Seven areas of fast-flowing ice on the Antarctic Peninsula have been formally named after Earth observation satellites, following a request by CPOM scientist Anna Hogg.

Dramatic changes in the shape of the Antarctic ice sheet have become emblematic of the climate crisis. Reports of iceberg calving, changes in ice-sheet speed, thickness and mass have informed the climate change debate, and are largely thanks to routine monitoring by an international fleet of Earth observation satellites.

Recognising the importance of observations from space, the UK Antarctic Place-names Committee has approved seven new names for international use.

The decision follows a request by Dr Hogg, who identified that the major glaciers flowing westwards from the Dyer Plateau on the Antarctic Peninsula are thinning and flowing at rates of more than 1.5 metres a day.

Dr Hogg is an expert in Earth observation of the Polar Regions and uses satellite data to study the remote Antarctic and Greenland Ice Sheets. Her research published in 2017 that identified the thinning of the Dyer Plateau and linked increase ice flow in Western Palmer Land to ocean melting would not have been possible without satellite observations.

In deference to the critical role that satellites play in measuring and monitoring Antarctic glaciology, Dr Hogg requested that seven glaciers monitored in her study be named after the satellites. The names will be added to the British Antarctic Territory Gazetteer and will be available for use on all maps, charts and in all future publications.

Dr Hogg said: “Naming the glaciers after the Earth observation satellites we use to measure them is a great way to celebrate the international collaboration in space, and on big science questions.

“Satellite observations provide scientists with information on some of the most inaccessible regions on Earth. Without this data we would have a very unclear picture of how our rapidly changing environment is affecting glaciers around the world.

“The European Space Agency satellite missions allow us not only to understand the changes that are taking place in the fastest warming region on the planet but give us the means to predict what could happen to this region in the future.

“It’s fantastic news that the Government of the British Antarctic Territory have formally approved these new place names, which will be on the record forever more.”

Seven newly named ice streams

The Ers Ice Stream that flows west between Jensen Nunataks and Gunn Peaks was named after the two ESA satellites ERS-1 and ERS-2 that operated between 1991 and 2011. They provided the first high-resolution, wide-swath and day-and-night images that were used to calculate the speed and direction of the flow of glacier ice.

The Envisat Ice Stream, lies further to the west and commemorates ESA’s largest Earth observation satellite, which was launched in 2002 and operated until 2012. It carried 10 instruments that extended the datasets generated by ERS-1 and ERS-2.

The Cryosat Ice Stream flows further west and is named after the ESA Earth Explorer satellite launched in 2010. CryoSat was designed specifically to detect changes in the height of polar ice using a sophisticated instrument that provides high-accuracy elevation measurements over the rugged ice-sheet margins and for sea ice in polar waters. CPOM Director Professor Andy Shepherd is the principal scientific advisor to ESA for this mission.

Still further west lies the Grace Ice Stream, which commemorates the joint Gravity Recovery and Climate Change Experiment (GRACE) mission run by NASA and the German Aerospace Center. Between 2002 and 2017, the mission mapped, for the first time, Earth’s time-varying gravitational field, detecting Antarctic ice-sheet mass changes with unprecedented accuracy.

The Sentinel Ice Stream is named after the more recent series of satellites that ESA develops for the EU’s Copernicus programme to the environment and climate change. This programme provides open access to images, allowing the public to easily view and witness ongoing, year-round changes in Antarctica and the rest of the world.

The ALOS Ice Rumples are named after a Japan Aerospace Exploration Agency mission. Its optical and radar image data acquired between 2006 and 2011 have been used to map ice in the polar regions, with dedicated imaging campaigns to capture Antarctic ice-sheet surface changes during the International Polar Year campaign that ran between 2007 and 2009.

Finally, the Landsat ice stream is the most westerly of the newly named glaciers. It is named after the joint NASA/US Geological Survey series of Landsat Earth observation satellites that have been operating since 1972. Landsat has been one of the primary satellite systems used in Antarctic studies, providing over 40 years of uninterrupted mapping of the continent for climate and environment studies.

