The hunt for hydroxyl radicals in Antarctica could reveal the secrets of our future climate

Updated

In every sense, gazing into an Antarctic time tunnel is a chilling experience. You lean over an icy entrance about the size of a dinner plate being exceptionally careful not to drop anything in.

It's hard to tell how far you are seeing. Five or 50 metres? A year, a decade, a century or more? As your eyes adjust they see beyond the snap-frozen present and deeper into the decades gone by.

The colour shifts from blinding white to electric blue and eventually to a darkness so unfathomable it could be a tunnel into deep space.

A core barrel is lowered into the cylindrical shaft, hanging on a cable. It travels at first through layers of hard-packed snow that still retain a connection to the atmosphere above.

Go deeper and those pore spaces close off under the weight of snow pushing down from above. The sheer compressive force compacts fluffy snowflakes into solid ice, trapping a tiny bubble of atmosphere from that moment.

Each bubble becomes a time capsule. The drill drops through the centuries, reaching for our pre-industrial past. To solve one of the enduring climate change riddles, we're going to need a lot of air from an awful lot of these bubbles.

Hunting for hydroxyl

In the summer of 2018-19, a team of Australian and US scientists headed "deep field" from the Australian Antarctic Division's Casey Station.

They had set themselves a difficult challenge: haul hundreds of tonnes of delicate equipment, drilling rigs and enough supplies to the far side of distant Law Dome for three months to camp out in the "home of the blizzard".

Their aim was to drill for a handful of atoms that could reveal how well the chemistry of the atmosphere had been removing problem greenhouse gases like methane.

"We know we're headed towards more [global] warming, but we don't know how exactly the atmosphere is going to behave as we continue to add more greenhouse gases to it," explains glaciologist Peter Neff.

Carbon dioxide, the main greenhouse gas, is mostly removed from the atmosphere by plants and absorption into the ocean, but it's a slow process.

Other warming gases like methane and chlorofluorocarbons (CFCs) are more chemically active. They are partly removed from the atmosphere by a highly reactive, naturally occurring molecule called hydroxyl (OH).

"The hydroxyl radical is sometimes called the detergent of the atmosphere," says atmospheric chemist Vasilii Petrenko.

Direct atmospheric measurements of hydroxyl only date from the mid-1980s. What climate modellers need is information back to the beginning of the industrial period so we can work out what OH was up to before we started adding to its workload with ever-increasing emissions.

"We know that it's probably been keeping up over the last couple of decades, but before that there's no information," adds co-investigator David Etheridge from the CSIRO.

There would be profound implications if this extremely helpful molecule is found to have been losing its capacity to scrub the skies over time. Corrections would be needed for how long methane hangs around and how quickly it will continue to build up in the future. In short, things could get hotter, much faster than currently predicted.

About six years ago, Petrenko and his colleagues realised they might have found a way to uncover hydroxyl's secret history. A technique they pioneered in Greenland to analyse tell-tale carbon 14 (14C) atoms in ice cores had allowed the underlying sources of our rising methane emissions to be pinpointed.

If they could now mine enough ice as quickly as possible, they reasoned, and from just the right spot in Antarctica, enough trapped 14C atoms could be recovered to reconstruct the OH chemistry of the past.

Just the right spot meant Law Dome.

A deep chill

Law Dome is not the sort of place most sensible people would choose to pitch a tent. Even penguins don't visit.

The weather can be truly awful — think -25C on a summer's day. That's before you add in wind chill from storm-force gales that sweep the summit and blizzards dumping more snow here than nearly anywhere else in Antarctica.

"A lot of snowfall comes off the coast, hits this very, very slight incline and dumps a lot of snow," Etheridge, an atmospheric scientist, shouts over a blizzard, "about 4 metres per year, which is enormous by Antarctic standards. "It's what we want, it's just not very comfortable."

Life expectancy for an exposed human caught out in bad weather here is counted in minutes, not days.

Of course, it's not the endless views of a white nothingness that attracted Etheridge and the team of polar veterans to such a challenging place. The lure is lying directly under the thin nylon floor of our tents.

"Law Dome is a stack of ancient snow that has been compressed into ice," Neff explains. "The snow that accumulates here never melts so it's just this layer cake of years, with the most recent year's snowfall on top of the dome and then successively older layers at depth."

We sleep on nearly a kilometre and a half of layered ice holding an impeccable atmospheric record stretching back at least 80,000 years.

Bounded by a pair of glaciers that drain ice from the enormous East Antarctic ice sheet, the 1,400-metre-high dome sits apart from the complicated ice flows of the continent like an island in a stream.

