West Antarctic Ice Sheet May Lie Close To A Tipping Point

[bluewave]

 

Chris Mooney in the Washington Post:

Warm ocean water has been discovered underneath a massive glacier in West Antarctica, a troubling finding that could speed its melt in a region with the potential to eventually unleash more than 10 feet of sea-level rise.

The unprecedented research, part of a multimillion-dollar British and U.S. initiative to study the remote Thwaites Glacier, involved drilling through nearly 2,000 feet of ice to measure water temperatures in a narrow cavity where the glacier first connects with the ocean. This is one of the most difficult-to-reach locations on Earth.

At a region known as the “grounding line,” where the ice transitions between resting on bedrock and floating on the ocean, scientists measured water temperatures of about 0 degrees Celsius (32 degrees Fahrenheit). That is more than 2 degrees warmer than the freezing point in that location, said David Holland, a New York University glaciologist. He performed the research with Keith Nicholls of the British Antarctic Survey.

“That is really, really bad,” said Holland. “That’s not a sustainable situation for that glacier.”

Scientists already knew that Thwaites was losing massive amounts of ice — more than 600 billion tons over the past several decades, and most recently as much as 50 billion tons per year. And it was widely believed that this was occurring because a layer of relatively warmer ocean water, which circles Antarctica below the colder surface layer, had moved closer to shore and begun to eat away at the glaciers themselves, affecting West Antarctica in particular.

But that had not been directly confirmed because Thwaites is gigantic (larger than the state of Pennsylvania) and exceedingly difficult to reach.

“The biggest thing to say at the moment is, indeed, there is very warm water there, and clearly, it could not have been there forever, or the glacier could not be there,” Holland said.

Thwaites is the most worrying glacier in Antarctica because of its size — it is unusually wide, presenting a 75-mile front of ice to the ocean, without any rocks or mountains to hem it in. This means very large volumes of ice could break off and flow uninhibited through this region into the sea.

Even worse, Thwaites gets deeper and thicker from its oceanfront region back into its interior in the heart of West Antarctica. This is known to be an unstable configuration for a glacier, because as the ocean continues to eat away at its base, the glacier becomes thicker, so more ice is exposed to the ocean. In turn, that ice flows outward faster. Scientists call this “marine ice sheet instability.”

Researchers believe that as recently as some 100,000 years ago, West Antarctica was not a sheet of ice at all — but rather, an open ocean that later converted to glacier. The fear is that the melting now taking place could lead to a return to open ocean.

Granted, it would still take a very long time to melt all of that ice, but there’s a fear that it could begin in a substantial way in our lifetimes, worsening sea level rise.

Because Thwaites is so vast, the measurements were confined to a region known as its eastern ice shelf, where a floating part of the glacier is 600 meters (nearly 2,000 feet thick) and underlain by just 40 meters (about 130 feet) of water. Scientists drilled through the ice using a technique known as hot-water drilling, and then extended an instrumented cable to take measurements in the ocean cavity.

They also detected turbulent water in the area, suggesting that saltwater and freshwater are swirling together as the ice melts. This process may draw the warm water in toward the glacier and speed the losses.

“The key here is that they drilled very close to the grounding line,” said Eric Rignot, a researcher with NASA and the University of California who also studies Thwaites closely and commented on the findings. “We do not know much about ocean-ice interaction in that narrow part of the cavity, yet this is the crucial part for ice dynamics, glacier stability, fast retreat.”

“Is the water moving around and releasing heat to the ice efficiently, is it stagnant instead?” Rignot continued. “Our sense from remote sensing is that it is not stagnant but very actively melting ice. So having temperature measurements in that narrow part is essential.”

Rignot said the water is probably even warmer in other regions of Thwaites, which could retreat even faster than the spot where the measurements were taken.

Nicholls of the British Antarctic Survey said in an email from Antarctica that the relatively warm water they discovered was actually “associated with low (for the area) melt rates because of the low currents.” Still, he too affirmed the water was more than warm enough to melt ice.

Climate change is believed to be shifting winds around Antarctica, which in turn are connected to a warming of the tropics and shifting patterns of atmospheric circulation. The winds drive ocean currents, and the change has meant that the warm offshore layer, called circumpolar deep water, has been pushing in closer to shore, where it can melt ice.

