text:
TC, 16, 1719–1739, 2022
The Cryosphere, 16, 1719–1739, 2022
https://doi.org/10.5194/tc-16-1719-2022
Research article | 06 May 2022
Polarimetric radar reveals the spatial distribution of ice fabric at domes and divides in East Antarctica
M. Reza Ershadi et al.
Inferring horizontal asymmetry of the bulk ice crystal fabric from phase-sensitive radar measurements
Ole Zeising, Tamara Annina Gerber, Olaf Eisen, M. Reza Ershadi, Nicolas Stoll, Ilka Weikusat, and Angelika Humbert
The Cryosphere Discuss., https://doi.org/10.5194/tc-2022-200,https://doi.org/10.5194/tc-2022-200, 2022
Revised manuscript accepted for TC
The flow of glaciers and ice streams is influenced by the crystal fabric orientation. Beside from sparse ice cores, these can be investigated by radar measurements. Here, we present an improved method which allows to infer the horizontal fabric asymmetry using polarimetric phase-sensitive radar data. A validation of the method on a deep ice core from the Greenland ice sheet shows near perfect agreement, which is a large improvement over previously used methods.
A parallel implementation of the confined-unconfined aquifer system model for subglacial hydrology: design, verification, and performance analysis (CUAS-MPI v0.1.0)
Yannic Fischler, Thomas Kleiner, Christian Bischof, Jeremie Schmiedel, Roiy Sayag, Raban Emunds, Lennart Frederik Oestreich, and Angelika Humbert
Preprint under review for GMD
Water underneath ice sheets affects the motion of glaciers. This study presents a newly developed code CUAS-MPI that simulates subglacial hydrology. It is designed for supercomputers and is hence a parallelized code. We measure the performance of this code for simulations of the entire Greenland ice sheet and find that the code works efficient. Moreover we validated the code to ensure the correctness of the solution. CUAS-MPI opens new possibilities for simulations of ice sheet hydrology.
An age scale for new climate records from Sherman Island, West Antarctica
Isobel Rowell, Helena Pryer, Carlos Martin, Dieter Tetzner, Emily Doyle, Robert Mulvaney, and Eric Wolff
Clim. Past Discuss., https://doi.org/10.5194/cp-2022-95,https://doi.org/10.5194/cp-2022-95, 2022
Preprint under review for CP
We present an age scale for a new type of ice core, from a vulnerable region in the West Antarctic which is lacking in longer term (greater than a few centuries) ice core records. The Sherman Island core extends to greater than 1000 years before present. We provide modelling evidence for the potential of a 10000-year long core. We show that this new type of ice core can be robustly dated and that climate records from this core will be a significant addition to existing regional climate records.
Antarctic ice sheet paleo-constraint database
Benoit S. Lecavalier, Lev Tarasov, Greg Balco, Perry Spector, Claus-Dieter Hillenbrand, Christo Buizert, Catherine Ritz, Marion Leduc-Leballeur, Robert Mulvaney, Pippa L. Whitehouse, Michael J. Bentley, and Jonathan Bamber
The Antarctic ice sheet evolution constraint database version 2 (AntICE2) consists of a large variety of observations that constrain the evolution of the Antarctic ice sheet over the last glacial cycle. This includes observations of past ice sheet extent, past ice thickness, past relative sea level, borehole temperature profiles, and present-day bedrock displacement rates. The database is intended to improve our understanding of past Antarctic changes and for ice sheet model calibrations.
Predicting the steady-state isochronal stratigraphy of ice shelves using observations and modeling
Vjeran Višnjević, Reinhard Drews, Clemens Schannwell, Inka Koch, Steven Franke, Daniela Jansen, and Olaf Eisen
The Cryosphere, 16, 4763–4777, https://doi.org/10.5194/tc-16-4763-2022,https://doi.org/10.5194/tc-16-4763-2022, 2022
We present a simple way to model the internal layers of an ice shelf and apply the method to the Roi Baudouin Ice Shelf in East Antarctica. Modeled results are compared to measurements obtained by radar. We distinguish between ice directly formed on the shelf and ice transported from the ice sheet, and we map the spatial changes in the volume of the locally accumulated ice. In this context, we discuss the sensitivity of the ice shelf to future changes in surface accumulation and basal melt.
Reviews and syntheses: A framework to observe, understand and project ecosystem response to environmental change in the East Antarctic Southern Ocean
Julian Gutt, Stefanie Arndt, David Keith Alan Barnes, Horst Bornemann, Thomas Brey, Olaf Eisen, Hauke Flores, Huw Griffiths, Christian Haas, Stefan Hain, Tore Hattermann, Christoph Held, Mario Hoppema, Enrique Isla, Markus Janout, Céline Le Bohec, Heike Link, Felix Christopher Mark, Sebastien Moreau, Scarlett Trimborn, Ilse van Opzeeland, Hans-Otto Pörtner, Fokje Schaafsma, Katharina Teschke, Sandra Tippenhauer, Anton Van de Putte, Mia Wege, Daniel Zitterbart, and Dieter Piepenburg
Biogeosciences, 19, 5313–5342, https://doi.org/10.5194/bg-19-5313-2022,https://doi.org/10.5194/bg-19-5313-2022, 2022
Long-term ecological observations are key to assess, understand and predict impacts of environmental change on biotas. We present a multidisciplinary framework for such largely lacking investigations in the East Antarctic Southern Ocean, combined with case studies, experimental and modelling work. As climate change is still minor here but is projected to start soon, the timely implementation of this framework provides the unique opportunity to document its ecological impacts from the very onset.
Antarctic Bedmap data: FAIR sharing of 60 years of ice bed, surface and thickness data
Alice C. Frémand, Peter Fretwell, Julien Bodart, Hamish D. Pritchard, Alan Aitken, Jonathan L. Bamber, Robin Bell, Cesido Bianchi, Robert G. Bingham, Donald D. Blankenship, Gino Casassa, Ginny Catania, Knut Christianson, Howard Conway, Hugh F. J. Corr, Xiangbin Cui, Daniel Damaske, Volkmar Damm, Reinhard Drews, Graeme Eagles, Olaf Eisen, Hannes Eisermann, Fausto Ferraccioli, Elena Field, René Forsberg, Steven Franke, Shuji Fujita, Yonggyu Gim, Vikram Goel, Siva Prasad Gogineni, Jamin Greenbaum, Benjamin Hills, Richard C. A. Hindmarsh, Per Holmlund, Nicholas Holschuh, John W. Holt, Angelika Humbert, Robert W. Jacobel, Daniela Jansen, Adrian Jenkins, Wilfried Jokat, Tom Jordan, Edward King, Jack Kohler, William Krabill, Kirsty Langley, Joohan Lee, German Leitchenkov, Carlton Leuschen, Bruce Luyendyk, Joseph MacGregor, Emma MacKie, Kenichi Matsuoka, Mathieu Morlinghem, Jeremie Mouginot, Frank O. Nitsche, Yoshifumi Nogi, Ole A. Nost, John Paden, Frank Pattyn, Sergey V. Popov, Mette Riger-Kusk, Eric Rignot, David M. Rippin, Andres Rivera, Jason Roberts, Neil Ross, Antonia Ruppel, Dustin M. Schroeder, Martin J. Siegert, Andrew M. Smith, Daniel Steinhage, Michael Studinger, Bo Sun, Ignazio Tabacco, Kirsty Tinto, Stefano Urbini, David Vaughan, Brian C. Welch, Douglas S. Wilson, Duncan A. Young, and Achille Zirizzotti
This paper presents the release of over 60 years of ice thickness, bed and surface elevation data acquired over Antarctica by the international community. These data are a crucial component of the Antarctic Bedmap initiative which aims to produce a new map and datasets of Antarctic ice thickness and bed topography for the international glaciology and geophysical community.
The ST22 chronology for the Skytrain Ice Rise ice core – part 2: an age model to the last interglacial and disturbed deep stratigraphy
Robert Mulvaney, Eric William Wolff, Mackenzie Grieman, Helene Hoffmann, Jack Humby, Christoph Nehrbass-Ahles, Rachael Rhodes, Isobel Rowell, Frédéric Parrenin, Loïc Schmidely, Hubertus Fischer, Thomas Stocker, Marcus Christl, Raimund Muscheler, Amaelle Landais, and Frédéric Prié
We present an age scale for a new ice core drilled at Skytrain Ice Rise, an ice rise facing the Ronne Ice Shelf in Antarctica. Various measurements in the ice and air phases are used to match the ice core to other Antarctic cores that have already been dated. The 651 m ice core includes ice that is confidently dated to the last interglacial, 126,000 years ago. Older ice is found deeper down, but there are flow disturbances in the deeper ice.
Direct measurement of warm Atlantic Intermediate Water close to the grounding line of Nioghalvfjerdsfjorden (79N) Glacier, North-east Greenland
Michael J. Bentley, James A. Smith, Stewart S. R. Jamieson, Margaret Lindeman, Brice R. Rea, Angelika Humbert, Timothy P. Lane, Christopher M. Darvill, Jeremy M. Lloyd, Fiamma Straneo, Veit Helm, and David H. Roberts
Preprint under review for TC
The North-East Greenland Ice Stream is a major outlet of the Greenland ice sheet. Some of its outlet glaciers and ice shelves have been breaking up and retreating, with inflows of warm ocean water identified as the likely reason. Here we report direct measurements of warm ocean water in an unusual lake that is connected to the ocean beneath the ice shelf in front of the 79N Glacier. This glacier has not yet shown much retreat but the presence of warm water suggests may cause retreat.
On the evolution of an ice shelf melt channel at the base of Filchner Ice Shelf, from observations and viscoelastic modeling
Angelika Humbert, Julia Christmann, Hugh F. J. Corr, Veit Helm, Lea-Sophie Höyns, Coen Hofstede, Ralf Müller, Niklas Neckel, Keith W. Nicholls, Timm Schultz, Daniel Steinhage, Michael Wolovick, and Ole Zeising
Ice shelves are normally flat structures that fringe the Antarctic continent. At some locations they have channels incised into their underside. On Filchner Ice Shelf, such a channel is more than 50 km long and up to 330 m high. We conducted field measurements of basal melt rates and found a maximum of 2 m yr−1. Simulations represent the geometry evolution of the channel reasonably well. There is no reason to assume that this type of melt channel is destabilizing ice shelves.
Hysteretic evolution of ice rises and ice rumples in response to variations in sea level
A. Clara J. Henry, Reinhard Drews, Clemens Schannwell, and Vjeran Višnjević
We used a 3D, idealised model to study features in coastal Antarctica called ice rises and ice rumples. These features regulate the rate of ice flow into the ocean. We show that when sea level is raised or lowered, the size of these features and the ice flow pattern can change. We find that the features depend on the ice history and do not necessarily fully recover after an equal increase and decrease in sea level. This shows that it is important to initialise models with accurate ice geometry.
Precursor of disintegration of Greenland's largest floating ice tongue
Angelika Humbert, Veit Helm, Niklas Neckel, Ole Zeising, Martin Rückamp, Shfaqat Abbas Khan, Erik Loebel, Dietmar Gross, Rabea Sondershaus, and Ralf Müller
The largest floating glacier mass in Greenland, the 79° N Glacier, is showing signs of an instability. We investigate how crack formation at the glaciers calving front has changed over the last decades by using satellite imagery and airborne data. The calving front is about to loose contact to stabilising ice islands. Simulations show that the glacier will accelerate as a result of this, leading to increase in ice discharge of more than 8 % if its calving front retreats by 46 %.
The new Kr-86 excess ice core proxy for synoptic activity: West Antarctic storminess possibly linked to ITCZ movement through the last deglaciation
Christo Buizert, Sarah Shackleton, Jeffrey P. Severinghaus, William H. G. Roberts, Alan Seltzer, Bernhard Bereiter, Kenji Kawamura, Daniel Baggenstos, Anaïs J. Orsi, Ikumi Oyabu, Benjamin Birner, Jacob D. Morgan, Edward J. Brook, David M. Etheridge, David Thornton, Nancy Bertler, Rebecca L. Pyne, Robert Mulvaney, Ellen Mosley-Thompson, Peter D. Neff, and Vasilii V. Petrenko
Revised manuscript accepted for CP
It is unclear how different components of the global atmospheric circulation, such as the El Niño effect, respond to large-scale climate change. We present a new ice core gas proxy, called Krypton-86 excess, that reflects past storminess in Antarctica. We present data from 11 ice cores that suggest the new proxy works. We present a reconstruction of changes in West Antarctic storminess over the last 24,000 years, and suggest these are caused by north-south movement of the tropical rain belt.
Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica
Franz Lutz, David J. Prior, Holly Still, M. Hamish Bowman, Bia Boucinhas, Lisa Craw, Sheng Fan, Daeyeong Kim, Robert Mulvaney, Rilee E. Thomas, and Christina L. Hulbe
Ice crystal alignment in the sheared margins of fast-flowing polar ice is important as it may control the ice sheet flow rate, from land to the ocean. Sampling shear margins is difficult because of logistical and safety considerations. We show that crystal alignments in a glacier shear margin in Antarctica can be measured using sound waves. Results from a seismic experiment on the 50 m scale and from ultrasonic experiments on the decimetre scale match ice crystal measurements from an ice core.
The ST22 chronology for the Skytrain Ice Rise ice core – Part 1: A stratigraphic chronology of the last 2000 years
Helene M. Hoffmann, Mackenzie M. Grieman, Amy C. F. King, Jenna A. Epifanio, Kaden Martin, Diana Vladimirova, Helena V. Pryer, Emily Doyle, Axel Schmidt, Jack D. Humby, Isobel F. Rowell, Christoph Nehrbass-Ahles, Elizabeth R. Thomas, Robert Mulvaney, and Eric W. Wolff
Clim. Past, 18, 1831–1847, https://doi.org/10.5194/cp-18-1831-2022,https://doi.org/10.5194/cp-18-1831-2022, 2022
The WACSWAIN project (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) investigates the fate of the West Antarctic Ice Sheet during the last warm period on Earth (115 000–130 000 years before present). Within this framework an ice core was recently drilled at Skytrain Ice Rise. In this study we present a stratigraphic chronology of that ice core based on absolute age markers and annual layer counting for the last 2000 years.
British Antarctic Survey's aerogeophysical data: releasing 25 years of airborne gravity, magnetic, and radar datasets over Antarctica
Alice C. Frémand, Julien A. Bodart, Tom A. Jordan, Fausto Ferraccioli, Carl Robinson, Hugh F. J. Corr, Helen J. Peat, Robert G. Bingham, and David G. Vaughan
This paper presents the release of large swaths of airborne geophysical data (including gravity, magnetics, and radar) acquired between 1994 and 2020 over Antarctica by the British Antarctic Survey. These include a total of 64 datasets from 24 different surveys, amounting to >30 % of coverage over the Antarctic Ice Sheet. This paper discusses how these data were acquired and processed and presents the methods used to standardize and publish the data in an interactive and reproducible manner.
Geomorphology and shallow sub-sea-floor structures underneath the Ekström Ice Shelf, Antarctica
Astrid Oetting, Emma C. Smith, Jan Erik Arndt, Boris Dorschel, Reinhard Drews, Todd A. Ehlers, Christoph Gaedicke, Coen Hofstede, Johann P. Klages, Gerhard Kuhn, Astrid Lambrecht, Andreas Läufer, Christoph Mayer, Ralf Tiedemann, Frank Wilhelms, and Olaf Eisen
This study combines a variety of geophysical measurements in front of and beneath the Ekström Ice Shelf in order to identify and interpret geomorphological evidences of past ice sheet flow, extent and retreat. The maximal extent of grounded ice in this region was 11 km away from the continental shelf break. The thickness of palaeo-ice on the calving front around the LGM was estimated to be at least 305 to 320 m. We provide essential boundary conditions for palaeo-ice-sheet models.
A scalability study of the Ice-sheet and Sea-level System Model (ISSM, version 4.18)
Yannic Fischler, Martin Rückamp, Christian Bischof, Vadym Aizinger, Mathieu Morlighem, and Angelika Humbert
Ice sheet models are used to simulate the changes of ice sheets in future but are currently often run in coarse resolution and/or with neglecting important physics to make them affordable in terms of computational costs. We conducted a study simulating the Greenland Ice Sheet in high resolution and adequate physics to test where the ISSM ice sheet code is using most time and what could be done to improve its performance for future computer architectures that allow massive parallel computing.
Comparison of ice dynamics using full-Stokes and Blatter–Pattyn approximation: application to the Northeast Greenland Ice Stream
Martin Rückamp, Thomas Kleiner, and Angelika Humbert
We present a comparative modelling study between the full-Stokes (FS) and Blatter–Pattyn (BP) approximation applied to the Northeast Greenland Ice Stream. Both stress regimes are implemented in one single ice sheet code to eliminate numerical issues. The simulations unveil minor differences in the upper ice stream but become considerable at the grounding line of the 79° North Glacier. Model differences are stronger for a power-law friction than a linear friction law.
Basal melt of the southern Filchner Ice Shelf, Antarctica
Ole Zeising, Daniel Steinhage, Keith W. Nicholls, Hugh F. J. Corr, Craig L. Stewart, and Angelika Humbert
Remote-sensing-derived basal melt rates of ice shelves are of great importance due to their capability to cover larger areas. We performed in situ measurements with a phase-sensitive radar on the southern Filchner Ice Shelf, showing moderate melt rates and low small-scale spatial variability. The comparison with remote-sensing-based melt rates revealed large differences caused by the estimation of vertical strain rates from remote sensing velocity fields that modern fields can overcome.
High-resolution aerosol concentration data from the Greenland NorthGRIP and NEEM deep ice cores
Tobias Erhardt, Matthias Bigler, Urs Federer, Gideon Gfeller, Daiana Leuenberger, Olivia Stowasser, Regine Röthlisberger, Simon Schüpbach, Urs Ruth, Birthe Twarloh, Anna Wegner, Kumiko Goto-Azuma, Takayuki Kuramoto, Helle A. Kjær, Paul T. Vallelonga, Marie-Louise Siggaard-Andersen, Margareta E. Hansson, Ailsa K. Benton, Louise G. Fleet, Rob Mulvaney, Elizabeth R. Thomas, Nerilie Abram, Thomas F. Stocker, and Hubertus Fischer
The datasets presented alongside this manuscript contain high-resolution concentration measurements of chemical impurities in deep ice cores, NGRIP and NEEM, from the Greenland ice sheet. The impurities originate from the deposition of aerosols to the surface of the ice sheet and are influenced by source, transport and deposition processes. Together, these records contain detailed, multi-parameter records of past climate variability over the last glacial period.
Airborne ultra-wideband radar sounding over the shear margins and along flow lines at the onset region of the Northeast Greenland Ice Stream
Steven Franke, Daniela Jansen, Tobias Binder, John D. Paden, Nils Dörr, Tamara A. Gerber, Heinrich Miller, Dorthe Dahl-Jensen, Veit Helm, Daniel Steinhage, Ilka Weikusat, Frank Wilhelms, and Olaf Eisen
The Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland. In order to better understand the past and future dynamics of the NEGIS, we present a high-resolution airborne radar data set (EGRIP-NOR-2018) for the onset region of the NEGIS. The survey area is centered at the location of the drill site of the East Greenland Ice-Core Project (EastGRIP), and radar profiles cover both shear margins and are aligned parallel to several flow lines.
On the contribution of grain boundary sliding type creep to firn densification – an assessment using an optimization approach
Timm Schultz, Ralf Müller, Dietmar Gross, and Angelika Humbert
The Cryosphere, 16, 143–158, https://doi.org/10.5194/tc-16-143-2022,https://doi.org/10.5194/tc-16-143-2022, 2022
Firn is the interstage product between snow and ice. Simulations describing the process of firn densification are used in the context of estimating mass changes of the ice sheets and past climate reconstructions. The first stage of firn densification takes place in the upper few meters of the firn column. We investigate how well a material law describing the process of grain boundary sliding works for the numerical simulation of firn densification in this stage.
