During the last Ice Age as ice sheets expanded and the rest of the world grew colder, there’s a pocket in Central Asia where glaciers did exactly the opposite. Glaciers in the high, dry mountains of Mongolia’s Gobi Desert were actually shrinking during this time, claims a new study.
It complicates our understanding of what happened during the last Ice Age, and it could change the way we think about how glaciers behave.
Translating to the “waterless place”, the Gobi Desert is a world of extremes. Encased by mountains, it stretches 1,610 kilometers (1,000 miles) across portions of Mongolia and China, with temperatures that vary from -40ºC (-40ºF) to more than 38ºC (100ºF).
University of Washington researchers compared glacial records from the Gobi-Altai ranges to see how the glaciers behave in these extreme climates. Data was collected at five sites in 2007 and 2010 from large, rocky deposits at the glacier’s edge called moraines. By measuring changes in the rock that happen as it is exposed to cosmic rays, researchers expected to find that the rocks were exposed at the peaks of the last ice age 20,000 years ago. The moraines, however, were much younger.
“That means that these glaciers were smaller when the climate was the coldest,” Batbaatar said. “The results were so surprising that we went back to double check.”
It suggests the glaciers in this dry, high-altitude environment are also controlled by precipitation, which ranges from 50 to 300 millimeters (2 to 12 inches) a year, rather than just temperature alone.
"Because the melting is so dominant a process, and the melting is mostly controlled by temperature, people think of glaciers as thermometers. But we all know that precipitation plays a role," said author Jigjidsurengiin Batbaatar in a statement.
In the Gobi, glaciers grow so slowly that they rarely reach low altitudes where melting is possible. Instead, glaciers shrink when sunlight hits their surface, turning the ice into water vapor in a process known as sublimation.
"In some of the Gobi mountains, the largest glaciers didn't happen during the last ice age," said Batbaatar. "Some of these glaciers were starving for precipitation then. Our measurements show that they actually shrank as cold, dry conditions of the ice age became more intense. Then they grew when the warming climate of the Holocene brought more moist air, feeding the glaciers with more snow."
The study is the first to date ancient glaciers in the high mountains after political changes in Central Asia allowed more research. It confirms the “starving glacier” theory, which suggests that in very cold and dry environments where rain and snow are scarce, glaciers are less sensitive to temperature shifts and are more influenced by precipitation levels.
Turns out, glaciers don’t behave the same across the world.
“Glaciers growing in cold, arid, desert mountains may be out of sync with those in wetter, warmer environments such as the Alps," said co-author Alan Gillespie."[These] findings move us toward a more complete understanding of how glaciers advance and retreat in response to climatic fluctuations."