Scientists warn on Antarctic ice shelf vulnerability


Larsen C could be set to follow Larsen A and B and split apart. Andrew Masterson reports.


NASA imaging showing melt water collecting on the surface of the Larsen C ice shelf.

NASA Earth Observatory/Lauren Dauphin

Unusual wind patterns might be driving Antarctica’s fourth largest ice shelf towards destruction, researchers warn.

In a paper published in the journal Geophysical Research Letters, a team led by Rajashree Tri Datta from the University of Maryland reveal that the Larsen C ice shelf experienced an unusual spike in late summer and early autumn surface melting in the years 2015 to 2017.

The finding raises fears that the shelf, part of the Antarctic Peninsula, the northernmost part of the continent, could follow the fate of two other large ice shelves, Larsen A and B.

Snow and ice melting on the land-surface prompted the break-up of Larsen A in 1995. In 2003, Larsen B calved a section comprising roughly 3000 square kilometres.

The Antarctic Peninsula is particularly vulnerable to changing global conditions, and to assess the stability of Larsen C – which lies to the south of where Larsen B used to be – Datta and colleagues studied data covering 1982 to 2017.

They found that in the past couple of years there has been an uptick in a particular type of wind – called foehn wind – that originates in the peninsula’s high central mountain range and sends warm, dry air heading downwards, close to the surface.

The increased foehn activity triggered a higher than average degree of melt, which has begun to reshape the Larsen C snowpack – a development which, if sustained, could put the integrity of the shelf at risk.

“Three years doesn't make a trend,” says Datta, “but it's definitely unusual that we are seeing enhanced foehn winds and associated melting in late summer and early autumn.”

Data for previous years show the winds tailing off much earlier in the season, and melt rates reducing. Fresh falls then replenish the snowpack.

However, because this hasn’t happened for three consecutive years, the topology of the shelf is changing, a situation that could lead to increasingly adverse outcomes.

“With enhanced densification, the ice enters the next warm season with a very different structure,” explains Datta.

“Our modelling results show that with less open space for the surface water to filter into, runoff increases year after year. The dominant theory suggests that enhanced densification led to the fracture of the Larsen A and B shelves.”

Because the ice shelf is floating, if the worst comes to the worst and Larsen C fractures and breaks up, it will not by itself lead to an increase in global sea levels. However, the picture is not that simple.

“The ice shelf does brace against the flow of the glaciers that feed it,” warns Datta.

“So if Larsen C goes, some of these glaciers will be free to accelerate their rate of flow and melt, which will result in a rise in global sea level.”

  1. http://dx.doi.org/10.1029/2018GL080845
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