Next generation ice-sheet bed measurements

06 - 07 May 2025 09:00 - 17:00 Apex Grassmarket Hotel, Edinburgh Free
Image of ice-sheet beds

Theo Murphy meeting organised by Professor Martin Siegert, Professor Richard Alley FRS, Professor Dorthe Dahl-Jensen and Associate Professor Christine Dow.

Projections of sea-level rise under strong warming are greatly uncertain, with estimates for 2100 varying by more than 1 m and far greater thereafter. Of the sources of uncertainty, lack of knowledge of ice-sheet bed topography and material composition is important and addressable, but requires coordination to focus on the most important regions in a timely manner. This meeting will discuss the benefits of bespoke optimised surveys of the polar ice sheets, the technology available to conduct it and the international collaborations, logistics and permissions necessary to make such surveys possible. 

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Enquiries: contact the Scientific Programmes team

Organisers

  • Professor Martin Siegert FRSE, University of Exeter, UK

    Professor Martin Siegert

    Martin Siegert is Professor of Geosciences and co-Director of the Grantham Institute, Imperial College London. He was formerly Head of the School of GeoSciences and Assistant Principal for Energy and Climate Change at the University of Edinburgh, where he led the creation of the Edinburgh Centre for Carbon Innovation (ECCI). He received his PhD from Cambridge University, completing his thesis on the numerical modelling of large ice sheets at the Scott Polar Research Institute. Siegert’s research interests are in the field of glaciology. He uses geophysical techniques to quantify the flow and form of ice sheets both now and in the past. Siegert has appeared regularly on TV and radio to discuss his research, including BBC Radio 4’s Life Scientific in August 2012. In 2007 he was elected a Fellow of the Royal Society of Edinburgh. He was awarded the 2013 Martha T Muse Prize in Antarctic Science and Policy.

  • Professor Richard B Alley ForMemRS, Pennsylvania State University, USA

    Professor Richard Alley ForMemRS

    Dr Richard B Alley (PhD 1987 Wisconsin; Evan Pugh University Professor, Geosciences, Penn State) studies the Antarctic and Greenland ice sheets to help predict future climate and sea-level changes.  He has been honoured for research, teaching, and service, including election to the US National Academy of Sciences and The Royal Society.  He participated in the UN Intergovernmental Panel on Climate Change (co-recipient, 2007 Nobel Peace Prize), and provided requested advice to high government officials from both major political parties in the USA.  He has authored or co-authored over 400 scholarly publications.  His was presenter for the PBS TV miniseries Earth: The Operators’ Manual, based on his book.  His popular account of climate change and ice cores, The Two-Mile Time Machine, was Phi Beta Kappa’s science book of the year.  He is happily married with two grown daughters, two stay-at-home cats, a bicycle, and a pair of soccer cleats.

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    Professor Dorthe Dahl-Jensen

    Dorthe Dahl-Jensen is professor in Ice Physics at the Niels Bohr Institute, University of Copenhagen. She heads the Centre of Excellence for Ice and Climate with the focus to use ice core data to improve our understanding of the past, the present and the future climate. In addition she leads the deep drilling program NEEM on the Greenland Ice Sheet with participation of researchers from 14 nations. The research of Dorthe Dahl-Jensen includes reconstruction of climate records from ice cores and borehole data and construction of ice flow models to date ice cores. The history and evolution of the Greenland Ice Sheet especially in the previous warm interglacial is the present focus of her research. In addition she coordinates the EU FP7 programme Past4Future and has an ERC Advanced grant WATERundertheICE. Dorthe Dahl-Jensen is lead author of the chapter “The Greenland Ice Sheet in a Changing Climate” of the Arctic Council AMAP report “Climate Change and the Cryosphere: Snow, Water, Ice and Permafrost in the Arctic”. She is member of the Danish Climate Commission that produced a report: Green Energy – the road to a Danish energy system without fossil fuels.

  • Dr Christine Dow, University of Waterloo, Canada

    Associate Professor Christine Dow

    Dr Christine Dow is an Associate Professor at the University of Waterloo, Ontario, and the Canada Research Chair in Glacier Hydrology and Ice Dynamics. Her research combines numerical modelling and geophysical field experiments to explore the role of subglacial water in influencing ice dynamics. Currently, her work focuses on the Antarctic and the Yukon, Canada, where her research group runs fully coupled models of subglacial hydrology and ice flow. In Antarctica, these models are applied both at the basin and continental scale to investigate past, present, and future ice conditions. In the St. Elias Mountains of the Yukon, field campaigns involve borehole drilling to assess basal water conditions, helicopter-based radar surveys to measure ice thickness, and dGPS measurements to track ice velocity, providing critical data for model input and validation.

