Join CPOM’s Anna Hogg and Paralympian Lauren Steadman in taking the Space to Earth View Challenge: Swim, bike or run the distance to orbiting satellites 717 km above the Earth
Author: Nicola Bortun
First look at 2017 Arctic sea ice volume from CryoSat
A new paper in Advances in Space Research, led by Rachel Tilling, provides a first look at 2017 Arctic sea ice volume from CryoSat.
Using data from CPOM’s sea ice processor, which has been under constant development at CPOM since the early 1990s, the 7 year time series also shows large year-on-year variations in the volume of sea ice which persists in the Arctic year round: between 2010 and 2012, volume declined by 31%, followed by an 89% increase in 2013 and then a 27% decrease from 2013-2016.
These changes impacted on the total autumn sea ice volume, which declined by 14% between 2010 and 2012, increased by 42% in 2013, then decreased by 25% from 2013-2016. The peak autumn volume in 2013 was seen as thick ice cover in the region north of Greenland and Ellesmere Island, with ice being 17% thicker than average, associated with a 5% drop in the number of days on which melting occurred – conditions more typical of the late 1990s. The sharp increase in sea ice volume after just one cool summer demonstrates the ability of Arctic sea ice to respond rapidly to a changing environment.
The paper also provides a comprehensive description of the data processing steps that CPOM uses to estimate Arctic sea ice thickness and volume from CryoSat’s radar altimetry data, along with associated uncertainties.
Next steps include testing the method on sea ice thickness retrievals in the Antarctic and developing sea ice processing systems for other satellites monitoring the polar regions.
The full paper Estimating Arctic sea ice thickness and volume using CryoSat-2 radar altimeter data is available now in Advances in Space Research.
Pine Island Glacier and Ice Sheet Stability in West Antarctica
In May 2017 CPOM Leeds hosted the concluding meeting of NERC’s Ice Sheet Stability Research Programme (iSTAR), an effort to improve understanding of West Antarctica’s combined Pine Island Glacier Amundsen Sea system.
Participants reviewed iSTAR’s combined achievements against the programme’s original objectives: understanding the transport of ocean heat toward the ice sheet, understanding the sub-ice processes affecting ice melt, and understanding the response of the inland glacier to the ocean-induced changes.
The main messages coming out of the research were:
- Future research in this field should include atmospheric processes, not just ice and ocean processes;
- Long time series observations are critical; and
- More observations are needed of the floating ice sheet before models can reliably predict Pine Island Glacier’s future behavior.
Read the full write-up of the meeting by Andy Smith of the British Antarctic Survey, published in Eos
Satellites reveal hidden ice canyons
CPOM’s Noel Gourmelen explains how ESA’s Sentinel-1 and CryoSat missions have shed light on the huge canyons hidden within the Antarctic ice shelf in a new ESA article, summarised in the video below.
Update on the Larsen-C iceberg breakaway
The largest remaining ice shelf on the Antarctic Peninsula lost 10% of its area when an iceberg four times the size of London broke free earlier this month.
Since the 12 July 2017 breakaway, CPOM’s Dr Anna Hogg and Dr Hilmar Gudmundsson, from the British Antarctic Survey (BAS), have continued to track the iceberg, known as A68, using the European Space Agency (ESA) and European Commission’s Copernicus Sentinel-1 satellite. This ESA video describes A68’s story.
A cluster of over 11 ‘smaller’ icebergs have also now formed, the largest of which is over 13 km long. These ‘bergy bits’ have broken off both the giant iceberg and the remaining ice-shelf
Dr Hogg, an ESA Research Fellow within CPOM said: “The satellite images reveal a lot of continuing action on Larsen-C Ice Shelf. We can see that the remaining cracks continue to grow towards a feature called Bawden Ice Rise, which provides important structural support for the remaining ice shelf.
“If an ice shelf loses contact with the ice rise, either through sustained thinning or a large iceberg calving event, it can prompt a significant acceleration in ice speed, and possibly further destabilisation. It looks like the Larsen-C story might not be over yet.”
Reporting this week in the journal Nature Climate Change Dr Hogg and Dr Gudmundsson, examine the events leading up to this dramatic natural phenomenon and discuss how calving of huge icebergs affects the stability of Antarctic ice shelves.
Their article asserts that a calving event is not necessarily due to changes in environmental conditions and may simply reflect the natural growth and decay cycle of an ice shelf.