A detailed radiostratigraphic data set for the central East Antarctic Plateau spanning from the Holocene to the mid-Pleistocene
Marie G. P. Cavitte, Duncan A. Young, Robert Mulvaney, Catherine Ritz, Jamin S. Greenbaum, Gregory Ng, Scott D. Kempf, Enrica Quartini, Gail R. Muldoon, John Paden, Massimo Frezzotti, Jason L. Roberts, Carly R. Tozer, Dustin M. Schroeder, and Donald D. Blankenship
We present a data set consisting of ice-penetrating-radar internal stratigraphy: 26 internal reflecting horizons that cover the greater Dome C area, East Antarctica, the most extensive IRH data set to date in the region. This data set uses radar surveys collected over the span of 10 years, starting with an airborne international collaboration in 2008 to explore the region, up to the detailed ground-based surveys in support of the European Beyond EPICA – Oldest Ice (BE-OI) project.
Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide ice core site
Tun Jan Young, Carlos Martín, Poul Christoffersen, Dustin M. Schroeder, Slawek M. Tulaczyk, and Eliza J. Dawson
If the molecules that make up ice are oriented in specific ways, the ice becomes softer and enhances flow. We use radar to measure the orientation of ice molecules in the top 1400 m of the Western Antarctic Ice Sheet Divide. Our results match those from an ice core extracted 10 years ago and conclude that the ice flow has not changed direction for the last 6700 years. Our methods are straightforward and accurate and can be applied in places across ice sheets unsuitable for ice coring.
Investigating the internal structure of the Antarctic ice sheet: the utility of isochrones for spatiotemporal ice-sheet model calibration
Johannes Sutter, Hubertus Fischer, and Olaf Eisen
Projections of global sea-level changes in a warming world require ice-sheet models. We expand the calibration of these models by making use of the internal architecture of the Antarctic ice sheet, which is formed by its evolution over many millennia. We propose that using our novel approach to constrain ice sheet models, we will be able to both sharpen our understanding of past and future sea-level changes and identify weaknesses in the parameterisation of current continental-scale models.
Indication of high basal melting at the EastGRIP drill site on the Northeast Greenland Ice Stream
Ole Zeising and Angelika Humbert
Greenland's largest ice stream – the Northeast Greenland Ice Stream (NEGIS) – extends far into the interior of the ice sheet. Basal meltwater acts as a lubricant for glaciers and sustains sliding. Hence, observations of basal melt rates are of high interest. We performed two time series of precise ground-based radar measurements in the upstream region of NEGIS and found high melt rates of 0.19 ± 0.04 m per year.
Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12, and CFC-113 isotopologues
Max Thomas, Johannes C. Laube, Jan Kaiser, Samuel Allin, Patricia Martinerie, Robert Mulvaney, Anna Ridley, Thomas Röckmann, William T. Sturges, and Emmanuel Witrant
CFC gases are destroying the Earth's life-protecting ozone layer. We improve understanding of CFC destruction by measuring the isotopic fingerprint of the carbon in the three most abundant CFCs. These are the first such measurements in the main region where CFCs are destroyed – the stratosphere. We reconstruct the atmospheric isotope histories of these CFCs back to the 1950s by measuring air extracted from deep snow and using a model. The model and the measurements are generally consistent.
Brief communication: New radar constraints support presence of ice older than 1.5 Myr at Little Dome C
David A. Lilien, Daniel Steinhage, Drew Taylor, Frédéric Parrenin, Catherine Ritz, Robert Mulvaney, Carlos Martín, Jie-Bang Yan, Charles O'Neill, Massimo Frezzotti, Heinrich Miller, Prasad Gogineni, Dorthe Dahl-Jensen, and Olaf Eisen
We collected radar data between EDC, an ice core spanning ~800 000 years, and BELDC, the site chosen for a new oldest ice core at nearby Little Dome C. These data allow us to identify 50 % older internal horizons than previously traced in the area. We fit a model to the ages of those horizons at BELDC to determine the age of deep ice there. We find that there is likely to be 1.5 Myr old ice ~265 m above the bed, with sufficient resolution to preserve desired climatic information.
Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics
Coen Hofstede, Sebastian Beyer, Hugh Corr, Olaf Eisen, Tore Hattermann, Veit Helm, Niklas Neckel, Emma C. Smith, Daniel Steinhage, Ole Zeising, and Angelika Humbert
Support Force Glacier rapidly flows into Filcher Ice Shelf of Antarctica. As we know little about this glacier and its subglacial drainage, we used seismic energy to map the transition area from grounded to floating ice where a drainage channel enters the ocean cavity. Soft sediments close to the grounding line are probably transported by this drainage channel. The constant ice thickness over the steeply dipping seabed of the ocean cavity suggests a stable transition and little basal melting.
The regional-scale surface mass balance of Pine Island Glacier, West Antarctica, over the period 2005–2014, derived from airborne radar soundings and neutron probe measurements
Stefan Kowalewski, Veit Helm, Elizabeth Mary Morris, and Olaf Eisen
This study presents estimates of total mass input for the Pine Island Glacier (PIG) over the period 2005–2014 from airborne radar measurements. Our analysis reveals a total mass input similar to an earlier estimate for the period 1985–2009 and same area. This suggests a stationary total mass input contrary to the accelerated mass loss of PIG over the past decades. However, we also find that its uncertainty is highly sensitive to the geostatistical assumptions required for its calculation.
Comparison of regolith physical and chemical characteristics with geophysical data along a climate and ecological gradient, Chilean Coastal Cordillera (26 to 38° S)
Mirjam Schaller, Igor Dal Bo, Todd A. Ehlers, Anja Klotzsche, Reinhard Drews, Juan Pablo Fuentes Espoz, and Jan van der Kruk
SOIL, 6, 629–647, https://doi.org/10.5194/soil-6-629-2020,https://doi.org/10.5194/soil-6-629-2020, 2020
In this study geophysical observations from ground-penetrating radar with pedolith physical and geochemical properties from pedons excavated in four study areas of the climate and ecological gradient in the Chilean Coastal Cordillera are combined. Findings suggest that profiles with ground-penetrating radar along hillslopes can be used to infer lateral thickness variations in pedolith horizons and to some degree physical and chemical variations with depth.
Quantifying the effect of ocean bed properties on ice sheet geometry over 40 000 years with a full-Stokes model
Clemens Schannwell, Reinhard Drews, Todd A. Ehlers, Olaf Eisen, Christoph Mayer, Mika Malinen, Emma C. Smith, and Hannes Eisermann
To reduce uncertainties associated with sea level rise projections, an accurate representation of ice flow is paramount. Most ice sheet models rely on simplified versions of the underlying ice flow equations. Due to the high computational costs, ice sheet models based on the complete ice flow equations have been restricted to < 1000 years. Here, we present a new model setup that extends the applicability of such models by an order of magnitude, permitting simulations of 40 000 years.
Representative surface snow density on the East Antarctic Plateau
Alexander H. Weinhart, Johannes Freitag, Maria Hörhold, Sepp Kipfstuhl, and Olaf Eisen
From 1 m snow profiles along a traverse on the East Antarctic Plateau, we calculated a representative surface snow density of 355 kg m−3 for this region with an error less than 1.5 %. This density is 10 % higher and density fluctuations seem to happen on smaller scales than climate model outputs suggest. Our study can help improve the parameterization of surface snow density in climate models to reduce the error in future sea level predictions.
Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the Alfred Wegener Institute (AWI) contribution to ISMIP6 Greenland using the Ice-sheet and Sea-level System Model (ISSM)
Martin Rückamp, Heiko Goelzer, and Angelika Humbert
Estimates of future sea-level contribution from the Greenland ice sheet have a large uncertainty based on different origins. We conduct numerical experiments to test the sensitivity of Greenland ice sheet projections to spatial resolution. Simulations with a higher resolution unveil up to 5 % more sea-level rise compared to coarser resolutions. The sensitivity depends on the magnitude of outlet glacier retreat. When no retreat is enforced, the sensitivity exhibits an inverse behaviour.
Extended enthalpy formulations in the Ice-sheet and Sea-level System Model (ISSM) version 4.17: discontinuous conductivity and anisotropic streamline upwind Petrov–Galerkin (SUPG) method
Martin Rückamp, Angelika Humbert, Thomas Kleiner, Mathieu Morlighem, and Helene Seroussi
We present enthalpy formulations within the Ice-Sheet and Sea-Level System model that show better performance than earlier implementations. A first experiment indicates that the treatment of discontinuous conductivities of the solid–fluid system with a geometric mean produce accurate results when applied to coarse vertical resolutions. In a second experiment, we propose a novel stabilization formulation that avoids the problem of thin elements. This method provides accurate and stable results.
The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6
Heiko Goelzer, Sophie Nowicki, Anthony Payne, Eric Larour, Helene Seroussi, William H. Lipscomb, Jonathan Gregory, Ayako Abe-Ouchi, Andrew Shepherd, Erika Simon, Cécile Agosta, Patrick Alexander, Andy Aschwanden, Alice Barthel, Reinhard Calov, Christopher Chambers, Youngmin Choi, Joshua Cuzzone, Christophe Dumas, Tamsin Edwards, Denis Felikson, Xavier Fettweis, Nicholas R. Golledge, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Sebastien Le clec'h, Victoria Lee, Gunter Leguy, Chris Little, Daniel P. Lowry, Mathieu Morlighem, Isabel Nias, Aurelien Quiquet, Martin Rückamp, Nicole-Jeanne Schlegel, Donald A. Slater, Robin S. Smith, Fiamma Straneo, Lev Tarasov, Roderik van de Wal, and Michiel van den Broeke
In this paper we use a large ensemble of Greenland ice sheet models forced by six different global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The results for two different greenhouse gas concentration scenarios indicate that the Greenland ice sheet will continue to lose mass until 2100, with contributions to sea-level rise of 90 ± 50 mm and 32 ± 17 mm for the high (RCP8.5) and low (RCP2.6) scenario, respectively.
ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century
Hélène Seroussi, Sophie Nowicki, Antony J. Payne, Heiko Goelzer, William H. Lipscomb, Ayako Abe-Ouchi, Cécile Agosta, Torsten Albrecht, Xylar Asay-Davis, Alice Barthel, Reinhard Calov, Richard Cullather, Christophe Dumas, Benjamin K. Galton-Fenzi, Rupert Gladstone, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Nicolas C. Jourdain, Thomas Kleiner, Eric Larour, Gunter R. Leguy, Daniel P. Lowry, Chistopher M. Little, Mathieu Morlighem, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aurélien Quiquet, Ronja Reese, Nicole-Jeanne Schlegel, Andrew Shepherd, Erika Simon, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Luke D. Trusel, Jonas Van Breedam, Roderik S. W. van de Wal, Ricarda Winkelmann, Chen Zhao, Tong Zhang, and Thomas Zwinger
The Antarctic ice sheet has been losing mass over at least the past 3 decades in response to changes in atmospheric and oceanic conditions. This study presents an ensemble of model simulations of the Antarctic evolution over the 2015–2100 period based on various ice sheet models, climate forcings and emission scenarios. Results suggest that the West Antarctic ice sheet will continue losing a large amount of ice, while the East Antarctic ice sheet could experience increased snow accumulation.
Bipolar volcanic synchronization of abrupt climate change in Greenland and Antarctic ice cores during the last glacial period
Anders Svensson, Dorthe Dahl-Jensen, Jørgen Peder Steffensen, Thomas Blunier, Sune O. Rasmussen, Bo M. Vinther, Paul Vallelonga, Emilie Capron, Vasileios Gkinis, Eliza Cook, Helle Astrid Kjær, Raimund Muscheler, Sepp Kipfstuhl, Frank Wilhelms, Thomas F. Stocker, Hubertus Fischer, Florian Adolphi, Tobias Erhardt, Michael Sigl, Amaelle Landais, Frédéric Parrenin, Christo Buizert, Joseph R. McConnell, Mirko Severi, Robert Mulvaney, and Matthias Bigler
We identify signatures of large bipolar volcanic eruptions in Greenland and Antarctic ice cores during the last glacial period, which allows for a precise temporal alignment of the ice cores. Thereby the exact timing of unexplained, abrupt climatic changes occurring during the last glacial period can be determined in a global context. The study thus provides a step towards a full understanding of elements of the climate system that may also play an important role in the future.
Overview: Integrative and Comprehensive Understanding on Polar Environments (iCUPE) – concept and initial results
Tuukka Petäjä, Ella-Maria Duplissy, Ksenia Tabakova, Julia Schmale, Barbara Altstädter, Gerard Ancellet, Mikhail Arshinov, Yurii Balin, Urs Baltensperger, Jens Bange, Alison Beamish, Boris Belan, Antoine Berchet, Rossana Bossi, Warren R. L. Cairns, Ralf Ebinghaus, Imad El Haddad, Beatriz Ferreira-Araujo, Anna Franck, Lin Huang, Antti Hyvärinen, Angelika Humbert, Athina-Cerise Kalogridis, Pavel Konstantinov, Astrid Lampert, Matthew MacLeod, Olivier Magand, Alexander Mahura, Louis Marelle, Vladimir Masloboev, Dmitri Moisseev, Vaios Moschos, Niklas Neckel, Tatsuo Onishi, Stefan Osterwalder, Aino Ovaska, Pauli Paasonen, Mikhail Panchenko, Fidel Pankratov, Jakob B. Pernov, Andreas Platis, Olga Popovicheva, Jean-Christophe Raut, Aurélie Riandet, Torsten Sachs, Rosamaria Salvatori, Roberto Salzano, Ludwig Schröder, Martin Schön, Vladimir Shevchenko, Henrik Skov, Jeroen E. Sonke, Andrea Spolaor, Vasileios K. Stathopoulos, Mikko Strahlendorff, Jennie L. Thomas, Vito Vitale, Sterios Vratolis, Carlo Barbante, Sabine Chabrillat, Aurélien Dommergue, Konstantinos Eleftheriadis, Jyri Heilimo, Kathy S. Law, Andreas Massling, Steffen M. Noe, Jean-Daniel Paris, André S. H. Prévôt, Ilona Riipinen, Birgit Wehner, Zhiyong Xie, and Hanna K. Lappalainen
The role of polar regions is increasing in terms of megatrends such as globalization, new transport routes, demography, and the use of natural resources with consequent effects on regional and transported pollutant concentrations. Here we summarize initial results from our integrative project exploring the Arctic environment and pollution to deliver data products, metrics, and indicators for stakeholders.
Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)
Stephen L. Cornford, Helene Seroussi, Xylar S. Asay-Davis, G. Hilmar Gudmundsson, Rob Arthern, Chris Borstad, Julia Christmann, Thiago Dias dos Santos, Johannes Feldmann, Daniel Goldberg, Matthew J. Hoffman, Angelika Humbert, Thomas Kleiner, Gunter Leguy, William H. Lipscomb, Nacho Merino, Gaël Durand, Mathieu Morlighem, David Pollard, Martin Rückamp, C. Rosie Williams, and Hongju Yu
We present the results of the third Marine Ice Sheet Intercomparison Project (MISMIP+). MISMIP+ is one in a series of exercises that test numerical models of ice sheet flow in simple situations. This particular exercise concentrates on the response of ice sheet models to the thinning of their floating ice shelves, which is of interest because numerical models are currently used to model the response to contemporary and near-future thinning in Antarctic ice shelves.
The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) high-priority candidate mission
Michael Kern, Robert Cullen, Bruno Berruti, Jerome Bouffard, Tania Casal, Mark R. Drinkwater, Antonio Gabriele, Arnaud Lecuyot, Michael Ludwig, Rolv Midthassel, Ignacio Navas Traver, Tommaso Parrinello, Gerhard Ressler, Erik Andersson, Cristina Martin-Puig, Ole Andersen, Annett Bartsch, Sinead Farrell, Sara Fleury, Simon Gascoin, Amandine Guillot, Angelika Humbert, Eero Rinne, Andrew Shepherd, Michiel R. van den Broeke, and John Yackel
The Copernicus Polar Ice and Snow Topography Altimeter will provide high-resolution sea ice thickness and land ice elevation measurements and the capability to determine the properties of snow cover on ice to serve operational products and services of direct relevance to the polar regions. This paper describes the mission objectives, identifies the key contributions the CRISTAL mission will make, and presents a concept – as far as it is already defined – for the mission payload.
Large-scale englacial folding and deep-ice stratigraphy within the West Antarctic Ice Sheet
Neil Ross, Hugh Corr, and Martin Siegert
Using airborne ice-penetrating radar we investigated the physical properties and structure of the West Antarctic Ice Sheet. Ice deep beneath the Institute Ice Stream has prominent layers with physical properties distinct from those around them and which are heavily folded like geological layers. In turn, these folds influence the present-day flow of the ice sheet, with implications for how computer models are used to simulate ice sheet flow and behaviour in a warming world.
Description and validation of the ice-sheet model Yelmo (version 1.0)
Alexander Robinson, Jorge Alvarez-Solas, Marisa Montoya, Heiko Goelzer, Ralf Greve, and Catherine Ritz
Here we describe Yelmo v1.0, an intuitive and state-of-the-art hybrid ice sheet model. The model design and physics are described, and benchmark simulations are provided to validate its performance. Yelmo is a versatile ice sheet model that can be applied to a wide variety of problems.
Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
Anders Levermann, Ricarda Winkelmann, Torsten Albrecht, Heiko Goelzer, Nicholas R. Golledge, Ralf Greve, Philippe Huybrechts, Jim Jordan, Gunter Leguy, Daniel Martin, Mathieu Morlighem, Frank Pattyn, David Pollard, Aurelien Quiquet, Christian Rodehacke, Helene Seroussi, Johannes Sutter, Tong Zhang, Jonas Van Breedam, Reinhard Calov, Robert DeConto, Christophe Dumas, Julius Garbe, G. Hilmar Gudmundsson, Matthew J. Hoffman, Angelika Humbert, Thomas Kleiner, William H. Lipscomb, Malte Meinshausen, Esmond Ng, Sophie M. J. Nowicki, Mauro Perego, Stephen F. Price, Fuyuki Saito, Nicole-Jeanne Schlegel, Sainan Sun, and Roderik S. W. van de Wal
Earth Syst. Dynam., 11, 35–76, https://doi.org/10.5194/esd-11-35-2020,https://doi.org/10.5194/esd-11-35-2020, 2020
We provide an estimate of the future sea level contribution of Antarctica from basal ice shelf melting up to the year 2100. The full uncertainty range in the warming-related forcing of basal melt is estimated and applied to 16 state-of-the-art ice sheet models using a linear response theory approach. The sea level contribution we obtain is very likely below 61 cm under unmitigated climate change until 2100 (RCP8.5) and very likely below 40 cm if the Paris Climate Agreement is kept.
Relating regional and point measurements of accumulation in southwest Greenland
Achim Heilig, Olaf Eisen, Martin Schneebeli, Michael MacFerrin, C. Max Stevens, Baptiste Vandecrux, and Konrad Steffen
We investigate the spatial representativeness of point observations of snow accumulation in SW Greenland. Such analyses have rarely been conducted but are necessary to link regional-scale observations from, e.g., remote-sensing data to firn cores and snow pits. The presented data reveal a low regional variability in density but snow depth can vary significantly. It is necessary to combine pits with spatial snow depth data to increase the regional representativeness of accumulation observations.
