Ice shelf stress response to large iceberg calving

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.

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.