̽��ֱ�� of Cambridge - Marion Bougamont

UK and US join forces to understand how quickly a massive Antarctic glacier could collapse

sc604 — Mon, 30 Apr 2018 08:45:00 +0000

̽��ֱ��collapse of the Thwaites Glacier in West Antarctica could significantly affect global sea levels. It already drains an area roughly the size of Britain or the US state of Florida, accounting for around four percent of global sea-level rise —an amount that has doubled since the mid-1990s.

As part of a new £20 million research collaboration, the UK Natural Environment Research Council and the US National Science Foundation will deploy scientists to gather the data needed to understand whether the glacier’s collapse could begin in the next few decades or centuries.

NERC and NSF have jointly funded eight large-scale projects that will bring together leading polar scientists in one of the most inhospitable regions of the planet. ̽��ֱ��programme, called the International Thwaites Glacier Collaboration (ITGC), is the largest joint project undertaken by the two nations in Antarctica for more than 70 years - since the conclusion of a mapping project on the Antarctic Peninsula in the late 1940s.

In addition to the £20 million-worth ($25 million) of awards to the research teams, the logistics of mounting a scientific campaign in one of the most remote places in Antarctica could cost as much again in logistical support. ̽��ֱ��nearest permanently occupied research station to the Thwaites Glacier is more than 1600km away, so getting the scientists to where they need to be will take a massive joint effort from both nations. While researchers on the ice will rely on aircraft support from UK and U.S. research stations, oceanographers and geophysicists will approach the glacier from the sea in UK and U.S. research icebreakers.

Dr Poul Christoffersen from the ̽��ֱ�� of Cambridge’s Scott Polar Research Institute is co-leading one of the eight projects with Professor Slawek Tulaczyk from the ̽��ֱ�� of California, Santa Cruz. Their project, Thwaites Interdisciplinary Margin Evolution (TIME) also includes researchers from the ̽��ֱ�� of Leeds, Stanford ̽��ֱ��, the ̽��ֱ�� of Texas and the ̽��ֱ�� of Oklahoma. ̽��ֱ��team will investigate how the margins of the drainage basin will evolve and influence ice flow over the coming decades.

“These margins have so far never been studied directly, due to the logistical challenges of working in such a remote region of Antarctica,” said Christoffersen. “ ̽��ֱ��margins, which separate the fast-flowing glacier from the surrounding slow-moving ice, are often thought of as being stationary, but they might not be. ̽��ֱ��hypothesis that drives our science is that they can move and thereby exert powerful control on the future evolution of ice flow in the whole drainage basin.”

“This international collaboration will lead to a step change in our understanding of ice sheet stability,” said Cambridge’s Dr Marion Bougamont, who will use observational data records gathered in the field to improve computer models needed to predict sea level rise. “ ̽��ֱ��glacier’s response will depend on where the margins are and how they evolve.”

Today’s collaboration involves around 100 scientists from world-leading research institutes in both countries alongside researchers from South Korea, Germany, Sweden, New Zealand and Finland, who will contribute to the various projects. These projects aim to deliver answers to some of the big questions for scientists trying to predict global sea-level rise.

Antarctica’s glaciers contribute to sea-level rise when more ice is lost to the ocean than is replaced by snow. To fully understand the causes of changes in ice flow requires research on the ice itself, the nearby ocean, and the Antarctic climate in the region. ̽��ֱ��programme will deploy the most up-to-date instruments and techniques available, from drills that can make access holes 1,500 meters into the ice with jets of hot water to autonomous submarines like the Autosub Long Range affectionately known around the world as Boaty McBoatface.

“Rising sea levels are a globally important issue which cannot be tackled by one country alone,” said UK Science Minister, Sam Gyimah. “ ̽��ֱ��Thwaites Glacier already contributes to rising sea levels and understanding its likely collapse in the coming century is vitally important. Science, research and innovation are at the heart of our Industrial Strategy and this UK-U.S. research programme will be the biggest field campaign of its type ever mounted by these countries. I’m delighted that our world-leading scientists will help to lead this work.”

̽��ֱ��science programme and logistics on the five-year programme begins in October 2018 and continues to 2021. ̽��ֱ��funding is for eight research projects and a co-ordination grant to maximise success.

Adapted from a NERC/NSF press release.

A Cambridge researcher will lead one of eight projects in a new joint UK-US research programme that is one of the most detailed and extensive examinations of a massive Antarctic glacier ever undertaken.

These margins have so far never been studied directly, due to the logistical challenges of working in such a remote region of Antarctica.

