During the 60 or so years that researchers in the United States Antarctic Program have been observing the Dry Valleys, the streambeds rarely, if ever, shifted. Gooseff and the Antarctic scientists before him have taken elaborate stream topography measurements, and the data have told the same story: The frozen earth remained relatively constant, untainted by the changes in climate seen everywhere else on the planet.

But then, just in the past decade or so, a new narrative in the numbers emerged as the ground visibly softened in some places and the permanence of some streambeds faltered.

“When that [solar] radiation is hitting the ground, you’re warming up the ground more,” says Gooseff. “It’s warming up and primed to be eroded.”

The squishy, swampy patches are a classic example of a landscape feature called thermokarst, which is caused by permafrost thawing. Thermokarst is common in the wake of Arctic permafrost thawing on the opposite side of the planet—largely attributed to global warming—but wasn’t documented much in Antarctica. Finding isolated occurrences of the sloshy sediment is becoming the “new normal” in the Dry Valleys. Now, scientists are trying to diagnose what’s changing—whether the thawing permafrost and fuller streams are a sign that global warming has arrived in this Antarctic desert.

“We have to be careful about [saying] warming,” Gooseff cautions. “A lot of what we think we’re seeing is actually just more sunlight and fewer cloudy days, which is very hard to believe on a day like this.”

In January, during the peak of summer in the Southern Hemisphere, it’s still bitter cold—temperatures have dropped to well below freezing. But even with frigid ambient air temperatures, the sun’s rays can provide just enough energy to melt the glaciers in the surrounding peaks, forming streamlets that meander down into the bottom of the valley. The combination of the sun’s energy, glacial ice, freezing winds, cloud cover, and the reflectivity of ice and soil trapped in the Dry Valley glaciers dictates when water flows and when it freezes. That freeze-thaw cycle is the pulse of the Dry Valleys ecosystem.