When polar ice sheets melt, the process doesn’t just raise sea levels – it also distorts Earth’s lower surface, a new study shows, and some of the effects can be seen over thousands of kilometers.
What’s happening is that the Earth’s crust is rising and spreading out as the weight of ice over Greenland, Antarctica and the Arctic islands rises. The movement is not huge, averaging less than a millimeter a year, but it is there and covers a large area.
There is also a feedback loop, because as the bedrock under the ice changes, this in turn affects how the ice continues to melt and separate. A comprehensive understanding of how this works is essential to modeling what our world might look like in the future.
“Scientists have done a lot of work right under the ice sheets and glaciers.” Geophysicist Sophie Coulson says:, from Los Alamos National Laboratory in New Mexico.
“So they knew this would define the area where the glaciers were, but they didn’t know it had a global scale.”
several of Previous Studies She has documented the uplift that can occur when ice sheets melt, but Coulson and her colleagues looked at horizontal shifts more closely and over a larger area. They found that the anomalies can vary greatly from year to year.
In some areas, researchers found that horizontal motion actually exceeds vertical motion. They used satellite data and field measurements from 2003 to 2018 to measure crustal movement in three dimensions.
This crustal regression can take thousands of years – the study shows that some changes are still being felt on Earth’s surface since the end of the last ice age about 11,000 years ago.
“On modern time scales, we think of the Earth as a flexible structure, like a rubber band, whereas on time scales of thousands of years, the Earth is like a very slow-moving fluid.” Coulson said.
“Ice age processes take a very long time to complete, so we can still see their results today.”
The researchers compared the effect of an ice pack on a wooden plate pressed down on water: When the slab is removed and the weight is removed, the liquid expands to fill the available space, and the same thing happens to the Earth’s crust.
And as the rate of ice melt continues to increase around the world, it’s important for scientists to understand its impact on the shape of Earth’s surface, even if the shifts each year are relatively small.
This new study gives us more detailed data than ever before – useful not only for studying snowmelt and changes in Earth’s shape, but also for many other areas of scientific research.
“Understanding all the factors that cause crustal movement is really important for a variety of Earth science problems.” Coulson says.
“For example, to accurately monitor tectonic movement and seismic activity, we need to be able to unravel that movement that results from the loss of ice mass in modern times.”