As global temperatures increase, glaciers melt and sea levels rise. The large Thwaites Glacier in West Antarctica — which alone contains enough water to raise the sea level between one and three metres — is already retreating rapidly.
A new study has released unique imaging of the seafloor at the front of the glacier which indicates that Thwaites Glacier has in the past experienced ‘pulses’ of even faster moving retreat than it is experiencing at the moment.
In 2019, using a specialised instruments aboard a robotic vehicle known as ‘Rán’, a team consisting of scientists from the US, UK and Sweden took high-resolution images of a large portion of the seafloor 700 m below the surface in front of the Thwaites Glacier, a critical area for understanding the motion of glaciers.
The 20-hour mission was the first time scientists have been able to access a glacier front in this way. “This pioneering study of the ocean floor has been made possible by recent technological advances in autonomous ocean mapping,” said Anna Wåhlin, a physical oceanographer from the University of Gothenburg who deployed Rán at Thwaites, and has delivered some surprising results.
What they found was a record of the glacier’s movements carved like fingernail scratches along the seabed.
The seafloor images show 160 parallel ridges created as the glacier’s leading edge retreated and rose and fell with the daily tides. By factoring in models of the tidal cycle, scientists were able to show that one of these ridges formed every single day, and that at some stage in the last two centuries, the glacier retreated at a rate of over 2.1 km per year – twice the current rate of retreat.
This was sparked by the front of the glacier losing contact with a seabed ridge, resulting in the extreme rate of retreat – something that scientists speculate could easily occur in current times.
“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.
This expedition is the first of five which make up the THwaites Offshore Research (THOR) project which aims to expand understanding of the glacier, in terms of how it responds to atmospheric and oceanic changes, and also its stability – both of which will be crucial for modelling of sea levels in climate change analysis.