SOURCE: Science Nordic

DATE: September 8, 2018

SNIP: At the peak of the last ice age, ice covered a much larger area of the Amundsen Sea Embayment than it does today, but it shrank to reach its modern configuration around 10,000 years ago, as shown in the figure below.

Since then, the glaciers in this region have been pretty much stable until about 200 years ago, when they started to melt and retreat. This happened slowly at first, but there has been a clear increase of ice loss since 2005.

Our study shows that the Earth surface, progressively relieved from the big burden of ice, is finally rising and it is doing so at an accelerating pace – up to 41 millimetres a year in 2014, which is between four and five times faster than expected.

Why does the land rise when the ice melts?
To explain this, we need to understand the process by which the earth rises, known as glacial isostatic adjustment to give it its proper name.

A useful analogy is to imagine the structure of the Earth beneath Antarctica as a double-layer mattress with a springy, elastic layer at the top and a thick, memory foam underneath.

As the ice thins, the land immediately underneath the ice sheet quickly springs back in response to the loss of weight. This is like the springy layer at the top of your mattress, which springs back as you get out of bed. This immediate response is called elastic rebound.

Secondly, there is a delayed uplift as the mantle beneath the bedrock responds. This is analogous to the deeper memory foam layer of the mattress. Like the memory foam, the mantle ‘remembers’ its past load for a while before slowly creeping back to its original, unloaded shape.

If the mantle is stiff, this delayed uplift, occurs very slowly on time scales of millennia or more. Conversely, if the mantle is soft and full of water, it will be far less viscous (i.e. less resistant to flow), and will respond much more rapidly to a loss of ice above.

It is this fast surface response that we have now detected underneath Antarctica, suggesting the presence of a soft mantle.