Seasonal change in Antarctic ice sheet motion observed for the first time – Is it increasing?

news7g10/11/2022

5 3 minutes read

Seasonal change in Antarctic ice sheet motion observed for the first time - Is it increasing?

UNIVERSITY OF CAMBRIDGE

Glacier flows into the George VI ice shelf — **IMAGES: CONCHIE, HUBERT, SATURN, VENUS AND URANUS GLACIERS DRAINING INTO LADEN GEORGE VI ICE MELTWATER-LADEN.** see more
CREDIT: COPERNICUS / EUROPEAN SPACE AGENT / KARLA BOXALL

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

The researchers, from the University of Cambridge and the Austrian engineering company ENVEO, have identified distinct, seasonal movements in the flow of land ice flowing into the George VI Ice Shelf – a floating iceberg the size of roughly the size of Wales – on the Antarctic Peninsula.

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

While it is not uncommon for ice flows in the Arctic and Alpine regions to accelerate during the summer, scientists have previously suggested that Antarctic ice does not experience the same seasonal movements, especially where it flows into large ice shelves and where temperatures are below freezing. Most of the year.

This assumption is also partly motivated by the lack of images collected of the frozen continent in the past. “Unlike the Greenland Ice Sheet, where vast amounts of data allow us to understand how the ice moves from season to season and year to year, we don’t have the overarching data to look for changes in the ocean. such changes in Antarctica until recently,” said Karla Boxall from Cambridge’s Scott Polar Research Institute (SPRI), first author of the study.

“Observations of ice speed changes in the Antarctic Peninsula are usually measured in consecutive years, so we missed a lot of the finer details of how the flow changes from month to month. of the year,” said co-author Dr. Frazer, Christie, also from SPRI.

Given the detailed records of ice speeds produced by the Sentinel-1 satellite, scientists wishing to study short-term variations in ice flow across Antarctica must rely on information gathered by satellites. optics like NASA’s Landsat 8.

Co-author Dr Thomas Nagler, CEO of ENVEO, said: “Optical measurements can only observe the Earth’s surface on cloudless days during the summer months. “But using Sentinel-1 radar imaging, we can detect seasonal ice flow changes thanks to the year-round and all-weather monitoring capabilities of these satellites.”

Currently, the cause of this seasonal change is uncertain. It can be caused by surface meltwater reaching the bottom 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 seawater that melts the ice from below, thinning the iceberg and allowing the glaciers upstream to move faster.

“These seasonal cycles could be due to one of two mechanisms or a combination of both,” Christie said. “Detailed ocean and surface measurements will be required to fully understand why this seasonal variation is occurring.”

The results suggest that similar seasonal variation may exist in other, more vulnerable locations in Antarctica, such as Pine Island and the Thwaites Glacier in West Antarctica. “If true, these seasonal cues may not be captured in some measurements of Antarctic ice mass loss, which has important implications for sea level rise estimates,” Boxall said. Global.

“This is the first time this seasonal signal has been found on the Antarctic Ice Sheet, so the questions it raises regarding the possible presence and causes of seasonality elsewhere. Antarctica is really exciting,” said co-author Professor Ian Willis, also from SPRI. “We look forward to taking a closer look and shedding light on these important questions.”

The research was supported in part by the Natural Environment Research Council (NERC), part by UK Research & Innovation (UKRI), Prince Albert II of Monaco and the European Space Agency. . Karla Boxall is a PhD student at Newnham College, Cambridge. Frazer Christie is a Fellow of Jesus College, Cambridge. Ian Willis is a Fellow of St Catharine’s College, Cambridge.