Bolstering climate research

Fifteen space agencies currently collaborate on coordinating Antarctic data collection from a wide range of satellites, and on the planning of data acquisition and products to address the needs of the scientific community, under the banner of the World Meteorological Organization’s Polar Space Task Group.

Mark Drinkwater, ESA chair of the task group, said: “Interagency planning is paying dividends for polar science, with more comprehensive multi-satellite, multi-instrument datasets and better coverage than previously possible, which enables the science community to address today’s key climate research challenges.

“This gesture of naming Antarctic glaciers after these ground-breaking satellites is a mark of recognition of the importance of Earth observation data in addressing the climate crisis.”

In only 25 years, ocean melting has caused ice thinning to spread across West Antarctica so rapidly that 24% of its glacier ice is now affected, according to a new study.

By combining 25 years of European Space Agency satellite altimeter measurements and a model of the regional climate, CPOM have tracked changes in snow and ice cover across the continent.

Led by CPOM Director Professor Andy Shepherd, the team found that Antarctica’s ice sheet has thinned by up to 122 metres in places, with the most rapid changes occurring in West Antarctica where ocean melting has triggered glacier imbalance.

This means that the affected glaciers are unstable as they are losing more mass through melting and iceberg calving than they are gaining through snowfall.

They also found that the pattern of glacier thinning has not been static.

Since 1992, the thinning has spread across 24% of West Antarctica and over the majority of its largest ice streams, the Pine Island and Thwaites Glaciers, which are now losing ice five times faster than they were at the start of the survey.

Professor Andrew Shepherd said: “We can see clearly now that a wave of thinning has spread rapidly across some of Antarctica’s most vulnerable glaciers, and their losses are driving up sea levels around the planet.”

The study, published today in Geophysical Research Letters, used over 800 million measurements of the Antarctic ice sheet height recorded by the ERS-1, ERS-2, Envisat, and CryoSat-2 satellite altimeter missions between 1992 and 2017 and simulations of snowfall over the same period produced by the RACMO regional climate model.

Together, these measurements allow changes in the ice sheet height to be separated into those due to weather patterns, such as less snowfall, and those due to longer term changes in climate, such as increasing ocean temperatures that eat away ice.

Professor Shepherd explained: “In parts of Antarctica the ice sheet has thinned by extraordinary amounts, and so we set out to show how much was due to changes in climate and how much was due to weather.”

To do this, the team compared the measured surface height change to the simulated changes in snowfall, and where the discrepancy was greater they attributed its origin to glacier imbalance.

They found that fluctuations in snowfall tend to drive small changes in height over large areas for a few years at a time, but the most pronounced changes in ice thickness are signals of glacier imbalance that have persisted for decades.

Professor Shepherd added: “Knowing how much snow has fallen has really helped us to detect the underlying change in glacier ice within the satellite record.

“We can see clearly now that a wave of thinning has spread rapidly across some of Antarctica’s most vulnerable glaciers, and their losses are driving up sea levels around the planet.

“Altogether, ice losses from East and West Antarctica have contributed 4.6 mm to global sea level rise since 1992.”

Dr Marcus Engdahl of the European Space Agency, a co-author of the study, added: “This is an important demonstration of how satellite missions can help us to understand how our planet is changing.

“The polar regions are hostile environments and are extremely difficult to access from the ground. Because of this, the view from space is an essential tool for tracking the effects of climate change.”

Further information:

The paper Trends in Antarctic Ice Sheet Elevation and Mass is published in Geophysical Research Letters 16 May 2019

The ERS-1, ERS-2, ENVISAT and CryoSat-2 satellite radar altimetry time-series produced in this study was funded by the European Space Agency Climate Change Initiative and the data is freely available online.

The RACMO regional climate model data used in this study were provided by Michiel van den Broeke and Stefan Ligtenberg of the University of Utrecht

A recently-launched satellite mission is now proving a valuable addition to Antarctic monitoring efforts, according to work published this week in The Cryosphere.

The study, carried out by CPOM researchers alongside European Space Agency (ESA) and industry partners, shows the potential of Sentinel-3 – one of the EU Copernicus satellite missions – to contribute towards long-term ice sheet monitoring programmes.

