated with surface slope at scales of a few hundred meters, resulting in anomalous zones of low SMB which represent as much as 8–10% of the total SMB on the inland plateau if the SMB-slope relationship is more widely valid. This impact should be investigated further to improve estimates of Antarctic mass balance and sea-level contribution., SCOPUS: le.j, info:eu-repo/semantics/published

We developed a high-performance, multichannel, ultra-wideband radar system for measurements of the base and interior of the East Antarctic Ice Sheet. We designed the radar to be of high power (4000-W peak) yet portable and to be able to operate with 60-MHz bandwidth at a center frequency of 200 MHz, providing high sensitivity and fine vertical resolution relative to current technology. We used the radar to perform extensive mea- surements as a part of a multinational collaboration. We collected data onboard a tracked vehicle outfitted with an array of high-gain antennas. We sounded 2- to 3-km thick ice near Dome Fuji. Prelim- inary ice thickness data match those obtained via semicoincident measurements performed with a different surface-based pulse- modulated radar system operated during the same field campaign, as well as previous airborne measurements. In addition, we mapped internal reflection horizons with fine vertical resolution from 300 m below the ice surface to ∼100 m above the bed. In this article, we provide a detailed overview of the radar instrument design, implementation, and field measurement setup. We present sample data to illustrate its capabilities and discuss how the data collected with it will be valuable for the assessment of promising drilling sites to recover ice cores that are 0.9–1.5 million years old.

Antarctic geothermal heat flow (GHF) affects the ice sheet temperature, determining how it slides and internally deforms, as well as the rheological behaviour of the lithosphere. However, GHF remains poorly constrained, with few borehole-derived estimates, and there are large discrepancies in currently available glaciological and geophysical estimates. This SCAR White Paper details current methods, discusses their challenges and limitations, and recommends key future directions in GHF research. We highlight the timely need for a more multidisciplinary and internationally-coordinated approach to tackle this complex problem.

The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3-D continental ice-sheet modelling. To this end, we present an ensemble of ice-sheet simulations spanning the last 2 Myr, employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the imprint of changing climate conditions, sea level and geothermal heat flux on the ice thickness, and basal conditions around previously identified sites with continuous records of old ice. Our modelling results show a range of configurational ice-sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate reorganisation and associated ice-dynamic changes, we identify several regions conducive to conditions maintaining 1.5 Myr (million years) old ice, particularly around Dome Fuji, Dome C and Ridge B, which is in agreement with previous studies. This finding strengthens the notion that continuous records with such old ice do exist in previously identified regions, while we are also providing a dynamic continental ice-sheet context.

To resolve the mechanisms behind the major climate reorganisation which occurred between 0.9 and 1.2 Ma, the recovery of a suitable 1.5 million-year-old ice core is fundamental. The quest for such an Oldest Ice core requires a number of key boundary conditions, of which the poorly known basal geothermal heat flux (GHF) is lacking. We use a transient thermodynamical 1D vertical model that solves for the rate of change of temperature in the vertical, with surface temperature and modelled GHF as boundary conditions. For each point on the ice sheet, the model is forced with variations in atmospheric conditions over the last 2 Ma, and modelled ice-thickness variations. The process is repeated for a range of GHF values to determine the value of GHF that marks the limit between frozen and melting conditions over the whole ice sheet, taking into account 2 Ma of climate history. These threshold values of GHF are statistically compared to existing GHF data sets. The new probabilistic GHF fields obtained for the ice sheet thus provide the missing boundary conditions in the search for Oldest Ice. High spatial resolution radar data are examined locally in the Dome Fuji and Dome C regions, as these represent the ice core community’s primary drilling sites. GHF, bedrock variability, ice thickness and other essential criteria combined highlight a dozen major potential Oldest Ice sites in the vicinity of Dome Fuji and Dome C, where GHF allows for Oldest Ice.

A key objective in palaeo-climatology is the retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma. The identification of a suitable Antarctic site requires sufficient knowledge of the subglacial landscape beneath the Antarctic Ice Sheet. Here, we present new ice thickness information from the Dome Fuji region, East Antarctica, based on airborne radar surveys conducted during the 2014/15 and 2016/17 southern summers. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results show that especially the region immediately south of Dome Fuji station persists as a good candidate site for obtaining an old ice core. An initial assessment of basal conditions revealed the existence of what appears to be subglacial lakes. Further radar data analysis shows overall high continuity of layer stratigraphy in the region. This indicates that extending the age–depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option.

To resolve the mechanisms behind the major climate reorganisation, which occurred between 0.9 and 1.2 Ma, the recovery of a suitable 1.5 million-year-old ice core is fundamental. The quest for an Oldest Ice core requires a number of key boundary conditions, of which the poorly known basal geothermal heat flux (GHF) is lacking. We use a transient thermodynamical 1-D vertical model that solves for the rate of change of temperature in the vertical, with surface temperature and modelled GHF as boundary conditions. For each point on the ice sheet, the model is forced with variations in atmospheric conditions over the last 2 Ma and modelled ice-thickness variations. The process is repeated for a range of GHF values to determine the value of GHF that marks the limit between frozen and melting conditions over the whole ice sheet, taking into account 2 Ma of climate history. These threshold values of GHF are statistically compared to existing GHF data sets. The new probabilistic GHF fields obtained for the ice sheet thus provide the missing boundary conditions in the search for Oldest Ice. High spatial resolution radar data are examined locally in the Dome Fuji and Dome C regions, as these represent the ice core community's primary drilling sites. GHF, bedrock variability, ice thickness and other essential criteria combined highlight a dozen major potential Oldest Ice sites in the vicinity of Dome Fuji and Dome C, where GHF could allow for Oldest Ice.

A key objective in palaeo-climatology is the retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma. The identification of a suitable Antarctic site requires sufficient knowledge of the subglacial landscape beneath the Antarctic Ice Sheet. Here, we present new ice thickness information from the Dome Fuji region, East Antarctica, based on airborne radar surveys conducted during the 2014/15 and 2016/17 southern summers. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results show that especially the region immediately south of Dome Fuji station persists as a good candidate site for obtaining an old ice core. An initial assessment of basal conditions revealed the existence of what appears to be subglacial lakes. Further radar data analysis shows overall high continuity of layer stratigraphy in the region. This indicates that extending the age-depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option., SCOPUS: ar.j, info:eu-repo/semantics/published

We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, since the last glacial. We use a set of 18 isochrones spanning all observable depths of the ice column, interpreted from various ice-penetrating radar surveys and a 1-D ice flow model to invert for accumulation rates in the region. The shallowest four isochrones are then used to calculate paleoaccumulation rates between isochrone pairs using a 1-D assumption where horizontal advection is negligible in the time interval of each layer. We observe that the large-scale (100sĝ€km) surface accumulation gradient is spatially stable through the last 73ĝ€kyr, which reflects current modeled and observed precipitation gradients in the region. We also observe small-scale (10ĝ€sĝ€km) accumulation variations linked to snow redistribution at the surface, due to changes in its slope and curvature in the prevailing wind direction that remain spatially stationary since the last glacial., SCOPUS: ar.j, info:eu-repo/semantics/published

In a warming world, glaciers and ice sheets have an increasingly large influence on the environment, particularly through their contribution to sea level rise. Their response to anthropogenic climate change, in addition to natural variability, has a critical impact on dependent populations and will be key to predict future climates. Understanding the past natural transitions is also important as if the natural variability of the climate system is not well understood, we stand little change of accurately predicting future climate changes, especially in the context of rapid global warming. Ice cores represent the best time capsules for the recovery of paleo-climate informations. For that, the recovery of a suitable 1.5 million-year-old ice core in Antarctica is fundamental to better understand the natural climate reorganisation which occurred between 0.9 and 1.2 Ma. Constraining the englacial and basal temperature evolution of glaciers and ice sheets through time is the first step in understanding their temporal stability and therefore potential impacts on climate. Furthermore, obtaining the best constraints on basal conditions is essential as such million-year-old ice will be located very near to the bedrock, where the thermal regime has the strongest impact. However, measurements of current englacial and basal temperature have only been obtained at a few drill sites for glaciers and ice sheets. We must therefore turn to thermodynamical models to provide theoretical and statistical constraints on governing thermal processes. Thermodynamical models rely on a suite of governing equations, which we describe in this thesis. Our first study area is the McCall glacier, in Alaska (USA), where we show that the glacier cooled down in the warming climate of the last 50 years using a 1D thermodynamical model. We calculate the present-day englacial temperature distribution using recently acquired data in the form of englacial temperature measurements and radio-echo sounding surv, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Finding suitable potential sites for an undisturbed record of million-year old ice in Antarctica requires slow-moving ice (preferably an ice divide) and basal conditions that are not disturbed by large topographic variations. Furthermore, ice should be thick and cold basal conditions should prevail, since basal melting would destroy the bottom layers. Therefore, ice-flow conditions and thermodynamic characteristics are crucial in identifying potential locations of undisturbed ice. Van Liefferinge and Pattyn (2013) identified suitable areas based on a pan-Antarctic simplified thermodynamic ice sheet model. In order to refine these estimates and potential location sites, we limited our analysis to the divide area of the East Antarctic ice sheet, i.e. Dome Fuji, Argus, Concordia, and Ridge B. The refined calculations are with a full thermo-mechanically coupled higher-order ice sheet model (Pattyn, 2003; Pattyn et al. 2004). Initial conditions for the calculations are based on an inversion of basal slipperiness, based on observed surface topography (Pollard and Deconto, 2012; Pattyn, in prep.). Uncertainty in geothermal conditions is introduced with the methodology previously applied (Pattyn, 2010; Van Liefferinge and Pattyn, 2013). The higher-order model approach has major advantages over previous approaches, as the calculated flow field is dynamically coupled to the thermal balance, which was not the case previously., info:eu-repo/semantics/nonPublished