Schedule

Chair

Professor Martin Siegert FRSE, University of Exeter, UK

Professor Martin Siegert

University of Exeter, UK

09:00-09:05 Welcome by the Royal Society and lead organiser
09:05-09:30 Mapping subglacial topography: from simple interpolations to physics-informed approaches

Subglacial bed topography is a critical input to understand the stability of ice sheets and for computer models to provide reliable estimates of future seal level rise. These topography maps are constructed based on line measurements collected by airborne radars. These measurements generally provide information only directly underneath the aircraft, and the bed topography in-between measurements has to be interpolated. The first maps of bed topography were constructed based on little data, and using very simple interpolation methods. Since the 2010s, significantly more data have bene acquired by different international agencies, and novel, more advanced interpolation approaches have been proposed. One of them is the use of mass conservation, which combines the radar information with satellite-derived ice flow speed and the principle of conservation of mass. This approach makes it possible to estimate how the bed topography changes in between flight lines by using other datasets for which we have complete coverage. Other new methods involving machine learning, surface features, or stochastic modelling have also been proposed. In this talk, we review the evolution of mapping method over the last 20 years, since the first release of Bedmap, discuss the benefits and limitations of different techniques, and provide inputs for how these maps are continuing to improve our ability to model ice sheet flow and their future contributions to sea level rise. We also discuss how future field campaigns should be designed to optimise these new mapping techniques.

Professor Mathieu Morlighem

Professor Mathieu Morlighem

Dartmouth College, USA

09:30-09:55 Lessons learned from Bedmap3, and the challenges to overcome in automating Bedmap4 and beyond

It is tempting to think that the key challenge in generating new Bedmaps is to re-run an interpolation algorithm with an ever-enlarging dataset of ice sheet thickness, as new airborne surveys are completed. This does help, but other challenges emerge. Surveys often don't agree, large data gaps remain, the ice thickness changes, algorithms work well for one landscape but not another. Similar problems afflict other key Bedmap components: the coastline, the grounding line, the ice shelves, and the bathymetry. The process of merging the interpolated ice sheets and shelves, and the grounded bed with the sea floor, can also inject spurious cliffs and bumps in the grounding zone - exactly where ice sheet models are most dependent on accurate boundary conditions. In each case, the unintended errors and artefacts that arise require careful checking, correction, and sometimes bespoke, local approaches to the interpolation. Can Bedmap be automated? Probably, but each of these challenges must be understood and overcome in ways that are robust to the data thrown at them. And it might still be quicker to do it by hand.

Dr Hamish Pritchard

Dr Hamish Pritchard

British Antarctic Survey, UK

09:55-10:20 An evaluation of synthetic bed topographies for ice sheet modelling

Bed topography plays a pivotal role in shaping the evolution of the Antarctic Ice Sheet, controlling ice flow dynamics, grounding line retreat, subglacial hydrological processes, and ice shelf melt rates. Despite its importance, Antarctic bed topography remains sparsely sampled, resulting in significant uncertainties in bed datasets that propagate in ice sheet model simulations. Synthetic bed topography datasets, generated using mass conservation methods, geostatistical approaches, and other multi-method integrations, are increasingly utilised ice sheet modelling applications. Here, we explore the role of synthetic bed topographies in advancing ice sheet modelling. We review methodologies for generating synthetic topographies, their applications in modelling ice flow, and examine the impact of topographic uncertainties on simulated ice and subglacial water flow in the Aurora Subglacial Basin, East Antarctica.

Dr Felicity McCormack

Dr Felicity McCormack

Monash University, Australia

10:20-10:30 Discussion I - bed DEMs
10:30-11:00 Break
11:00-11:25 Using machine learning to help plan future ice thickness surveys

Accurate subglacial topography is essential for ice sheet models that project past and future ice-climate interactions. Widely used datasets of subglacial topography, such as those for the Greenland Ice Sheet (GrIS), rely heavily on interpolation, for which uncertainties remain poorly constrained. Improved knowledge of these uncertainties is necessary for the optimisation of the next generation of ice sheet bed measurements. We show that a novel quantile regression forest approach to radio echo sounding (RES) observations of the GrIS improves both estimates of derived bed elevations and uncertainty mapping. By providing improved uncertainty estimates, this method offers a way to optimise the design of future airborne RES surveys, ensuring more accurate subglacial topography mapping for ice sheet modelling efforts.