From its orbit 815 km above the Earth, Sentinel-3 is able to detect the height of the ice surface at the remote Lake Vostok test site in East Antarctica to within tens of centimetres.

The scientists also found that Sentinel-3 could detect where the ice surface was rapidly lowering, establishing the satellite’s credentials as a new platform which can help to monitor Antarctica’s contribution to sea level rise.

Determining how well Sentinel-3 functions over ice sheets is particularly important given that CryoSat-2, ESA’s dedicated polar mission, is already operating well beyond its planned lifetime.

CryoSat-2 is designed to fly in a unique orbit, maximising coverage of coastal areas of the ice sheet, and mapping the regions close to the North and South Poles that were beyond the reach of previous satellites.

Although Sentinel-3 “which has to balance many tasks“ cannot match this coverage, it still holds potential as a valuable long-term monitoring platform for decades to come.

Lead author Dr Mal McMillan, CPOM scientist at Lancaster University, said: “Although the Sentinel-3 altimeter was primarily designed to monitor the oceans, we wanted to test how well it works over ice, and to see whether it is able to detect signs of ice sheet change. Through the support offered by ESA’s Scientific Exploitation of Operational Missions element, we have been able to study the performance of the Sentinel-3 mission for several years now, and we are pleased to be able to publish these results”

He added: “From what we can see here, with just two years’ worth of data, Sentinel-3 is going to be a very useful tool for surveying the Antarctic ice sheet.”

Sentinel-3 uses a radar technique called Delay-Doppler altimetry to make high resolution measurements of the height of the ice sheet.

Where the ice is relatively flat, Sentinel-3 could map its height to within 10 cm of measurements taken by aircraft, as part of NASA’s Operation Icebridge campaign.

Dr McMillan explained: “This level of accuracy means that we can also use Sentinel-3 to track important features on the ice surface, like the fingerprint of active subglacial lakes draining and refilling beneath several kilometres of ice.”

Using radar satellites like Sentinel-3 over ice nonetheless has its challenges.  For example, measurements over Antarctica’s steeper, craggy coastal areas were less accurate because of how the rough landscape affects the radar signal.

Future research into Sentinel-3’s performance, as well as further improvements to data processing, will help take these effects into account. In the meantime, Sentinel-3 has already shown its value as a new tool for detecting ice sheet change.

Co-author Jerome Benveniste of the European Space Agency summarised: “We are delighted with the early promise shown by Sentinel-3 for ice sheet monitoring, and are increasingly confident that it will be a long-term asset to climate science.”

Notes

The full paper is: McMillan, M. et al. (2019) Sentinel-3 Delay-Doppler altimetry over Antarctica, The Cryosphere 13, 1-14 doi:10.5194/tc-13-1-2019

The Sentinel-3A satellite, part of the European Union’s Copernicus Programme was launched on 16 February 2016, followed by Sentinel-3B on 25 April 2018. Each satellite provides coverage up to a latitude of 81.35áµ’, yielding regular, monthly observations of much of Earth’s polar ice sheets.  Sentinel-3 is unique in being the first mission to operate in high-resolution Delay-Doppler (or Synthetic Aperture Radar—SAR) mode across the entire ice sheet.

The work was supported by the UK NERC Centre for Polar Observation and Modelling, ESA’s Sentinel-3 Performance Improvement for Ice Sheets (SPICE) study and the Sentinel-3 Mission Performance Centre.

By David Schroeder, CPOM researcher, University of Reading

Reproduced from the Weather and Climate @ Reading blog

Climate model projections are our best approach to make predictions about future sea ice in both hemispheres for the whole 21^st century. Given the large spread between individual model projections and distinct discrepancies between model results and satellite-based observations for the last decades, the question arises how accurate these projections are. The reliability of such simulations depends on how well key processes are captured in the climate model. CMIP5 (Coupled Model Intercomparison Project Phase 5) models generally simulate the observed sea ice decline better than the older CMIP3 models indicating that, for example, the improved representation of sea ice processes is important (Stroeve et al., 2012).

