Atmospheric Rivers, Open-Ocean Polynyas, And The Prospects For The Melting Of Antarctica
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In her previous work, lead author Diana Francis, an atmospheric scientist at Khalifa University in the United Arab Emirates, found that cyclones played a role in creating the polynya. However, since these storms are relatively common and don’t always result in such major openings in the ice, she continued to search for another contributor; that’s when she landed on atmospheric rivers.
Atmospheric rivers are long streams in the atmosphere that carry moisture from the tropics toward the north and south poles. They can be hundreds of kilometers wide, thousands of kilometers long, and carry more water vapor than the world’s largest rivers. Francis and her colleagues found that a series of them crossed the Weddell Sea in the days before and after the massive polynya opened in 2017. They carried an exceptional amount of water vapor—itself a potent greenhouse gas—that warmed and weakened the sea ice and helped intensify the cyclones that followed. The atmospheric rivers also brought large amounts of warm snow that likely enhanced the melt, Francis says.
Looking back at historical events, Francis and her team found that atmospheric rivers were also associated with the last big polynya in the Weddell Sea, in 1973–1974, and with another smaller hole in 2016. Sarah Gille, an atmospheric scientist and physical oceanographer at Scripps Institution of Oceanography at the University of California San Diego who was not involved in the work, calls Francis’s study “transformative.” “We tend to think the oceans are the real driver of [polynya formation]. The paper suggests a much more complex set of processes may precondition the ocean and allow a polynya to exist,” she says.
Atmospheric conditions may even enhance the oceanic processes involved in polynya formation. The blanket of snow the atmospheric rivers delivered, for instance, may have acted as an insulator, trapping heat from the ocean and magnifying the ice melt from below, explains Ethan Campbell, a graduate student at the University of Washington, who has studied the Weddell polynya. The rarity of open-ocean polynyas means there isn’t much data to help scientists understand whether they are as important for marine animals as polynyas closer to shore, says Mia Wege, a marine predator ecologist with South Africa’s University of Pretoria.
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https://www.hakaimagazine.com/news/how-rivers-in-the-sky-melted-antarctic-ice/
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