Dr Steven Palmer

Dr Steven Palmer

University of Exeter, UK

11:25-11:50 Quantifying knowledge gaps in subglacial topography to refine subglacial hydrology and ice discharge estimates, and survey requirements for Antarctic RINGS missions at the ice sheet margin

The margin of the Antarctic ice sheet has multiple tipping mechanisms that could trigger large, rapid, and potentially irreversible changes in the coming centuries. While bed topography largely controls these mechanisms, it remains poorly known beneath the ice sheet and ocean. Antarctic RINGS, a collaborative initiative under the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of Antarctic National Programs (COMNAP), aims to address critical data gaps in the ice-sheet margin, including subglacial topography, ice discharge, surface mass balance, subglacial hydrology, geological settings, and ice-shelf mass balance. Using the Bedmap3 FAIR database, we generated stochastic ensemble bed topographies within 100km of the grounding line. Our analysis reveals a much rougher bed than previously suggested by gridded map products, introducing significant uncertainty into assessments of future grounding line retreat, including marine ice sheet instability scenarios. We further estimate the uncertainty in ice discharge caused by ice thickness uncertainty, demonstrating how targeted RINGS survey at the grounding line can significantly reduced these uncertainties. Additionally, we assess how bed elevation uncertainty relates to bed roughness and the proximity of survey profiles. This provides an empirical framework for determining optimal survey spacing to meet specific uncertainty tolerances. International collaboration is essential for conducting dense surveys along the ice sheet margin and inland. Ultimately, these efforts will enable the development high-resolution bed topography products with documented uncertainties for diverse scientific applications.

Dr Kenichi Matsuoka

Dr Kenichi Matsuoka

Norwegian Polar Institute, Norway

11:50-12:30 Discussion II - survey design

Chair

Professor Richard B Alley ForMemRS, Pennsylvania State University, USA

Professor Richard Alley ForMemRS

Pennsylvania State University, USA

13:30-13:55 Modelling past and future sea level rise
Professor Rob DeConto

Professor Rob DeConto

University of Massachusetts, USA

13:55-14:20 Bed topography records, controls, and constrains long-term ice-sheet behaviour

An overarching objective of the glaciological community is to develop numerical models of ice-sheet behaviour that are capable of robustly projecting the future evolution of the Antarctic and Greeland ice sheets in a warming world. A robust understanding of bed topography, and how it has evolved through time, is central to this challenge because bed topography: (i) influences how the overlying ice sheet behaves and responds to climate change, and (ii) provides a record of long-term glacial history, for example under past warmer climates that serve as analogues for projected future change.

The aim of this presentation is twofold. First, we will demonstrate how changes in bed topography over geological timescales (via processes such as erosion, sedimentation, tectonic activity, and isostasy) have influenced the behaviour of the Antarctic ice sheet. For example, glacial erosion and crustal subsidence have caused the development of increasingly low-lying and reverse sloping beds over time, particularly within near-coastal subglacial basins, which has amplified the sensitivity of the ice sheet to atmosphere and ocean forcing. Second, we will explore how bed topography can encode valuable records of long-term ice-sheet behaviour. For example, subglacial landscapes in Greenland and Antarctica retain the signatures of surface processes that operated prior to glaciation and/or during times when the ice configuration was substantially different to today. These findings provide important opportunities as constraints for models of past and present-ice sheet behaviour, as well as potentially informing future geophysical survey and ice/bedrock drill planning.

Dr Guy Paxman

Dr Guy Paxman

Durham University, UK

14:20-14:45 Are continental scale Antarctic simulations still relevant?

Simulations of the Antarctic ice sheet evolution over the coming century continue to dominate uncertainties in sea level projections. Despite a decade of rapid progress in numerical modelling of ice sheet flow - including the addition of new processes and the validation with a rapidly growing number of remote-sensing observations - the ability of continental scale simulations to capture recent changes in Antarctic dynamics remains limited. While uncertainties arise from a number of factors, including the choice of climate forcing, greenhouse gas emission scenarios and processes captured, the choice of ice sheet model itself is the dominant source of uncertainty for both decadal and century time scales. 

In this presentation, we will assess the viability of using continental scale simulations and explore whether regional or basin-scale models may provide more robust insights. We will first review recent results on Antarctic ice sheet projections and the main sources of uncertainty in these projections. We will then compare results performed at continental scale with regional scale models of the Amundsen Sea Sector and Wilkes Land, as well as models simulating individual glaciers for these two regions. We will compare uncertainty coming from these three spatial scales with uncertainty stemming from the choice of climate model, scenario, as well as uncertainties in bedrock elevation. Our results will highlight differences in the model’s simulated ice mass loss and grounding line retreat, and provide a new perspective on how to refine Antarctic ice sheet projections and improve confidence in future sea level rise estimates.

