Antarctic exploration has entered a “new era” after a submarine made a remote-controlled dive beneath an ice shelf to study the Earth’s melting poles.
The uncrewed Swedish craft brought back map readings from underneath the ice in what polar oceanographer Anna Wahlin likened to “seeing the back of the Moon”.
The submarine failed to return from its final dive in January, leaving scientists wondering whether curious seals were to blame for its demise.
Nonetheless, its findings shed new light on the melting of Antarctic ice, which could fuel a catastrophic rise in sea levels.
One Antarctic landmark is known as the Doomsday Glacier because sea levels would rise by more than half a metre if it melted due to climate change.
A warming ocean is the obvious culprit but the University of Gothenburg craft found “dramatic and distinct features” under the ice that may help predict the rate of melting.
“It’s a little bit like being able to look into a black box,” Prof Wahlin, who led the expedition from on board an icebreaker, told The National.
“We have, for a long time, had tools that allow us to observe what goes into ice shelf cavities, and what comes out. Based on that data we have created models.
“Now, when we can see what it actually looks like, we can see that it’s very diverse. The melting can be very, very local. That part of the melting is a new process that we don’t yet have in our models.”
Polar explorer
The battery-powered submarine, known as Ran, was programmed to dive as far as 17km into a cavity of the Dotson ice shelf, in western Antarctica.
Scientists accompanied it on a Korean icebreaker called RV/IB Araon, before lowering it into the water for what could be 24 hours at a time.
Once it dived under the Antarctic ice shelf, which can be hundreds of metres thick, its acoustic sensors went dark.
It had no contact with its owners as it set about scanning the base of the ice shelf and measuring the ocean currents and temperature.
In a 27-day expedition, it travelled more than 1,000km back and forth under the ice shelf.
Once it resurfaced, Ran would return to a designated point where the icebreaker would pick it up.
If it came up early it was programmed to send a satellite signal so scientists could come and collect it.
Disappearance
During a repeat dive in January, the submarine was reported missing after it failed to arrive at its rendezvous point.
A helicopter and drone search failed to locate the bright orange craft, its batteries by now long dead.
Scientists have two theories on Ran’s fate. One is that the ice shelf could have changed so much since an earlier dive that the craft’s programmed path led it into danger.
Or were animals to blame? There were Antarctic seals in the area. The crew noticed there were more of them than usual.
A herd of curious seals could have encircled the craft. It might have gone into emergency mode and never found its way back.
Unless it is found, we may never know.
It will take a couple of years to replace Ran, for which a science foundation had paid $3.8 million, but Prof Wahlin believes that “this will be the beginning of a new era” of Antarctic discovery.
“This was, in a way, a proof of concept,” she said. “We can see what we can do.”
Discoveries
In the meantime, oceanographers have plenty to pore over from Ran’s findings and its images of teardrop-shaped dents in the ice shelf.
They can start to fill what a new paper based on the expedition calls the “knowledge gaps” about the ice shelf so critical to the future of the planet.
The collapse of Antarctic ice is what climate scientists call a tipping point, an event that cannot be reversed even if temperatures one day fall.
Scientists predicting the melting of the ice sheet must now take into account the “wealth of processes” known to be occurring under the ice, the study says.
Prof Wahlin, who had expected the glacier to look as smooth from below as from above, said she was “still a little bit mind-blown” by what the submarine found.
“I’m hoping, really, that this will give rise to many new studies, in particular models in areas where you don’t have so much melt,” she said.
Existing models “tell us that, obviously, the warmer the water is, the more it melts, and also a little bit faster the water flows, the more it melts.
“There’s this whole other part of the ice shelf with smaller melt and we don’t seem to get that right presently.”
The article Swirls and scoops: Ice-base melt revealed by multibeam imagery of an Antarctic ice shelf, by Anna Wahlin et al, is published in the journal Science Advances.
