Fishing for a
glacier's secrets
It’s an ice fishing trip like no other.
A five-metre long drill. More than a kilometre of line. On a glacier tongue over an unmapped ocean.
In the summer of 2025, glaciologists Sarah Thompson and Maria ‘Coti’ Manassero from the University of Tasmania are in East Antarctica to plumb the depths beneath the floating ice shelf of the Scott Glacier.
Their mission: to suspend a string of sensors under the ice that will monitor the temperature, salinity and currents of the ocean below, every hour for the next few years.
Dr Maria 'Coti' Manassero (left) from the Australian Centre for Excellence in Antarctic Studies (ACEAS) and Dr Sarah Thompson from the Australian Antarctic Program Partnership (AAPP)
Dr Maria 'Coti' Manassero (left) from the Australian Centre for Excellence in Antarctic Studies (ACEAS) and Dr Sarah Thompson from the Australian Antarctic Program Partnership (AAPP)
Around 5,000 kilometres south of Australia is a vast ‘verandah’ of interlocking ice shelves and glacier tongues, extending over the ocean covering more than half the area of Tasmania.
One of the largest in East Antarctica, Shackleton is the most northerly ice shelf system outside of the Antarctic Peninsula.
The Shackleton ice shelf buttresses glaciers like the Scott and Denman, restraining their flow of ice into the sea. But for glaciers like the Denman, their ‘grounding lines’ (where the ice sits on bedrock) appear to be retreating each year as warm ocean waters melt them from below.
In most places the ice is many hundreds, even thousands, of metres thick. So to get to the ocean underneath to measure its properties, you need to find a ‘window’ that opens into the water body you want to investigate.
Enter Duanne White, a geomorphologist from the University of Canberra.
Satellite imagery and field reconnaissance led him to discover an ‘epishelf lake’ — a frozen freshwater lake formed when meltwater flowing off a glacier is trapped behind a floating ice shelf.
“It’s a small window of sea ice right near the grounding line of the Scott Glacier, tucked in behind rocky Cape Hoadley,” Duanne says.
“It’s the ideal site because it gives access to the southernmost part of the ocean cavity beneath the ice shelf without having to drill through more than 600 metres of glacial ice, so you can use tools designed for ice fishing on lakes in North America.”
The trick is to install a mooring line at the right spot via a hole drilled through the ice.
“Here you can measure the speed and characteristics of meltwater flowing out from the base of the ice shelf, right up near the grounding line, where ice from the Scott Glacier lifts off the bed and starts to form the ice shelf,” says Duanne.
In East Antarctica, the main changes to the ice happen at the interface between the ice shelf and the ocean, where melt rates are thought to be highest.
Are warm waters reaching right to the back of the ice shelf? That’s what the fishing team plans to find out.
Sarah, Coti and polar field guide Nick Morgan from the Australian Antarctic Division camped on the frozen lake, where they knew the ice was thick enough to work on but easier to drill through.
“It was a really beautiful site to stay as there were pressure ridges from the lake ice on one side of us and cliffs on Cape Hoadley on the other side.”
“We were also very lucky with the weather and once the morning katabatic winds dropped had great conditions to work in,” says Sarah.
Using a battery-powered auger, over a few hours they drilled a hole about 25 centimetres wide.
“Luckily, the ice was 4.8 metres thick, as we only had five metres of drill flights!” Sarah says.
Coti with the full drill length for scale (photo: Sarah Thompson)
Coti with the full drill length for scale (photo: Sarah Thompson)
“We drilled one hole, and once we were through, we sent the camera down to get an estimate of depth and to see what the bottom looked like.”
Coti says it was also fortunate they brought 1500 metres of cable.
“We were astonished to find depths exceeding 1200 metres below sea level, with rocky and rugged slopes.”
“We were also amazed by the abundance of marine life we saw with the camera, like sponges and brittle-stars,” Coti says.
This is where the hard work came in: reeling the camera and sediment core up and down for over 1200 metres, taking about three hours each time.
The only thing that didn’t go to plan was the sediment core. They expected to retrieve some sediments, but couldn’t collect any due to the rocky slopes on the seafloor.
Sarah agrees the depth of the ocean was surprising given they were so close to the grounding line.
“We expected it to be quite deep but not close to 1300 metres! The site is only a few hundred metres away from the shore so it must be a really steep drop-off.”
Coti and Nick prepare to deploy the sediment corer (photo: Sarah Thompson)
Coti and Nick prepare to deploy the sediment corer (photo: Sarah Thompson)
The sensors on the mooring line were carefully lowered to a depth of 690 metres and secured to a frame with a power source and transmitter at the surface.
“The hardest part for me was being confident that I’d done it all correctly!” laughs Sarah.
“I checked everything three times, but we didn’t have confirmation until we got back to the main field camp with internet and started to receive data. That was a huge relief!”
Back in Hobart, oceanographer Madi Rosevear at the University of Tasmania is thrilled to be in touch with the mooring station.
“Every day at 11am I’m getting four emails from Antarctica with hourly measurements of ocean temperature, salinity, and current speed. Hopefully, this will continue for the next two to three years.”
“These data will tell us how much heat is available to melt the nearby Scott Glacier ice tongue and will give important insights into the ocean circulation, including how it changes over time.”
“The discovery of seafloor more than 1200 metres deep at this location, close to the Scott Glacier, is very significant."
"Deep troughs and canyons around Antarctica provide pathways for warm, salty Circumpolar Deep Water to access ice shelves, where it can drive rapid melting,” Madi says.
It ties in with a single data point showing Circumpolar Deep Water under Shackleton ice shelf collected in fieldwork last year.
For Sarah the successful installation means invaluable science infrastructure in a location not reached before.
“If warmer ocean water can reach the point at which the glacier starts to float there is significant potential to accelerate melting and speed up the glacier flow, transferring more ice into the ocean.”
“By installing the mooring, we can not only measure what is happening at this site but we can monitor any changes in the next few years and start to predict the stability of the system with greater confidence.”
Sarah prepares the mooring for deployment (photo: Coti Manassero)
Sarah prepares the mooring for deployment (photo: Coti Manassero)
The lonely mooring station secured in the wilds of East Antarctica (photo: Coti Manassero)
The lonely mooring station secured in the wilds of East Antarctica (photo: Coti Manassero)
Even better, says Madi, mooring data from the terrestrial side will dovetail with upcoming research from the marine side.
“Having the mooring in the water making measurements during the Denman Marine Voyage this year is extremely powerful, since we’ll be able to compare the water properties inside and outside of the ice shelf cavity.”
“Hopefully, we’ll be able to assess the circulation pathways beneath the ice, and ascertain how vulnerable the ice shelf is to changes in the ocean around Antarctica.”
Sarah says it will provide the vital link between what we see just offshore in the ocean and how that might be affecting the ice shelves.
“Because we don’t have a lot of information about the shape and depth of the ocean floor beneath the ice shelves, we don’t know whether the warmer water masses we see offshore can reach the grounding line and contribute to melting at the base of the ice.”
“With the mooring in place close to the grounding line of Scott Glacier we can directly compare, in real time, the ocean properties there with the offshore CTD profiles that will be collected as part of the marine voyage on Australia’s icebreaker RSV Nuyina.”
Written and produced by Mark Horstman, February 2025
Australian Antarctic Program Partnership
Institute for Marine and Antarctic Studies
University of Tasmania, Hobart
Imagery by Sarah Thompson, Coti Manassero and Nick Morgan
Thanks to the Australian Antarctic Program, ACEAS and
the Denman Terrestrial Campaign, 2023-25
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