During the last Ice Age when our planet was experiencing extremely chilly conditions and ice sheets in all of Europe and North America were expanding, there was one region on Earth where glaciers were actually shrinking, according to a new study carried out by researchers at the University of Washington (UW). The study, whose findings were published in Quaternary Science Reviews, claims that glaciers in the high mountains of Mongolia’s Gobi Desert actually shrank during the last Ice Age.
Gobi Desert, the fifth-largest desert in the world, is spread in southern region of Mongolia and north and northwestern part of China. This rain shadow desert extends about 1,600 km from southwest to northeast and 800 km from north to south. This desert was formed due to Tibetan Plateau blocking the precipitation from the Indian Ocean reaching the Gobi territory.
The UW study, which compares glaciers in Gobi Desert with glacial records from nearby mountains, is also the first to date the ancient glaciers in Gobi. The study found that glaciers on some of the Gobi mountain ranges started growing thousands of years after the last ice age ended.
“In some of the Gobi mountains, the largest glaciers didn’t happen during the last ice age,” said first author Jigjidsurengiin Batbaatar, a UW doctoral student in Earth and Space Sciences.
“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.”
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In this study, Batbaatar and co-author Alan Gillespie, a UW research professor emeritus in Earth and Space Sciences, gathered rock samples from moraines, which are long ridges of rocky debris dropped at a glacier’s edge. The data was collected in the period from 2007 to 2010. The researchers used a dating technique to measure the elemental changes occurring when the rock gets bombarded by cosmic rays after the glacier’s retreat.
“We were expecting to find rocks exposed for 20,000 years, the date of the peak of the last ice age, but these moraines 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.”
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These findings also confirm the results of an earlier theoretical study that suggested that in very cold and dry environments, where snow and rain are scarce, the temperature would not always be the main factor driving a glacier’s growth. This theoretical study was carried out by Summer Rupper, a former UW doctoral student now at the University of Utah, and UW faculty member Gerard Roe.
“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,” Batbaatar said.
The UW study also confirms that “starving glaciers” in high-altitude, dry environments are indeed controlled by precipitation. These glaciers grow so slowly that they rarely reach the lower altitudes where melting is possible. Instead, such glaciers shrink when sunlight hits the surface and transforms ice into water vapor. These glaciers are very sensitive to precipitation amounts but less sensitive to temperature shifts.