Climate change: What ‘fast ice’ could tell us about Antarctica – NZ Herald

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What is the United Nations climate summit in Glasgow all about? Video / Ben Cummins

New Zealand scientists are venturing to a remote region in Antarctica to gain crucial observations that could tell us much more about how the frozen continent is changing.

With its vast, icy stores holding the equivalent of tens of metres of global sea level rise, and its essential role in regulating the world’s climate, understanding how Antarctica is responding to global warming remains one of science’s most important questions.

A major part of that puzzle is the sea ice that, each year, expands out into oceans surrounding the continent and then retreats back, in a seasonal, breath-like pattern.

Most of this is pack ice, or freely floating sea ice floes, which drifts with ocean currents and winds and can be monitored from space using satellite remote sensing.

What’s called “fast ice”, meanwhile, is fastened to the Antarctic coastline and helps to stabilise ice shelves, while buffering them from the effects of ocean swell.

To scientists, fast ice offers an important way to glean tell-tale signals from the complex interplay between Antarctica’s ice, ocean and atmosphere, at a time that parts of continent are seeing some of the most rapid changes of anywhere on Earth.

Over the next few weeks, a team of scientists hope to develop a new way to observe fast ice in a two-week expedition to Terra Nova Bay, some 340km from New Zealand’s Scott Base.

“There’s only been a handful of locations around Antarctica where measurements have been made of fast ice,” explained Dr Gemma Brett, a sea ice scientist from University of Canterbury’s Gateway Antarctica.

Fast ice pictured near Observation Hill, on Antarctica's Ross Island. Photo / Supplied
Fast ice pictured near Observation Hill, on Antarctica’s Ross Island. Photo / Supplied

She said the fast ice found at Terra Nova Bay, in Antarctica’s Victoria Land, was particularly special because it has a crystallographic signature of deep-origin glacial meltwater in the form of platelet ice which forms thick masses of crystals called a sub-ice platelet layer.

Platelet ice was only able to form where the ocean contained meltwater originating from deep beneath ice shelves and outlet glaciers – the floating extensions of Antarctica’s continental ice sheets.

Although this meltwater was colder than the surrounding sea water, it was also fresher, making it less dense, and able to rise toward the surface in plumes.

As these cold plumes rose, the change in pressure allowed the water to a reach a state called “supercooled” – below its normal freezing temperature, yet still remaining liquid – which created the appearance of small crystals.

Platelet ice is an unusual form of ice consisting of tiny, thin plates that grow and collect on the underside of sea ice. Photo / Gemma Brett
Platelet ice is an unusual form of ice consisting of tiny, thin plates that grow and collect on the underside of sea ice. Photo / Gemma Brett

“What’s really special about this platelet ice, is that it provides information about interactive processes between the atmosphere, ocean and land ice, which are really difficult to observe,” Brett said.

“But this fast ice carries the crystallographic signature of the entire process that we can physically measure.”

Brett said the only other two regions where this type of platelet ice has been studied in detail are in McMurdo Sound, in the Ross Sea, and Atka Bay, in the Weddell Sea.

“We know that it occurs in Terra Nova Bay too – but we don’t understand why.”

In their expedition, Brett and colleagues PhD researcher Natasha Gardiner, of Canterbury University, and Professor Ian Hawes, of Waikato University, will team up with Dr Sanghee Kim from the Korean Polar Research Institute (KOPRI).

One major goal was to gain a clearer understanding of the links between platelet ice and regional ocean-atmosphere interactions that played a critical part in deep water formation and global thermohaline circulation.

Terra Nova Bay - pictured here during a Niwa expedition last summer - lies around 340km from New Zealand's Antarctic outpost, Scott Base. Photo / Stuart Mackay
Terra Nova Bay – pictured here during a Niwa expedition last summer – lies around 340km from New Zealand’s Antarctic outpost, Scott Base. Photo / Stuart Mackay

As well, it could shed more light on the processes that form ice shelf water – and its source regions around Antarctica.

“We know that it comes from the melting of land ice, and we know that freshening by increased meltwater from land ice could have a big impact on the circulation of the Southern Ocean,” she said.

“But we don’t really know where it’s coming out, how much of it is coming out, and how it affects sea ice formation.”

Another reason to learn more about platelet ice was the fact its layers serve as a unique habitat for microalgae, while offering a sheltered nursery for Antarctic silverfish to hatch.

Scientists therefore believe the platelet ice ecosystem could be hugely important for underpinning Antarctica’s marine food web – yet it is still unclear how it might be threatened by warming oceans.

At the team’s study site, near Korea’s Jang Bogo Station and Italy’s Mario Zucchelli Station, the researchers also aim to further develop satellite techniques, enabling them to monitor glacially-influenced fast ice from space.

“We’ve already applied this technique in McMurdo Sound, and we were able to identify where the meltwater was circulating out of the ice shelf cavity, and where it was influencing fast ice,” Brett said.

“If we can continue to develop this technique, we could identify new regions around Antarctica, before going in and doing more detailed field investigations.”

Sea ice floats near Antarctica's McMurdo Sound, as Mt Erebus looms in the background. Photo / Jamie Morton
Sea ice floats near Antarctica’s McMurdo Sound, as Mt Erebus looms in the background. Photo / Jamie Morton

The study – a collaborative venture with Kim’s Coastal Marine Science Programme – is supported by KOPRI and New Zealand’s Antarctic Science Platform.

While the team is on the ice, world leaders will be meeting in Glasgow for the UN’s long-anticipated climate change summit.

Fresh commitments pledged at the conference will prove critical to keep Earth’s warming below 1.5C and avoid tipping points which lock in disastrous changes to our climate.

Antarctic Science Platform director Dr Nancy Bertler said the UN’s recently-released Sixth Assessment Report delivered stark warnings about our future unless global greenhouse gas emissions are cut.

Antarctic geological and ice core research underpinned the report’s conclusion that atmospheric CO2 concentrations are now higher than at any time in at least 2 million years.

Future changes in climate are directly linked to what happens in Antarctica, including potential tipping points for rapid and irreversible sea-level rise.

“The time for action is quickly running out, and we need bold targets and strong commitments to urgently reduce emissions,” she said.

“The choices made today will have long-lasting consequences.”

Antarctica New Zealand chief scientist Dr John Cottle said the melting of Antarctic ice remained a major wildcard – and global sea-level rise of up to 2m by 2100, though considered unlikely, could not be ruled out.

Already, insights gleaned from Antarctica have told us that the planet’s sea level is rising faster than at any point in at least the past 3000 years – and that melting ice sheets and glaciers are major contributors.

Even with reduced emissions, the world may likely see 50cm of sea-level rise by 2100 – and more than 1m with higher emissions levels.

“Understanding ice sheet melt will increase confidence in projections for sea-level rise under different emissions pathways, which are effectively different possible futures based on how much CO2 goes into the atmosphere,” Cottle said.

“Ongoing research will reduce uncertainty about what will happen over coming decades.”

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