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The Tweeting Ice Shelf: geophysics and outreachBrice Van Liefferinge, Sophie Berger, Reinhard Drews, and Frank PattynUniversité Libre de Bruxelles, Laboratoire de Glaciologie, Brussels, Belgium (bvlieffe@ulb.ac.be)Over the last decade the Antarctic and Greenland ice sheets have contributed about one third of the annual sea levelrise (Hanna et al. 2013). However, it remains difficult to reconcile global mass balance estimates obtained fromdifferent satellite-based methods. A typical approach is to balance the mass input from atmospheric modellingwith the outgoing mass flux at the ice-sheet boundary (Shepherd et al. 2012). The flux calculations at the boundaryrely on satellite-derived surface velocities, which are currently only available as snapshots in time, and which needground truth for validation. Here, we report on continuous, year-round measurements that aim at improving theinput-output method in several aspects and carefully map the flow speed allowing for detecting seasonal variability.For this purpose, we set up in December 2014 three stand-alone single-frequency GPSes on the Roi Baudouinice shelf (East Antarctica). The GPSes are installed across a surface depression (typical for large ice-shelfchannels), where subglacial melting is expected. This setup allows us to investigate how these channels behave,i.e. if they become wider, whether or not they enhance the ice flow, and, in combination with an installedphase-sensitive radar, what amount of melting occurs below the channels in contact with the ocean.The GPS data are transmitted on a daily basis. Ice-shelf velocity is derived from the raw hourly locationfollowing the methods described in den Ouden et al. (2010), Dunse et al. (2012), and Ahlstrøm et al. (2013).However, a reference station has not been used for the correction. Basic processing involves outliers removal,smoothing, time-series analysis and comparison with tidal models.The project comes alongside an outreach event: on a weekly basis, the ice s, info:eu-repo/semantics/nonPublished

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Knowledge of glacier equilibrium-line altitude (ELA) changes and trends in time is essentialfor future predictions of glacier volumes. We present a novel method for determining trends in ELAchange at McCall Glacier, Alaska, USA, over the last 50 years, based on mapping of the cold–temperatetransition surface (CTS), marking the limit between cold and temperate ice of a polythermal glacier.Latent heat release from percolating meltwater and precipitation keeps the ice column temperate in theaccumulation area. A change from accumulation to ablation zone reduces this heat release, leadinglocally to glacier ice cooling. By mapping the CTS along the whole glacier length using radio-echosounding and employing a thermodynamic model, the timing of the cooling was determined, fromwhich past ELAs were constructed. These are in accord with mass-balance measurements carried out onMcCall Glacier since the 1950s. We show that with a warming climate, McCall Glacier tends to cool ina counter-intuitive way, info:eu-repo/semantics/published

The geothermal heat flux is one of the least well known parameters of subglacial Antarctica. Several techniques exist to obtain this essential information. However, since direct measurements are only limited to a few deep drillings to the bed, there is always a substantial amount of ice sheet and thermodynamical modeling involved. This can either be done based on a fully coupled thermomechanical ice sheet model, or a thermodynamical model coupled to present-day ice sheet geometry and environmental conditions. The latter technique was recently employed by Pattyn (2010) in an attempt to determine the likelihood of basal temperate conditions of the Antarctic ice sheet using a series of existing datasets on mass balance and geothermal heat flux. Here, we present an update of this estimate using new data on bedrock elevation and ice thickness (Bedmap2; Fretwell et al. 2012) and observed surface velocities obtained from interferometric analysis (Rignot et al. 2011). The latter were further constrained by a hybrid ice sheet/ice shelf model to correct for the interior ice flow (where error of observations are to high) and for correcting the ice flow across subglacial lakes. We coupled the model with a new lake inventory from Wright et al. (in review) to improve the contribution of the geothermal heat flux to the temperature. This revised calculation of the temperature allows us to improve our knowledge of basal melting.We determined different areas with a high likelihood to find million year-old ice, further constrained by low horizontal flow velocities and relative thick ice to ensure a straightforward climatic signal over such long period of time., info:eu-repo/semantics/nonPublished