Associate Professor Hélène Seroussi

Associate Professor Hélène Seroussi

Dartmouth College, USA

14:45-15:00 Discussion III - integrating with modelling
15:00-15:30 Break
15:30-15:55 Antarctic grounding zone and bedrock: the interplay shaping Antarctic sea-level contribution

The Antarctic ice sheet's grounding zone, the critical transition between grounded ice and floating ice shelves, exerts a profound influence on ice flow and therefore global sea-level rise. Its dynamics is highly sensitive to ocean temperature and bed topography and accurate sea-level projections hinge on understanding these processes. Rapid changes in grounding line position, driven by ocean warming or ice shelf buttressing, can trigger significant ice mass loss through accelerated ice flow.

However, the complex and often poorly constrained bed topography beneath the ice sheet grounding zone introduces substantial uncertainty into ice sheet models. Bed roughness, subglacial channels, saltwater intrusion, and bedrock slope directly impact ice flow velocity and basal melt rates. Current topographic datasets, relying on sparse radar and seismic measurements, often lack the resolution needed to capture crucial bedrock features in grounding zone. This uncertainty propagates into sea-level rise projections, hindering our ability to accurately predict future coastal inundation. In this presentation, we will review knowledge of the current understanding of grounding line and grounding zone dynamics and how improved measurement of bed topography in these regions is essential to refine ice sheet models and reduce the range of uncertainty in sea-level predictions.

Professor Sophie Nowicki

Professor Sophie Nowicki

University at Buffalo, USA

15:55-16:20 Impacts of bed topography resolution on sea level rise projects from coupled subglacial hydrology and ice dynamics for the Amundsen Sea drainage basin

Ice sheet models require explicit knowledge of the underlying bed. However, much remains unknown regarding the subglacial environment due to the difficulty associated with measuring it. Extensive radar surveys have been conducted across Antarctica, but the requirement of full coverage bed topography for models necessitates the usage of interpolation methods over gaps between existing observations, which often span several kilometres or more. Uncertainties in bed topography contribute to the large range in projections of future sea level rise. Advances in modelling capabilities now allow for the application of dynamic coupling between subglacial hydrology and ice dynamics in models of the Antarctic ice sheet. While a bed resolution of around 500m is recommended for modelling Antarctic ice sheet, it has been suggested that finer spatial resolutions are needed to accurately resolve subglacial water flow. We use a coupled model configuration within ISSM to generate projections of ice sheet evolution, including the subglacial hydrologic system, for the Amundsen Sea drainage basin in Antarctica initiated with several different bed topographies. We examine the impacts of the spatial resolution of the bed on modelled future sea level rise. Bed topographics of varying spatial resolution are obtained by manipulating BedMachine Antarctica data. We compare model outputs obtained with the original dataset, which has a 500m spatial resolution, to simulations initiated with a high and low-res variation of the original dataset. We reduce BedMachine data to a 5km spatial resolution to generate the low-res variation, and to simulate potential impacts from including high-res bed topography we add randomly generated noise to the original dataset. We use climate and ocean forcing from the CESM SSP 5-8.5 contribution for ISMIP6 experiments to project ice mass change and analyse impacts in the evolution of the subglacial environment over the 21st century when bed topographies with varying spatial resolution are employed. We discuss implications for sea level rise projections and make recommendations where additional bed observations will be the most impactful with respect to reducing uncertainties associated with modelling the subglacial environment in particular.

Dr Shivani Ehrenfeucht

Dr Shivani Ehrenfeucht

Potsdam Institute for Climate Impact Research, Germany

16:20-17:00 Discussion IV - benefits to modelling from improved DEMs

Chair

Dr Christine Dow, University of Waterloo, Canada

Associate Professor Christine Dow

University of Waterloo, Canada

09:00-09:30 Panel Discussion
09:30-10:00 Time-series radar sounding as the next key ice-sheet observable