Dr Gudmundsson said: “Although floating ice shelves have only a modest impact on of sea-level rise, ice from Antarctica’s interior can discharge into the ocean when they collapse. Consequently we will see increase in the ice-sheet contribution to global sea-level rise.
“With this large calving event, and the availability of satellite technology, we have a fantastic opportunity to watch this natural experiment unfolding before our eyes. We can expect to learn a lot about how ice shelves break up and how the loss of a section of an ice shelf affects the flow of the remaining parts.”
Ice-shelf retreat on the Antarctic Peninsula, has been observed throughout the satellite era about 50 years. Large sections of the Larsen Ice Shelf A and B, and the Wilkins1 ice-shelf collapsed in a matter of days in 1995, 2002, and 2008, respectively.
Geological evidence suggests that ice-shelf decay of this magnitude is not unprecedented, however, prior to 2002 the Larsen-B ice shelf remained intact for the last 11,000 years. While Antarctic ice shelves are in direct contact with both the atmosphere and the surrounding oceans, and thus subject to changes in environmental conditions, they also go through repeated internally-driven cycles of growth and collapse.
Further information:
Impacts of the Larsen-C ice-shelf calving event by Anna E Hogg and G Hilmar Gudmundsson is published in Nature Climate Change on 2 August 2017. URL: http://www.nature.com/nclimate/journal/v7/n8/full/nclimate3359.html
Broadcast-quality footage of Larsen Ice Shelf is also available from the British Antarctic Survey Press Office.
Giant iceberg in the making at Larsen-C
ESA satellites are monitoring a deep crack that continues to cut across the Larsen C ice shelf. When it eventually gives way, it will create one of the largest icebergs on record.
Sentinel-1 now shows the crack in the ice is around 200 km long, leaving just 5 km between the end of the fissure and the ocean.
While we wait for Sentinel-1 to tell us when this 6600 sq km iceberg is spawned, CryoSat can reveal what the berg’s measurements will be.
CPOM’s Noel Gourmelen explained: “Using information from CryoSat, we have mapped the elevation of the ice above the ocean and worked out that the eventual iceberg will be about 190 m thick and contain about 1155 cubic kilometres of ice.
“We have also estimated that the depth below sea level could be as much as 210 m.”
Icebergs calve from Antarctica all the time, but because this one is particularly large its path across the ocean needs to be monitored as it could pose a hazard to maritime traffic.
Again, Sentinel-1 and CryoSat will play an important role in tracking the berg and keeping an eye on how it changes.
Dr Gourmelen added, “We will continue to use CryoSat to monitor how the berg changes as it drifts away from the ice shelf.”
A berg, similar in size, drifted around the Brunt ice shelf in December 2015, causing alarm for those stationed at the Halley research base, which sits on the floating section of the shelf.
Anna Hogg from the University of Leeds said, “Measurements from CryoSat showed that the Brunt berg was around 390 m, so too thick to come close to shore since the sea is shallow here.
“As for this new Larsen C berg, we are not sure what will happen. It could, in fact, even calve in pieces or break up shortly after. Whole or in pieces, ocean currents could drag it north, even as far as the Falkland Islands. If so it could pose a hazard for ships in Drake Passage.
“What is certain, though, is that we shall continue to use CryoSat to keep a check on its progress.”
Antarctic Peninsula ice more stable than thought
Glacier flow at the southern Antarctic Peninsula has increased since the 1990s, but a new study has found the change to be only a third of what was recently reported.
An international team of researchers, led by CPOM, is the first to map the change in ice speed. The team collated measurements recorded by five different satellites to track changes in the speed of more than 30 glaciers since 1992.
The findings, published today in Geophysical Research Letters, represent the first detailed assessment of changing glacier flow in Western Palmer Land – the southwestern corner of the Antarctic Peninsula.
Credit: A. E. Hogg/CPOM
The new research calls into question a recent study from the University of Bristol that reported 45 cubic kilometres per year increase in ice loss from the sector. CPOM’s research found the increase to be three times smaller.
Lead author Dr Anna Hogg said: “Dramatic changes have been reported in this part of Antarctica, so we took a closer look at how its glaciers have evolved using 25 years of satellite measurements dating back to the early 1990s.”
