Giant Iceberg Breaks Off Antarctica as Climate Warms

Thermal heat signature in red and orange shows where Iceberg A-68 calved away from the Larsen C ice shelf, July 12, 2017 (Image courtesy NASA)


GREENBELT, Maryland, July 13, 2017 (ENS) – An iceberg weighing one trillion metric tonnes, one of the largest ever recorded, calved away from the Larsen C Ice Shelf in Antarctica sometime between July 10 and July 12 in what NASA classifies as a sign of global climate change.

Ice shelves surround 75 percent of the Antarctic ice sheet. Larsen C, a floating platform of glacial ice on the east side of the Antarctic Peninsula, is Antarctica’s fourth largest ice shelf.

Antarctic Peninsula showing location of new iceberg (Image courtesy NASA)

The calving of the giant iceberg was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite, and confirmed by the Visible Infrared Imaging Radiometer Suite instrument on the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite.

The final breakage was first reported by Project Midas, an Antarctic research project based in the United Kingdom, which says that because it was already floating before it calved away the new iceberg will have no immediate impact on sea level.

Professor Adrian Luckman of Swansea University, lead investigator of the Midas project, said, “We have been anticipating this event for months, and have been surprised how long it took for the rift to break through the final few kilometres of ice. We will continue to monitor both the impact of this calving event on the Larsen C Ice Shelf, and the fate of this huge iceberg.”

Now that the 2,240 square-mile (5,800 square kilometer) chunk of ice has broken away, the Larsen C shelf area has shrunk by about 10 percent.

The iceberg’s future progress is difficult to predict, Luckman said. “It may remain in one piece but is more likely to break into fragments. Some of the ice may remain in the area for decades, while parts of the iceberg may drift north into warmer waters.”

The recent development in satellite systems such as the the European Space Agency Sentinel-1 satellites and MODIS have vastly improved scientists’ ability to monitor events such as this, Luckman said.

Thermal heat signature in red and orange shows where Iceberg A-68 calved away from the Larsen C ice shelf, July 12, 2017 (Image courtesy NASA)

In 2014, scientists saw that a crack slowly growing into the ice shelf for decades suddenly started to spread northwards, creating the nascent iceberg.

“The interesting thing is what happens next, how the remaining ice shelf responds,” said Kelly Brunt, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland in College Park.

“Will the ice shelf weaken? Or possibly collapse, like its neighbors Larsen A and B? Will the glaciers behind the ice shelf accelerate and have a direct contribution to sea level rise? Or is this just a normal calving event?” Brunt speculated.

One way to assess the health of ice sheets is to look at their balance: when an ice sheet is in balance, the ice gained through snowfall equals the ice lost through melting and iceberg calving.

Even relatively large calving events, where tabular ice chunks the size of Manhattan or bigger calve from the seaward front of the shelf, can be considered normal if the ice sheet is in overall balance.

But sometimes ice sheets destabilize, either through the loss of a big iceberg or through disintegration of an ice shelf, such as that of the Larsen A Ice Shelf in 1995 and the Larsen B Ice Shelf in 2002.

Map of Larsen C, overlaid with NASA MODIS thermal image from July 12 2017, showing the iceberg has calved (Image courtesy Swansea University / Project Midas)

When floating ice shelves disintegrate, they reduce the resistance to glacial flow and allow the grounded glaciers they were holding back to dump more ice into the ocean, raising sea levels.

Now, researchers will monitor the response of Larsen C, and the glaciers that flow into it, through the use of satellite imagery, airborne surveys, automated geophysical instruments and field work.

Scientists have worried about the possible loss of a pinning point that helped keep Larsen C stable. In a shallow part of the sea floor underneath the ice shelf, a bedrock protrusion, named the Bawden Ice Rise, has been an anchor point for the floating shelf for decades. But they say the ice shelf is still attached to the Bawden Ice Rise.

“The remaining 90 percent of the ice shelf continues to be held in place by two pinning points: the Bawden Ice Rise to the north of the rift and the Gipps Ice Rise to the south,” said Chris Shuman, a glaciologist with NASA’s Goddard Space Flight Center, Oceans and Ice Branch, and the University of Maryland.

“I just don’t see any near-term signs that this calving event is going to lead to the collapse of the Larsen C ice shelf. But we will be watching closely for signs of further changes across the area,” Shuman said.

The first available images of Larsen C are airborne photographs from the 1960s and an image from a U.S. satellite captured in 1963. The rift that has produced the new iceberg was already identifiable in those pictures, along with a dozen other fractures.

ice crack
Satellite image of a long crack in the Larsen C ice shelf, taken on March 8, 2017, by the Operational Land Imager on the NASA/USGS Landsat 8 spacecraft. (Image courtesy NASA)

The crack remained dormant for decades, stuck in a section of the ice shelf called a suture zone, an area where glaciers flowing into the ice shelf come together.

In 2014, this particular crack started to rapidly grow and traverse the suture zones.

“We don’t currently know what changed in 2014 that allowed this rift to push through the suture zone and propagate into the main body of the ice shelf,” said Dan McGrath, a glaciologist at Colorado State University who has been studying the Larsen C ice shelf since 2008.

“The Antarctic Peninsula has been one of the fastest warming places on the planet throughout the latter half of the 20th century. This warming has driven really profound environmental changes, including the collapse of Larsen A and B,” McGrath said.

“But with the rift on Larsen C, we haven’t made a direct connection with the warming climate,” he said. “Still, there are definitely mechanisms by which this rift could be linked to climate change, most notably through warmer ocean waters eating away at the base of the shelf.”

The U.S. National Ice Center will monitor the trajectory of the new iceberg, which is likely to be named A-68. The currents around Antarctica generally dictate the path that the icebergs follow. In this case, the new berg is likely to follow a similar path to the icebergs produced by the collapse of Larsen B: north along the coast of the Peninsula, then northeast into the South Atlantic.

Scientists say it’s unlikely the massive iceberg will cause any trouble for ships navigating the area.

Copyright Environment News Service (ENS) 2017. All rights reserved.


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