24/07/2020

Biggest Ice Sheet On Earth More Vulnerable To Melting Than Thought

National Geographic - Douglas Fox

Shocking evidence suggests that the last time the East Antarctic ice sheet collapsed, it added over 10 feet to sea level rise, and that it’s likely to happen again.

A new study concludes that the East Antarctic ice sheet last collapsed much more recently than believed, and that it could happen again over the next centuries. Photograph by George Steinmetz, Nat Geo Image Collection

A rare, translucent, black-and-white crystal that sat in a box for 30 years has led scientists to a startling discovery: The East Antarctic ice sheet, which holds 80 percent of the world’s ice, may be even more vulnerable to warming than once believed.

Scientists had determined that this ice sheet last retreated about three million years ago. But a new paper in the journal Nature suggests—based on a study of crystals collected from the region—that a large part of it collapsed only 400,000 years ago. Most startling of all, the team’s calculations suggest that the dramatic change happened during an extended but relatively mild warm spell.

NG MAPS

During that time period, the amount of carbon dioxide in the atmosphere never rose very high, peaking at only about 300 parts per million (ppm), says David Harwood, who studies Antarctic glacial history at the University of Nebraska in Lincoln.

“That’s the scary thing,” says Harwood. Modern carbon dioxide levels blew past 300 ppm way back in 1915—and they currently sit at 410 ppm. In the coming centuries, that extra carbon dioxide could raise temperatures, and sea level, well above what happened 400,000 years ago, he says. “This doesn’t bode well for the future.”

The world’s other ice sheets, including those in Greenland and West Antarctica, are already predicted to lose ice in the coming century. Greenland sits far from the North Pole, exposing it to warm air, and West Antarctica sits in a broad bowl that dips below sea level, exposing it to warm ocean currents. But the East Antarctic ice sheet was considered more secure, because it occupies the frigid South Pole, and most of it sits on land that shields it from the ocean’s warmth.

“For decades, the East Antarctic ice sheet has been dressed in this armor of invincibility,” says Slawek Tulaczyk, a glaciologist at the University of California, Santa Cruz, who took part in the research. To speak of it shrinking “was, until recently, unthinkable.”

If these new findings bear out, then East Antarctica may contribute to sea level rise sooner than expected. The greenhouse gases that humans have produced to date may have already locked in 42 feet of eventual sea level rise from all of the glaciers predicted to melt in the coming centuries, including the ones in East Antarctica.

Solving a mystery

This discovery stemmed from a study of the delicate layers of a black-and-white crystal from deep beneath the ice sheet. Tulaczyk and Terry Blackburn, a geochemist at UC Santa Cruz, happened upon the crystal while studying something else. It began in 2017, as they visited Taylor Valley, on the coast of East Antarctica, to investigate a mystery: Measurements by them and other scientists had shown that water seeping through the ground there was unusually high in uranium.

“This signal was coming from somewhere else” further up the valley, says Graham Edwards, Blackburn’s doctoral student who was also on that trip. And so they went looking for the source of the uranium signal, hoping it might reveal something interesting about the history of the ice sheet.

Although most people know uranium as a nuclear fuel, tiny traces of it are found throughout the world’s rocks, rivers, and oceans. Most of it exists in a heavy form, called uranium-238. But mixed in with it, scientists always find a few atoms of a lighter version, called uranium-234, which is produced when its heavier cousin undergoes radioactive decay. Across the world’s oceans, the ratio of these two forms is relatively constant—about one atom of uranium-234 for every 16,000 atoms of uranium-238.

Crystal layers like these, which formed 200,000 years ago beneath the East Antarctic ice sheet, reveal that it melted 400,000 years ago, much more recently than thought. Photograph by Michael Scudder

Scientists theorize that when an ice sheet covers a continent for a long time, the water trapped under it slowly accumulates uranium-234. This happens as uranium-238 in the rocks and gravel under the ice decays, tossing atoms of light uranium into the water, where they accumulate over time.

The water seeping through Taylor Valley is unusual because it holds two to five times the usual level of the lighter uranium-234. “Those fluids have been in contact with rock for a significant period of time,” speculates Blackburn.

Measuring the amount of uranium-234 under the East Antarctic ice sheet could therefore provide clues about how much time has passed since the ice sheet’s most recent retreat.

Unlocking the rocks

However, no one had ever measured uranium-234 under an ice sheet. So Blackburn, Edwards, and Tulaczyk set out to try to find minerals that formed in the water beneath the one in East Antarctica. Those rocks might record how much uranium-234 was in the water where they were created, which could, in turn, reveal when the sheet had last melted.

