A glacier the size of Florida is said to be in “fast retreat” and should it fall it would increase global sea levels by ten feet putting hundreds of millions in danger of losing their homes and livelihoods.
The Thwaites Glacier in West Antarctica has the potential to transform the world’s oceans and a new study has added new cause for concern at the speed in which it is melting, being described as hanging in by its fingernails.
It had already been deemed to be in what scientists described as already in a phase of fast retreat (a collapse when viewed on geological timescales) leading to widespread concern about exactly how much, or how fast, its ice will cascade into the ocean.
The team form the University of South Florida has described the potential impact of Thwaites’ retreat as “spine-chilling” with a total loss of the glacier and surrounding icy basins could raise sea level from three to 10 feet.
The study led by marine geophysicist Alastair Graham at the University of South Florida’s College of Marine Science has for the first time mapped in high-resolution a critical area of the seafloor in front of the glacier that gives them a window into how fast Thwaites retreated and moved in the past.
The imagery shows geologic features that are new to science, and also provides a kind of crystal ball to see into Thwaites’ future. In people and ice sheets alike, past behaviour is key to understanding future behaviour.
The team documented more than 160 parallel ridges that were created, like a footprint, as the glacier’s leading edge retreated and bobbed up and down with the daily tides.
What is alarming is that the rate of Thwaites’ retreat that scientists have documented more recently are small compared to the fastest rates of change in its past, said Graham.
To understand Thwaites’ past retreat, the team analysed the rib-like formations submerged 700 meters) beneath the polar ocean and factored in the tidal cycle for the region, as predicted by computer models, to show that one rib must have been formed every single day.
At some point in the last 200 years, over a duration of less than six months, the front of the glacier lost contact with a seabed ridge and retreated at a rate of more than 2.1 kilometres per year, twice the rate documented using satellites between 2011 and 2019.
“Our results suggest that pulses of very rapid retreat have occurred at Thwaites Glacier in the last two centuries, and possibly as recently as the mid-20th Century,” Graham said.
“Thwaites is really holding on today by its fingernails, and we should expect to see big changes over small timescales in the future, even from one year to the next, once the glacier retreats beyond a shallow ridge in its bed,” said marine geophysicist and study co-author Robert Larter from the British Antarctic Survey.
While many questions remain, one thing’s for sure: It used to be that scientists thought of the Antarctic ice sheets as sluggish and slow to respond, but that’s simply not true, said Graham.
“Just a small kick to Thwaites could lead to a big response,” he said.
According to the United Nations, roughly 40 percent of the human population lives within 60 miles of the coast.
“This study is part of a cross-disciplinary collective effort to understand the Thwaites Glacier system better,” said Tom Frazer, dean of the USF College of Marine Science, “and just because it’s out of sight, we can’t have Thwaites out of mind. This study is an important step forward in providing essential information to inform global planning efforts.”