Multi-tracer study of gas trapping in an East Antarctic ice core
Kévin Fourteau, Patricia Martinerie, Xavier Faïn, Christoph F. Schaller, Rebecca J. Tuckwell, Henning Löwe, Laurent Arnaud, Olivier Magand, Elizabeth R. Thomas, Johannes Freitag, Robert Mulvaney, Martin Schneebeli, and Vladimir Ya. Lipenkov
Understanding gas trapping in polar ice is essential to study the relationship between greenhouse gases and past climates. New data of bubble closure, used in a simple gas-trapping model, show inconsistency with the final air content in ice. This suggests gas trapping is not fully understood. We also use a combination of high-resolution measurements to investigate the effect of polar snow stratification on gas trapping and find that all strata have similar pores, but that some close in advance.
Kinematic response of ice-rise divides to changes in ocean and atmosphere forcing
Clemens Schannwell, Reinhard Drews, Todd A. Ehlers, Olaf Eisen, Christoph Mayer, and Fabien Gillet-Chaulet
Ice rises are important ice-sheet features that archive the ice sheet's history in their internal structure. Here we use a 3-D numerical ice-sheet model to simulate mechanisms that lead to changes in the geometry of the internal structure. We find that changes in snowfall result in much larger and faster changes than similar changes in ice-shelf geometry. This result is integral to fully unlocking the potential of ice rises as ice-dynamic archives and potential ice-core drilling sites.
Modelling the Antarctic Ice Sheet across the mid-Pleistocene transition – implications for Oldest Ice
Johannes Sutter, Hubertus Fischer, Klaus Grosfeld, Nanna B. Karlsson, Thomas Kleiner, Brice Van Liefferinge, and Olaf Eisen
The Antarctic Ice Sheet may have played an important role in moderating the transition between warm and cold climate epochs over the last million years. We find that the Antarctic Ice Sheet grew considerably about 0.9 Myr ago, a time when ice-age–warm-age cycles changed from a 40 000 to a 100 000 year periodicity. Our findings also suggest that ice as old as 1.5 Myr still exists at the bottom of the East Antarctic Ice Sheet despite the major climate reorganisations in the past.
Age stratigraphy in the East Antarctic Ice Sheet inferred from radio-echo sounding horizons
Anna Winter, Daniel Steinhage, Timothy T. Creyts, Thomas Kleiner, and Olaf Eisen
A rapidly converging initialisation method to simulate the present-day Greenland ice sheet using the GRISLI ice sheet model (version 1.3)
Sébastien Le clec'h, Aurélien Quiquet, Sylvie Charbit, Christophe Dumas, Masa Kageyama, and Catherine Ritz
To provide reliable projections of the ice-sheet contribution to future sea-level rise, ice sheet models must be able to simulate the observed ice sheet present-day state. Using a low computational iterative minimisation procedure, based on the adjustment of the basal drag coefficient, we rapidly minimise the errors between the simulated and the observed Greenland ice thickness and ice velocity, and we succeed in stabilising the simulated Greenland ice sheet state under present-day conditions.
initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6
Hélène Seroussi, Sophie Nowicki, Erika Simon, Ayako Abe-Ouchi, Torsten Albrecht, Julien Brondex, Stephen Cornford, Christophe Dumas, Fabien Gillet-Chaulet, Heiko Goelzer, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Thomas Kleiner, Eric Larour, Gunter Leguy, William H. Lipscomb, Daniel Lowry, Matthias Mengel, Mathieu Morlighem, Frank Pattyn, Anthony J. Payne, David Pollard, Stephen F. Price, Aurélien Quiquet, Thomas J. Reerink, Ronja Reese, Christian B. Rodehacke, Nicole-Jeanne Schlegel, Andrew Shepherd, Sainan Sun, Johannes Sutter, Jonas Van Breedam, Roderik S. W. van de Wal, Ricarda Winkelmann, and Tong Zhang
We compare a wide range of Antarctic ice sheet simulations with varying initialization techniques and model parameters to understand the role they play on the projected evolution of this ice sheet under simple scenarios. Results are improved compared to previous assessments and show that continued improvements in the representation of the floating ice around Antarctica are critical to reduce the uncertainty in the future ice sheet contribution to sea level rise.
10,000 years of melt history of the 2015 Renland ice core, EastGreenland
Tetsuro Taranczewski, Johannes Freitag, Olaf Eisen, Bo Vinther, Sonja Wahl, and Sepp Kipfstuhl
Preprint withdrawn
We used melt layers detected in ice cores from the Renland ice cap in East Greenland to find evidence of past climate trends in this region. Our record provides such information for the past 10,000 years. We developed an attempt to increase the reliability of such a record by correcting deformation-induced biases. It proves that such simple to obtain melt records can be used to gather information about paleoclimate especially for regions where climate records are sparse.
Assessment of the Greenland ice sheet–atmosphere feedbacks for the next century with a regional atmospheric model coupled to an ice sheet model
Sébastien Le clec'h, Sylvie Charbit, Aurélien Quiquet, Xavier Fettweis, Christophe Dumas, Masa Kageyama, Coraline Wyard, and Catherine Ritz
Quantifying the future contribution of the Greenland ice sheet (GrIS) to sea-level rise in response to atmospheric changes is important but remains challenging. For the first time a full representation of the feedbacks between a GrIS model and a regional atmospheric model was implemented. The authors highlight the fundamental need for representing the GrIS topography change feedbacks with respect to the atmospheric component face to the strong impact on the projected sea-level rise.
A confined–unconfined aquifer model for subglacial hydrology and its application to the Northeast Greenland Ice Stream
Sebastian Beyer, Thomas Kleiner, Vadym Aizinger, Martin Rückamp, and Angelika Humbert
The evolution of subglacial channels below ice sheets is very important for the dynamics of glaciers as the water acts as a lubricant. We present a new numerical model (CUAS) that generalizes existing approaches by accounting for two different flow situations within a single porous medium layer: (1) a confined aquifer if sufficient water supply is available and (2) an unconfined aquifer, otherwise. The model is applied to artificial scenarios as well as to the Northeast Greenland Ice Stream.
The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet
Aurélien Quiquet, Christophe Dumas, Catherine Ritz, Vincent Peyaud, and Didier M. Roche
This paper presents the GRISLI (Grenoble ice sheet and land ice) model in its newest revision. We present the recent model improvements from its original version (Ritz et al., 2001), together with a discussion of the model performance in reproducing the present-day Antarctic ice sheet geometry and the grounding line advances and retreats during the last 400 000 years. We show that GRISLI is a computationally cheap model, able to reproduce the large-scale behaviour of ice sheets.
The effect of overshooting 1.5 °C global warming on the mass loss of the Greenland ice sheet
Martin Rückamp, Ulrike Falk, Katja Frieler, Stefan Lange, and Angelika Humbert
Earth Syst. Dynam., 9, 1169–1189, https://doi.org/10.5194/esd-9-1169-2018,https://doi.org/10.5194/esd-9-1169-2018, 2018
Sea-level rise associated with changing climate is expected to pose a major challenge for societies. Based on the efforts of COP21 to limit global warming to 2.0 °C by the end of the 21st century (Paris Agreement), we simulate the future contribution of the Greenland ice sheet (GrIS) to sea-level change. The projected sea-level rise ranges between 21–38 mm by 2100 and 36–85 mm by 2300. Our results indicate that uncertainties in the projections stem from the underlying climate data.
Simulation of the future sea level contribution of Greenland with a new glacial system model
Reinhard Calov, Sebastian Beyer, Ralf Greve, Johanna Beckmann, Matteo Willeit, Thomas Kleiner, Martin Rückamp, Angelika Humbert, and Andrey Ganopolski
We present RCP 4.5 and 8.5 projections for the Greenland glacial system with the new glacial system model IGLOO 1.0, which incorporates the ice sheet model SICOPOLIS 3.3, a model of basal hydrology and a parameterization of submarine melt of outlet glaciers. Surface temperature and mass balance anomalies from the MAR climate model serve as forcing delivering projections for the contribution of the Greenland ice sheet to sea level rise and submarine melt of Helheim and Store outlet glaciers.
Promising Oldest Ice sites in East Antarctica based on thermodynamical modelling
Brice Van Liefferinge, Frank Pattyn, Marie G. P. Cavitte, Nanna B. Karlsson, Duncan A. Young, Johannes Sutter, and Olaf Eisen
Our paper provides an important review of the state of knowledge for oldest-ice prospection, but also adds new basal geothermal heat flux constraints from recently acquired high-definition radar data sets. This is the first paper to contrast the two primary target regions for oldest ice: Dome C and Dome Fuji. Moreover, we provide statistical comparisons of all available data sets and a summary of the community's criteria for the retrieval of interpretable oldest ice since the 2013 effort.
Glaciological characteristics in the Dome Fuji region and new assessment for "Oldest Ice"
Nanna B. Karlsson, Tobias Binder, Graeme Eagles, Veit Helm, Frank Pattyn, Brice Van Liefferinge, and Olaf Eisen
In this study, we investigate the probability that the Dome Fuji region in East Antarctica contains ice more than 1.5 Ma old. The retrieval of a continuous ice-core record extending beyond 1 Ma is imperative to understand why the frequency of ice ages changed from 40 to 100 ka approximately 1 Ma ago. We use a new radar dataset to improve the ice thickness maps, and apply a thermokinematic model to predict basal temperature and age of the ice. Our results indicate several areas of interest.
Brief communication: Candidate sites of 1.5 Myr old ice 37 km southwest of the Dome C summit, East Antarctica
Olivier Passalacqua, Marie Cavitte, Olivier Gagliardini, Fabien Gillet-Chaulet, Frédéric Parrenin, Catherine Ritz, and Duncan Young
Locating a suitable drill site is a key step in the Antarctic oldest-ice challenge. Here we have conducted a 3-D ice flow simulation in the region of Dome C using a refined bedrock description. Five selection criteria are computed that together provide an objective overview on the local ice flow conditions. We delineate kilometer-scale favorable areas that overlap with the ones recently proposed by another group. We propose a few drill sites that should be surveyed during the next field seasons.
Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling
Achim Heilig, Olaf Eisen, Michael MacFerrin, Marco Tedesco, and Xavier Fettweis
This paper presents data on temporal changes in snow and firn, which were not available before. We present data on water infiltration in the percolation zone of the Greenland Ice Sheet that improve our understanding of liquid water retention in snow and firn and mass transfer. We compare those findings with model simulations. It appears that simulated accumulation in terms of SWE is fairly accurate, while modeling of the individual parameters density and liquid water content is incorrect.
Spatial and temporal distributions of surface mass balance between Concordia and Vostok stations, Antarctica, from combined radar and ice core data: first results and detailed error analysis
Emmanuel Le Meur, Olivier Magand, Laurent Arnaud, Michel Fily, Massimo Frezzotti, Marie Cavitte, Robert Mulvaney, and Stefano Urbini
This paper presents surface mass balance measurements from both GPR and ice core data collected during a traverse in a so-far-unexplored area between the DC and Vostok stations. Results presented here will contribute to a better knowledge of the global mass balance of the Antarctic ice sheet and thus help in constraining its contribution to sea level rise. Another novelty of the paper resides in the comprehensive error budget proposed for the method used for inferring accumulation rates.
Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations
Johanna Kerch, Anja Diez, Ilka Weikusat, and Olaf Eisen
We investigate the effect of crystal anisotropy on seismic velocities in glacier ice by calculating seismic phase velocities using the exact c axis angles to describe the crystal orientations in ice-core samples for an alpine and a polar ice core. Our results provide uncertainty estimates for earlier established approximative calculations. Additionally, our findings highlight the variation in seismic velocity at non-vertical incidence as a function of the horizontal azimuth of the seismic plane.
Variability of sea salts in ice and firn cores from Fimbul Ice Shelf, Dronning Maud Land, Antarctica
Carmen Paulina Vega, Elisabeth Isaksson, Elisabeth Schlosser, Dmitry Divine, Tõnu Martma, Robert Mulvaney, Anja Eichler, and Margit Schwikowski-Gigar
Ions were measured in firn and ice cores from Fimbul Ice Shelf, Antarctica, to evaluate sea-salt loads. A significant sixfold increase in sea salts was found in the S100 core after 1950s which suggests that it contains a more local sea-salt signal, dominated by processes during sea-ice formation in the neighbouring waters. In contrast, firn cores from three ice rises register the larger-scale signal of atmospheric flow conditions and transport of sea-salt aerosols produced over open water.
Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison
Heiko Goelzer, Sophie Nowicki, Tamsin Edwards, Matthew Beckley, Ayako Abe-Ouchi, Andy Aschwanden, Reinhard Calov, Olivier Gagliardini, Fabien Gillet-Chaulet, Nicholas R. Golledge, Jonathan Gregory, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Joseph H. Kennedy, Eric Larour, William H. Lipscomb, Sébastien Le clec'h, Victoria Lee, Mathieu Morlighem, Frank Pattyn, Antony J. Payne, Christian Rodehacke, Martin Rückamp, Fuyuki Saito, Nicole Schlegel, Helene Seroussi, Andrew Shepherd, Sainan Sun, Roderik van de Wal, and Florian A. Ziemen
We have compared a wide spectrum of different initialisation techniques used in the ice sheet modelling community to define the modelled present-day Greenland ice sheet state as a starting point for physically based future-sea-level-change projections. Compared to earlier community-wide comparisons, we find better agreement across different models, which implies overall improvement of our understanding of what is needed to produce such initial states.
Accumulation patterns around Dome C, East Antarctica, in the last 73 kyr
Marie G. P. Cavitte, Frédéric Parrenin, Catherine Ritz, Duncan A. Young, Brice Van Liefferinge, Donald D. Blankenship, Massimo Frezzotti, and Jason L. Roberts
We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, over the last 73 kyr. We use internal isochrones interpreted from ice-penetrating radar surveys and a 1-D ice flow model to invert for time-averaged and paleo-accumulation rates. We observe that surface accumulation patterns are stable through the last 73 kyr, consistent with current observed regional precipitation gradients and consistent interactions between prevailing winds and surface slope.
A new bed elevation model for the Weddell Sea sector of the West Antarctic Ice Sheet
Hafeez Jeofry, Neil Ross, Hugh F. J. Corr, Jilu Li, Mathieu Morlighem, Prasad Gogineni, and Martin J. Siegert
Accurately characterizing the complexities of the ice-sheet dynamic specifically close to the grounding line across the Weddell Sea (WS) sector in the ice-sheet models provides challenges to the scientific community. Our main objective is to comprehend these complexities, adding accuracy to the projection of future ice-sheet dynamics. Therefore, we have developed a new bed elevation digital elevation model across the WS sector, which will be of value to ice-sheet modelling experiments.
Critical porosity of gas enclosure in polar firn independent of climate
Christoph Florian Schaller, Johannes Freitag, and Olaf Eisen
In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. In our study, we present the first extensive data set of direct firn microstructure measurements and use it to show that the critical porosity of gas enclosure is independent of the climatic site conditions (such as temperature and accumulation rate). This leads to significant changes in dating and interpretation of ice-core gas records.
Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica
Sophie Berger, Reinhard Drews, Veit Helm, Sainan Sun, and Frank Pattyn
Floating ice shelves act as a plug for the Antarctic ice sheet. The efficiency of this ice plug depends on how and how much the ocean melts the ice from below. This study relies on satellite imagery and a Lagrangian approach to map in detail the basal mass balance of an Antarctic ice shelf. Although the large-scale melting pattern of the ice shelf agrees with previous studies, our technique successfully detects local variability (< 1 km) in the basal melting of the ice shelf.
Strong tidal variations in ice flow observed across the entire Ronne Ice Shelf and adjoining ice streams
Sebastian H. R. Rosier, G. Hilmar Gudmundsson, Matt A. King, Keith W. Nicholls, Keith Makinson, and Hugh F. J. Corr
Earth Syst. Sci. Data, 9, 849–860, https://doi.org/10.5194/essd-9-849-2017,https://doi.org/10.5194/essd-9-849-2017, 2017
Tides can affect the flow of ice at hourly to yearly timescales. In some cases the ice responds at a different frequency than is found in the tidal forcing; for example, on Rutford Ice Stream the strongest response is at a fortnightly period. A new compilation of GPS data across the Ronne Ice Shelf and adjoining ice streams shows that this fortnightly modulation in ice flow is found across the entire region. Measurements of this kind can provide insights into ice rheology and basal processes.
Is there 1.5-million-year-old ice near Dome C, Antarctica?
Frédéric Parrenin, Marie G. P. Cavitte, Donald D. Blankenship, Jérôme Chappellaz, Hubertus Fischer, Olivier Gagliardini, Valérie Masson-Delmotte, Olivier Passalacqua, Catherine Ritz, Jason Roberts, Martin J. Siegert, and Duncan A. Young
The oldest dated deep ice core drilled in Antarctica has been retrieved at EPICA Dome C (EDC), reaching ~ 800 000 years. Obtaining an older palaeoclimatic record from Antarctica is one of the greatest challenges of the ice core community. Here, we estimate the age of basal ice in the Dome C area. We find that old ice (> 1.5 Myr) likely exists in two regions a few tens of kilometres away from EDC: Little Dome C Patch and North Patch .
Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling
Olivier Passalacqua, Catherine Ritz, Frédéric Parrenin, Stefano Urbini, and Massimo Frezzotti
As the Dome C region is a key area for oldest-ice research, we need to better constrain the geothermal flux (GF) so that past basal melt rates are well constrained. Our inverse heat model significantly reduces the confidence intervals of the GF regional field around Dome C, which ranges from 48 to 60 mW m−2. Radar echoes need to be interpreted knowing the time lag of the climate signal to reach the bed. Several old-ice targets are confirmed and a new one is suggested, in which the GF is very low.
High-resolution boundary conditions of an old ice target near Dome C, Antarctica
Duncan A. Young, Jason L. Roberts, Catherine Ritz, Massimo Frezzotti, Enrica Quartini, Marie G. P. Cavitte, Carly R. Tozer, Daniel Steinhage, Stefano Urbini, Hugh F. J. Corr, Tas van Ommen, and Donald D. Blankenship
To find records of the greenhouse gases found in key periods of climate transition, we need to find sites of unmelted old ice at the base of the Antarctic ice sheet for ice core retrieval. A joint US–Australian–EU team performed a high-resolution survey of such a site (1 km line spacing) near Concordia Station in East Antarctica, using airborne ice-penetrating radar. We found promising targets in rough subglacial terrain, surrounded by subglacial lakes restricted below a minimum hydraulic head.
Dynamic changes on the Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations
Melanie Rankl, Johannes Jakob Fürst, Angelika Humbert, and Matthias Holger Braun
How accurate are estimates of glacier ice thickness? Results from ITMIX, the Ice Thickness Models Intercomparison eXperiment
Daniel Farinotti, Douglas J. Brinkerhoff, Garry K. C. Clarke, Johannes J. Fürst, Holger Frey, Prateek Gantayat, Fabien Gillet-Chaulet, Claire Girard, Matthias Huss, Paul W. Leclercq, Andreas Linsbauer, Horst Machguth, Carlos Martin, Fabien Maussion, Mathieu Morlighem, Cyrille Mosbeux, Ankur Pandit, Andrea Portmann, Antoine Rabatel, RAAJ Ramsankaran, Thomas J. Reerink, Olivier Sanchez, Peter A. Stentoft, Sangita Singh Kumari, Ward J. J. van Pelt, Brian Anderson, Toby Benham, Daniel Binder, Julian A. Dowdeswell, Andrea Fischer, Kay Helfricht, Stanislav Kutuzov, Ivan Lavrentiev, Robert McNabb, G. Hilmar Gudmundsson, Huilin Li, and Liss M. Andreassen
ITMIX – the Ice Thickness Models Intercomparison eXperiment – was the first coordinated performance assessment for models inferring glacier ice thickness from surface characteristics. Considering 17 different models and 21 different test cases, we show that although solutions of individual models can differ considerably, an ensemble average can yield uncertainties in the order of 10 ± 24 % the mean ice thickness. Ways forward for improving such estimates are sketched.
