ANtarctic Grounding LInes from Cryosat (ANGeLIC)

Lead Research Organisation: University of Bristol
Department Name: Geographical Sciences

Abstract

The grounding line of the Antarctic Ice Sheet is the point at which ice leaves the continent and enters the ocean and contributes to sea level. It is where the ocean has its greatest influence on inland flow through bottom melting of floating ice shelves. It is, in fact, a zone (the Grounding Zone) where tidal motion, basal melting and ice dynamics are all key controls on its structure. The GZ is a dynamic feature of the ice sheet and changes in its location and structure may indicate the development of an instability in ice flow or a change in ice motion that will impact sea level and the future evolution of the ice sheet. Identifying and monitoring the evolution of the GZ is important, therefore, for providing i) an early warning of changes in state of the inland ice, ii) as an input into numerical models of ice sheet flow and iii) for measuring the flux of ice leaving the ice sheet.

The ice thickness at the grounding line is an essential variable for determining the flux of ice leaving the ice sheet based on observations of ice velocity. To date, there has been no satisfactory way to investigate the evolution of the GZ for the whole of Antarctica. The aim of this project is to achieve this goal using a novel approach applied to CryoSat 2 data. This satellite was launched in 2010 and has a unique instrument on board called the SIRAL, which provides, for the first time, the ability to resolve at high temporal and spatial resolution the detailed structure of the GZ. Proof of concept analyses indicate its huge potential for this but work is required to i) improve and verify the accuracy of the CryoSat 2 data and ii) fully develop the methods for studying the GZ. Once this is achieved, we intend to monitor the evolution of the GZ over at least a seven year period and hopefully extending this further into the future using the same methods. In the process, we will also address an outstanding issue related to the accuracy of the ice thickness estimates derived from surface elevation in the GZ and greatly improve the accuracy of ice thickness estimates over the freely floating shelves that fringe almost the entire coastline of Antarctica.

Planned Impact

There are four broad categories of user groups who will benefit from the results and activities of the project in addition to scientists working directly on ice sheets and sea level rise. These are i) climate scientists, ii) the climate change policy community, iii) the general public, (including schools and teachers) and iv) Earth Observation and CryoSat data users.

i) Climate scientists (outside of the field of research). This includes, for example, the Earth System modelling community who are attempting to embed realistic ice sheet evolution into AOGCMs. Grounding line migration is a key component in this work. They will benefit from this project by having observational evidence for GZ dynamics, which can be used to calibrate or validate their model response. Some groups are even considering a data assimilation approach for key processes.

ii) Policy community. We have direct links with the following organizations who have benefited from previous related research and who will benefit from this work. The list below is not meant to be exhaustive but to illustrate the type of beneficiary in this category with an indication of how they might benefit.
UK Met Office & DECC: coordinating the AVOID programme (a DECC/DEFRA funded project, http://www.avoid.uk.net/)
Public Interest Research Centre (http://www.pirc.info/) provides climate policy documents for the public and UNFCC.
Scientific Committee on Antarctic Research: coordinating role for Antarctic science.
UN Environment Programme: provides information about climate change and sea level rise to general public and educational establishments.
European Environment Agency: delivers policy information to the EC and member states.
Resources for the Future (www.rff.org) is a US-based think tank that provides briefing information to the US govt. See for example: http://www.rff.org/Events/Pages/Ice-Sheets-on-the-Move.aspx.

These and other organisations will benefit from this project through gaining an understanding of how, and to what extent, the Antarctic ice sheet is changing with time and the implications of these changes for prediction. We have in the past, and will continue to in the future, provide direct input to these groups via briefing notes, technical reports, workshops and public events and informal contacts. These channels have been used to inform the groups on the latest understanding and the state of the art regarding Antarctic ice sheet dynamics. We will provide regular updates during the project and the final Project Report and invite them to comment on the project website. Past experience indicates that this category of end user has greatly benefited from a strong interaction and involvement with the experts doing the work.

iii) The general public. Antarctic research has huge potential for capturing the public imagination and engaging students at both primary and secondary level in issues related to climate change, environmental policy, glaciology and polar processes. We know this from first hand experience. The PI currently undertakes talks to local schools and to Secondary School Geography teachers through the Princes Teaching Institute (http://www.princes-ti.org.uk/SummerSchool/) and will continue to do this for this project.

iv) Finally, as mentioned in the previous section, we are working closely with ESA to ensure that the CryoSat 2 validation work undertaken in the project is of most value and benefit to them and to the CryoSat-2 user community. The recently launched Antarctic Climate Change Initiative (CCI) coordinated by ESA provides a powerful mechanism to widen the reach and impact of the project beyond the standard academic beneficiaries (http://cci.esa.int/). The CCI aims to provide Essential Climate Variables required by the UNFCC for scientific and operational applications and users.
 
