The climate-induced collapse of the Antarctic Peninsula ice shelves Larsen A in 1995 and Larsen B in 2002 caused acceleration and retreat of tributary glaciers, leading to major losses in ice mass. Since then, the glaciers have been out of balance, however with major variations in time depending on changes in atmospheric and oceanic forcing.

Larsen A Ice Shelf, November 1994, two months before ice shelf collapse. (© Helmut Rott)
Research Objectives
Ice shelves stretch across a main part of Antarctica’s coastline, exerting a critical control on the ice flow to the ocean. With the warming climate ice shelves retreat and become susceptible to collapse which causes acceleration and thinning of grounded glaciers that are draining into the floating ice shelves, resulting in increased loss of ice mass. The driving processes are complex, causing variations in glacier response in space and time, a topic addressed in this study referring to glaciers draining into the Larsen B embayment.

Satellite radar image (ASAR of Envisat), 22 March 2007. Ice shelf fronts: red – 8 December 1992, blue – 30 January 1995, purple (Larsen A) – 22 March 1995, green (Larsen B) – 6 October 2000. Yellow – coastline on 18 March 2002. H, G, E – Hektoria, Green, Evans glaciers. (© Helmut Rott)
Ice Shelf Collapse Triggering Glacier Flow Acceleration and Retreat
Since the 1980’s several ice shelves along the Antarctic Peninsula coast retreated and disintegrated in response to climate warming. Spectacular collapse events happened on the east coast (Weddell Coast) of the northern Antarctic Peninsula: The Larsen A Ice Shelf disintegrated within a few days in January 1995 and the Larsen B Ice Shelf in March 2002. Outlet glaciers of the peninsula, previously feeding the floating ice shelves, became calving glaciers discharging directly into the ocean.
“For evaluating the response of Antarctic outlet glaciers to climate change and estimating future contributions to sea level rise, impacts of glacier size and shape, ice thickness, surface and bedrock topography, pre-frontal sea ice and ocean currents need to be assessed.”
Helmut Rott
During the first few years after ice shelf collapse the flow velocity of the glaciers discharging into the Larsen A and B embayments increased largely, causing increased calving of icebergs, glacier thinning and frontal retreat. Later-on the individual glaciers showed differences in the adaptation to the new boundary conditions. Various factors, including glacier size and shape, ice thickness, surface and bedrock topography, pre-frontal sea ice and ocean currents play a role. Variations in the atmospheric circulation at annual to multi-annual time scale are also of relevance. For evaluating the response of glaciers to climate change and estimating future contributions to sea level rise, impacts of these factors need to be assessed. This is shown below for glaciers draining into the Larsen B embayment that have been subject to variations in flow dynamics and mass balance since ice shelf collapse.
Response of Larsen B Glaciers to Changes in Atmospheric and Oceanic Circulation

Satellite radar images showing changes in sea ice cover of the Larsen B embayment. Left: TerraSAR-X, 5 January 2011; Centre: Sentinel-1, 2 March 2017; Right: Sentinel-1, 4 February 2022. H, G, E, C: Hektoria, Green, Evans, Crane glaciers. (© Helmut Rott)
The examples on glacier response shown here refer to recent years. Up to 2011/2012 the sea ice in front of the Larsen B glaciers cleared away in summer, bringing about several weeks with open water. As of winter 2012, a permanent sea ice cover (fast ice) formed that persisted also during summer and grew in thickness and extent, reaching its maximum in March 2017. Fast ice persisted in the main part of the embayment up to January 2022 when it fractured and drifted away rapidly. The retreat and breakup of fast ice was associated with southward shift and intensification of westerly and north-westerly winds after 2017, resulting in rising average temperature and increased frequency of strong offshore winds and currents.

Sentinel-1 image of Hektoria-Green-Evans glaciers and the pre-frontal bay, 18 May 2023. The location of the glacier fronts is shown for 16 June 2011 (before the fast ice period), 30 November 2021 (maximum seaward extent of the glacier front), 5 April 2022 and 18 May 2023 (receding front after fast ice break-up). (© Helmut Rott)
During the years of fast ice presence most of the glaciers slowed down and floating ice tongues formed that pushed forward well beyond the 2011 glacier front position. The maximum frontal advance, 12 km, was observed for Hektoria Glacier. After break-up of the fast ice the floating tongues fractured rapidly and the glacier flow accelerated. The glacier fronts retreated to the 2011 location and even farther inland. Satellite-based measurements of change in glacier thickness show that during the fast ice period the losses in glacier mass were reduced compared to the previous years.

Velocity (metre/day) at points along the central flow line of Hektoria Glacier, derived from Sentinel-1 data, January 2015 to July 2023. After break-up of the fast ice in January 2022 the floating section of the glacier terminus fractured and drifted away as icebergs, guided by offshore currents. The inset shows the measurement points along the flowline. (© Helmut Rott)
Accounting for Changes in Atmospheric and Oceanic Forcings.
22 years after ice shelf collapse, induced by climate warming, the tributary glaciers to the Larsen B embayment are still out of balance. To some extent this can be attributed to the aftermath of stress perturbation and dynamical changes caused by ice shelf disintegration. Main drivers for variations in glacier flow and mass balance and for transient frontal advance during the last decade were changes in atmospheric and oceanic circulation. This underlines the complexity of processes determining the response of Antarctic outlet glaciers to climate change. Careful consideration of these factors and their temporal evolution is essential for obtaining reliable projections of future Antarctica’s ice loss and sea level contributions. To this end it is also necessary to account for regional differences in atmospheric and oceanic forcings and to separate in mass balance records the changes due to short-term fluctuations and longer-term trends.

Annual rate of surface elevation change (metre per year) on HGE glaciers, derived from TanDEM-X topographic radar images. Left: 2011 to 2013. Right: 2013 to 2016. In 2011 to 2013 glacier thinning up to 25 m/year was observed. In 2011 to 2013 the mass deficit of grounded (non-floating) ice at HGE glaciers amounted to 4.2 Gt/year, in 2013 to 2016 to 1.7 Gt/year. (© Helmut Rott)
Media information
Written by Helmut Rott.
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Photos: © Helmut Rott.
About the scientific authors
Helmut Rott is managing director of ENVEO IT, Innsbruck. He was professor at the Institute for Meteorology and Geophysics, University of Innsbruck.
Literature:
Rott, H., Abdel Jaber, W., Wuite, J., Scheiblauer, S., Floricioiu, D., van Wessem, J.M., Nagler, T., Miranda, N., and van den Broeke, M.R. 2018. Changing pattern of ice flow and mass balance for glaciers discharging into the Larsen A and B embayments, Antarctic Peninsula, 2011 to 2016. The Cryosphere, 12, p.1273-1291, https://doi.org/10.5194/tc-12-1273-2018.
Rott, H., Wuite, J., De Rydt, J., Gudmundsson, G.H., Floricioiu, D., Rack, W. 2020. Impact of marine processes on flow dynamics of northern Antarctic Peninsula outlet glaciers. Nature Communications (2020) 11:2969, https://doi.org/10.1038/s41467-020-16658-y.