What lies beneath: Why NZ's slice of Antarctica is at the centre of an eco-mystery

Friday, 24 November 2017

Why you should care about sea ice in Antarctica and what happens if we lose it. (Video first published 2017)

Parts of Antarctica aren't behaving the way climate change models predict. It turns out that special things are going on in the Ross Sea, New Zealand's wedge of the icy continent.

There's a problem in Antarctica.

Most climate change models say ice around the southern continent should be decreasing. It should be melting as the planet heats up.

The field training camp on the Ross Ice shelf.

But sea ice around Antarctica isn't shrinking. It's been growing.

'Since the satellites went up – and that's about 30 or 40 years of records – there's been a gradual trend toward more sea ice around Antarctica,' say Dr Natalie Robinson, a marine physicist at Niwa, New Zealand's Institute for Water and Atmospheric Research. 'Which is not what you'd predict in a warming ocean.'

Frozen icebergs in the Ross Sea. 'There's something particular going on with the Ross Sea,' Robinson says.

University of Otago physicist Pat Langhorne, right, and her team drill holes in sea ice in the Ross Sea.

* Antarctic orca check out their world

* Unusual seal pup spotedt near Scott Base

The sea ice here is 2 metres thick this spring. Last spring it was about 3m.

* New Zealand Air Force trains for Antarctic crash**

This sort of thing makes climate change skeptics shout from the roof tops. Obviously the world isn't heating up!

Scientist Natalie Robinson, left, and Peter de Joux drill into sea ice looking for platelet ice.

But it's not so simple. Little about climate change and Antarctica is capable of being shouted from roof tops.

'All we're measuring is area,' says Dr Pat Langhorne, a professor of physics at the University of Otago. 'We don't know anything about the volume or mass' of the sea ice.

Orca are seen near the edge of the sea ice.

There might be more square kilometres of sea ice, but it could just be spread thinner. We don't know.

Which is why, a few weeks ago, I was standing on frozen McMurdo Sound near Scott Base, Antarctica, as teams led by Langhorne and a few days later by Robinson drilled into the sea ice to figure out what's going on.

Sea ice around Antarctica isn't shrinking - in fact, it's growing in area. But we don't know about its volume.

Sometimes the skies were the colour of a bluebird. The snow sparkled so brightly most people had to wear sunglasses or goggles. Temperatures got as high as minus 15 degrees Celsius, so it was fairly balmy.

When there was no wind, the sound of Antarctica was silence. No birds, no roads, no streams. The unlucky could sometimes hear the drone of distant helicopters. Perfect silence is a mighty experience.

A glacier face. Antarctica is not a monolithic ice block.

The sea ice hereabouts is 2 metres thick this spring. Last spring it was about 3m. McMurdo Sound is roughly V shaped but let's say it's about 50km wide. This is a big plate of ice and it's flatter than the Canterbury Plains.

Many years, all of the sea ice in McMurdo Sound breaks up and is pushed north by winds and currents and it eventually melts.

When there was no wind, the sound of Antarctica was silence. Apart from a few seals.

Other years, the sea ice doesn't blow away or melt. An icebreaker is needed to resupply Antarctica New Zealand's Scott Base and the nearby American base, McMurdo Station.

These swings are probably natural variations that have little do with climate change and a warming world, say Langhorne and Robinson. But they can't say for sure until the results of their research – and much more from colleagues and competitors around the continent – into sorting out what Antarctic sea ice is doing.

An iceberg floats in the frozen Ross Sea.

And it turns out that McMurdo Sound and the broader Ross Sea are pretty special compared with other seas around Antarctica. Remember those 40 years of data showing expanding sea ice?

'About half of that signal is from the Ross Sea itself,' says Robinson. 'There's something particular going on with the Ross Sea.'

This shouldn't surprise, Antarctica New Zealand's chief scientist Gary Wilson told me earlier this year. Antarctica is not a monolithic ice block. It's larger than Australia so of course different things are happening at different places on the coastline, he said.

The sea ice off the Antarctic Peninsula – south of Argentina – is shrinking on a massive scale, for example.

Pressure ridges are caused by sea ice being crushed against land.

The Ross Sea may be Antarctica's 'baseline', says Langhorne. It's the place that has changed the least under climate change and may tell us what Antarctica was like before humans started adding industrial levels of carbon to the atmosphere.

So why would the Ross Sea not melt as fast as other Antarctic seas?

Emperor penguins on the edge of sea ice and open water.

One easy reason is that the Ross Sea is further south than any other salt water around the continent. This is why Scott and Amundsen raced to the South Pole from here in 1911-12.

SCALING UP

Sea ice breaks up in the Ross Sea north of New Zealand's Scott Base. This happens most years but scientists are worried climate change will disrupt the pattern.

'Sea ice thickness is really difficult to measure,' says Langhorne, the physicist from Otago. 'Satellites can't measure it directly.'

There's a plan afoot to change this and it starts with Langhorne and her team from Otago, Canterbury and Canadian universities measuring sea ice with traditional methods – drilling holes in the ice and measuring its thickness. It's accurate but inefficient.

Dr Natalie Robinson, a marine physicist at Niwa, is intrigued by 'platelet ice', which exists only in Antarctica.

It's expensive to haul scientists and their gear to the southern continent. There are many places around the continent that are inaccessible. And because sea ice breaks up many years, it has to be done in the few months of spring.

