Geography Can Temporarily Halt Ice-Sheet Retreat

A new study led by researchers from Durham University in the UK has found that the geometry of channels beneath an ice-sheet play a much stronger role in mitigating retreat than previously understood.

The findings are part of a study which simulate ice-sheet retreat and collapse over a ten thousand year period in Antarctica, and shed new light on what makes ice stable or unstable.

These findings add to our growing understanding of ice-sheets and, subsequently, their impact on future sea-level rise.

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

The results of the new study are published in the journal Nature Geoscience.

“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,” said Dr. Jamieson. “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.”

The researchers looked at the landscape of the seafloor in Marguerite Bay, in the Antarctic Peninsula. They found that during a rapid phase of ice retreat 13,000 years ago the ice paused many times on its journey. Using a computer model simulation they found that ice dragged on the sides of the channel more when it was narrow, causing the ice above to slow in its retreat and in some places stop altogether for decades to centuries before it started up again.

The new findings show that the width of the channels plays an important role and that narrow bottlenecks in the landscape beneath the ice can hamper an ice-sheet’s retreat.

Dr Andreas Vieli, Department of Geography, Durham University, said: “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. 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 behaviour and the rate of mass loss from ice sheets and glaciers is essential.

DrClaus-Dieter Hillenbrand, from the British Antarctic Survey, said: “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.”

Source: Durham University

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