In Danny Feltham’s sea ice group we have added and improved several sea ice processes in the Los Alamos sea ice model CICE which is used in many climate models (e.g. the current U.K. Met Office model HadGEM3). The most important contributions are a physical melt pond model describing the evolution of melt ponds (Flocco et al., 2012; Schroeder et al., 2014), an elastic anisotropic plastic rheology accounting for the subcontinuum anisotropy of the sea ice cover (Tsamados et al., 2013) and a spatially and temporally variable form drag parameterization for the momentum exchange between ice and atmosphere as well as ice and ocean (Tsamados et al., 2014).

These new developments increase the realism of the sea ice model. However, incorporating these developments in a climate model does not result in better climate simulations as a matter of course. Many physical and empirical parameters are not very well constrained in a sea ice model requiring a tuning process applying observational data. In the past, most of the tuning has been based on sea ice concentration data derived from passive microwave imagery. This is a problem because realistic sea ice thickness is crucial for simulating variability and trends of the sea ice cover. Using radar altimetry, sea ice thickness estimates are available from CryoSat-2 (CS2) (e.g. from the CPOM portal) during the ice growth seasons since 2010. However, the discrimination of ice and open water, the discrimination of ice type, retracking radar waveforms to obtain height estimates, constructing of sea surface height beneath the ice, and estimating the depth of the snow cover result in a grid cell ice thickness uncertainty of about 25%.

Figure 1:  Mean effective sea ice thickness over read region shown in inlet above. Verification of CICE-default and CICE-best with Cryosat CS2 CPOM. Results from the ocean sea-ice model PIOMAS are added for comparison. Red area is defined as region where impact of winter growth on thickness change dominates other factors and where CS2 data are most accurate.

In a current study we selected an optimal region for comparing sea ice thickness between simulations with the sea ice model CICE and CS2 data (see red region in Figure 1) by taking into account the strengths and weaknesses of both approaches excluding locations where the number of CS2 observations is limited and the sea ice is thin (Schroeder et al., 2018). Figure 1 shows that a default CICE simulation (blue) strongly underestimates ice thickness, but a new CICE setup (red) agrees well. The most important impact comes from implementing a new process: accounting for the loss of drifting snow. Our optimal model configuration does not only improve the simulated sea ice thickness, but also summer sea ice concentration, melt pond fraction, and length of the melt season. In spite of its uncertainties we successfully applied CS2 sea ice thickness data to improve sea ice model physics.

Reducing uncertainty in sea ice projections requires better representation of key processes, not only of the sea ice component, but also in the atmosphere, the ocean and regarding the coupling. Polar cloud formation and the interaction with the sea ice surface has been identified as a key process which is currently not represented satisfactorily.

References:

Flocco, D., D. Schroeder, Feltham D. L., Hunke E. C., 2012: Impact of melt ponds on Arctic sea ice simulations from 1990 to 2007. J. Geophys. Res., 117, C09032, https://doi.org/10.1029/2012JC008195.

Schroeder, D., Feltham D. L., Flocco D., Tsamados M., 2014: September Arctic sea-ice minimum predicted by spring melt-pond fraction. Nat. Climate Change, 4, 353-357, https://doi.org/10.1038/NCLIMATE2203.

Schröder, D., Feltham D. L., Tsamados M., Ridout A., Tilling R., 2018: New insight from CryoSat-2 sea ice thickness for sea ice modelling. The Cryosphere Discuss. (in review), https://doi.org/10.5194/tc-2018-159

Stroeve, J. C., Kattsov V., Barrett A., Serreze M., Pavlova T., Holland M., Meier W. N., 2012: Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations. Geophys. Res. Lett., 39, L16502, https://doi.org/10.1029/2012GL052676.

Tsamados, M., Feltham D. L., Schroeder D., Flocco D., Farrell S. L., Kurtz N., Laxon S. W., Bacon S., 2014: Impact of Variable Atmospheric and Oceanic Form Drag on Simulations of Arctic Sea Ice. J. Phys. Oceanog., 44, 1329-1353, https://doi.org/10.1175/JPO-D-13-0215.1

Tsamados, M., Feltham D. L., Wilchinsky A., 2013: Impact of a new anisotropic rheology on simulations of Arctic sea ice. J. Geophys. Res.: Oceans, 118, 91-107, https://doi.org/10.1029/2012JC007990