Scientists say there is much more to learn about this process, but the most important fact is clear — warm water is causing Thwaites to melt and retreat.

“This is the first verification ever of warm water at a grounding zone on the Thwaites Glacier, arguably the most important one in West Antarctica,” said Holland. “So the pieces fit.”

https://www.nyu.edu/about/news-publications/news/2020/january/scientists-find-record-warm-water-in-antarctica--pointing-to-cau.html

 

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Jan 29, 2020

Jan 29, 2020

Engineering, Science and Technology

 

New York City

A team of scientists has observed, for the first time, the presence of warm water at a vital point underneath a glacier in Antarctica—an alarming discovery that points to the cause behind the gradual melting of this ice shelf while also raising concerns about sea-level rise around the globe. 

 

Researchers digging out the drill site after a three-day storm with winds reaching 50 knots. Image courtesy of David Holland, NYU's Courant Institute of Mathematical Sciences

Discovery Serves as Warning Signal for Sea-Level Rise

A team of scientists has observed, for the first time, the presence of warm water at a vital point underneath a glacier in Antarctica—an alarming discovery that points to the cause behind the gradual melting of this ice shelf while also raising concerns about sea-level rise around the globe.

“Warm waters in this part of the world, as remote as they may seem, should serve as a warning to all of us about the potential dire changes to the planet brought about by climate change,” explains David Holland, director of New York University’s Environmental Fluid Dynamics Laboratory and NYU Abu Dhabi’s Center for Global Sea Level Change, which conducted the research. “If these waters are causing glacier melt in Antarctica, resulting changes in sea level would be felt in more inhabited parts of the world.”

The recorded warm waters—more than two degrees above freezing—flow beneath the Thwaites Glacier, which is part of the Western Antarctic Ice Sheet. The discovery was made at the glacier’s grounding zone—the place at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf and which is key to the overall rate of retreat of a glacier.

VIDEO: Working in the isolated conditions of Antarctica, researchers from NYU and NYU Abu Dhabi operate a borehole winch to lower a turbulence device in the ocean cavity on Thwaites Glacier.

Thwaites’ demise alone could have significant impact globally.

It would drain a mass of water that is roughly the size of Great Britain or the state of Florida and currently accounts for approximately 4 percent of global sea-level rise. Some scientists see Thwaites as the most vulnerable and most significant glacier in the world in terms of future global sea-level rise—its collapse would raise global sea levels by nearly one meter, perhaps overwhelming existing populated areas.

While the glacier’s recession has been observed over the past decade, the causes behind this change had previously not been determined.

“The fact that such warm water was just now recorded by our team along a section of Thwaites grounding zone where we have known the glacier is melting suggests that it may be undergoing an unstoppable retreat that has huge implications for global sea level rise,” notes Holland, a professor at NYU’s Courant Institute of Mathematical Sciences.

The scientists’ measurements were made in early January, after the research team created a 600-meter deep and 35-centimeter wide access hole and deployed an ocean-sensing device to measure the waters moving below the glacier’s surface. This device gauges the turbulence of the water as well as other properties such as temperature. The result of turbulence is the mixing of fresh meltwater from the glacier and salty water from the ocean.

It marks the first time that ocean activity beneath the Thwaites Glacier has been accessed through a bore hole and that a scientific instrument measuring underlying ocean turbulence and mixing has been deployed. The hole was opened on January 8 and 9 and the waters beneath the glacier measured January 10 and 11.

 

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Aurora Basinski, an NYU graduate student who made the turbulence measurement, said, “From our observations into the ocean cavity at the grounding zone we observed not only the presence of warm water, but also its turbulence level and thus its efficiency to melt the ice shelf base.”

Another researcher, Keith Nicholls, a scientist with the British Antarctic Survey, added, “This is an important result as this is the first time turbulent dissipation measurements have been made in the critical grounding zone of the West Antarctic Ice Sheet.”

