Ice shelves fracture under weight of meltwater lakes

Ice shelves fracture under weight of meltwater lakes

When air temperatures in Antarctica rise and glacier ice melts, water can pool on the surface of floating ice shelves, weighing them down and causing the ice to bend. Now, for the first time in the field, new research shows that ice shelves don’t just buckle under the weight of meltwater lakes — they fracture. As the climate warms and melt rates in Antarctica increase, this fracturing could cause vulnerable ice shelves to collapse, allowing inland glacier ice to spill into the ocean and contribute to sea level rise.

“Ice shelves are extremely important for the Antarctic Ice Sheet’s overall health as they act to buttress or hold back the glacier ice on land,” said Alison Banwell (CIRES, Earth Science and Observation Centre, University of Colorado), lead author of the study published today in the Journal of Glaciology. “Scientists have predicted and modelled that surface meltwater loading could cause ice shelves to fracture, but no one had observed the process in the field, until now.”

The new work may help explain how the Larsen B Ice Shelf abruptly collapsed in 2002. In the months before its catastrophic breakup, thousands of meltwater lakes littered the ice shelf’s surface, which then drained over just a few weeks.

To investigate the impacts of surface meltwater on ice shelf stability, the team of researchers, including Dr Laura Stevens, Associate Professor at Oxford Earth Sciences, travelled to the George VI Ice Shelf on the Antarctic Peninsula in November 2019. First, the team identified a depression or “doline” in the ice surface that had formed by a previous lake drainage event where they thought meltwater was likely to pool again on the ice. Then, they ventured out into the frigid landscape on snowmobiles, pulling all their science equipment and safety gear behind on sleds.

Around the doline, the team installed high-precision GPS stations to measure small changes in elevation at the ice’s surface, water-pressure sensors to measure lake depth, and a time-lapse camera system to capture images of the ice surface and meltwater lakes every 30 minutes. “We returned from that first field season feeling really excited about having installed all of our instruments in the intended places, and looking forward to the two remaining field seasons,” Stevens said.

Photograph of the doline at the field site as captured by the timelapse camera

The doline at the field site as captured by the timelapse camera. Image credit: Alison Banwell/CIRES and ESOC

In 2020, the COVID-19 pandemic brought their fieldwork to a screeching halt. When the team finally made it back to their field site in November 2021, only two GPS sensors and one time-lapse camera remained; two other GPS and all water pressure sensors had been flooded and buried in solid ice. Fortunately, the surviving instruments captured the vertical and horizontal movement of the ice’s surface and images of the meltwater lake that formed and drained during the record-high 2019/2020 melt season.

The team also found that the horizontal distance between the edge and center of the meltwater lake basin increased by over a foot. This was most likely due to the formation and/or widening of circular fractures around the meltwater lake, which the timelapse imagery captured. “We can also see this fracture widening in the GPS data,” Stevens said, “which shows a sudden increase in the horizontal distance between two GPS stations, indicating the exact timing and horizontal extent of the fracture widening.” Their results provide the first field-based evidence of ice shelf fracturing in response to a surface meltwater lake weighing down the ice.

Photograph of the field team installing science instruments on the George VI Ice Shelf

The field team installing science instruments on the George VI Ice Shelf. Image credit: Alison Banwell/CIRES ESOC

“This is an exciting discovery,” Banwell said. “We believe these types of circular fractures were key in the chain reaction style lake drainage process that helped to break up the Larsen B Ice Shelf.”

The work supports modelling results that show the immense weight of thousands of meltwater lakes and subsequent draining caused the Larsen B Ice Shelf to bend and break , contributing to its collapse.

“These observations are important because they can be used to improve models to better predict which Antarctic ice shelves are more vulnerable and most susceptible to collapse in the future,” Banwell said.

This research was jointly funded by the U.S. National Science Foundation (NSF) and the U.K. Natural Environment Research Council (NERC). The full study is available on the Journal of Glaciology website. This story was adapted from a Cooperative Institute for Research in Environmental Sciences press release.