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Scientists link ‘atmospheric rivers’ to melting Antarctica

Larsen C – in which this 180 km long fault appeared in 2017 – is the fourth largest remaining ice shelf in Antarctica, spanning around 44,200 km2. Photo/NASA

New research has linked wet “atmospheric river” systems – like those that flooded the North Island this week – to recording the melting of ice shelves in Antarctica.

A study just published in Nature Communications shows intense tropical thunderstorms near Fiji, triggered by strong cold fronts that moved north from New Zealand, can in summer generate an atmospheric river of warm, moist air that crosses the South Pacific Ocean towards the Antarctic Peninsula.

This air then rises as it crosses the mountainous peninsula and descends as a hot, dry föhn wind on the east side, causing extremely high temperatures and the melting of the sea ice.

The research, led by University of Victoria meteorologist Dr Kyle Clem, found the two highest temperatures ever observed in Antarctica coincided with record levels of surface melt on the Larsen C Ice Shelf. .

These temperatures were 17.5°C on March 24, 2015 and 18.3°C on February 6, 2020, at Esperanza station on the peninsula.

Clem said it had generally been assumed that ozone depletion and the ozone hole had been responsible for strengthening westerly winds and increasing warming on the eastern side of the peninsula, causing the Larsen A and B Ice Shelves to collapse farther north.

“We showed that this is not necessarily the case and that there is another mechanism that can help us predict what might happen with the Larsen C ice shelf.”

Clem said the research suggests that the future of Larsen C and the global effects of sea level rise that may occur after the sea ice collapse depends on the variability of convection in the tropics, it -even determined by other factors affected by climate change.

“Surface melting can have a devastating effect on ice shelves. Intense surface melting and pooling can cause ice shelves to collapse through a process called hydrofracture, in which the Meltwater from the surface flows downward through small cracks and fractures, freezes and expands, mechanically breaking apart the pack ice over a period of weeks.”

The Larsen Ice Shelf on the Eastern Peninsula has experienced a series of dramatic collapses since the mid-1990s due to this process, including the northernmost section Larsen A in 1995 and the largest Larsen B section to the south in 2002.

Further south, the largest remaining section, the Larsen C Ice Shelf, was now thinning.

Larsen C was Antarctica’s fourth largest remaining ice shelf, spanning approximately 44,200 km2.

The loss of these ice shelves in recent decades has triggered a rapid thinning and acceleration of the glaciers that once fed them and resulted in an accelerating rate of contribution to peninsular sea level rise. Antarctica, Clem said.

“In our study, we show for the first time that the pattern, which results from convection near Fiji, leads to a broad and deep area of ​​low pressure off the coast of West Antarctica and a strong anticyclonic system at north of the peninsula on Drake Passage.

“Together, these features transport very warm and humid air from the mid-latitude and subtropical eastern South Pacific to the Antarctic Peninsula in the form of intense atmospheric rivers.

“We find that variability in deep convective activity in the central tropical Pacific region explains 40% of the year-to-year variability in total Larsen C surface melt in summer and 50% of the variability in the total number of intense atmospheric rivers landing during the summer.”

In both cases, the atmospheric rivers arrived at the Antarctic Peninsula hours before the record high temperatures occurred.

The research team included experts from the University of Valparaiso, the Center for Climate and Resilience Research in Santiago, the University of Concepcion and the British Antarctic Survey.