So international teams – including Langhorne's – are scaling up.

Platelet ice is slushy half-ice, half-water that exists just under the sea ice.

They're using a technique called electromagnetic induction, which measures the distance between the instrument and the first conductive layer, in this case sea water. A laser also measures the distance between the instrument and the snow surface.

Langhorne is a professor of physics and knows perfectly well how electromagnetic induction works, but even she calls the set-up an 'EM gadget'.

Platelet ice, photographed here underneath sea ice in the Ross Sea, is fished from 'impossibly blue' holes in the sea ice.

One member of Langhorne's team dragged an EM gadget behind a snowmobile and will compare these measurements with those acquired by traditional methods.

And when that was done, a Canadian EM gadget (and a laser) were flown over the sea ice while dangling from a plane – and not just any plane, but a DC3 built in 1943. It's the only plane in the world that's been modified to dangle the EM gadget.

Pilots flew the EM gadget at a constant 15m above the surface of the snow. It's possible with some maths to determine ice thickness (distance between gadget and first conductive layer, less 15m, and take into account variable snow thickness.)

The purpose was to 'validate' the plane data, Langhorne says, to see if it matched the traditional data. If so, 'it will give us confidence that the bird can go flying off into the unknown, up the coast, where we can't get to and make its measurements up there', she says.

Humans can stop drilling holes every spring. Or fewer, anyway.

Satellites were taking similar measurements over the exact same patch of ice in the Ross Sea. The plan is to compare that data to the numbers acquired by the plane, snowmobile and traditional holes. All going to plan, there will be a match – or close enough.

'We're trying to scale up so that one day we'll be able to use satellites to measure sea ice thickness in Antarctica,' Langhorne says. 'That's the holy grail. That's the thing that doesn't exist.'

And maybe then, after some years of data collection, we'll know if Antarctic sea ice is growing or shrinking.

And then that information can be fed into climate change models and the world – including those who shout from roof tops – will have better a better sense of what's going on in Antarctica.

COLDEST WATER IN THE WORLD

Sea ice thickness isn't the only story in the Ross Sea, and Niwa's Natalie Robinson is especially interested in 'platelet ice'. Think of it as slushy half-ice, half-water that exists just under the sea ice.

Using a net, she fishes it out of impossibly blue holes drilled through the ice.

It's an odd thing, but once you've got a platelet in your hands, the temptation is to eat it. They taste vaguely salty and crunchy. Robinson laughs when confirming that many newbies have a chew.

A single platelet is thin – 1 to 2 millimetres – and vaguely round. Some grow to the size of dinner plates. Untold billions gather in layers just under the sea ice.

The platelet layer can be thick. 'Last year we had 3m of ice and then 3m of slushy platelet ice,' she says. It's been measured at 9m thick in some places.

Platelet ice exists only in Antarctica. It requires both deep ice shelves and sea ice to form. Those two things don't exist together in the Arctic.

Ice shelves are land glaciers that have flowed out to sea. They float. The water under an ice shelf is the coldest in the world, minus 1.8C.

That 'super-cooled' water travels out from under the ice shelves. As it rises towards the surface, it finds ice crystals to solidify onto and becomes a platelet. These become more buoyant and eventually join the platelet layer.

In winter, the layer helps sea ice form. In spring and summer, it seems to insulate sea ice from melting from below, at least for a time.

In other words, platelet ice is thought to be one reason sea ice around Antarctica isn't melting as much as the climate change models suggest.

And it follows that the lack of platelet ice in the Arctic may partially explain why sea ice melt up north is more serious.

Robinson, colleagues and students want to know how far these effects are felt. 'We're looking at how the ocean responds to having that platelet ice there,' says Robinson.

'The question we're trying to answer is how far away from the ice shelf that influence extends … it might be a local one or might it extend a few hundred kilometres.'

'Based on the data we've collected so far, we're comfortable it extends at least 200km.' At that point, it gets confused with the water coming from other sources.

But this is where Robinson's platelets meets Langhorne's scaling up. With some maths, the gadgets flying under the DC3 can measure the platelet layer. This is new.

'There are little ice shelves all the way up the coast, where nobody has ever looked for platelet ice,' says Langhorne.

They hope to fly the gadgets over new areas of the Ross Sea. 'There might be something to see. There might not,' she says.

If these teams can measure the platelet layer from the air and sea ice from space, then a much fuller understanding of the Ross Sea will be possible.

It's the baseline, remember, the coast least affected by global warming. Elsewhere along the Antarctic coast, ice shelves are melting at an alarming rate.

'At the moment, we can say that water flowing through McMurdo Sound from the Ross Ice Shelf probably hasn't changed much in at least 200 years,' says Robinson.

'It's a good place to understand the processes as they happen because they are pretty stable.'

And then scientists can learn more about ice systems that aren't stable, that have changed.

And the knowledge can be plugged into climate change models to get better predictions of how long we've got.

'We go every year and we find out new things each time,' says Robinson. 'This really is a place that science is still exploring.

'We are literally pushing frontiers with our science with every field season.'

❑ Will Harvie and Iain McGregor spent 10 days in Antarctica as part of Antarctica New Zealand's community engagement programme, which allows New Zealand media, artists and other non-scientists to visit Scott Base to learn and report on the work of scientists on the ice.