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.

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

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.

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.

CPOM’s Harry Heorton blogs about sea ice formation and dynamics and why it’s important for global climate on the Reading Meteorology Department blog here.