The Larsen C ice shelf break has sparked groundbreaking research

Anticipation of one of the biggest rifts ever detected reached a fever pitch in summer 2017

Larsen C ice shelf break

WIDENING GULF   A Delaware-sized iceberg calved when a crack in the Larsen C ice shelf reached the Weddell Sea this year. In this satellite image from September, rifts are visible in the ice and clouds cast a shadow on the new iceberg.

NASA Earth observatory, joshua stevens, Landsat data, USGS

In 2015, glaciologist Daniela Jansen reported that a large rift was rapidly growing across one of the Antarctic Peninsula’s ice shelves, known as Larsen C. When the shelf broke, she and colleagues predicted, it would be the largest calving event in decades.

It was. In July, a Delaware-sized iceberg split off from Larsen C  (SN: 8/5/17, p. 6). And researchers knew practically the moment it happened.

After Jansen’s 2015 paper, a U.K.-led group called Project MIDAS began keeping close track of the rift, aided by new data delivered every six days from a pair of European polar-orbiting satellites known as Sentinel-1. Jansen, of the Alfred Wegener Institute in Bremerhaven, Germany, and glaciologist Adrian Luckman of Swansea University in Wales were among the MIDAS team members who reported their observations on the team’s blog.

To the scientists’ surprise, the news media, perhaps anticipating a climate change moment, began to track the trackers. When interviewed, the researchers repeatedly noted that ice shelves calve naturally, and that any link between the new rift and climate change is complicated at best. But the crescendo of public interest still rose, particularly during the spring and summer of 2017 as the final break loomed.

DRIFTING OFF By mid-September, the southern edge of the iceberg calved from Larsen C had shifted about 18 kilometers from the rest of the ice sheet. Copernicus Sentinel data (2017), processed by ESA (CC BY-SA 3.0 IGO)
Although surprised by the press frenzy, Jansen says she understands why people were so captivated by the big break: “It’s just an amazing thing. Even if people are not into polar research, it’s fascinating to see it and think about the dimensions of it.”

Public interest may have plummeted in the aftermath of the split, but scientists are eager to start on the next chapter, Luckman says. “Now we want to understand how the ice shelf will react to this calving event.”

By the end of 2017, the race to the southernmost continent was on. It’s the first time that researchers have been able to put boots on the ground so quickly after a massive calving event, and they have a lot of questions. Some scientists plan to assess the stability of the remaining ice shelf, others will map the region’s seafloor topography and still others want to study the newly exposed ecosystem that’s been hidden from the sun for up to 120,000 years (SN Online: 10/13/17).

It’s an unprecedented opportunity, Luckman says. “We’ve never had such tools as we have now to really measure what happens after big calving events.” The last time a large iceberg calved from Antarctica was in 2002, when a chunk about half the size of the Larsen C iceberg calved from a different ice shelf on the Antarctic Peninsula, Larsen B (SN: 3/30/02, p. 197).

“We just didn’t have the satellite data to really see what would happen next,” Luckman says. Now, he says, scientists have both vastly superior satellite monitoring capabilities and computer simulations to predict how the remaining ice will behave after the loss of so much mass. Current simulations suggest that the truncated ice shelf will react to this change by flowing faster into the ocean, which will also lead to more calving.

To improve those simulations, Luckman says, scientists need to directly measure changes in the ice shelf, particularly while it is still in its initial response phase. In November, a team led by the University of Leeds in England was the first to journey to the peninsula. To map out subsurface structures in the ice, the researchers conducted geophysical surveys, including using ground-penetrating radar, on the still-intact part of the ice shelf. Using GPS, the team also monitored the shelf’s movements.

Another team of scientists, led by marine biologist Katrin Linse of the British Antarctic Survey in Cambridge, is preparing for a separate voyage to the ice shelf in February. Linse and colleagues’ mission is to learn what was living on the seafloor in the shadow of the ice. What creatures might inhabit that region is a bit of a mystery. Linse says she expects to find something similar to ecosystems found in the deep sea — a dark, extremely food-sparse environment with no plant life. Such environments can spawn odd creatures, such as carnivorous sponges and bivalves that snatch at the tiniest sources of food to survive. But it’s also possible that the team will find nothing living there at all, she says.

A Delaware-sized iceberg that broke off the Larsen C ice shelf, dubbed A68 and seen at upper right, continued to distance itself from the shelf (foreground) in early November. Nathan Kurtz/NASA

Meanwhile, the new Larsen C iceberg, now dubbed A68, is still in the picture and could present a navigational headache. As of October, the southern edge of the berg was about 25 to 30 kilometers from the shelf, offering a research ship some wiggle room to examine the seafloor, Linse says. But the northern edge was still just two kilometers away, a gap much too close for comfort.

But the headache is worth it, as the researchers may have little time to examine that ecosystem before it begins to change. Now that sunlight can penetrate the waters, microalgae will quickly begin to grow, providing an abundant food source to any seafloor denizens — and an enticement to new colonizers. In one to three years, species such as krill may become abundant. After several more years or even decades, there may be enough food to support top predators such as penguins, seals and whales.                                   

Scientists have previously documented a recently exposed Antarctic seafloor ecosystem only after it was already in transition. In 2007, marine ecologist Julian Gutt of the Alfred Wegener Institute led an expedition to the Larsen B ice shelf to study the seafloor that had emerged from its ice shadow five years earlier. The researchers found strange new species, but also discovered that some pioneering critters had already moved in (SN: 9/7/13, p. 11).

Gutt plans to return to the region in 2019. That expedition, led by Alfred Wegener Institute scientists, originally planned to map the seafloor along the Antarctic Peninsula. Now the project will include time to study the biodiversity of the seafloor at Larsen C, as well as a return to Larsen B nearly 20 years after its big break, he says.

“Each species occurring under the former ice shelf would be interesting,” Gutt says, “because the question is, how can they survive under such unusual conditions?”

In fact, whatever the researchers find — even if it’s nothing — Linse says she will consider her mission a success: “If no communities could thrive, that would be a very interesting result because I expect to find life there.”

The vigil over the Larsen C break may be over, but for Antarctic scientists, the aftermath is taking on a life of its own.

Carolyn Gramling is the earth & climate writer. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.

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