Summit County Citizens Voice

Antarctica study suggests shape of channels beneath ice can slow or temporarily halt retreat of ice sheets

Despite steady global warming, ice sheet retreat may slow or even stop temporarily, based on the shape of the ground beneath the ice. Bob Berwyn photo.

By Summit Voice

SUMMIT COUNTY — Even as global warming shrinks many of the world’s major ice sheets, new research suggest that the underlying topography can significantly influence how fast they retreat, and in some cases even halt temporarily during long phases of climate warming.

The researchers reached their conclusions after studying the landscape of the seafloor in Marguerite Bay, in the Antarctic Peninsula. They saw that, during a rapid phase of recession 13,000 years ago, retreat paused many times.

Computer models showed that ice dragged on the sides of the channel more where it was narrow, causing retreat to slow and in places temporarily stop for decades to centuries before retreat continued.

The findings provide the first simulation of past ice-sheet retreat and collapse over a ten thousand year period in Antarctica and shed new light on what makes ice stable or unstable. That could help scientists refine predictions of future ice extent and global sea level rise, according to the researchers from the UK’s Durham University.

“Our research shows that the physical shape of the channels is a more important factor in controlling ice stability than was previously realized,” said Durham University glaciologist Stewart Jamieson. “Channel width can have a major effect on ice flow, and determines how fast retreat, and therefore sea-level rise, can happen.”

The International Panel on Climate Change has stated that one of the main challenges in predicting future sea-level rise is to quantify and model the interactions between evolving ice sheets, oceans, sea level and climate. Significant efforts have been made over the last decade to develop computer models and collect data in order to reduce uncertainties and understand the potential impacts under scenarios of future climate change.

“Our results suggest that during an overall phase of retreat an ice stream can appear almost stable when in fact, in the longer-term, the opposite may be the case,” Jamieson said. “Getting a clearer picture of the landscape beneath the ice is crucial if future predictions of change in the ice-sheets and sea level are to be improved.”

Marine-based ice streams are the fast flowing arteries of ice sheets, draining approximately 90 percent of the ice that reaches the sea. They flow through large channels where the ice can move thousands of metres in a year. According to the scientists, the unpredictable nature of ice streams makes forecasting ice-sheet retreat extremely difficult. If ice streams speed up they can cause sea level to rise.

“Ice streams are like taps filling a bath, but the problem here is that we do not know if something is suddenly going to turn them up or even turn them down,” said Durham University’s Chris Stokes.

Many ice streams are found in channels with beds that are below sea level and that deepen inland. Current theory suggests that ice loss can increase rapidly in deeper water, but the new findings show that channel width plays a crucial role and that narrow bottlenecks in the landscape beneath the ice can cause retreat to slow down.

“We can see from our simulations and from new maps of the ocean floor that these bottlenecks occur in the same place as pauses or slowdowns in past ice retreat,” said  Durham University geographer Andreas Vieli. “This means we should look more closely at the shape of the bed underneath Greenland and Antarctica to better understand how ice might retreat in the future.”

The researchers say that understanding ice-stream behavior and the rate of mass loss from ice sheets and glaciers is essential.

“Knowledge of the factors influencing stability and retreat of ice streams is of particular concern because significant portions of the West Antarctic and Greenland ice sheets are currently losing mass that contributes significantly to sea-level rise. Our model results help to explain the apparently time-transgressive retreat of ice streams around Antarctica following the last ice age,” said Dr Claus-Dieter Hillenbrand, of the British Antarctic Survey.

The results of the new research from Durham University, the University of Sheffield, the University of Cambridge, and the British Antarctic Survey are published in the journal Nature Geoscience.

Filed under: climate and weather, Environment, global warming Tagged: | Antarctic Peninsula, Antarctica, British Antarctic Survey, climate change, Durham University, global warming, Intergovernmental Panel on Climate Change, Marguerite Bay