Seasonal change in Antarctic ice sheet movement observed for first time

Some estimates of Antarctica’s total contribution to sea-level rise may be over- or underestimated after researchers discovered a previously unknown source of variability in ice loss.

The researchers, from the University of Cambridge and Austrian engineering firm ENVEO, identified distinct, seasonal movements in the flow of land ice that drained into the George VI Ice Shelf — a floating platform of ice about the size of Wales — in the Antarctic. Peninsula.

Using images from the Copernicus/European Space Agency Sentinel-1 satellites, the researchers found that the glaciers feeding the ice shelf accelerate by about 15% during the Antarctic summer. This is the first time such seasonal cycles have been detected on land ice flowing into Antarctic ice shelves. The results are reported in the journal The cryosphere.

While it is not uncommon for ice flow in the Arctic and Alpine regions to accelerate in summer, scientists had previously assumed that ice in Antarctica was not subject to the same seasonal movements, especially where it flows in large ice shelves and where temperatures are below freezing for the most of the year.

This assumption was also partly fueled by a lack of images collected about the icy continent in the past. “Unlike the Greenland Ice Sheet, where a large amount of data has allowed us to understand how the ice moves from season to season and year to year, until recently we have not had comparable data coverage to look for such changes over Antarctica. search,” said Karla Boxall of Cambridge’s Scott Polar Research Institute (SPRI), the study’s lead author.

“Observations of changes in ice speed in the Antarctic Peninsula have typically been measured over consecutive years, so we missed a lot of details about how the flow varies from month to month throughout the year,” said study co-author Dr. Frazer Christie, also from SPRI.

Prior to the detailed record of ice speed made possible by the Sentinel-1 satellites, scientists looking to study short-term variations in the Antarctic ice flow had to rely on information gathered by optical satellites such as NASA’s Landsat 8.

“Optical measurements can only observe the Earth’s surface on cloud-free days during the summer months,” said study co-author Dr. Thomas Nagler, CEO of ENVEO. “But by using Sentinel-1 radar imagery, we were able to detect seasonal changes in the ice flow thanks to the ability of these satellites to monitor year-round and in all weather conditions.”

Currently, the causes of this seasonal change are uncertain. It can be caused by meltwater at the surface reaching the base of the ice and acting as a lubricant, as is the case in the Arctic and Alpine regions, or it can be caused by relatively warm ocean water melting the ice from below, causing it to melt. floating ice thins and allows upstream glaciers to move faster.

“These seasonal cycles could be due to either mechanism, or a combination of both,” Christie said. “Detailed ocean and surface measurements will be needed to fully understand why this seasonal change occurs.”

The results imply that similar seasonal variability may exist in other more vulnerable locations in Antarctica, such as the Pine Island and the Thwaites Glaciers in West Antarctica. “If true, these seasonal features may not have been captured in some measurements of Antarctic ice mass loss, with potentially important implications for estimates of global sea level rise,” Boxall said.

“It’s the first time this seasonal signal has been found on the Antarctic ice sheet, so the questions it raises about the possible presence and causes of seasonality elsewhere in Antarctica are really interesting,” said study co-author Professor Ian Willis, also of SPRI. “We look forward to taking a closer look at and highlighting these important questions.”