The average winter temperature on the Antarctic peninsula is a chilly -15掳C. Yet automated instruments on the Larsen C ice shelf have recorded extensive surface melting even during the long, dark winter.
When wind blows over high mountains, the descending air can warm by several degrees. On the Antarctic peninsula, this phenomenon 鈥� known as a foehn wind 鈥� can sometimes raise air temperature above zero. This was known to happen during summer but has now been found to be occurring even in mid-winter.
As the peninsula continues to warm, it will happen more and more often. 鈥淲e can thus expect more winter melt this century,鈥� of Utrecht University in the Netherlands told a meeting of the European Geosciences Union in Vienna this week.
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This winter melting is likely helping to destabilise the Larsen C ice shelf, which lost a huge chunk last year. Surface melting is thought to have played a big part in the breakup of the nearby Larsen B ice shelf in 2002.
and his colleagues made their discovery after installing an automated weather station in Cabinet Inlet, a region of the Larsen C ice shelf, in 2015. The station has instruments that can detect snow melt. They were surprised to discover extensive winter melting often lasting several days.
鈥淥ver the three-year period, up to 25 per cent of the melt was happening in winter,鈥� said Kuipers Munneke. 鈥淧eak intensities of this winter melt even exceed summertime values.鈥� The findings will soon be published in Geophysical Research Letters.
It鈥檚 been known for decades that foehn winds can cause surface melting in the Antarctic, but no one knew such extensive melting occurred even in winter.
Really surprising
鈥淭he fact that a significant fraction of melt happens in the dead of the Antarctic winter is really surprising, but the evidence is there,鈥� says geophysicist Adam Booth of the University of Leeds in the UK, who was not involved in the research.
鈥淲e鈥檝e seen the fingerprint of this refrozen meltwater in the snowpack of Larsen C in some of our radar data, but we鈥檝e always assumed that this originates in summer. It means that there are more melt days available than we might previously have anticipated.鈥�
Meltwater can destabilise ice shelves in several ways, says Gareth Marshall of the British Antarctic Survey in the UK. For instance, it can drain into crevasses and refreeze, forcing the crevasses to open up more.
The loss of ice shelves does not raise sea level directly, as they are already floating on the sea. However, land-based glaciers speed up when ice shelves are lost, which does raise sea level. Most Antarctic ice shelves are thinning and retreating, mainly because of warm currents melting them from below.