This research was supported by a $2.1 million, five-year grant from the National Science Foundation (PLR-1739003). The grant is part of the International Thwaites Glacier Collaboration (ITGC), headed by the United Kingdom’s Natural Environment Research Council and the National Science Foundation, which has been deploying scientists to gather the data needed to understand whether the glacier’s collapse could begin in the next few decades or centuries. Other members of the field team included researchers from Penn State, Georgia Tech, and the British Antarctic Survey.

For more about the project, please visit https://thwaitesglacier.org/projects/melt.

 

 

 

[LibertyBell]

highest temp ever recorded in Antarctica- 65.1 and accelerating ice melt saw a 130 ft tall slab of ice fall into the ocean recently.

 

[bluewave]

Ancient Antarctic ice melt increased sea levels by 3+ metres – and it could happen again 

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12 FEB 2020 

 

 SHERRY LANDOW 

Rising ocean temperatures drove the melting of Antarctic ice sheets and caused extreme sea level rise more than 100,000 years ago, a new international study led by UNSW Sydney shows.
 

https://newsroom.unsw.edu.au/news/science-tech/ancient-antarctic-ice-melt-increased-sea-levels-3-metres-–-and-it-could-happen

Mass melting of the West Antarctic Ice Sheet was a major cause of high sea levels during a period known as the Last Interglacial (129,000-116,000 years ago), an international team of scientists led by UNSW’s Chris Turney has found. The research was published today in Proceedings of the National Academy of Sciences (PNAS).
 
The extreme ice loss caused a multi-metre rise in global mean sea levels – and it took less than 2˚C of ocean warming for it to occur. 

“Not only did we lose a lot of the West Antarctic Ice Sheet, but this happened very early during the Last Interglacial,” says Chris Turney, Professor in Earth and Climate Science at UNSW Sydney and lead author of the study. 

Fine layers of ancient volcanic ash in the ice helped the team pinpoint when the mass melting took place. Alarmingly, the results indicated that most ice loss occurred within the first millennia, showing how sensitive the Antarctic is to higher temperatures. 

“The melting was likely caused by less than 2°C ocean warming – and that's something that has major implications for the future, given the ocean temperature increase and West Antarctic melting that’s happening today,” Professor Turney says. 

During the Last Interglacial, polar ocean temperatures were likely less than 2˚C warmer than today, making it a useful period to study how future global warming might affect ice dynamics and sea levels. 

“This study shows that we would lose most of the West Antarctic Ice Sheet in a warmer world,” says Professor Turney. 

In contrast to the East Antarctic Ice Sheet – which mostly sits on high ground – the West Antarctic sheet rests on the seabed. It’s fringed by large areas of floating ice, called ice shelves, that protect the central part of the sheet. 

As warmer ocean water travels into cavities beneath the ice shelves, ice melts from below, thinning the shelves and making the central ice sheet highly vulnerable to warming ocean temperatures. 

Blue ice areas are created by fierce, high-density winds that remove the top layer of snow and erode the exposed ice. As the ice is removed, ancient ice flows up to the surface, offering an insight into the ice sheet's history. Image: AntarcticScience.cm

Going back in time

To undertake their research, Professor Turney and his team travelled to the Patriot Hills Blue Ice Area, a site located at the periphery of the West Antarctic Ice Sheet, with support from Antarctic Logistics and Expeditions (or ALE). 

Blue ice areas are the perfect laboratory for scientists due to their unique topography – they are created by fierce, high-density katabatic winds. When these winds blow over mountains, they remove the top layer of snow and erode the exposed ice. As the ice is removed, ancient ice flows up to the surface, offering an insight into the ice sheet’s history.

While most Antarctic researchers drill down into the ice core to extract their samples, this team used a different method – horizontal ice core analysis.  

“Instead of drilling kilometres into the ice, we can simply walk across a blue ice area and travel back through millennia. By taking samples of ice from the surface we are able to reconstruct what happened to this precious environment in the past,” Professor Turney says.

Through isotope measurements, the team discovered a gap in the ice sheet record immediately prior to the Last Interglacial. This period of missing ice coincides with the extreme sea level increase, suggesting rapid ice loss from the West Antarctic Ice Sheet. The volcanic ash, trace gas samples and ancient DNA from bacteria trapped in the ice all support this finding.

