Ice shelf stress response to large iceberg calving

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

Ice loss from the Antarctic ice sheet is buffered by the floating ice shelves that fringe much of the continent. Acting like natural dams, ice shelves restrict the delivery of terrestrial ice from Antarctica into the southern oceans, therefore the stability of ice shelves is highly important when predicting the contribution of Antarctic ice to sea-level rise. Ice shelves can destabilise in the years following the calving of large icebergs; for example, in January 1995, Larsen B Ice Shelf (LBIS) calved an iceberg 1720 sq.km in area, and progressively retreated until collapsing in a matter of weeks in early 2002; with the removal of LBIS, its tributary glaciers were seen to accelerate and discharge more ice into the ocean.

While the consequences of shelf collapse are well-appreciated, the processes involved in the transition from stable to unstable ice shelves following calving are poorly understood. To date, we have had few opportunities to study such processes because large-scale iceberg calving is rare. This urgency proposal therefore seeks to address this issue, by mobilising a study in the aftermath of a recent calving event on Larsen C Ice Shelf (LCIS). On 12th July 2017, LCIS calved one of the largest icebergs ever recorded; termed A68, this iceberg has an area of 5800 sq.km (12% of LCIS) and separated from the shelf following 3.5 years of rift propagation.

Predicting how the remaining LCIS will evolve following the loss of A68 is the key motivator for our project, which is an integrated campaign of predictive numerical modelling, satellite remote sensing and in situ geophysical survey on LCIS. Many simulations of ice flow highlight the important role of englacial damage in determining the future stability of LCIS: existing weaknesses (such as surface and basal crevasses) in the shelf would tend to open in the new extensional regime. However, local heterogeneities in the structure of the ice shelf may complicate this response, and the timescale on which the shelf will react and stabilise is also unclear. To resolve these ambiguities, it is our goal to capture the early-stage response of LCIS to resolve these ambiguities hence our application for urgency funding.

Our project considers two hypotheses:
1) Increased stresses on LCIS will progressively increase calving rates, particularly where the shelf is already damaged by crevasses.
2) The response of LCIS stabilises as the shelf adapts, but accurate forecasts of long-term stability require constraint of the earliest responses.

Our assembled team are experts in 4 key methods, integrated to test our hypotheses. We will use:
i) satellite imagery, to measure stress evolution at the surface of the ice shelf, by mapping changes in crevasse patterns,
ii) seismic surveys, to be deployed on LCIS, to measure variations in damage at depth within the shelf,
iii) GPS sensors, also deployed on LCIS, to record short-term fluctuations in the motion of the shelf, and
iv) numerical modelling, to integrate all data and predict how damage evolved before, through and after the calving of the A68 iceberg.

Satellite analysis and numerical modelling will commence at the initiation of the project in early October, with field deployment taking place at the earliest logistical opportunity (to be confirmed with the British Antarctic Survey, but likely in November 2017). This vital initial appraisal will serve as the basis of further grant applications through 2018, which will include the deployment of a comprehensive suite of field instruments.

Our project offers an initial description of the new stress-state for LCIS, providing a reference baseline for any future study. The most immediate benefits will be for the specific understanding of the A68 calving event, and its implications for the stability of the remaining LCIS, but we also improve the understanding of the mechanisms involved with any equivalent calving process.

Planned Impact

We prioritise public engagement in our impact efforts, aiming to improve their appreciation of key ice shelf processes. Government policy makers will also benefit from our improved predictions of ice shelf stability and their implications for sea-level rise - however we recognise that the most effective contributions to such bodies come not from a single project but from a consensus view from the academic community. Our efforts towards these policy impacts are therefore directed towards maximising our engagement with other researchers in glaciology.

The general public is broadly familiar with processes active on Larsen C Ice Shelf, following the vigorous attention it received from the media in the months leading up to, and immediately after, the calving of iceberg A68. Given its focus on this event, this project has a clear pathway to continue public engagement and, in particular, to develop this into an improved understanding of important ice shelf processes. For example, it was evident in the media's treatment of the A68 calving event that reporters wished to link the process to global climate warming - yet the academic consensus was that no clear evidence of a climate change link was present. While it is therefore important that climate change issues remain prominent in the public eye, it is important that they are not misled from its genuine influences and impacts. By maintaining public engagement through this project, its investigators will improve public interest and understanding of the key processes involved in iceberg calving and ice shelf evolution.

