ESA GOCE and NASA GRACE detect Gravity Anomaly in Antarctic Ice Loss

Changes in Earth’s gravity field resulting from loss of ice from West Antarctica between November 2009 and June 2012 (mE = 10–12 s–2). 

 A combination of data from ESA’s GOCE mission and NASA’s Grace satellites shows the ‘vertical gravity gradient change’. 

Credit: ESA

Although not designed to map changes in Earth's gravity over time, ESA's extraordinary satellite has shown that the ice lost from West Antarctica over the last few years has left its signature.

Artist rendering of ESA's GOCE satellite in orbit. 

Credit: ESA

More than doubling its planned life in orbit, GOCE spent four years measuring Earth's gravity in unprecedented detail.

Scientists are now armed with the most accurate gravity model ever produced.

This is leading to a much better understanding of many facets of our planet, from the boundary between Earth's crust and upper mantle to the density of the upper atmosphere.

The strength of gravity at Earth's surface varies subtly from place to place owing to factors such as the planet's rotation and the position of mountains and ocean trenches.

Changes in the mass of large ice sheets can also cause small local variations in gravity.

Recently, the high-resolution measurements from GOCE over Antarctica between November 2009 and June 2012 have been analysed by scientists from the German Geodetic Research Institute, Delft University of Technology in the Netherlands, the Jet Propulsion Lab in USA and the Technical University of Munich in Germany.

Remarkably, they found that the decrease in the mass of ice during this period was mirrored in GOCE's measurements, even though the mission was not designed to detect changes over time.

Using gravity data to assess changes in ice mass is not new.

The NASA, DLR (Germany) Grace satellite, which was designed to measure change, has been providing this information for over 10 years.

However, measurements from Grace are much coarser than those of GOCE, so they cannot be used to look at features such as Antarctica's smaller 'catchment basins'.

For scientific purposes, the Antarctic ice sheet is often divided into catchment basins so that comparative measurements can be taken to work out how the ice in each basin is changing and discharging ice to the oceans. Some basins are much bigger than others.

By combining GOCE's high-resolution measurements with information from Grace, scientists can now look at changes in ice mass in small glacial systems, offering even greater insight into the dynamics of Antarctica's different basins.



They have found that that the loss of ice from West Antarctica between 2009 and 2012 caused a dip in the gravity field over the region.

In addition, GOCE data could be used to help validate satellite altimetry measurements for an even clearer understanding of ice-sheet and sea-level change.

Using gravity data to assess changes in ice mass is not new. The NASA, DLR (Germany) Grace satellite, which was designed to measure change, has been providing this information for over 10 years.

However, measurements from Grace are much coarser than those of GOCE, so they cannot be used to look at features such as Antarctica's smaller 'catchment basins'.

For scientific purposes, the Antarctic ice sheet is often divided into catchment basins so that comparative measurements can be taken to work out how the ice in each basin is changing and discharging ice to the oceans. Some basins are much bigger than others.

By combining GOCE's high-resolution measurements with information from Grace, scientists can now look at changes in ice mass in small glacial systems, offering even greater insight into the dynamics of Antarctica's different basins.

They have found that that the loss of ice from West Antarctica between 2009 and 2012 caused a dip in the gravity field over the region.

In addition, GOCE data could be used to help validate satellite altimetry measurements for an even clearer understanding of ice-sheet and sea-level change.

Using 200 million measurements collected by ESA’s CryoSat mission between January 2011 and January 2014, researchers from the Alfred Wegener Institute in Germany have discovered that the Antarctic ice sheet is shrinking in volume by 125 cubic kilometres a year. 

The study, which was published in a paper published on 20 August 2014 in the European Geosciences Union’s Cryosphere journal, also showed that Greenland is losing about 375 cubic kilometres a year. 

Credit: ESA

ESA's CryoSat satellite, which carries a radar altimeter, has recently shown that since 2009 the rate at which ice is been lost from the West Antarctic Ice Sheet every year has increased by a factor of three.

And, between 2011 and 2014, Antarctica as a whole has been shrinking in volume by 125 cubic kilometres a year.

Johannes Bouman from the German Geodetic Research Institute said, "We are now working in an interdisciplinary team to extend the analysis of GOCE's data to all of Antarctica.

"This will help us gain further comparison with results from CryoSat for an even more reliable picture of actual changes in ice mass."

This new research into GOCE's gravity data revealing ice loss over time is being carried out through ESA's Earth Observation Support to Science Element.

ESA Cryosat-2 finds sharp rise in Antarctica ice loss

Three years of observations from ESA’s CryoSat-2 satellite show that the Antarctic ice sheet is now losing 159 billion tonnes of ice each year – twice as much as when it was last surveyed.

The polar ice sheets are a major contributor to the rise in global sea levels, and these newly measured losses from Antarctica alone are enough to raise global sea levels by 0.45 mm each year.

These latest findings by a team of scientists from the UK’s Centre for Polar Observation and Modelling show that the pattern of imbalance continues to be dominated by glaciers thinning in the Amundsen Sea sector of West Antarctica.

Between 2010 and 2013, West Antarctica, East Antarctica and the Antarctic Peninsula lost 134, 3 and 23 billion tonnes of ice each year, respectively.

The average rate of ice thinning in West Antarctica has increased compared to previous measurements, and this area’s yearly loss is now one third more than measured over the five years before CryoSat’s launch.

Launched in 2010, CryoSat-2 carries a radar altimeter that can measure the surface height variation of ice in fine detail, allowing scientists to record changes in its volume with unprecedented accuracy.

CryoSat-2 surveys almost all – 96% – of the Antarctic continent, reaching to within 215 km of the South Pole. In addition, it has increased coverage over coastal regions, where today’s ice losses are concentrated.

Andrew Shepherd

“Thanks to its novel instrument design and to its near-polar orbit, CryoSat-2 allows us to survey coastal and high-latitude regions of Antarctica that were beyond the capability of past altimeter missions, and it seems that these regions are crucial for determining the overall imbalance,” said Prof. Andrew Shepherd from the University of Leeds, UK, who led the study.

In particular, newly mapped areas by CryoSat-2 in West Antarctica have now brought altimeter observations closer to estimates based on other approaches.

“We find that ice losses continue to be most pronounced along the fast-flowing ice streams of the Amundsen Sea sector, with thinning rates of 4-8 m per year near to the grounding lines, where the ice streams lift up off the land and begin to float out over the ocean, of the Pine Island, Thwaites and Smith Glaciers,” said Dr Malcolm McMillan from the University of Leeds, UK, and lead author of the study.

Malcolm McMillan

This area has long been identified as the most vulnerable to changes in climate.

Recent assessments say its glaciers may have passed a point of irreversible retreat.

“Although we are fortunate to now have, in CryoSat-2, a routine capability to monitor the polar ice sheets, the increased thinning we have detected in West Antarctica is a worrying development,” said Prof. Shepherd.

“It adds concrete evidence that dramatic changes are under way in this part of our planet. The challenge is to use this evidence to test and improve the predictive skill of climate models.”

The findings were published in Geophysical Research Letters.

Deeper and Longer Greenland Canyons - Video

The below sea-level canyons beneath the ocean-feeding glacier cut further inland than previously estimates. Accelerated ice loss of the glacier was thought to be limited, but this finding calls into question its duration.

Credit: NASA and University of California, Irvine