Trace gas bubbles in the ice samples. Image: AntarcticScience.com

Learning from the Last Interglacial 

Ice age cycles occur approximately every 100,000 years due to subtle changes in Earth’s orbit around the Sun. These ice ages are separated by warm interglacial periods. The Last Interglacial is the most recent warm period to our current interglacial period, the Holocene.

While human contribution to global warming makes the Holocene unique, the Last Interglacial remains a useful research point to understand how the planet responds to extreme change. 

“The future is heading far beyond the range of anything we've seen observed in the scientific instrumental record of the last 150 years,” says Professor Turney. “We have to look further into the past if we’re going to manage future changes.” 

During the Last Interglacial, global mean sea levels were between 6m and 9m higher than present day, although some scientists suspect this could have reached 11m. 

The sea level rise in the Last Interglacial can’t be fully explained by the Greenland Ice Sheet melt, which accounted for a 2m increase, or ocean expansion from warmer temperatures and melting mountain glaciers, which are thought to have caused less than a 1m increase.

“We now have some of the first major evidence that West Antarctica melted and drove a large part of this sea level rise,” says Professor Turney.

An urgent need to minimise future warming

The severity of the ice loss suggests that the West Antarctic Ice Sheet is highly sensitive to future ocean warming.

“The West Antarctic Ice Sheet is sitting in water, and today this water is getting warmer and warmer,” says Professor Turney, who is also a Chief Investigator of the ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH). 

Using data gained from their fieldwork, the team ran model simulations to investigate how warming might affect the floating ice shelves. These shelves currently buttress the ice sheets and help slow the flow of ice off the continent. 

The results suggest a 3.8m sea level rise during the first thousand years of a 2˚C warmer ocean. Most of the modelled sea level rise occurred after the loss of the ice shelves, which collapsed within the first two hundred years of higher temperatures. 

The researchers are concerned that persistent high sea surface temperatures would prompt the East Antarctic Ice Sheet to melt, driving global sea levels even higher.

“The positive feedbacks between a warming ocean, ice shelf collapse, and ice sheet melt suggests that the West Antarctic may be vulnerable to passing a tipping point,” stressed Dr Zoë Thomas, co-author and ARC Discovery Early Career Research Award (DECRA) Fellow at UNSW.

Professor Chris Turney drilling for ice in the Patriot Hills area. Image: AntarcticScience.com

“As it reaches the tipping point, only a small increase in temperature could trigger abrupt ice sheet melt and a multi-metre rise in global sea level.”

At present, the consensus of the Intergovernmental Panel on Climate Change (IPCC) 2013 report suggests that global sea level will rise between 40cm and 80cm over the next century, with Antarctica only contributing around 5cm of this. 

The researchers are concerned that Antarctica’s contribution could be much greater than this.

“Recent projections suggest that the Antarctic contribution may be up to ten times higher than the IPCC forecast, which is deeply worrying,” says Professor Christopher Fogwill, co-author and Director of The Institute for Sustainable Futures at the UK University of Keele.

“Our study highlights that the Antarctic Ice Sheet may lie close to a tipping point, which once passed may commit us to rapid sea level rise for millennia to come. This underlines the urgent need to reduce and control greenhouse gas emissions that are driving warming today.” 

Notably, the researchers warn that this tipping point may be closer than we think.

“The Paris Climate Agreement commits to restricting global warming to 2˚C, ideally 1.5˚C, this century,” says Professor Turney.   

“Our findings show that we don’t want to get close to 2˚C warming.” 

Professor Turney and his team hope to expand the research to confirm just how quickly the West Antarctic Ice Sheet responded to warming and which areas were first affected.

“We only tested one location, so we don’t know whether it was the first sector of Antarctica that melted, or whether it melted relatively late. How these changes in Antarctica impacted the rest of the world remains a huge unknown as the planet warms into the future” he says. 

“Testing other locations will give us a better idea for the areas we really need to monitor as the planet continues to warm.”

[donsutherland1]

On February 9, 2020, a record temperature of 20.75 degrees C (69.35 degrees F) was recorded on Antarctica's Seymour Island.

https://www.theguardian.com/world/2020/feb/13/antarctic-temperature-rises-above-20c-first-time-record

[LibertyBell]

melting of the antarctic ice sheet can cause a quick sea level rise in 10-20 years