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This glacier is losing ice faster than any other in Antarctica



Close-up view of the crack separating the Pine Island Glacier and the B-46 iceberg, as seen on an IceBridge Operation flight on November 7, 2018.
Close-up view of the crack separating the Pine Island Glacier and the B-46 iceberg, as seen on an IceBridge Operation flight on November 7, 2018. NASA / Brooke Medley

Down in the notoriously vulnerable The ice sheet of West Antarctica, the Pine Island Glacier seems to be breaking faster than ever, and it looks like 2019 could be another busy year. The ice shelf produced large icebergs in 2013, 2015, 2017 and 2018, and now, another is preparing to break free.

The instability of this glacier is not only bad for the southernmost continent. It's bad for the balloon. This glacier is contributing more to sea level rise than any other in Antarctica. New research has shown that, since 1979, the Pine Island Glacier has lost 58 billion tons of ice per year, making it the continent's biggest loser. Combined with its unstable neighbor, the Thwaites glacier, these glaciers contribute one millimeter per decade to the global rise in sea level.

While large masses of ice may appear solid, they are actually dynamic and complicated flow systems. On the Antarctic continent, kilometer-thick glaciers settle as their ice slowly flows into the sea, creating a floating ice shelf that can produce icebergs. While this movement is a normal process, the frequent birth of icebergs and the retreat of glaciers inland may indicate that something out of the ordinary is happening. As the floating ice shelves retreat and shrink, the pressure on the Earth's glacier is relieved, allowing it to flow faster into the ocean, where it can then melt and cause the sea level to rise.

New sea ice forms in a crevice created when the B-46 iceberg broke away from the Pine Island glacier.
New sea ice forms in a crevice created when the B-46 iceberg broke away from the Pine Island glacier. NASA / Kate Ramsayer

Thanks to satellite data from the European Space Agency's Sentinel-1 satellite network, NASA's Landsat satellite network and NASA's IceBridge reconnaissance flights, the acceleration of the Pine Island Glacier has been monitored for decades from the sky. In regards to the recent history of this glacier, in 2016, a crack began to form in the 22-mile-wide main trunk of the Pine Island ice shelf and finally stopped an iceberg called B-44 a year later, in September of 2017. Other The rupture appeared in September of 2018, and only a month later, the iceberg B-46 was born of the glacier.

These icebergs may look small on satellite images, but they are tens to hundreds of square miles in size. The most recent B-46 iceberg had an area of ​​more than 70 square miles (in comparison, Manhattan is just over 22 square miles). This iceberg was seen by human eyes for the first time during a NASA IceBridge flight on November 7, 2018.

In December 2018, Robert Larter, a marine geophysicist of the British Antarctic Survey, signaled on Twitter that the Sentinel-1 satellite clearly captured an active formation crack only a few weeks after the B-46 delivery. "There's a good chance we'll see another birthing event this year," says Larter in early 2019. "You can see the fragments [in the satellite images] of the previous icebergs have not gone far, so now there are many icebergs stored to leave the Bay of Pine Island. "

Stef Lhermitte, assistant professor of geoscience and remote sensing at the Delft University of Technology, agrees: "We hope that this new rupture will result in a major birthing event in weeks, months or up to a year and a half."

Over the years, the calf front has moved drastically towards the land.
Over the years, the calf front has moved drastically towards the land. Stef Lhermitte

Before this iceberg calf marathon since 2013, Pine Island only stopped an iceberg every six years. This animation by Lhermitte shows that the birth front, the line where the icebergs are detached from the ice shelf, has moved drastically towards the land. "In 2015, the birth event took the front 15 kilometers (9.3 miles) farther back than ever before," says Larter.

An ice shelf can be like a slow car in traffic, says Lhermitte, because all the cars (or ice) behind it get stuck and they also have to slow down. Once the slow car gets out of the way, the cars behind it can accelerate again. But in the case of a glacier that flows into the sea, moving slowly is not necessarily a bad thing.

"The ice shelf also reduces the speed of ice movement because it is connected to the bottom of the ocean," explains Lhermitte. "In 2015, we saw that the ice shelf lost the connection with one of these anchor points at the bottom of the ocean." The ice shelf had been losing contact with this anchor point for years, but was completely lost after the birth event of 2015. Although this seems alarming, the observation data should be considered as a whole, says Lhermitte: "An event of Individual labor does not mean anything, but over time we can see that the front is receding. I do not think we have observational records that the ice front is so far behind. "

On December 15, 2017, the Earth orbit satellite Landsat 8 took this image of the broken iceberg known as B-44.
On December 15, 2017, the Earth orbit satellite Landsat 8 took this image of the broken iceberg known as B-44. POT

Why all the sudden ruptures? A study conducted in 2016 showed that the cracks from which these recent icebergs began to crack were relatively far inland, which is not a great signal, since it means that the ice is being heated by ocean water. In general, glacial ice thinens when more ice melts during the summer that is replaced by snow in the winter. For decades, the Pine Island Glacier has declined drastically, at some points up to 16 feet per year, due to the hot water found in the depths of the Amundsen Sea, near the glacier. This warm, salty water is part of the circumpolar deep water, a body of water that brings heat, salt and nutrients to the continental shelves of Antarctica. This body of water flows along the continental shelf and is in direct contact with the glacier.

Direct contact between this mass of hot water and the glacier does not occur in most places in Antarctica, says Larter, but notes that something different is happening near the Pine Island Glacier. "The hot water flows along the deep valleys that the glaciers themselves have eroded from the seabed when the ice sheet used to spread further," he says. "It's not a surprise that when you put warm water in contact with the base of an ice shelf it melts."

The dynamics of the loss of ice and glacier mass is complex, says Lhermitte, and it is difficult to explicitly attribute any specific event to climate change, but what is happening is exceptional in this area. "There is something that is happening in this area of ​​Antarctica," says Lhermitte. "This is the hot spot where Antarctica is losing most of its ice. The question that still remains is: How fast will it go and how much ice will it lose?

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