The researchers found that between 1992 and 2016, the flow of most of the region’s glaciers increased by between 20 and 30 centimetres per day, equating to an average 13% speedup across the glaciers of Western Palmer Land as a whole.
These measurements provide the first direct evidence that Western Palmer Land is losing ice due to increased glacier flow – a process known as dynamical imbalance.
The team also combined their satellite observations with an ice flow model using data assimilation to fill in gaps where the satellites were unable to produce measurements. This allowed the complete pattern of ice flow to be mapped, revealing that the region’s glaciers are now pouring an additional 15 cubic kilometres of ice into the oceans each year compared to the 1990s.
Ice flow in Western Palmer Land from 1992 to 2016, from an optimised ice sheet model. Credit: S. Cornford, CPOM/Univ. Swansea
The earlier study reported that the region was losing three times this amount of ice, based on measurements of glacier thinning and mass loss determined from other satellite measurements. CPOM’s study casts doubt on that interpretation, because the degree of glacier speedup is far too small.
CPOM Director Andy Shepherd explained: “Although Western Palmer Land holds a lot of ice – enough to raise global sea levels by 20 centimetres – its glaciers can’t be responsible for a major contribution to sea level rise, because their speed has barely changed over the past 25 years. It’s possible that it has snowed less in this part of Antarctica in recent years – that would also cause the glaciers to thin and lose mass, but it’s a not a signal of dynamical imbalance.”
The greatest speedup in flow was observed at glaciers that were grounded at depths more than 300 m below the ocean surface.
Dr Hogg said: “We looked at water temperatures in front of the glaciers which have sped up the most, and we found that they flow through deep bedrock channels into the warmest layer of the ocean. This circumpolar deep water, which is relatively warm and salty compared to other parts of the Southern Ocean, has warmed and shoaled in recent decades, and can melt ice at the base of glaciers which reduces friction and allows them to flow more freely.”
With much of Western Palmer Land’s ice mass lying well below sea level it is important to monitor how remote areas such as this, are responding to climate change. Satellites are the perfect tool to do this.
Pierre Potin, ESA’s Manager of the Copernicus Sentinel-1 Mission which was used in the study, said:
“We will continue to use Sentinel-1’s all weather, day-night imaging capability to extend the long term climate data record from European satellites.”
Paper reference:
Hogg, A. E., et al. (2017), Increased ice flow in Western Palmer Land linked to ocean melting, Geophys. Res. Lett., 44 (DOI:10.1002/2016GL072110)
The University of Bristol study can be found at: http://science.sciencemag.org/content/348/6237/899
Sentinel-1 monitors growing crack in Larsen-C
Radar mission Sentinel-1 continues to monitor the growing crack in Antarctica’s Larsen-C ice shelf, which is expected to produce a massive iceberg
Two Sentinel-1 radar images from 7 and 14 April 2017 have been combined to reveal the growing crack in Antarctica’s Larsen-C ice shelf.
CPOM scientist Dr Anna Hogg said: “We can measure the iceberg crack propagation much more accurately when using the precise surface deformation information from an interferogram like this, rather than the amplitude – or black and white – image alone where the crack may not always be visible.”
When the ice shelf calves this iceberg it will be one of the largest ever recorded – but exactly how long this will take is difficult to predict. The sensitivity of ice shelves to climate change has already been observed on the neighbouring Larsen-A and Larsen-B ice shelves, both of which collapsed catastrophically in 1995 and 2002 respectively.
These ice shelves are important because they act as buttresses, holding back the grounded ice that flows towards the sea, and contributes to present day sea level rise.
The Copernicus Sentinel-1 two-satellite constellation is indispensable for discovering and monitoring events like these because it delivers radar images every six days, even when Antarctica is shrouded in darkness for several months of the year.
CPOM is continuing to analyse Sentinel-1 data, distributing maps of ice velocity for key outlet glaciers of the Antarctic and Greenland ice sheets in near real time. The velocity maps are produced by tracking moving features in synthetic aperture radar data acquired by Sentinel-1.
Phytoplankton blooms under Arctic sea ice
In 2011, researchers observed a massive bloom of phytoplankton growing under Arctic sea ice – conditions that should have been far too dark for anything requiring photosynthesis to survive.
Using mathematical modelling, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) found that thinning Arctic sea ice may be responsible for these blooms and that the conditions that cause phytoplankton blooms have become more common. This has the potential to cause significant disruption in the Arctic food chain.