Our public outreach activities will include:

1) Maintaining a project website, which will report activity and observations throughout the span of the project. Rather than launching a new website, we will open dedicated space within the existing "Project MIDAS" website - www.projectmidas.org. This was established during a previous NERC-funded project on the Larsen C Ice Shelf and included updates on the development of the rift that ultimately led to the calving of iceberg A68. Since January 2017, the Project MIDAS website received over 200,000 unique visitors hence is a viable route to effective public engagement. With its dedicated pages, this urgency project will have its own identity but will benefit from the existing public/media familiarity with the existing MIDAS resource.

2) Daily updates (website blogs, social media posts) from field teams deployed at Rothera Station. It is our experience that the public, particularly schoolchildren, engage well with accounts of "life in the field". We will include field photographs, initial science observations, and will investigate the possibility of a live webchat (or at least phonecall) from Rothera to schools local to the partner institutes. By involving local schools in this way, we anticipate a potential benefit to recruitment into higher-education STEM subjects.

3) Continued attendance at public science events, including Welsh National Eisteddfod's (Swansea University, Aberystywth University), the Leeds Festival of Science (University of Leeds) and the British Geological Survey open days. The academic partner institutes have dedicated outreach staff who will assist with maximising the impact of these engagements.

Publications

10 25 50
 
Description Key to the stability of Larsen C ice shelf is the way that warm ocean water access the underside of the ice shelf. Warm ocean currents are directed through sea-bed channels beneath Larsen C, but their geometry is not well known and therefore it is difficult to predict where the shelf will be vulnerable to basal melting. The seismic data recorded on Larsen C has been useful for evaluating the thickness of the ocean cavity, and has contributed to a new draft publication that collates all seismic data from the ice shelf.
Exploitation Route The data are available for any researcher to access and use to benchmark any future analyses of the properties of Larsen C ice shelf. The data include archives of seismic and GPR responses, and satellite-derived maps of ice sheet flow velocity.
Sectors Environment

 
Description The project has already societal impact, by liaising with media outlets and local schools education programmes. This raises the public prominence of the research, but also of the wider research issue of Antarctic ice sheet stability. In the run-up to our Antarctic field deployment, the project was reported in the blog pages of the European Geosciences Union, and our associated twitter accounts received positive interaction from the wider public. Following the deployment, we ran a "Facebook live" presentation about the project, reaching ~12,000 people and receiving 3,500 individual views. The project also participated in the "Antarctica Day" initiative, whereby Antarctic flags made by schoolchildren were taken to Antarctica along with the field team and photographed on the continent. The project was also presented to a public audience as a "Pint of Science" outreach talk, in which the role of Antarctic ice shelves, and the importance of understanding them, was explained. This event was attended by ~50 members of the public.
First Year Of Impact 2017
Sector Education
Impact Types Societal

 
Description INTERACT-Transnational Access
Amount € 3,300 (EUR)
Organisation INTERACT 
Sector Charity/Non Profit
Country Finland
Start 04/2018 
End 07/2018
 
Title Flow velocity and along-flow stress products for Larsen C Ice Shelf, Antarctica, modelled before and after the calving event of Iceberg A68 in July 2017 (Version 1.0) 
Description Velocity and along-flow stress states were modelled for Larsen C ice shelf, before and after the calving of iceberg A68 in July 2017. The archive contains two sets of model outputs: i) flow velocity before and after calving, and the difference between these periods, and ii) along-flow stress before and calving, and the difference between these periods. The models are produced with the BISICLES ice sheet model. Additionally to high-resolution geo-referenced model outputs, a low-resolution image of each is provided for reference. The maps were produced by Dr Stephen Cornford, Swansea University 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
Impact Currently, none. 
URL https://doi.org/10.5285/664C6EBA-7C6D-422D-BB13-7DD1BF5F6DBA
 