Finding rocks from under the ice sheet might sound like a pipe dream, but Tulaczyk and Blackburn knew of a place where rocks from beneath the ice make their way to the surface, an area called Elephant Moraine, just over the mountains from Taylor Valley.

Thousands of rocks cover the ice there. They are lifted from the bottom of the ice as it oozes over a buried mountain ridge, like a wave breaking at a glacial pace. Constant dry winds evaporate the ice surface by several inches a year, so the rocks eventually make their way to the surface.

At the end of Taylor Glacier, a hypersaline brine known as "Blood Falls" flows onto the ice surface. The red color comes from iron oxide. Researchers studied mineral deposits from such fluids and found surprising evidence of glacial retreat about 400,000 years ago. It was thought that the East Antarctic ice sheet had been stable for millions of years. Photograph by Terry Blackburn

During the 1980s, a scientist from Ohio State University collected hundreds of rocks from Elephant Moraine. Most were granites, sandstones, and basalts that formed before the ice sheet covered the continent. But among these, he found a few mysterious chunks of crystal, which sat in the collection for 30 years, until Blackburn read about them and acquired three from OSU’s Polar Rock Repository in 2019.

One of the rocks was especially striking, with paper-thin alternating bands of creamy-white opal and amber or black calcite stacked like tree rings throughout.

Blackburn chipped off individual layers and determined their ages by measuring their uranium-234 and another radioactive element, thorium-230, which the uranium decays into at a known rate. He found that the layers in the fist-sized rock had formed over a span of 120,000 years, starting about 270,000 years ago.

Next he measured the percentage of the lighter uranium-234 in each layer. He thought it would be constant from one layer to the next—because, he says, “there are these ideas that the East Antarctic ice sheet had been stable for millions of years.”

To his surprise, the crystals told him something very different: The amount of uranium-234 in successive layers actually grew by 50 percent. In the precise world of geochemistry, “this is a massive change,” says Blackburn. Two other layered crystals from Elephant Moraine showed similar results.

That finding could mean only one thing: The East Antarctic ice sheet had retreated more recently than anyone thought. When the ice disappeared, the water beneath it spilled into the ocean—resetting the amount of uranium-234 back down to a low level. Only after the ice sheet grew back did uranium-234 once again start to accumulate under it; it was that accumulation that was captured in the crystals.

This wasn’t a small retreat, either, says Tulaczyk. For seawater to approach Elephant Moraine, the ice would have had to retreat 400 miles from its present-day coastline. Elephant Moraine sits on the edge of a vast area, called Wilkes Basin, where the rocky, icy bed drops as far as 5,000 feet below sea level—exposing the ice to deep ocean currents that could have melted its underside.

Tulaczyk estimates that over an area of 115,000 square miles (about the size of Arizona), the ice sheet thinned by thousands of feet—until it peeled off its bed and floated on the ocean. Weakened, it couldn’t support as much ice upstream, and the Wilkes Basin lost more than 250,000 cubic miles of ice, enough to raise the sea level 10 to 13 feet.

It happened before

The new results fill in much-needed details, says Maureen Raymo, a marine geologist at the Lamont-Doherty Earth Observatory in New York. She studies ancient shorelines around the world that now sit high above the waves, complete with sand, shells, and fossil shrimp burrows. Those shorelines show multiple times when sea levels were higher in the past, including 400,000 years ago, when she estimates that they peaked somewhere between 33 and 42 feet higher than today’s levels.

Greenland, West Antarctica, and other glaciers globally might contribute 30 feet of rise if they melted. Adding another 10 to 13 feet from the Wilkes Basin in East Antarctica “is completely consistent” with those estimates, says Raymo.

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First Active Leak Of Sea-Bed Methane Discovered In Antarctica

The Guardian - 

Researchers say potent climate-heating gas almost certainly escaping into atmosphere

An image of the sea floor at the Cinder Cones dive site in Antarctica’s McMurdo Sound. The white patches indicate the presence of microbes feeding on methane as it seeps to the surface. Photograph: Andrew Thurber/Oregon State University

The first active leak of methane from the sea floor in Antarctica has been revealed by scientists.

The researchers also found microbes that normally consume the potent greenhouse gas before it reaches the atmosphere had only arrived in small numbers after five years, allowing the gas to escape.

Vast quantities of methane are thought to be stored under the sea floor around Antarctica. The gas could start to leak as the climate crisis warms the oceans, a prospect the researchers said was “incredibly concerning”.