The research, published in Science Advances, involved CPOM scientists David Schroeder, Daniela Flocco and Danny Feltham from the University of Reading.
Phytoplankton shouldn’t be able to grow under the ice because ice reflects most sunlight light back into space, blocking it from reaching the water below.
But over the past decades, Arctic ice has gotten darker and thinner due to warming temperatures, allowing more and more sunlight to penetrate to the water beneath. Large, dark pools of water on the surface of the ice, known as melt ponds, have increased, lowering the reflectivity of the ice. The ice that remains frozen is thin and getting thinner.
The big question was how much sunlight gets transmitted through the sea ice, both as a function of thickness, which has been decreasing, and the melt pond percentage, which has been increasing.
Chris Horvat, first author of the paper and graduate student in applied mathematics at SEAS explained: “What we found was that we went from a state where there wasn’t any potential for plankton blooms to massive regions of the Arctic being susceptible to these types of growth.”
The team’s mathematical modeling found that while the melt ponds contribute to conditions friendly to blooms, the biggest culprit is ice thickness.
Twenty years ago, only about 3 to 4% of Arctic sea ice was thin enough to allow large colonies of plankton to bloom underneath. Today, the researchers found that nearly 30% of the ice-covered Arctic Ocean permits sub-ice blooms in summer months.
Horvat added: “All of a sudden, our entire idea about how this ecosystem works is different. The foundation of the Arctic food web is now growing at a different time and in places that are less accessible to animals that need oxygen.”
Dr Schroeder summarised: “This study demonstrates that improving the sea ice model leads to a step forward in our understanding of how the Arctic is responding to climate change.”
The researchers hope their model will be helpful for planning future expeditions to observe these blooms and measuring the impact this shift will have on ecosystems.
Read the full paper: Horvat et al. (2017) The frequency and extent of sub-ice phytoplankton blooms in the Arctic Ocean, Science Advances, 3, 3, 2375-2548.
Further information can be found on the Harvard and Reading University websites, as well as via extensive media coverage.
CryoSat reveals Antarctica in 3D
Around 250 million measurements taken by ESA’s CryoSat mission over the last six years have been used to create a unique 3D view of Antarctica, offering a snapshot of the undulating surface of this vast ice sheet.
CryoSat’s radar altimeter detects tiny variations in the height of the ice across the entire continent, including on the steeper continental margins where the vast majority of ice losses occur.
Importantly, the satellite’s orbit takes it to latitudes within 200 km of the north and south poles – closer than other Earth observation satellites.
Naturally, the mission is also used to map changes in the thickness of ice floating in the polar oceans, which is particularly important for the Arctic.
This new ‘digital elevation model’ was revealed at this week’s gathering of CryoSat scientists in Banff, Canada.
Tom Slater, researcher at the UK Centre for Polar Observation and Modelling (CPOM), said, “We used around 250 million measurements taken by CryoSat between 2010 and 2016 to create the most comprehensive picture of Antarctic ice elevation currently available.”
It offers wide range of applications showing the surface of Antarctica in such detail means it can be used in anything from planning fieldwork to modelling the ice sheet.
It also allows scientists to distinguish between changes in topography and ice motion when working with other satellite measurements, such as those used to calculate the balance between how much the ice sheet is gaining by accumulating snow and losing through melting and creating icebergs.
The model will soon be freely available via the CPOM portal, which already provides information on sea-ice volume and thickness, ice velocity and, shortly, ice sheets. In the meantime, however, the model can be downloaded here.
CPOM Director Andrew Shepherd added, “We want the digital elevation model to be accessible to anyone who uses ice-sheet surface topography measurements in their work.
“This should benefit not only studies of the Antarctic ice sheet, but also projections of future sea-level rise.â€
ESA’s CryoSat mission manager, Tommaso Parrinello, said, “We are hearing some great results from our mission at the meeting here in Banff.
“It’s now widely recognised that dwindling polar ice is one of the first casualties of climate change, but it’s important to provide the hard facts and this we can do with CryoSat.
I”t’s equally important to make sure the satellite’s data are correct and so we have a huge international field campaign just started in the Arctic to take ‘ground truth’ measurements from aircraft and on the ice to compare with those of CryoSat. It’s a tough environment, so we wish them lots of luck.”