Cores drilled here by Etheridge in the 1980s revealed, with unparalleled clarity, the rapid increase in greenhouse gases expelled over the industrial period. Now the team hopes to chart hydroxyl alongside carbon dioxide and methane through this same interval.

The team begins a military-style operation to extract ice cores in all weather conditions, with constant speed and absolute cleanliness.

The clock is ticking from the moment each ice core arrives at the surface. Cosmic rays start to create new radiocarbon atoms that can compromise the final counts.

"We drill a lot of ice and then we destroy it really quickly in a very precise way to capture those ancient air bubbles that are trapped in the ice," says Neff.

It's a surreal sight. In the whiteout of a blizzard, Petrenko and Neff emerge from what looks to be a white circus tent dressed in white cleanroom coveralls, hauling precious blueish cores on a sled behind them to the melter shelter.

Here they process the ice, placing core after core in a giant stainless-steel vessel that looks part space capsule, part pot still.

"The Hot Tub Time Machine — I thought that was an appropriate descriptor," quips Neff. "Once the hot tub melts the ice, your time machine is there in those air bubbles."

Each of the 20 sled runs sees about half a tonne of ice loaded into the melter, yielding around 50 litres of ancient air per sample for processing back in the US and Australia.

The deepest ice is retrieved from about 240 metres, holding air from the world of the 1870s — the time of Ned Kelly, Edison's first lightbulb and the dawn of the Age of Oil.

The problem for scientists is that there is absolutely no hydroxyl left in it.

"The hydroxyl radical is naturally produced in the atmosphere via what's called photochemistry," explains Petrenko. "Hydroxyl radicals are extremely reactive. They stick around for typically a small fraction of a second."

It's an instant reaction that helps scrub the atmosphere, but if an OH molecule in 1875 survived for less than a second, how can anyone hope to measure its fleeting existence so many years later?

Hydroxyl might be long gone but the air trapped in the bubbles should retain its lingering radioactive fingerprint in the form of individual carbon 14 atoms of carbon monoxide.

"Carbon 14 monoxide is produced in the atmosphere through cosmic rays at a rate that we can pretty much understand," says Etheridge. "It's removed almost entirely by hydroxyl. All we need then is to measure the concentration and we can balance the equation and work out the amount of hydroxyl."

Fire and ice

A year later, the processed gas samples arrive in a black plastic case at the Australian Nuclear Science and Technology Organisation (ANSTO) in Sydney.

The timing is profound. Sydney is sweltering under a blanket of smoke from climate-fuelled fires burning up and down the coast. The ice was drilled during Australia's then-hottest summer on record. Now the air from it will be analysed during the Black Summer of 2019.

"This carbon, if you put a price tag on it, is possibly the most expensive carbon there is on the planet," says Andrew Smith from ANSTO's Centre for Accelerator Science.

Weight for weight, the atoms might be more expensive than diamond but their value to the world at large could be priceless.

"Ten million dollars in the slot!" Smith shouts over the roar of vacuum pumps as he loads a sample carousel into the ion source of the 10 million-volt ANTARES tandem accelerator. "It's critical that we get this right … otherwise we'll have nothing."

Deep inside the machine, each sample in turn is hammered by a caesium plasma, liberating carbon 14 atoms and shooting them towards the detector at 10 per cent of the speed of light.

The ANSTO accelerator runs for 50 straight hours. The tests deliver a good set of data and it's now a matter of interpreting the results. Over the coming months scientists will analyse how well hydroxyl has kept mopping up the pollutants we have been throwing at it over the last 150 years. We'll be able to chart hydroxyl alongside carbon dioxide and methane through the industrial age.

It could be that the final calculations will reveal hydroxyl continues to clean the atmosphere without hindrance. But the fear is that the ice reveals the opposite.

There will be profound implications if it's found that this detergent has been losing its capacity to clean the atmosphere over time. Climate modellers would need to make corrections for how long methane hangs around and how quickly it might build up in the future. In short, things could get hotter faster than currently predicted.

"We certainly are warming the planet," says Petrenko. "The climate models are predicting [it is] going to result in things like sea-level rise and increases in extreme climate events, which are going to be dangerous and in some cases potentially catastrophic for our civilisation."

Science, for the most part, is neither quick nor easy. Whether grappling with a viral pandemic or an angry atmosphere, both the scientific process and its practitioners construct an evolving framework of understanding based on evidence.

Now, more than ever, our civilisation depends on it.

Watch Atom Hunters of Antarctica on Foreign Correspondent on ABC TV and iview.

Topics: climate-change, science, environment, air-pollution, antarctica

First posted