Description Pine Island Glacier has contributed more to sea level rise over the last four decades than any other glacier in Antarctica. Model projections indicate that this will continue in the future but at conflicting rates. Some models suggest that mass loss could dramatically increase over the next few decades, resulting in a rapidly growing contribution to sea level, and fast retreat of the grounding line, where the grounded ice meets the ocean. Other models indicate more moderate losses. Resolving this contrasting behaviour is important for sea level rise projections. We used high resolution satellite observations of elevation change since 2010 to show that thinning rates are now highest along the slow-flow margins of the glacier and that the present-day amplitude and pattern of elevation change is inconsistent with fast grounding line migration and the associated rapid increase in mass loss over the next few decades. Instead, our results support model simulations that imply only modest changes in grounding line location over that timescale. We also showed how the pattern of thinning is evolving in complex ways both in space and time and how rates in the fast-flowing central trunk have decreased by about a factor five since 2007.
Exploitation Route The approach we used is fairly generic to any satellite altimetry mission and, in fact, we are now using the same concept with ICESat-2 data, which has lower noise, higher precision and accuracy and is proving more successful for determining the grounding line in low tidal amplitude regions. The drawback is that the mission has only just launched so there is no temporal record of grounding line change.
Sectors Aerospace, Defence and Marine,Environment

 
Title Grounding zone location across Antarctica from CryoSat-2 radar altimetry 2010-2017 
Description This dataset provides a map of the Antarctic grounding zone. The map is assembled using CryoSat-2 satellite radar altimetry data spanning between 2010-2017. This dataset provides both the limit of tidal flexure (point F) and hydrostatic equilibrium (point H) of the grounding zone. Funding was provided by the NERC grant NE/N011511/1. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Description Collaboration with Bert Wouters (Universiteit Utrecht) 
Organisation Utrecht University
Country Netherlands 
Sector Academic/University 
PI Contribution Joint development of CryoSat processing and combining with GRACE
Collaborator Contribution Joint development of CryoSat processing and combining with GRACE
Impact The collaboration has resulted in the following papers relevant to RCUK grants: -Wouters, B., J. L. Bamber, M. R. van den Broeke, J. T. M. Lenaerts and I. Sasgen (2013). "Limits in detecting acceleration of ice sheet mass loss due to climate variability." Nature Geosci advance online publication. - Martin Espanol, A., Zammit Mangion, A., Clarke, P. J., Flament, T., Helm, V., King, M. A., Luthcke, S.B, Petrie, E., Rémy, F. Schön, N., Wouters, B. and Bamber, J. (2016). Spatial and temporal Antarctic Ice Sheet mass trends, glacio-isostatic adjustment, and surface processes from a joint inversion of satellite altimeter, gravity, and GPS data. Journal of Geophysical Research: Earth Surface, 121(2), 182-200. DOI:10.1002/2015JF003550 - Wouters, B., Martin-Español, A., Helm, V., Flament, T., van Wessem, J. M., Ligtenberg, S.R.M., Van den Broeke, M.R. and Bamber, J.L. "Dynamic thinning of glaciers on the Southern Antarctic Peninsula." Science 348, no. 6237 (2015): 899-903. - Sasgen, I., Martín-Español, A., Horvath, A., Klemann, V., Petrie, E.J., Wouters, B., Horwath, M., Pail, R., Bamber, J.L., Clarke, P.J. and Konrad, H., 2017. Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a lateral varying Earth structure (ESA STSE Project REGINA). Geophysical Journal International, 211(3), pp.1534-1553.
Start Year 2011
 
Description Collaboration with Ian Joughin (University of Washington) 
Organisation University of Washington
Country United States 
Sector Academic/University 
PI Contribution Joint programmes of research
Collaborator Contribution Provision of data and expert advice on data issues
Impact The collaboration has resulted in the following papers relevant to RCUK grants post 2006: -Joughin, I., S. Tulaczyk, J. L. Bamber, D. Blankenship, J. W. Holt, T. Scambos and D. G. Vaughan (2009). "Basal conditions for Pine Island and Thwaites Glaciers, West Antarctica, determined using satellite and airborne data." J. Glaciology 55(190): 245-257. -Hurkmans, R. T. W. L., J. L. Bamber, L. S. Sørensen, I. R. Joughin, C. H. Davis and W. B. Krabill (2012). "Spatiotemporal interpolation of elevation changes derived from satellite altimetry for Jakobshavn Isbræ, Greenland." J. Geophys. Res. 117(F3): F03001. - Hurkmans, R. T. W. L., Bamber, J. L., Davis, C. H., Joughin, I. R., Khvorostovsky, K. S., Smith, B. S., and Schoen, N.: Time-evolving mass loss of the Greenland Ice Sheet from satellite altimetry, The Cryosphere, 8, 1725-1740, https://doi.org/10.5194/tc-8-1725-2014, 2014.
 
Description Press release linked to paper on Pine Island Glacier 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Issued a press release that was distributed to syndicating agencies such as Eureka alert. Article was reported in the media and in climate blogs.
Year(s) Of Engagement Activity 2020
 
Description Princes Teaching Institute 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The teachers follow up on my presentation with a number of activities and ideas for classroom teaching.

Teachers express an increased awareness of the polar regions in global processes
Year(s) Of Engagement Activity 2013,2014,2015,2016,2017,2018
URL http://www.princes-ti.org.uk/