Comparison of measurements from different radio-echo sounding systems and synchronization with the ice core at Dome C, Antarctica
Anna Winter, Daniel Steinhage, Emily J. Arnold, Donald D. Blankenship, Marie G. P. Cavitte, Hugh F. J. Corr, John D. Paden, Stefano Urbini, Duncan A. Young, and Olaf Eisen
Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica
Lionel Favier, Frank Pattyn, Sophie Berger, and Reinhard Drews
We demonstrate the short-term unstable retreat of an East Antarctic outlet glacier triggered by imposed sub-ice-shelf melt, compliant with current values, using a state-of-the-art ice-sheet model. We show that pinning points – topographic highs in contact with the ice-shelf base – have a major impact on ice-sheet stability and timing of grounding-line retreat. The study therefore calls for improving our knowledge of sub-ice-shelf bathymetry in order to reduce uncertainties in future ice loss.
Ice core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East Antarctica
Morgane Philippe, Jean-Louis Tison, Karen Fjøsne, Bryn Hubbard, Helle A. Kjær, Jan T. M. Lenaerts, Reinhard Drews, Simon G. Sheldon, Kevin De Bondt, Philippe Claeys, and Frank Pattyn
The reconstruction of past snow accumulation rates is crucial in the context of recent climate change and sea level rise. We measured ~ 250 years of snow accumulation using a 120 m ice core drilled in coastal East Antarctica, where such long records are very scarce. This study is the first to show an increase in snow accumulation, beginning in the 20th and particularly marked in the last 50 years, thereby confirming model predictions of increased snowfall associated with climate change.
A representative density profile of the North Greenland snowpack
Christoph Florian Schaller, Johannes Freitag, Sepp Kipfstuhl, Thomas Laepple, Hans Christian Steen-Larsen, and Olaf Eisen
Along a traverse through North Greenland in May 2015 we collected snow cores up to 2 m in depth and analyzed their properties (e.g., density). A new technique for this sampling and an adapted algorithm for comparing data sets from different positions and aligning stratigraphic features are presented. We find good agreement of the density layering in the snowpack over hundreds of kilometers. This allows the construction of a representative density profile that is statistically validated.
Performance and applicability of a 2.5-D ice-flow model in the vicinity of a dome
Olivier Passalacqua, Olivier Gagliardini, Frédéric Parrenin, Joe Todd, Fabien Gillet-Chaulet, and Catherine Ritz
In ice-flow modelling, computing in 3-D requires a lot of resources, but 2-D models lack physical likelihood when the flow is diverging. That is why 2-D models accounting for the divergence, so-called 2.5-D models, are an interesting trade-off. However, the applicability of these 2.5-D models has never been systematically examined. We show that these models are ineffective in the case of highly diverging flows, but also for varying temperature, which was not suspected.
Constraining variable density of ice shelves using wide-angle radar measurements
Reinhard Drews, Joel Brown, Kenichi Matsuoka, Emmanuel Witrant, Morgane Philippe, Bryn Hubbard, and Frank Pattyn
The thickness of ice shelves is typically inferred using hydrostatic equilibrium which requires knowledge of the firn density. Here, we infer density from wide-angle radar using a novel algorithm including traveltime inversion and ray tracing. We find that firn is denser inside a 2 km wide ice-shelf channel which is confirmed by optical televiewing of two boreholes. Such horizontal density variations must be accounted for when using the hydrostatic ice thickness for determining basal melt rate.
The influence of a model subglacial lake on ice dynamics and internal layering
Eythor Gudlaugsson, Angelika Humbert, Thomas Kleiner, Jack Kohler, and Karin Andreassen
This paper explores the influence of a subglacial lake on ice dynamics and internal layers by means of numerical modelling as well as simulating the effect of a subglacial drainage event on isochrones. We provide an explanation for characteristic dip and ridge features found at the edges of many subglacial lakes and conclude that draining lakes can result in travelling waves at depth within isochrones, thus indicating the possibility of detecting past drainage events with ice penetrating radar.
Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores
Lucie Bazin, Amaelle Landais, Emilie Capron, Valérie Masson-Delmotte, Catherine Ritz, Ghislain Picard, Jean Jouzel, Marie Dumont, Markus Leuenberger, and Frédéric Prié
Clim. Past, 12, 729–748, https://doi.org/10.5194/cp-12-729-2016,https://doi.org/10.5194/cp-12-729-2016, 2016
We present new measurements of δO2⁄N2 and δ18Oatm performed on well-conserved ice from EDC covering MIS5 and between 380 and 800 ka. The combination of the observation of a 100 ka periodicity in the new δO2⁄N2 record with a MIS5 multi-site multi-proxy study has revealed a potential influence of local climatic parameters on δO2⁄N2. Moreover, we propose that the varying delay between d18Oatm and precession for the last 800 ka is affected by the occurrence of ice sheet discharge events.
Modelling calving front dynamics using a level-set method: application to Jakobshavn Isbræ, West Greenland
Johannes H. Bondzio, Hélène Seroussi, Mathieu Morlighem, Thomas Kleiner, Martin Rückamp, Angelika Humbert, and Eric Y. Larour
We implemented a level-set method in the ice sheet system model. This method allows us to dynamically evolve a calving front subject to user-defined calving rates. We apply the method to Jakobshavn Isbræ, West Greenland, and study its response to calving rate perturbations. We find its behaviour strongly dependent on the calving rate, which was to be expected. Both reduced basal drag and rheological shear margin weakening sustain the acceleration of this dynamic outlet glacier.
Verification of the multi-layer SNOWPACK model with different water transport schemes
N. Wever, L. Schmid, A. Heilig, O. Eisen, C. Fierz, and M. Lehning
The Cryosphere, 9, 2271–2293, https://doi.org/10.5194/tc-9-2271-2015,https://doi.org/10.5194/tc-9-2271-2015, 2015
A verification of the physics based SNOWPACK model with field observations showed that typical snowpack properties like density and temperature are adequately simulated. Also two water transport schemes were verified, showing that although Richards equation improves snowpack runoff and several aspects of the internal snowpack structure, the bucket scheme appeared to have a higher agreement with the snow microstructure. The choice of water transport scheme may depend on the intended application.
How might the North American ice sheet influence the northwestern Eurasian climate?
P. Beghin, S. Charbit, C. Dumas, M. Kageyama, and C. Ritz
The present study investigates the potential impact of the North American ice sheet on the surface mass balance of the Eurasian ice sheet through changes in the past glacial atmospheric circulation. Using an atmospheric circulation model and an ice-sheet model, we show that the albedo of the American ice sheet favors the growth of the Eurasian ice sheet, whereas the topography of the American ice sheet leads to more ablation over North Eurasia, and therefore to a smaller Eurasian ice sheet.
Evolution of ice-shelf channels in Antarctic ice shelves
R. Drews
Floating ice shelves extend the continental ice of Antarctica seawards and mediate ice-ocean interactions. Many ice shelves are incised with channels where basal melting is enhanced. With data and modeling it is shown how the channel geometry depends on basal melting and along-flow advection (also for channels which are not freely floating), and how channel formation imprints the general flow pattern. This opens up the opportunity to map the channel formation from surface velocities only.
Measurement of the fracture toughness of polycrystalline bubbly ice from an Antarctic ice core
J. Christmann, R. Müller, K. G. Webber, D. Isaia, F. H. Schader, S. Kipfstuhl, J. Freitag, and A. Humbert
Earth Syst. Sci. Data, 7, 87–92, https://doi.org/10.5194/essd-7-87-2015,https://doi.org/10.5194/essd-7-87-2015, 2015
Thermal structure and basal sliding parametrisation at Pine Island Glacier – a 3-D full-Stokes model study
N. Wilkens, J. Behrens, T. Kleiner, D. Rippin, M. Rückamp, and A. Humbert
The Cryosphere, 9, 675–690, https://doi.org/10.5194/tc-9-675-2015,https://doi.org/10.5194/tc-9-675-2015, 2015
Inferring palaeo-accumulation records from ice-core data by an adjoint-based method: application to James Ross Island's ice core
C. Martín, R. Mulvaney, G. H. Gudmundsson, and H. Corr
Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties
A. Diez and O. Eisen
Seismic wave propagation in anisotropic ice – Part 2: Effects of crystal anisotropy in geophysical data
A. Diez, O. Eisen, C. Hofstede, A. Lambrecht, C. Mayer, H. Miller, D. Steinhage, T. Binder, and I. Weikusat
Enthalpy benchmark experiments for numerical ice sheet models
T. Kleiner, M. Rückamp, J. H. Bondzio, and A. Humbert
We present benchmark experiments and analytical solutions to test the implementation of enthalpy and the corresponding boundary conditions in numerical ice sheet models. The results of the applied models agree well with the analytical solutions if the change in conductivity between cold and temperate ice is properly considered in the model.
Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2
V. Helm, A. Humbert, and H. Miller
Adding a dynamical cryosphere to iLOVECLIM (version 1.0): coupling with the GRISLI ice-sheet model
D. M. Roche, C. Dumas, M. Bügelmayer, S. Charbit, and C. Ritz
How old is the ice beneath Dome A, Antarctica?
B. Sun, J. C. Moore, T. Zwinger, L. Zhao, D. Steinhage, X. Tang, D. Zhang, X. Cui, and C. Martín
An ETKF approach for initial state and parameter estimation in ice sheet modelling
B. Bonan, M. Nodet, C. Ritz, and V. Peyaud
Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area
T. Zwinger, M. Schäfer, C. Martín, and J. C. Moore
Interdependence of the growth of the Northern Hemisphere ice sheets during the last glaciation: the role of atmospheric circulation
P. Beghin, S. Charbit, C. Dumas, M. Kageyama, D. M. Roche, and C. Ritz
Modeling Northern Hemisphere ice-sheet distribution during MIS 5 and MIS 7 glacial inceptions
F. Colleoni, S. Masina, A. Cherchi, A. Navarra, C. Ritz, V. Peyaud, and B. Otto-Bliesner
Probabilistic parameterisation of the surface mass balance–elevation feedback in regional climate model simulations of the Greenland ice sheet
T. L. Edwards, X. Fettweis, O. Gagliardini, F. Gillet-Chaulet, H. Goelzer, J. M. Gregory, M. Hoffman, P. Huybrechts, A. J. Payne, M. Perego, S. Price, A. Quiquet, and C. Ritz
Effect of uncertainty in surface mass balance–elevation feedback on projections of the future sea level contribution of the Greenland ice sheet
Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core
H. Fischer, J. Severinghaus, E. Brook, E. Wolff, M. Albert, O. Alemany, R. Arthern, C. Bentley, D. Blankenship, J. Chappellaz, T. Creyts, D. Dahl-Jensen, M. Dinn, M. Frezzotti, S. Fujita, H. Gallee, R. Hindmarsh, D. Hudspeth, G. Jugie, K. Kawamura, V. Lipenkov, H. Miller, R. Mulvaney, F. Parrenin, F. Pattyn, C. Ritz, J. Schwander, D. Steinhage, T. van Ommen, and F. Wilhelms
Clim. Past, 9, 2489–2505, https://doi.org/10.5194/cp-9-2489-2013,https://doi.org/10.5194/cp-9-2489-2013, 2013
Capabilities and performance of Elmer/Ice, a new-generation ice sheet model
O. Gagliardini, T. Zwinger, F. Gillet-Chaulet, G. Durand, L. Favier, B. de Fleurian, R. Greve, M. Malinen, C. Martín, P. Råback, J. Ruokolainen, M. Sacchettini, M. Schäfer, H. Seddik, and J. Thies
An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120–800 ka
L. Bazin, A. Landais, B. Lemieux-Dudon, H. Toyé Mahamadou Kele, D. Veres, F. Parrenin, P. Martinerie, C. Ritz, E. Capron, V. Lipenkov, M.-F. Loutre, D. Raynaud, B. Vinther, A. Svensson, S. O. Rasmussen, M. Severi, T. Blunier, M. Leuenberger, H. Fischer, V. Masson-Delmotte, J. Chappellaz, and E. Wolff
Influence of ablation-related processes in the build-up of simulated Northern Hemisphere ice sheets during the last glacial cycle
S. Charbit, C. Dumas, M. Kageyama, D. M. Roche, and C. Ritz
Greenland ice sheet contribution to sea level rise during the last interglacial period: a modelling study driven and constrained by ice core data
A. Quiquet, C. Ritz, H. J. Punge, and D. Salas y Mélia
Clim. Past, 9, 353–366, https://doi.org/10.5194/cp-9-353-2013,https://doi.org/10.5194/cp-9-353-2013, 2013
Greenland ice sheet contribution to sea-level rise from a new-generation ice-sheet model
F. Gillet-Chaulet, O. Gagliardini, H. Seddik, M. Nodet, G. Durand, C. Ritz, T. Zwinger, R. Greve, and D. G. Vaughan
Discipline: Ice sheets | Subject: Ice Physics
Ice fabrics in two-dimensional flows: beyond pure and simple shear
Daniel H. Richards, Samuel S. Pegler, and Sandra Piazolo
Understanding the orientation of ice grains is key for predicting ice flow. We explore the evolution of these orientations using a new efficient model. We present an exploration of the patterns produced under a range of temperatures and 2D deformations, including for the first time a universal regime diagram. We do this for deformations relevant to ice sheets but not studied in experiments. These results can be used to understand drilled ice cores and improve future modelling of ice sheets.
Modeling enhanced firn densification due to strain softening
Falk M. Oraschewski and Aslak Grinsted
Old snow (denoted as firn) accumulates in the interior of ice sheets and gets densified into glacial ice. Typically, this densification is assumed to only depend on temperature and accumulation rate. However, it has been observed that stretching of the firn by horizontal flow also enhances this process. Here, we show how to include this effect in classical firn models. With the model we confirm that softening of the firn controls firn densification in areas with strong horizontal stretching.
Geothermal heat flux from measured temperature profiles in deep ice boreholes in Antarctica
Pavel Talalay, Yazhou Li, Laurent Augustin, Gary D. Clow, Jialin Hong, Eric Lefebvre, Alexey Markov, Hideaki Motoyama, and Catherine Ritz
Sensitivity of ice loss to uncertainty in flow law parameters in an idealized one-dimensional geometry
Maria Zeitz, Anders Levermann, and Ricarda Winkelmann
The flow of ice drives mass losses in the large ice sheets. Sea-level rise projections rely on ice-sheet models, solving the physics of ice flow and melt. Unfortunately the parameters in the physics of flow are uncertain. Here we show, in an idealized setup, that these uncertainties can double flow-driven mass losses within the possible range of parameters. It is possible that this uncertainty carries over to realistic sea-level rise projections.
Observation of an optical anisotropy in the deep glacial ice at the geographic South Pole using a laser dust logger
Martin Rongen, Ryan Carlton Bay, and Summer Blot
We report on the observation of a directional anisotropy in the intensity of backscattered light. The measurement was performed using a laser dust logger in the SPC14 drill hole at the geographic South Pole. We find the anisotropy axis to be compatible with the ice flow direction. It is discussed in comparison to a similar anisotropy observed by the IceCube Neutrino Observatory. In future, the measurement principle may provide a continuous record of crystal properties along entire drill holes.
Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m
Ernst-Jan N. Kuiper, Ilka Weikusat, Johannes H. P. de Bresser, Daniela Jansen, Gill M. Pennock, and Martyn R. Drury
A composite flow law model applied to crystal size distributions from the NEEM deep ice core predicts that fine-grained layers in ice from the last Glacial period localize deformation as internal shear zones in the Greenland ice sheet deforming by grain-size-sensitive creep. This prediction is consistent with microstructures in Glacial age ice.
Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 2: The role of grain size and premelting on ice deformation at high homologous temperature
Ernst-Jan N. Kuiper, Johannes H. P. de Bresser, Martyn R. Drury, Jan Eichler, Gill M. Pennock, and Ilka Weikusat
Fast ice flow occurs in deeper parts of polar ice sheets, driven by high stress and high temperatures. Above 262 K ice flow is further enhanced, probably by the formation of thin melt layers between ice crystals. A model applying an experimentally derived composite flow law, using temperature and grain size values from the deepest 540 m of the NEEM ice core, predicts that flow in fine-grained layers is enhanced by a factor of 10 compared to coarse-grained layers in the Greenland ice sheet.
The role of subtemperate slip in thermally driven ice stream margin migration
Marianne Haseloff, Christian Schoof, and Olivier Gagliardini
The widths of the Siple Coast ice streams evolve on decadal to centennial timescales. We investigate how the rate of thermally driven ice stream widening depends on heat dissipation in the ice stream margin and at the bed, and on the inflow of cold ice from the ice ridge. As determining the migration rate requires resolving heat transfer processes on very small scales, we derive a parametrization of the migration rate in terms of parameters that are available from large-scale model outputs.
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Corr, H., Ritz, C., and Martin, C.: Polarimetric ApRES data on a profile across Dome C, East Antarctica, 2013–2014, British Antarctic Survey [data set], https://doi.org/10.5285/634EE206-258F-4B47-9237-EFFF4EF9EEDD, 2021. a
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Diez, A. and Eisen, O.: Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties, The Cryosphere, 9, 367–384, https://doi.org/10.5194/tc-9-367-2015, 2015. a, b
Diez, A., Eisen, O., Hofstede, C., Lambrecht, A., Mayer, C., Miller, H., Steinhage, D., Binder, T., and Weikusat, I.: Seismic wave propagation in anisotropic ice – Part 2: Effects of crystal anisotropy in geophysical data, The Cryosphere, 9, 385–398, https://doi.org/10.5194/tc-9-385-2015, 2015. a, b
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Gillet-Chaulet, F., Hindmarsh, R. C. A., Corr, H. F. J., King, E. C., and Jenkins, A.: In-situ quantification of ice rheology and direct measurement of the Raymond Effect at Summit, Greenland using a phase-sensitive radar, Geophys. Res. Lett., 38, L24503, https://doi.org/10.1029/2011GL049843, 2011. a
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Helm, V., Humbert, A., and Miller, H.: Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2, The Cryosphere, 8, 1539–1559, https://doi.org/10.5194/tc-8-1539-2014, 2014. a, b
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Jordan, T. M., Schroeder, D. M., Castelletti, D., Li, J., and Dall, J.: A Polarimetric Coherence Method to Determine Ice Crystal Orientation Fabric From Radar Sounding: Application to the NEEM Ice Core Region, IEEE T. Geosci. Remote, 57, 8641–8657, https://doi.org/10.1109/TGRS.2019.2921980, 2019. a, b, c, d, e, f, g, h, i, j, k, l, m
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Radio waves transmitted through ice split up and inform us about the ice sheet interior and orientation of single ice crystals. This can be used to infer how ice flows and improve projections on how it will evolve in the future. Here we used an inverse approach and developed a new algorithm to infer ice properties from observed radar data. We applied this technique to the radar data obtained at two EPICA drilling sites, where ice cores were used to validate our results.
Radio waves transmitted through ice split up and inform us about the ice sheet interior and...


text:
package lmath

import (
	"github.com/stretchr/testify/assert"
	"testing"
)

func Test_fractionToDecimal(t *testing.T) {
	assert := assert.New(t)

	assert.Equal("0.5", fractionToDecimal(1, 2))
	assert.Equal("2", fractionToDecimal(2, 1))
	assert.Equal("0.(6)", fractionToDecimal(2, 3))
	assert.Equal("-6.25", fractionToDecimal(-50, 8))
	assert.Equal("-0.58(3)", fractionToDecimal(7, -12))
}

redpajama_set_name: RedPajamaGithub