Ice penetrating radar observation of bed echoes is a core geophysical geophysical technique for observational glaciology.  In the beginning these data were collected as part of real exploration and mapping and so places were there little or no data were often prioritized. This has led to very few time-series observations of radar sounding profiles. Although the few we do have have been very impactful. In the meantime, there have been major advances in radar sounding instruments, platforms, and analysis approaches and the information they make available are dramatically opening up the possibility space for future observations, experiments, and missions. Here, we discuss these advances and possibilities and the opportunities they present for "next generation" observations. To this end we explore the relative reflectivity signatures both as 1-time mapping observables, both as a baseline for time series and as an end in-and-of-itself for one-time model/assimilation informed mapping by a (comparatively) rich instrument suite. We also (especially) investigate mapping as part of a time-series of radar sounding profiles to observe changes in bed echo power profiles. Based on this analysis, we argue that time-series observations of bed echoes and englacial layers should be the next key observational priority to constrain ice sheet processes and conditions and for future sea level projections. In this context we also discuss the detectability of both static and evolving subglacial water bodies (including ocean intrusion in the grounding zone). And we also discuss this implication of this mapping  for platforms and instruments.

Professor Dustin Schroeder

Professor Dustin Schroeder

Stanford University, USA

10:00-10:30 Swath radar in glaciology 1
Associate Professor Knut Christianson

Associate Professor Knut Christianson

University of Washington, USA

10:30-11:00 Break
11:00-11:30 High-resolution bed topography from radar swath imaging to infer ice stream dynamics

Radar swath imaging provides high-resolution 3D data sets of an ice sheets basal interface. To demonstrate the capabilities, we investigate the onset region of the Northeast Greenland Ice Stream (NEGIS), which dominates the flow features of the Greenland Ice Sheet, recognisable almost 600 km inland, and extends close to the central ice divide. Numerical ice sheet models are unable to accurately reproduce the configuration of the NEGIS, but understanding its bed properties and spatial and temporal evolution is critical to predicting its future contribution to sea-level change. Here, we use swath radar imaging to create a high-resolution Digital Elevation Model of the bed close to where the NEGIS initiates. The data set has a horizontal resolution of 25 m and 10 m vertical, covering 40 x 60 km2. Surprisingly, the data set reveals mega-scale glacial lineations (MSGLs) that are often assumed to be indicative of rapid ice stream flow (100s m yr-1), under present day flow velocities of only ~60 m yr-1. Given that MSGLs are thought to form under much higher flow velocities, their presence so far inland at an onset zone raises important questions about their formation and preservation under ice streams, as well as past configurations of the NEGIS. Elongate bedrock landforms outside the current shear margins also suggest that the NEGIS was wider than its present configuration at some point in the past. Our example shows that radar swath imaging is a game changer for characterizing subglacial properties and interpreting ice dynamics.

Professor Olaf Eisen

Professor Olaf Eisen

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Germany

11:30-11:50 Discussion V - new systems and instruments
11:50-12:30 Discussion VI

Chair

Professor Martin Siegert FRSE, University of Exeter, UK

Professor Martin Siegert

University of Exeter, UK

13:30-13:55 Coordinating nation polar programmes
Dame Jane Francis FRS DCMG

Dame Jane Francis FRS DCMG

British Antarctic Survey, UK

13:55-14:25 International policy engagement on sea level rise
Ms Pam Pearson

Ms Pam Pearson

International Cryosphere Climate Initiative, Sweden

14:25-15:00 Discussion VII - international logistics and operations
15:00-15:30 Break
15:30-15:55 Radio echo sounding comes of age: SPRI-NSF-TUD Antarctic campaigns

Radio echo sounding (RES) of ice sheet commenced in the mid-1960s with exploratory over-snow expeditions to NW Greenland and Antarctica. At that time the techniques were being developed principally by scientists at the Scott Polar Research Institute in Cambridge with similar developments in Leningrad (Arctic and Antarctic Research Institute). Earlier experiments had been undertaken by engineers at the US Army Electronics Laboratory.

Long-range operations of SPRI were facilitated by logistics cooperation with the US NSF and later by scientists from the Technical University of Denmark. Over 12 years and six campaigns to 1979 the programme covered 400,000 line-km of sounding from the operating base at McMurdo. During these years there was rapid progress in RES systems and antennae design, data recording, analysis techniques, integration of magnetics sounding and database structures. Navigation was a key concern prior to gps, but inertial systems enabled the more accurate flying of grid patterns to collect data. By 1979 the broad pattern of ice thickness, flow characteristics, and sub-ice topography had been determined over about half of the continent in addition to studies of ice shelf and ice stream dynamics, internal reflecting horizons, the discovery of sub-ice lakes and geological inferences resulting in the publishing of the Antarctic Folio in 1983.

Professor David Drewry

Professor David Drewry

UK National Commission for UNESCO, UK

16:00-17:00 Final panel discussion