NEWS STORY: Glacier thinning at point of no return
Focus on Pine Island Glacier, Antarctica
Pine Island Glacier, on the West Antarctic Ice Sheet (WAIS) is the largest single contributor to sea-level rise in Antarctica. The stability of the WAIS and its likely contribution to sea level rise is the focus of international research efforts. This month (January 2014) sees the publication of new research, the completion of the first leg of a major ice traverse, and the start of a ship-based research cruise to the seas around Pine Island Glacier.
Reporting this week (13 January 2014) in the journal Nature Climate Change an international team of scientists says that recent and rapid thinning of Pine Island Glacier has probably reached a point of no return. This glacier currently contributes 25 per cent of the total ice loss from West Antarctica, and this is likely to increase over the next 20 years.
In recent years the point at which the glacier ice separates from the land to become a floating ice shelf (known as the grounding line) has retreated inland by tens of kilometres. Understanding the cause and implications of this retreat is paramount for international investigations including the EU-funded Ice2sea programme, the NERC-funded iSTAR programme, and the British Antarctic Survey’s Ice Sheets and Polar Oceans programmes.
Most of the bedrock of WAIS lies below sea level and deepens towards the interior of the ice sheet. Marine ice sheets resting on such reverse slopes have the potential to retreat in an unstable and catastrophic manner. The fact that Pine Island Glacier is currently retreating and thinning more rapidly than any other ice-covered area on earth is a major concern for scientists.
A big challenge for glaciologists looking to make projections about future sea level rise is that no one glacier computer model has sufficient data sources to create an accurate simulation. In the Nature Climate Change paper scientists from France, Britain, China, and Finland describe how they joined forces to provide the most detailed and comprehensive study of the stability of the Pine Island Glacier so far.
Using field observations combined with data from three different ice-flow models containing information about the bedrock topography beneath the glacier, the ice surface features, ocean melting and atmospheric conditions, the team created simulations of how Pine Island Glacier will change over coming decades. All the models agreed that the Pine Island Glacier has become unstable, and will continue to retreat for tens of kilometers.
Dr Hilmar Gudmundsson of British Antarctic Survey is involved the European Commission’s Framework 7-funded programme Ice2sea as well as the BAS Ice Sheets programme, the NERC-funded research into the role of atmosphere-ocean-ice interactions in ice loss from Pine Island and Thwaites Glaciers, West Antarctica, and the iSTAR programme. He says,
“Pine Island Glacier shows the biggest changes in this area at the moment, but if it is unstable it may have implications for the entire West Antarctic Ice Sheet. Currently we see around three millimeters of sea level rise a year, and the Pine Island Glacier retreat could contribute an additional 3.5 – 10 millimeters in the next twenty years, so it would lead to a considerable increase from this area alone. But the potential is much larger. At the Pine Island Glacier we have seen that not only is more ice flowing from the glacier into the ocean, but it’s also flowing faster across the grounding line – the boundary between the grounded ice and the floating ice. We also can see this boundary is migrating further inland.”
Dr Gaël Durand of CNRS, Laboratoire de Glaciologie et de Géophysique de l’Environnement at the University of Grenoble is lead author on the Nature Climate Change paper ‘Retreat of Pine Island Glacier controlled by ice-sheet instability’. He said,
“The models show a strong agreement and the result is a striking vision of the near future. All the models suggest that this recession will not stop, cannot be reversed and that more ice will be transferred into the ocean.”
Meanwhile this month, out on the ice a team of UK scientists is heading to BAS’s Rothera Research Station after spending weeks deep-field on the first leg of a major NERC-funded research expedition to investigate what’s causing the rapid ice loss from Pine Island Glacier.
During an ambitious over-ice crossing by tractor train (a traverse) this team deployed radar and seismic technologies to investigate the variation in ice-flow from the ice shelf up the glacier and into its tributaries. They are testing the hypothesis that it is glacier bed conditions that are responsible for the fact that the tributaries of Pine Island Glacier appear to be thinning at different rates.
In an email from deep-field iSTAR programme leader Dr Andy Smith of British Antarctic Survey reports,
“At 01:30 (GMT) on 8th January, the final science task for this year’s iSTAR Traverse on Pine Island Glacier was completed; the neutron probe made it’s measurement of snow density at the last work site, bringing to an end the scheduled scientific experiments. The Traverse has been a huge success, visiting all the proposed sites on the route, conducting considerably more experiments than had been originally planned and completing much quicker than expected. Our success has been thanks to the excellent support we have received, the sheer hard work and dedication of all the traverse members and some good luck with the weather”
The iSTAR Programme is not over for this season yet. The Traverse will move to its overwinter location, whilst supporting further iSTAR instrument deployments. The next part of the iSTAR mission is the research cruise onboard RRS James Clark Ross which departs for the Amundsen Sea later this month.
BAS oceanographer Pierre Dutrieux is a member of the iSTAR team. Earlier this month, publishing in the journal Science, Dutrieux reported a 50 percent decrease in melting from 2010 to 2012 of the floating ice shelf into which Pine Island Glacier flows. This reduction may have been induced by a La Niña event in the tropical Pacific.
Ice2sea brings together the EU’s scientific and operational expertise from 24 leading institutions across Europe and beyond. Improved projections of the contribution of ice to sea-level rise produced by this major programme funded by the European Commission’s Framework 7 Programme (grant agreement 226375) informed the fifth IPCC report. In 2007, the fourth Intergovernmental Panel on Climate Change (IPCC) report highlighted ice-sheets as the most significant remaining uncertainty in projections of sea-level rise.
The retreat of Pine Island Glacier controlled by marine ice-sheet instability by L Favier, G Durand, S L Cornford, G.H. Gudmundsson, O. Gagliardini, F. Gillet-Chaulet, T. Zwinger, A. J. Payne and A.M. le Brocq is published in Nature Climate Change.
The paper Strong sensitivity of Pine Island ice-shelf meting to climatic variability by P. Dutrieux, J. De Rydt, A. Jenkins, P.R. Holland, H.K. Ha, S.H. Lee, E. Steig, Q. Din, P. Abrahamsen and M. Schröder was published in Science.
For latest news and background information about iSTAR visit www.istar.ac.uk