̽��ֱ�� of Cambridge - Poul Christoffersen

Researchers build more detailed picture of the movement of Greenland Ice Sheet

sc604 — Fri, 10 Feb 2023 15:14:39 +0000

Researchers have found that the movement of glaciers in Greenland is more complex than previously thought, with deformation in regions of warmer ice containing small amounts of water accounting for motion that had often been assumed to be caused by sliding where the ice meets the bedrock beneath.

Accelerating melt rate makes Greenland Ice Sheet world’s largest ‘dam’

sc604 — Mon, 21 Feb 2022 19:47:29 +0000

̽��ֱ��world’s second-largest ice sheet is melting from the bottom up – and generating huge amounts of heat from hydropower.

Fibre-optics used to take the temperature of Greenland Ice Sheet

sc604 — Fri, 14 May 2021 17:09:27 +0000

Scientists have used fibre-optic sensing to obtain the most detailed measurements of ice properties ever taken on the Greenland Ice Sheet. Their findings will be used to make more accurate models of the future movement of the world’s second-largest ice sheet, as the effects of climate change continue to accelerate.

Drone images show Greenland Ice Sheet becoming more unstable as it fractures

sc604 — Tue, 03 Dec 2019 09:49:11 +0000

̽��ֱ��world’s second-largest ice sheet, and the single largest contributor to global sea level rise, is potentially becoming unstable because of fractures developing in response to faster ice flow and more meltwater forming on its surface.

Rapid melting of the world’s largest ice shelf linked to solar heat in the ocean

sc604 — Mon, 29 Apr 2019 15:00:00 +0000

In a study of Antarctica’s Ross Ice Shelf, which covers an area roughly the size of France, the scientists spent several years building up a record of how the north-west sector of this vast ice shelf interacts with the ocean beneath it. Their results, reported in the journal Nature Geoscience, show that the ice is melting much more rapidly than previously thought due to inflowing warm water.

“ ̽��ֱ��stability of ice shelves is generally thought to be related to their exposure to warm deep ocean water, but we’ve found that solar heated surface water also plays a crucial role in melting ice shelves,” said first author Dr Craig Stewart from the National Institute of Water and Atmospheric Research (NIWA) in New Zealand, who conducted the work while a PhD student at the ̽��ֱ�� of Cambridge.

Although the interactions between ice and ocean occurring hundreds of metres below the surface of ice shelves seem remote, they have a direct impact on long-term sea level. ̽��ֱ��Ross Ice Shelf stabilises the West Antarctic ice sheet by blocking the ice which flows into it from some of the world’s largest glaciers.

“Previous studies have shown that when ice shelves collapse, the feeding glaciers can speed up by a factor or two or three,” said co-author Dr Poul Christoffersen from Cambridge’s Scott Polar Research Institute. “ ̽��ֱ��difference here is the sheer size of Ross Ice Shelf, which over one hundred times larger than the ice shelves we’ve already seen disappear.”

̽��ֱ��team collected four years of data from an oceanographic mooring installed under the Ross Ice Shelf by collaborators at NIWA. Using instruments deployed through a 260 metre-deep borehole, the team measured temperature, salinity, melt rates and ocean currents in the cavity under the ice.

̽��ֱ��team also used an extremely precise custom-made radar system to survey the changing thickness of the ice shelf. Supported by Antarctica New Zealand and the Rutherford Foundation’s Scott Centenary Scholarship at the Scott Polar Research Institute, Dr Stewart and Dr Christoffersen travelled more than 1000 km by snowmobile in order to measure ice thicknesses and map basal melt rates.

Data from the instruments deployed on the mooring showed that solar heated surface water flows into the cavity under the ice shelf near Ross Island, causing melt rates to nearly triple during the summer months.

̽��ֱ��melting is affected by a large area of open ocean in front of the ice shelf that is empty of sea ice due to strong offshore winds. This area, known as the Ross Sea Polynya, absorbs solar heat quickly in summer and this solar heat source is clearly influencing melting in the ice shelf cavity.

̽��ֱ��findings suggest that conditions in the ice shelf cavity are more closely coupled with the surface ocean and atmosphere than previously assumed, implying that melt rates near the ice front will respond quickly to changes in the uppermost layer of the ocean.

“Climate change is likely to result in less sea ice, and higher surface ocean temperatures in the Ross Sea, suggesting that melt rates in this region will increase in the future,” said Stewart.

̽��ֱ��potential for increasing melt rates in this region has implications for ice shelf stability due to the shape of the ice shelf. Rapid melting identified by the study happens beneath a thin and structurally important part of the ice shelf, where the ice pushes against Ross Island. Pressure from the island, transmitted through this region, slows the flow of the entire ice shelf.

“ ̽��ֱ��observations we made at the front of the ice shelf have direct implications for many large glaciers that flow into the ice shelf, some as far as 900 km away,” said Christoffersen.

While the Ross Ice Shelf is considered to be relatively stable, the new findings show that it may be more vulnerable than thought so far. ̽��ֱ��point of vulnerability lies in the fact that that solar heated surface water flows into the cavity near a stabilising pinning point, which could be undermined if basal melting intensifies further. ̽��ֱ��study shows that melting in this specific region is 10 times higher than the average melt rate expected for the ice shelf as a whole.

̽��ֱ��researchers point out that melting measured by the study does not imply that the ice shelf is currently unstable. ̽��ֱ��ice shelf has evolved over time and ice lost by melting due to inflow of warm water is roughly balanced by the inputs of ice from feeding glaciers and snow accumulation. This balance is, however, depending on the stability provided by the Ross Island pinning point, which the new study identifies as a point of future vulnerability.

Reference:
Craig L. Stewart et al. ‘Basal melting of Ross Ice Shelf from solar heat absorption in an ice-front polynya.’ Nature Geoscience (2019). DOI: 10.1038/s41561-019-0356-0

Adapted from a NIWA press release.

A bold response to the world’s greatest challenge
̽��ֱ�� ̽��ֱ�� of Cambridge is building on its existing research and launching an ambitious new environment and climate change initiative. Cambridge Zero is not just about developing greener technologies. It will harness the full power of the ̽��ֱ��’s research and policy expertise, developing solutions that work for our lives, our society and our biosphere.

An international team of scientists has found part of the world’s largest ice shelf is melting 10 times faster than the overall ice shelf average due to solar heating of the surrounding ocean surface.

̽��ֱ��observations we made at the front of the ice shelf have direct implications for many large glaciers that flow into the ice shelf

Poul Christoffersen

̽��ֱ��Ross Polynya where solar heat is absorbed by the ocean. ̽��ֱ��vertical wall of the ice front stretches a distance of 600 km

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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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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