The reason for the emergence of the new seep remains a mystery, but it is probably not global heating, as the Ross Sea where it was found has yet to warm significantly. The research also has significance for climate models, which currently do not account for a delay in the microbial consumption of escaping methane.

The active seep was first spotted by chance by divers in 2011, but it took scientists until 2016 to return to the site and study it in detail, before beginning laboratory work.

“The delay [in methane consumption] is the most important finding,” said Andrew Thurber, from Oregon State University in the US, who led the research. “It is not good news. It took more than five years for the microbes to begin to show up and even then there was still methane rapidly escaping from the sea floor.”

The release of methane from frozen underwater stores or permafrost regions is one of the key tipping points that scientists are concerned about, which occur when a particular impact of global heating becomes unstoppable.

“The methane cycle is absolutely something that we as a society need to be concerned about,” said Thurber. “I find it incredibly concerning.”

Very little was known about the Antarctic methane cycle but the good news, he said, was that the new seep provided a natural laboratory for further research.

Why the new seep formed is unknown. “That is a mystery that we still do not have an answer to,” Thurber said. “It is on the side of an active volcano but it doesn’t seem like it came from that.”

Prof Jemma Wadham, at the University of Bristol, UK, who was not involved in the study, said: “Antarctica and its ice sheet are huge black holes in our understanding of Earth’s methane cycle – they are difficult places to work.

“We think that there is likely [to be] significant methane beneath the ice sheet,” she said. “The big question is: how large is the lag [in methane-consuming microbes] compared with the speed at which new leaks of methane might potentially form in the wake of retreating ice?”

The research, published in the journal Proceedings of the Royal Society B, reports the discovery of the methane seep at a 10-metre (30ft) deep site known as Cinder Cones in McMurdo Sound. It is a 70-metre long patch of white microbial mats, and a second seep was found during the 2016 expedition.

“We stumbled upon the methane seep at a site that has been dived at since the 1960s and it had just turned on,” said Thurber. There were no bubbles of methane, he said. “Most of the methane in many seeps actually comes out in what we call diffuse flows. So it’s just dissolved in the water.”

The source of the methane is probably decaying algae deposits buried under sediments and is likely to be thousands of years old. In most parts of the oceans, methane leaking from the sea bed is consumed by microbes in the sediment or the water column above. But the slow growth of microbes at the Cinder Cones site, and its shallow depth, means methane is almost certain to be leaking into the atmosphere.

Thurber said the first microbes to grow at the site were of an unexpected strain. “We’re probably in a successional stage, where it may be five to 10 years before a community becomes fully adapted and starts consuming methane.”

Widespread active methane seepage was reported off the sub-Antarctic island of South Georgia in 2014, a first for the Southern Ocean. “But that’s really a different oceanographic area than the Antarctic continent,” Thurber said.

Wadham said the five years for which the Cinder Cones seep has been studied is a short amount of time. “So it would be good to see what happens to this seep into the future. The discovery also makes you wonder if these features are more common than we might think around Antarctica, but are rarely stumbled upon.”

However, the researchers are unlikely to be able to return to Antarctica soon. The continent is currently free of coronavirus but the risk of infection has disrupted expedition plans.

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(AU) Australia Wants To Build A Huge Concrete Runway In Antarctica. Here’s Why That’s A Bad Idea

The Conversation -  | 

AAD

Authors
  •  is a University Associate, University of Tasmania
  •  is an Adjunct Senior Lecturer, University of Tasmania
Australia wants to build a 2.7-kilometre concrete runway in Antarctica, the world’s biggest natural reserve. The plan, if approved, would have the largest footprint of any project in the continent’s history.

The runway is part of an aerodrome to be constructed near Davis Station, one of Australia’s three permanent bases in Antarctica. It would be the first concrete runway on the continent.

The plan is subject to federal environmental approval. It coincides with new research published this week showing Antarctica’s wild places need better protection. Human activity across Antarctica has been extensive in the past 200 years – particularly in the coastal, ice-free areas where most biodiversity is found.

The area around Davis Station is possibly Antarctica’s most significant coastal, ice-free area. It features unique lakes, fjords, fossil sites and wildlife.

Australia has successfully operated Davis Station since 1957 with existing transport arrangements. While the development may win Australia some strategic influence in Antarctica, it’s at odds with our strong history of environmental leadership in the region.

