Antarctica retreating across the sea floor

Antarctica retreating across the sea floor

Antarctica’s great ice sheet is losing ground as it is eroded by warm ocean water circulating beneath its floating edge, a new study has found.

Research by CPOM at the University of Leeds has produced the first complete map of how the ice sheet’s submarine edge, or ‘grounding line’, is shifting. Most Antarctic glaciers flow straight into the ocean in deep submarine troughs, the grounding line is the place where their base leaves the sea floor and begins to float.

The study, published today in Nature Geoscience, shows that the Southern Ocean melted 1,463 km2 of Antarctica’s underwater ice between 2010 and 2016 – an area the size of Greater London.

Map showing rates of grounding line migration and their coincidence with ocean conditions around Antarctica between 2010 and 2016 (seabed temperatures: Locarnini et al., 2013. World Ocean Atlas 2013, Volume 1: Temperature. S. Levitus, Ed., A. Mishonov Technical Ed.; NOAA Atlas NESDIS 73, 40 pp.). Grounding line locations are from Rignot et al., 2013, Science 341 (6143), pp. 266-270.
Credit: Konrad et al.

The team, led by Dr Hannes Konrad, found that grounding line retreat has been extreme at eight of the ice sheet’s 65 biggest glaciers. The pace of deglaciation since the last ice age is roughly 25 metres per year. The retreat of the grounding line at these glaciers is more than five times that rate.

The biggest changes were seen in West Antarctica, where more than a fifth of the ice sheet has retreated across the sea floor faster than the pace of deglaciation.

Dr Konrad said: “Our study provides clear evidence that retreat is happening across the ice sheet due to ocean melting at its base, and not just at the few spots that have been mapped before now. This retreat has had a huge impact on inland glaciers, because releasing them from the sea bed removes friction, causing them to speed up and contribute to global sea level rise.”

The researchers also found some unexpected behaviour. Although retreat of the Thwaites Glacier grounding line in West Antarctica has sped up, at the neighbouring Pine Island Glacier – until recently one of the fastest retreating on the continent – has halted. This suggests that the ocean melting at its base may have paused.

Dr Konrad added: “These differences emphasise the complex nature of ice sheet instability across the continent, and being able to detect them helps us to pinpoint areas that deserve further investigation.”

Grounding lines typically lie a kilometre or more below sea level and are inaccessible even to submersibles, so remote sensing methods for detecting them are extremely valuable.

The team were able to track the movement of Antarctica’s grounding line using European Space Agency’s CryoSat-2 across 16,000 km of the coastline. Although CryoSat-2 is designed to measure changes in the ice sheet elevation, these can be translated into horizontal motion at the grounding line using knowledge of the glacier and sea floor geometry and the Archimedes principle of buoyancy – which relates the thickness of floating ice to the height of its surface.

Study co-author Professor Andy Shepherd said: “We were delighted at how well CryoSat-2 is able to detect the motion of Antarctica’s grounding lines. They are impossible places to access from below, and usually invisible on the ground, so it’s a fantastic illustration of the value of satellite measurements for identifying and understanding environmental change.”

Further information:

Images and animation are available for download: https://goo.gl/JXkX24

The paper Net retreat of Antarctic glacier grounding lines by Hannes Konrad, Andrew Shepherd, Lin Gilbert, Anna Hogg, Malcolm McMillan, Alan Muir and Thomas Slater is published 2 April in Nature Geoscience (doi:10.1038/s41561-018-0082-z).

Space to Earth View challenges kids to aim high!

CPOM’s Anna Hogg has been inspiring schoolchildren to take their fitness to new heights and learn about space science at the same time.

Funded by the UK Space Agency, the ‘Space to Earth View Challenge’ is a fun way of inspiring children of all abilities to get more active and work towards a shared goal whilst learning about the exciting topic of Earth Observation.

Anna has been working alongside Triathlon Trust ambassador and Team GB Paralympian Lauren Steadman, encouraging children to run, swim and cycle a total of 717km – the height at which CryoSat, the European Space Agency’s polar mission, orbits the Earth.

22 events across the UK have been delivered, with 6,826 children (52% male/48% female) taking part and 25,852 km travelled – meaning the challenges have successfully been hitting CryoSat’s orbit!

Map of the UK showing the location of the schools that have taken part in the challenge

Anna said: “The challenge is a fantastic opportunity to engage children in both Earth Observation and keeping fit, paving the way for healthy lifestyles and an interest in space science as they get older.”

100% of teachers rated the event ‘Excellent’. 100% of teachers agreed that the activity increased their pupil’s understanding of Earth Observation and 92% of teachers intend to continue learning about earth observation with their pupils. 92% of teachers agreed that the activity was inclusive and that children enjoyed it.

The Triathlon Trust has provided all the equipment schools need to take part, including bikes mounted on turbo trainers.

Children taking part in the Space to Earth View challenge

Astronaut Tim Peake has meanwhile given his full support to the project as a way of promoting both fitness and space – having experienced them at the same time!

Tim Peake keeping fit on the ISS Treadmill. Credit: AP/ESA

Tweeting about the challenge this week, he said:

Watch Anna and Lauren explain more about the challenge in this video:

 Further information:

The Space to Earth View Challenge is a partnership between The Triathlon Trust, CPOM, the Ideas Foundation, Venture Thinking and Accenture. They would like to thank the UK Space Agency for making the project possible.

The Triathlon Trust is the official charity of British Triathlon, using the engaging sport of triathlon to encourage young people to lead healthy, more active lifestyles.

To see videos from the events visit: https://www.youtube.com/channel/UCPlhQD_vQ4o2a_b5q6rPwpg