Title Ground penetrating radar common-midpoint gathers from Antarctica's Larsen C Ice Shelf, Nov 2017, following the calving of Iceberg A68 
Description Ground penetrating radar (GPR) data were acquired at a site on Antarctica's Larsen C Ice Shelf, in November 2017. The acquisition was performed to measure radar anisotropy, a potential proxy for the stress condition in the upper ice shelf, following the calving of Iceberg A68 in July 2017. Two GPR common midpoint (CMP) gathers were acquired at Site S2, a site previously surveyed during the NERC funded NE/E013414/1 SOLIS project. These gathers were acquired first with GPR antennas extended in the flow-parallel direction (~ east), and then in the flow-orthogonal direction. The GPR system is a Sensors & Software pulseEKKO PRO, with 200 MHZ antennas. All acquisitions were performed by Dr Jim White (British Geological Survey) and Emma Pearce (University of Leeds, School of Earth and Environment), with support from BAS. The data is part of the NERC RACE project, NE/R012334/1. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
URL https://data.bas.ac.uk/full-record.php?id=GB/NERC/BAS/PDC/01227
 
Title Satellite-derived velocity maps for Larsen C Ice Shelf, Antarctica, between November 2017-April 2019 (Version 1.0) 
Description Velocity maps were derived, for regions of Larsen C ice shelf, from satellite imagery spanning the period November 2017 to April 2019. This period was selected to monitor any change in the velocity field of Larsen C, in the months following the calving of iceberg A68 from the front of the ice shelf. The archive contains two sets of maps. The first are derived from Sentinel-1 satellite data, and span the complete ice shelf for the full 18-month epoch. The second are derived from TerraSAR-X data, and show high-resolution velocity trends between 2017 and 2018, covering the frontal region of Larsen C ice shelf. The maps were produced by Professor Adrian Luckman, Swansea University. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact N/A 
URL https://data.bas.ac.uk/full-record.php?id=GB/NERC/BAS/PDC/01433
 
Title Seismic refraction data from two sites on Antarctica's Larsen C Ice Shelf, Nov 2017, following the calving of Iceberg A68 
Description Seismic refraction data were acquired at two sites on Antarctica's Larsen C Ice Shelf, in November 2017. The acquisition was performed to measure seismic anisotropy, a proxy for the stress condition, in the ice shelf following the calving of Iceberg A68 in July 2017. 2D seismic profiles were acquired at two sites: S1, close to the new calving front of the ice shelf, and S2, advected downstream from the site surveyed in the NERC funded project NE/E013414/1 (SOLIS). Profiles were rotated about a common midpoint to examine the variation in seismic properties with azimuth. Throughout, 24 geophones were deployed at 10 m offset, with data recorded at a Geometrics GEODE system; data are presented here in SEG-2 format. All acquisitions were performed by Dr Jim White (British Geological Survey) and Emma Pearce (University of Leeds, School of Earth and Environment), with support from BAS. The data is part of the NERC RACE project, NE/R012334/1. Associated datasets are an archive of ground penetrating radar data from S2, and velocity products derived from satellite remote sensing. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Description Broadcast of radio interview about glacier geophysics, for El Paso (Texas, USA) radio station KTEP 88.5 programme "Science Studio" 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Interviewed as part of a regular science programme on the radio station, something like Radio 4's "The Life Scientific". The programme discussed how scientists first got into their field, and then talked about their ongoing research projects.
Year(s) Of Engagement Activity 2019
URL https://www.ktep.org/post/science-studio-dr-adam-booth
 
Description Pint of Science public outreach talk. I delivered a talk on the role of Antarctic ice shelves and the importance of studying them, entitled "Larsen C - what's the crack?". 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The intended purpose was to educate and entertain the general public about science in general, and more specifically to highlight the importance of cryospheric science. The Pint Of Science event featured two science talks, from myself and a colleague researching ocean sediment. The talks were accompanied by demos of geophysics methods during an interval, and a Q+A session in which the audience could put their questions to the speakers. The event was attended by ~50 members, mostly made up of the general public, and feedback from the series of Pint Of Science talks, as a whole event, has been positive.
Year(s) Of Engagement Activity 2018
URL https://pintofscience.co.uk/event/do-you-want-ice-with-that