The McMurdo Dry Valleys of Antarctica are aptly named, as they are among the driest regions on Earth. Surrounded by mountains that block melting glacier water, the valleys experience extremely low humidity, and no rainfall was recorded there between the 1960s and early 2020s.

When Virginia Tech biological sciences Professor J.E. "Jeb" Barrett heard about an unusually warm day in the McMurdo Dry Valleys in March 2022, where temperatures soared to more than 70°F above the average, he believed that studying this extreme weather event would yield important insights.

In a paper published on August 5 in the American Geophysical Union journal Earth's Future, Barrett and his colleagues reported that this "weather whiplash" in March 2022 caused record-high death rates among invertebrate organisms that rely on surviving the winter in an "inactive freeze-dried state."

The event that spurred Barrett's research occurred on March 18, 2022. On that day, a subtropical air current swept over Antarctica, generating a sudden heat wave on a continent already entering the dark polar night of winter. The temperature surge in the McMurdo Dry Valleys mirrored that of recent days when another Antarctic heat wave alarmed scientists and others.

"Unfortunately, atmospheric scientists anticipate more weather anomalies like this in Antarctica," Barrett noted. "Studying the impact of the March 2022 event can help us predict how the ecosystem and its inhabitants will respond to future climate changes."

The McMurdo Dry Valleys are particularly valuable for scientific research because they may be the only location in Antarctica with a continuous three-decade record of meteorology, stream flow, and soil organisms.

The extreme climate of the McMurdo Dry Valleys restricts the organisms that can survive there to microscopic or nearly microscopic animals like rotifers, tardigrades, and nematodes. In March, the equivalent of autumn in the Northern Hemisphere, these animals begin transitioning into a dry, frozen state that is essential for their survival during the coldest months of the year.

Barrett and his team used multispectral satellite images to assess how much the temperature spike on March 18 melted the frozen ground. They compared satellite images from before and after March 18, looking for areas that had darkened following the warm weather.

"Only two factors could explain the darker images we observed: shadows from cloud cover or mountainous terrain, or the presence of water from melting ice," Barrett explained.

After ruling out the possibility of shadows, Barrett and the other researchers concluded that the unusually hot day led to a rapid, extensive thaw. The valleys had been inundated, and anything near the surface was no longer frozen.

In December 2022, researchers collected soil samples from various areas within the valleys and counted the number of live or dead invertebrates. They discovered a mortality rate exceeding 50% in areas that had become wet during the March 2022 event. The only other instances of such high mortality rates have occurred during experiments simulating extreme "freeze-thaw treatments."