Intense tropical thunderstorms triggered by cold weather in New Zealand has been linked to ice-shelf melt in Antarctica, new research has found.
The New Zealand-led research, recently published in journal Nature Communications, found the two highest temperatures ever observed in Antarctica coincided with record levels of surface melt on the Larsen C ice shelf.
The temperatures were 17.5C on March 24, 2015 and 18.3C on February 6, 2020.
Kyle Clem from the Victoria University of Wellington led the research and explained intense tropical thunderstorms near Fiji, triggered by strong cold fronts that moved north from New Zealand, can generate an "atmospheric river" of warm, moist air which heads towards the Antarctic Peninsula.
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Clem said the air then rises as it passes across the mountainous peninsula and descends as what is called a föhn wind - warm and dry - on the eastern side, leading to extreme high temperatures and ice-shelf melt.
"In our study, we show for the first time the pattern, which results from the convection near Fiji, leads to a large and deep area of low pressure off the coast of West Antarctica and a strong high-pressure system north of the peninsula over Drake Passage.
Researchers have found the two highest temperatures ever observed on the continent coincided with record levels of surface melt on the Larsen C ice shelf. (Source: 1News)
"Together, these features transport very warm and moist air from middle and sub-tropical latitudes of the eastern South Pacific to the Antarctic Peninsula in the form of intense atmospheric rivers."
Clem said himself and his fellow researchers had found the variability in "deep convective activity" over the central tropical Pacific region accounted for 40% of the year-to-year variability in total summertime Larsen C surface melt and 50% of the variability in the total number of intense atmospheric rivers making landfall during summer.
"In both cases, the atmospheric rivers arrived at the Antarctic Peninsula a few hours before the record temperatures occurred."
Clem explained surface melt can have a devastating effect on ice shelves.
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"Intense surface melting and ponding can cause ice shelves to collapse through a process called hydrofracture, in which the surface melt water flows downward through small cracks and fractures, refreezes, and expands, mechanically breaking apart the ice shelf over a period of weeks."
It had generally been assumed ozone depletion and the hole in the ozone layer had been behind the strengthening of westerly winds and enhancing warming on the eastern side of the peninsula - leading to the collapse of the Larsen A and B ice shelves, Clem said.
"We have shown that may not necessarily be the case and that there is another mechanism which may help us predict what might happen with the Larsen C ice shelf."
The Larsen C ice shelf, Antarctica's fourth largest remaining ice shelf at 44,200sq kilometres, is thinning.
Located on the eastern peninsula, the entire Larsen ice shelf has experienced a series of collapses since the mid-1990s. Larsen A, the most northern section, collapsed in 1995, while the larger Larsen B section collapsed in 2002.
The collapses have triggered rapid thinning and acceleration of the glaciers that once fed into them, resulting in an accelerated pace of sea-level rise contribution from the Antarctic peninsula, Clem said.
Clem added the research suggests the future of Larsen C - and the effects of sea-level rise from any collapse - hinge on the variability of convection in the tropics, which is tied into climate change.
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