And speaking of melting sea ice…
Just how does a long stable ice shelf suddenly melt and break up? In this case, we are spoiled for choice. Warmer water, warmer air, changes in storms, changes in currents, other stuff. Any and all can weaken ice. Plus the effects can feed back in different ways over time. And each shoreline has its own peculiarities.
This spring researchers report a study of two “large and dramatic collapses” of Antarctic ice shelves, Larsen A in 1995 and Larsen B in 2002 [2]. (We’re working on Larsen C now.)
The study identified “atmospheric rivers” (AR), “narrow long bands of enhanced moisture fluxes originating from the mid-latitudes and sub-tropics” ([2], p. 2). These patterns were found in satellite data recording moisture and the flow of moisture over large areas. These AR occur frequently, and especially large ones reach Antarctica, bringing a burst of warm, wet air.
They found that extreme AR are associated with extreme conditions on the ice shelves, temperature, melting, disintegration, swells. These winds were followed by calving and breakup of the Larsen ice shelves (observed in other satellite imagery). They also were associate with changes in onshore Foehn winds that lead to ice breakup.
These results are intriguing, though far from complete. These bursts are, as the researchers say, “an event that is temporally minuscule in comparison to the age of the ice shelf” ([2], p. 11), so there is more to the story.
If nothing else, it looks like these bursts of warm air may be the last straw, the trigger than sets off a large scale disruption of already weakened ice. Other changes, including water temperature, currents, and long term precipitation patterns probably led up to these dramatic events.
The researchers also speculate that these AR events, which are fairly common overall, “only become detrimental above a certain average temperature threshold” ([2], p. 9). If so, then increases in overall atmospheric temperature extremes may lead to more AR triggered breakups.
- Henry Fountain, Scientists Solve an Antarctic Puzzle, in New York Times. 2022: New York. https://www.nytimes.com/2022/04/14/climate/antarctic-ice-shelves-atmospheric-rivers.html
- Jonathan D. Wille, Vincent Favier, Nicolas C. Jourdain, Christoph Kittel, Jenny V. Turton, Cécile Agosta, Irina V. Gorodetskaya, Ghislain Picard, Francis Codron, Christophe Leroy-Dos Santos, Charles Amory, Xavier Fettweis, Juliette Blanchet, Vincent Jomelli, and Antoine Berchet, Intense atmospheric rivers can weaken ice shelf stability at the Antarctic Peninsula. Communications Earth & Environment, 3 (1):90, 2022/04/14 2022. https://doi.org/10.1038/s43247-022-00422-9
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