Finding suitable potential sites for an undisturbed record of million-year old ice in Antarctica requires slow-moving ice (preferably an ice divide) and basal conditions that are not disturbed by large topographic variations. Furthermore, ice should be thick and cold basal conditions should prevail, since basal melting would destroy the bottom layers. However, thick ice (needed to resolve the signal at sufficient high resolution) increases basal temperatures, which is a conflicting condition for finding a suitable drill site. In addition, slow moving areas in the center of ice sheets are also low-accumulation areas, and low accumulation reduces potential cooling of the ice through vertical advection. While boundary conditions such as ice thickness and accumulation rates are relatively well constrained, the major uncertainty in determining basal thermal conditions resides in the geothermal heat flow (GHF) underneath the ice sheet. We explore uncertainties in existing GHF data sets and their effect on basal temperatures of the Antarctic Ice Sheet, and propose an updated method based on Pattyn (2010) to improve existing GHF data sets in agreement with known basal temperatures and their gradients to reduce this uncertainty. Both complementary methods lead to a better comprehension of basal temperature sensitivity and a characterization of potential ice coring sites within these uncertainties. The combination of both modeling approaches show that the most likely oldest ice sites are situated near the divide areas (close to existing deep drilling sites, but in areas of smaller ice thickness) and across the Gamburtsev Subglacial Mountains., info:eu-repo/semantics/published

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Antarctic subglacial conditions can be elucidated through several techniques. However, since direct measurements are only limited to a few deep drillings to the bed, there is always a substantial amount of ice sheet and thermodynamical modeling involved. This can either be done based on a fully coupled thermomechanical ice sheet model, or a thermodynamical model coupled to present-day ice sheet geometry and environmental conditions. The latter technique was recently employed by Pattyn (2010) in an attempt to determine the likelihood of basal temperate conditions of the Antarctic ice sheet using a series of existing datasets on mass balance and geothermal heat flux. Here, we made an update of this estimate using new data on bedrock elevation and ice thickness (ALBMAP; Le Brocq et Al. 2010) and observed surface velocities obtained from interferometric analysis (Rignot et Al. 2011). The latter were further constrained by a hybrid ice sheet/ice shelf model to correct for the interior ice flow (where error of observations are to high) and for correcting the ice flow across subglacial lakes. We coupled the model with a new lake inventory from Wright et Al. (in review) to improve the contribution of the geothermal heat flux to the temperature. This revised calculation of the temperature allows us to improve our knowledge of basal melting and its contribution to present-day sea-level rise.Le Brocq, A. Payne, A. Vieli, A. 2010, An improved Antarctic dataset for high resolution numerical ice sheet models (ALBMAP V1), Earth Syst. Sci. Data Discuss. 3, 195-230.Pattyn, F. 2010, Antarctic subglacial conditions inferred from a hybrid ice sheet/ice stream model, Earth Planet. Sci. Lett. 295, 451-461.Rignot, E. Mouginot, J. Scheuchl, B. 2011, Ice Flow of the Antarctic Ice Sheet, Science 333, 1427-1429.Wright, A. and Siegert, M. (in review), A fourth inventory of Antarctic subglacial lakes., info:eu-repo/semantics/nonPublished

Antarctic subglacial conditions can be elucidated through several techniques. However, since direct measurements are only limited to a few deep drillings to the bed, there is always a substantial amount of ice sheet and thermodynamical modeling involved. This can either be done based on a fully coupled thermomechanical ice sheet model, or a thermodynamical model coupled to present-day ice sheet geometry and environmental conditions. The latter technique was recently employed by Pattyn (2010) in an attempt to determine the likelihood of basal temperate conditions of the Antarctic ice sheet using a series of existing datasets on mass balance and geothermal heat flux. Here, we made an update of this estimate using new data on bedrock elevation and ice thickness (ALBMAP; Le Brocq et al. 2010) and observed surface velocities obtained from interferometric analysis (Rignot et al. 2011). The latter were further constrained by a hybrid ice sheet/ice shelf model to correct for the interior ice flow (where observations are lacking) and for correcting the ice flow across subglacial lakes. The new estimates are compared to the initial basal temperature calculation.Le Brocq, A. Payne, A. Vieli, A. 2010, An improved Antarctic dataset for high resolution numerical ice sheet models (ALBMAP V1), Earth Syst. Sci. Data Discuss. 3, 195-230.Pattyn, F. 2010, Antarctic subglacial conditions inferred from a hybrid ice sheet/ice stream model, Earth Planet. Sci. Lett. 295, 451-461.Rignot, E. Mouginot, J. Scheuchl, B. 2011, Ice Flow of the Antarctic Ice Sheet, Science 333, 1427-1429., info:eu-repo/semantics/nonPublished