The Vestfold Hills, the proposed site of the aerodrome. Nick Roden

Year-round access

The Australian Antarctic Division (AAD), a federal government agency, argues the runway would allow year-round aviation access between Hobart and Antarctica.

Presently, the only Australian flights to Antarctica take place at the beginning and end of summer. Aircraft land at an aerodrome near the Casey research station, with interconnecting flights to other stations and sites on the continent. The stations are inaccessible by both air and ship in winter.

The AAD says year-round access to Antarctica would provide significant science benefits, including:
  • better understanding sea level rise and other climate change impacts
  • opportunities to study wildlife across the annual lifecycle of key species including krill, penguins, seals and seabirds
  • allowing scientists to research through winter.
Leading international scientists had called for improved, environmentally responsible access to Antarctica to support 21st-century science. However, the aerodrome project is likely to reduce access for scientists to Antarctica for years, due to the need to house construction workers.

Australia says the runway would have significant science benefits. Australian Antarctic Division





Australia: an environmental leader?

Australia has traditionally been considered an environmental leader in Antarctica. For example, in 1989 under the Hawke government, it urged the world to abandon a mining convention in favour of a new deal to ban mining on the continent.

Australia’s 20 Year Action Plan promotes “leadership in environmental stewardship in Antarctica”, pledging to “minimise the environmental impact of Australia’s activities”.

But the aerodrome proposal appears at odds with that goal. It would cover 2.2 square kilometres, increasing the total “disturbance footprint” of all nations on the continent by 40%. It would also mean Australia has the biggest footprint of any nation, overtaking the United States.

The contribution of disturbance footprint from countries in Antarctica measured from Brooks et al. 2019, with Australia’s share increasing to 35% including the aerodrome proposal. Shaun Brooks



Within this footprint, environmental effects will also be intense. Construction will require more than three million cubic metres of earthworks - levelling 60 vertical metres of hills and valleys along the length of the runway. This will inevitably cause dust emissions – on the windiest continent on Earth - and the effect of this on plants and animals in Antarctica is poorly understood.

Wilson’s storm petrels that nest at the site will be displaced. Native lichens, fungi and algae will be destroyed, and irreparable damage is expected at adjacent lakes.

Weddell seals breed within 500 metres of the proposed runway site. Federal environment officials recognise the dust from construction and subsequent noise from low flying aircraft have the potential to disturb these breeding colonies.

The proposed area is also important breeding habitat for Adélie penguins. Eight breeding sites in the region are listed as “important bird areas”. Federal environment officials state the penguins are likely to be impacted by human disturbance, dust, and noise from construction of the runway, with particular concern for oil spills and aircraft operations.

The summer population at Davis Station will need to almost double from 120 to 250 during construction. This will require new, permanent infrastructure and increase the station’s fuel and water consumption, and sewage discharged into the environment.

The AAD has proposed measures to limit environmental damage. These include gathering baseline data (against which to measure the project’s impact), analysing potential effects on birds and marine mammals and limiting disturbance where practicable.

But full details won’t be provided until later in the assessment process. We expect Australia will implement these measures to a high standard, but they will not offset the project’s environmental damage.

An Adélie penguin colony near Davis Station. Nick Roden





Playing politics

So given the environmental concern, why is Australia so determined to build the aerodrome? We believe the answer largely lies in Antarctic politics.

Australian officials have said the project would “contribute to both our presence and influence” on the continent. Influence in Antarctica has traditionally corresponded to the strength of a nation’s scientific program, its infrastructure presence and engagement in international decision-making.

Australia is a well-regarded member of the Antarctic Treaty. It was an original signatory and claims sovereignty over 42% of the continent. It also has a solid physical and scientific presence, maintaining three large year-round research stations.

But other nations are also vying for influence. China is constructing its fifth research station. New Zealand is planning a NZ$250 million upgrade to Scott Base. And on King George Island, six stations have been built within a 5km radius, each run by different nations. This presence is hard to justify on the basis of scientific interest alone.

A Weddell seal and her pup near Davis Station. Nick Roden

Getting our priorities straight

We believe there are greater and more urgent opportunities for Australia to assert its leadership in Antarctica.

For example both Casey and Mawson stations – Australia’s two other permanent bases – discharge sewage into the pristine marine environment with little treatment. And outdated fuel technology at Australia’s three stations regularly causes diesel spills.

At Wilkes station, which Australia abandoned in the 1960s, thousands of tonnes of contaminants have been left behind.

Australia should fix such problems before adding more potentially damaging infrastructure. This would meet our environmental treaty obligations and show genuine Antarctic leadership.

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