The elusive Antarctic ice and sediment core that could answer sea level rise questions

Source: Radio New Zealand

All Huw Horgan wants for Christmas is a geological core sample.

For the third year running, Huw and the team of scientists he now co-leads are on a quest that takes them to the farthest reaches of Antarctica, hundreds of kilometres from any base.

On the inner edge of the Ross ice shelf, where it meets the main West Antarctic ice sheet covering this part of the continent, they’ll set up camp.

And then they’ll drill.

What they’re after is not minerals, or the fossil fuels driving climate change, but a sediment sample that lies below hundreds of metres of ice.

What it contains will help answer the question of when, and how drastically, the West Antarctic ice sheet might collapse as the climate keeps warming – releasing up to five metres of sea level rise as it goes.

Plenty of cores have been collected from Antarctica over the years, but extracting one this deep, this far from a permanent base, has never been done.

They’ve already tried twice, but equipment failures have forced the team to abandon the attempt two seasons running.

“What we’re trying to do is difficult, right?” Horgan says. “It’s difficult and it’s a harsh environment. It’s a long way from any support. So we’ve had two attempts prior to this from which we’ve learned a lot.”

This year is not third time lucky. “I think it’s third time really well prepared.”

“It would be really lovely to have a bit of geological core for Christmas down there.”

Unlocking the secrets of the West Antarctic Ice Sheet

Over the decades, the work of climate scientists has helped to build an increasingly accurate picture of climate change-driven sea level rise, and what we might expect in the coming years.

But there are some crucial gaps.

“If we look at sea level rise estimates up to the end of the century, they range anywhere between about 30 centimeters and about a metre, or even, with some estimates, double that,” Horgan says. “A lot of the uncertainty in those estimates come from the West Antarctic.”

At the moment, the West Antarctic Ice Sheet is protected by ice shelves – floating layers of ice formed by the ice sheet flowing off the Antarctic continent.

Without them, the flow of ice into the ocean will accelerate, meaning the potential collapse of the entire ice sheet.

Some of these smaller shelves could collapse within years, but the Ross Ice Shelf, the largest of them, is still stable – for now.

Whether that will remain true as the climate warms, and the ocean with it, is one of the uncertainties.

Before the team could even start drilling, an advance team towing the rig and freight containers of equipment had to complete a 1100km traverse across the Ross Ice Shelf – dodging crevasses – to reach their field camp and drilling site.

Antarctic Research Centre director Rob McKay – who will be offering support from New Zealand – says it’s clear from ice sheet models that ice loss can rapidly accelerate.

“We just don’t know under what threshold, what temperature change that would occur under. Is it 1.5°C, 2°C, as defined by the target of dangerous climate change, by the Paris Climate Agreement?”

That’s where the expedition – formally known as SWAIS2°C (Sensitivity of the West Antarctic Ice Sheet to 2°C) – comes in.

“We’re trying to drill to find, when was the last time it was those temperatures and did we lose completely the West Antarctic ice sheet?” Rob says.

“That will help us fine-tune those models … that are predicting future sea level loss.”

A finely tuned machine

A few weeks ago, an advance crew set out on an 1100km journey across the Ross Ice Shelf, using snow vehicles to lug tents, provisions, and a huge drilling rig; navigating crevasses as they went.

They were heading for Crary Ice Rise, this season’s sampling location, where hundreds of metres of ice sits directly on top of bedrock.

With a rudimentary camp set up and a runway on the ice cleared, the rest of the 29-strong team will gradually assemble, flying first to Scott Base and then on to Crary to continue building up the site.

Horgan is one of this year’s two co-chief scientists on the ice.

“It’s not a town, but it’s certainly a small neighborhood of tents,” he says. “So there’ll be a couple of weeks of preparation, a very large drill tent has to be put up, all of the hot water drilling system has to be installed in that tent, and then the deep drilling system has to be installed.”

The drill system itself is a traditional drilling rig of the same type that’s used in mining, and the irony is not lost on Rob McKay.

“Rather perversely, we’re looking for climate change, but we’re using extractive industry technology to get these climate records that are preserved in the sediment.”

Once everything is in place, the team will have a window of about 10 days to complete the drilling.

First up is the hot water drilling team, whose task is to get through more than 500m of ice.

“That’s no small undertaking,” Horgan says. “The hole they make is about 35cm wide, right down to the base of the ice sheet.”

From there, the rock drilling team takes over, with the aim of extracting up to 200m of sediment from beneath the ice sheet.

The whole time they’re drilling, the hole through the ice will be threatening to close over.

“It’s cold, and it’s pressing in from the side, so we continuously have to be feeding hot water down through the system,” Horgan says. “And the rock drilling team is spinning their drill down at the base and pulling up geological core three metres at a time.”

For the first two seasons, the team was drilling at a different site, where there was an ‘ocean cavity’ – a layer of sea water between the bottom of the ice sheet and the sediment layer.

At the new site, there’s no water – the ice sheet sits directly on top of the rock.

McKay says while that means the team doesn’t need to contend with the ice sheet shifting with the tides, it creates a different technical challenge.

“When the ice is actually sitting on the ground, that ground ends up being frozen. So what we want to make sure is that that drill pipe is spinning fast enough and there’s enough heat going down the hole that it doesn’t actually freeze and stick in the hole.”

They also don’t know whether they’ll encounter chunks of ice encased in the sediment layer, which could add to the challenge.

“It’s what we call frontier science,” McKay says. “We’ll find out only when we’re drilling.”

Try – and try again

During both previous attempts, the bad news landed in late December like a lump of coal.

“I’ve destroyed one Christmas Eve dinner with the first news, and then I think it was the 23rd of December last year.”

Unlike the team on the ice, though, Rob had the “luxury” of being surrounded by family.

“I know it sounds romantic being in a tent in Antarctica and the adventure of all that, but when you invest so much of your life into this and then you have to sit there for two or three weeks after not achieving your objectives… their disappointment far outweighs mine.”

Different things have gone wrong in each season, Huw says.

The team that headed down in 2023 were using a novel fibreglass drill tube, which would have had great pay-off if it had worked. But it didn’t behave as expected at extremely cold temperatures, and they were forced to abandon the drilling.

Next season they headed back with more conventional steel equipment, but the main drive shaft – “the part that never breaks” – broke.

Despite that, Horgan says they’re sticking with steel. “There’s been a great deal of work, a great deal of testing, and some great failsafes, some redundancies built into it, giving us more confidence.”

There is no question of giving up the project. “We don’t do it because we think it’s fun. We do it because it’s important.”

Huw Horgan’s co-chief scientist on the ice, Molly Patterson, says it’s always disappointing when something doesn’t work.

“But … those setbacks and challenges are really a part of this process of success that maybe we don’t talk about in science enough.”

She’s been encouraged by how the drillers and engineers have responded in the intervening year. “That’s actually what gives me a lot of confidence going into this season.”

She pays “enough” attention to climate politics to really want the project to succeed this year, though. “I guess that might be the best way to say that. I think science just needs a win right now.”

What they find could have huge implications for communities.

“Globally, there’s about 68 million people that live near coastlines and are going to be exposed to these hazards that are caused by sea level rise,” Patterson says.

Seas are already rising, and some Antarctic melt is inevitable.

“We see our job as helping to determine sort of how much and how fast sea level is going to rise,” Huw says. “That’s where we have to hand it over to policymakers and to engineers and to our coastal communities so they can then use that knowledge to adapt and prepare in the best way fit.”

There is no time to hesitate, she says.

“These systems can move quickly, they can move in unexpected ways. On one level that doesn’t scare me, but to have that knowledge and to not act on it, that scares me.”

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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand