Media gets high on Antarctic Crack

I thought I’d take a moment from my R&R to write about all the hullabaloo surrounding the calving of the large iceberg off the Larsen C ice shelf in Antarctica. First, a few of the headlines:

LA Times: After Antarctica sheds a trillion-ton block of ice, the world asks: Now what?

The Grauniad: Iceberg twice size of Luxembourg breaks off Antarctic ice shelf

NYT: Warnings from Antarctica

Each of these stories has dire warnings in it about warming and climate change, I found this quote from NYT to be most telling:

Talk to scientists who have worked in the Arctic, Antarctic or the world’s glacial zones for decades, and what they keep coming back to is that they have witnessed

monumental physical changes in these once-frozen regions within their professional lifetimes.

So what? There weren’t any “Arctic or Antarctic scientists” a mere half-decade ago, and bases weren’t even established until World War II followed by a hectic post-war expansion:

Bases were established during February (1944) near the abandoned Norwegian whaling station on Deception Island, where the Union Flag was hoisted in place of Argentine flags, and at Port Lockroy (on February 11) on the coast of Graham Land. A further base was founded at Hope Bay on February 13, 1945, after a failed attempt to unload stores on February 7, 1944. These bases were the first ever to be constructed on the mainland Antarctica.[10]

The Operation provoked a massive expansion in international activity after the war. Chile organized its First Chilean Antarctic Expedition in 1947–48. Among other accomplishments, it brought the Chilean president Gabriel González Videla to personally inaugurate one of its bases, thereby becoming the first head of state to set foot on the continent.[11] Signy Research Station (UK) was established in 1947, Australia’s Mawson Station in 1954, Dumont d’Urville Station was the first French station in 1956. In the same year McMurdo Station was built by the United States and the Mirny Station was established by the Soviet Union.

And, our record of observing Antarctica by satellite only extends back to 1979, as shown by this graph from NASA up to March 2017:

So basically, we’ve got about the length of a scientific career’s worth of observing actual data from Antarctica, and from NYT, we get history lessons:

The ice shelf has been floating in the frigid waters on the eastern side of the Antarctic Peninsula for at least 10,000 years.

OK, so what was there before? No Antarctic ice shelf due to a warmer climate then?

How many icebergs the size of Delaware or Luxemborg (neither of which existed 10k years ago) broke off in that time that we never observed? They don’t know.

Just because we can see changes happening on the most remote region of our planet in exquisite detail for the first time in the history of mankind doesn’t necessarily mean those changes are unprecedented. The media has this odd viewpoint that Earth’s processes act over human lifetimes, but in reality they act over millennia.

I can’t get too worked up about this, even though the usual suspects are. Back to R&R, Ta – Anthony

P.S. Be sure to read the quote in my bold below, from Swansea’s Dr Martin O’Leary.

The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

SWANSEA UNIVERSITY

July 12, 2017 – A one trillion tonne iceberg – one of the biggest ever recorded — has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice, monitored by the Swansea University-led MIDAS project, finally completed its path through the ice.

The calving occurred sometime between Monday 10th July and Wednesday 12th July, when a 5,800 square km section of Larsen C finally broke away.

The final breakthrough was detected in data from NASA’s Aqua MODIS satellite instrument, which images in the thermal infrared at a resolution of 1km.

• The iceberg, which is likely to be named A68, weighs more than a trillion tonnes.
• Its volume is twice that of Lake Erie, one of the Great Lakes.

The iceberg weighs more than a trillion tonnes (1,000,000,000,000 metric tonnes), but it was already floating before it calved away so has no immediate impact on sea level. The calving of this iceberg leaves the Larsen C Ice Shelf reduced in area by more than 12%, and the landscape of the Antarctic Peninsula changed forever.

The development of the rift over the last year was monitored using data from the European Space Agency Sentinel-1 satellites — part of the European Copernicus Space Component. Sentinel-1 is a radar imaging system capable of acquiring images regardless of cloud cover, and throughout the current winter period of polar darkness. The detachment of the iceberg was first revealed in a thermal infrared image from NASA’s MODIS instrument, which is also able to acquire data in the Antarctic winter when cloud cover permits.

Although the remaining ice shelf will continue naturally to regrow, Swansea researchers have previously shown that the new configuration is potentially less stable than it was prior to the rift. There is a risk that Larsen C may eventually follow the example of its neighbour, Larsen B, which disintegrated in 2002 following a similar rift-induced calving event in 1995.

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.

The iceberg is one of the largest recorded and its future progress is difficult to predict. 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 Sentinel-1 and MODIS has vastly improved our ability to monitor events such as this.”

The Larsen C Ice Shelf, which has a thickness of between 200 and 600 metres, floats on the ocean at the edge of The Antarctic Peninsula, holding back the flow of glaciers that feed into it.

Researchers from the MIDAS Project have been monitoring the rift in Larsen C for many years, following the collapse of the Larsen A ice shelf in 1995 and the sudden break-up of the Larsen B shelf in 2002. They reported rapid advances of the rift in January, May and June, which increased its length to over 200 km and left the iceberg hanging on by a thread of ice just 4.5 km (2.8 miles) wide.

The team monitored the earlier development of the rift using a technique called satellite radar interferometry (SRI) applied to ESA Sentinel-1 images. While the rift is only visible in radar images when it is more than 50m wide, by combining pairs of images, SRI allows the impact of very small changes in ice shelf geometry to be detected, and the rift tip to be monitored precisely.

Dr Martin O’Leary, a Swansea University glaciologist and member of the MIDAS project team, said of the recent calving:

“Although this is a natural event, and we’re not aware of any link to human-induced climate change, this puts the ice shelf in a very vulnerable position. This is the furthest back that the ice front has been in recorded history. We’re going to be watching very carefully for signs that the rest of the shelf is becoming unstable.”

Professor Adrian Luckman of Swansea University added:

“In the ensuing months and years, the ice shelf could either gradually regrow, or may suffer further calving events which may eventually lead to collapse – opinions in the scientific community are divided. Our models say it will be less stable, but any future collapse remains years or decades away.”

Whilst this new iceberg will not immediately raise sea levels, if the shelf loses much more of its area, it could result in glaciers that flow off the land behind speeding up their passage towards the ocean. This non-floating ice would have an eventual impact on sea levels, but only at a very modest rate.

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Massive iceberg breaks off from Antarctica

NASA/GODDARD SPACE FLIGHT CENTER

An iceberg about the size of the state of Delaware split off from Antarctica’s Larsen C ice shelf sometime between July 10 and July 12. The calving of the massive new iceberg was captured by the Moderate Resolution Imaging Spectroradiometer 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.

Larsen C, a floating platform of glacial ice on the east side of the Antarctic Peninsula, is the fourth largest ice shelf ringing Earth’s southernmost continent. In 2014, a crack that had been slowly growing into the ice shelf for decades suddenly started to spread northwards, creating the nascent iceberg. Now that the close to 2,240 square-mile (5,800 square kilometers) chunk of ice has broken away, the Larsen C shelf area has shrunk by approximately 10 percent.

“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?”

Ice shelves fringe 75 percent of the Antarctic ice sheet. 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 particularly 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. When floating ice shelves disintegrate, they reduce the resistance to glacial flow and thus allow the grounded glaciers they were buttressing to significantly dump more ice into the ocean, raising sea levels.

Scientists have monitored the progression of the rift throughout the last year was using data from the European Space Agency Sentinel-1 satellites and thermal imagery from NASA’s Landsat 8 spacecraft. Over the next months and years, 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 associated field work.

In the case of this rift, scientists were 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 served as an anchor point for the floating shelf for many decades. Ultimately, the rift stopped short of separating from the protrusion.

“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 Goddard and the University of Maryland at Baltimore County. “So 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.”

The first available images of Larsen C are airborne photographs from the 1960s and an image from a US satellite captured in 1963. The rift that has produced the new iceberg was already identifiable in those pictures, along with a dozen other fractures. 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. Suture zones are complex and more heterogeneous than the rest of the ice shelf, containing ice with different properties and mechanical strengths, and therefore play an important role in controlling the rate at which rifts grow. In 2014, however, this particular crack started to rapidly grow and traverse the suture zones, leaving scientists perplexed.

“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.

McGrath said the growth of the crack, given our current understanding, is not directly linked to climate change.

“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. 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.”

While the crack was growing, scientists had a hard time predicting when the nascent iceberg would break away. It’s difficult because there are not enough measurements available on either the forces acting on the rift or the composition of the ice shelf. Further, other poorly observed external factors, such as temperatures, winds, waves and ocean currents, might play an important role in rift growth. Still, this event has provided an important opportunity for researchers to study how ice shelves fracture, with important implications for other ice shelves.

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.

“It’s very unlikely it will cause any trouble for navigation,” Brunt said.

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