Poul Christoffersen

US National Science Foundation/US Antarctic Program

Reconnaissance flight over the Thwaites glacier

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Chain reaction of fast-draining lakes poses new risk for Greenland ice sheet

sc604 — Wed, 14 Mar 2018 10:00:00 +0000

Researchers from the UK, Norway, US and Sweden have used a combination of 3D computer modelling and real-world observations to show the previously unknown, yet profound dynamic consequences tied to a growing number of lakes forming on the Greenland ice sheet.

Lakes form on the surface of the Greenland ice sheet each summer as the weather warms. Many exist for weeks or months, but drain in just a few hours through more than a kilometre of ice, transferring huge quantities of water and heat to the base of the ice sheet. ̽��ֱ��affected areas include sensitive regions of the ice sheet interior where the impact on ice flow is potentially large.

Previously, it had been thought that these ‘drainage events’ were isolated incidents, but the new research, led by the ̽��ֱ�� of Cambridge, shows that the lakes form a massive network and become increasingly interconnected as the weather warms. When one lake drains, the water quickly spreads under the ice sheet, which responds by flowing faster. ̽��ֱ��faster flow opens new fractures on the surface and these fractures act as conduits for the drainage of other lakes. This starts a chain reaction that can drain many other lakes, some as far as 80 kilometres away.

These cascading events – including one case where 124 lakes drained in just five days – can temporarily accelerate ice flow by as much as 400%, which makes the ice sheet less stable, and increases the rate of associated sea level rise. ̽��ֱ��results are reported in the journal Nature Communications.

̽��ֱ��study demonstrates how forces within the ice sheet can change abruptly from one day to the next, causing solid ice to fracture suddenly. ̽��ֱ��model developed by the international team shows that lakes forming in stable areas of the ice sheet drain when fractures open in response to a high tensile shock force acting along drainage paths of water flowing beneath the ice sheet when other lakes drain far away.

“This growing network of melt lakes, which currently extends more than 100 kilometres inland and reaches elevations as high a 2,000 metres above sea level, poses a threat for the long-term stability of the Greenland ice sheet,” said lead author Dr Poul Christoffersen, from Cambridge’s Scott Polar Research Institute. “This ice sheet, which covers 1.7 million square kilometres, was relatively stable 25 years ago, but now loses one billion tonnes of ice every day. This causes one millimetre of global sea level rise per year, a rate which is much faster than what was predicted only a few years ago.”

̽��ֱ��study departs from the current consensus that lakes forming at high elevations on the Greenland ice sheet have only a limited potential to influence the flow of ice sheet as climate warms. Whereas the latest report by Intergovernmental Panel on Climate Change concluded that surface meltwater, although abundant, does not impact the flow of the ice sheet, the study suggests that meltwater delivered to the base of the ice sheet through draining lakes in fact drives episodes of sustained acceleration extending much farther onto the interior of the ice sheet than previously thought.

“Transfer of water and heat from surface to the bed can escalate extremely rapidly due to a chain reaction,” said Christoffersen. “In one case we found all but one of 59 observed lakes drained in a single cascading event. Most of the melt lakes drain in this dynamic way.”

Although the delivery of small amounts of meltwater to the base of the ice sheet only increases the ice sheet’s flow locally, the study shows that the response of the ice sheet can intensify through knock-on effects.

When a single lake drains, the ice flow temporarily accelerates along the path taken by water flowing along the bottom of the ice sheet. Lakes situated in stable basins along this path drain when the loss of friction along the bed temporarily transfers forces to the surface of the ice sheet, causing fractures to open up beneath other lakes, which then also drain.

“ ̽��ֱ��transformation of forces within the ice sheet when lakes drain is sudden and dramatic,” said co-author Dr Marion Bougamont, also from the Scott Polar Research Institute. “Lakes that drain in one area produce fractures that cause more lakes to drain somewhere elsewhere. It all adds up when you look at the pathways of water underneath the ice.”

̽��ֱ��study used high-resolution satellite images to confirm that fractures on the surface of the ice sheet open up when cascading lake drainage occurs. “This aspect of our work is quite worrying,” said Christoffersen. “We found clear evidence of these crevasses at 1,800 metres above sea level and as far 135 kilometres inland from the ice margin. This is much farther inland than previously considered possible.”

While complete loss of all ice in Greenland remains extremely unlikely this century, the highly dynamic manner in which the ice sheet responds to Earth’s changing climate clearly underscores the urgent need for a global agreement that will reduce the emission of greenhouse gases.

̽��ֱ��work was funded by the Natural Environment Research Council (NERC) and the European Research Council (ERC).

Reference:
Poul Christoffersen et al. ‘Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture.’ Nature Communications (2018). DOI: 10.1038/s41467-018-03420-8

A growing network of lakes on the Greenland ice sheet has been found to drain in a chain reaction that speeds up the flow of the ice sheet, threatening its stability.

Timo Lieber

Melting of Greenland ice sheet forms lakes that drain in summer

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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