Temps, not snowfall, drive shrinkage of Peru’s Quelccaya Ice Cap
By Summit Voice
FRISCO — Geologists are getting better at unraveling the mysteries of historic glacial episodes, as technology helps understand how the ice sheets respond to climate change.
One recent research project led by scientists from Dartmouth University suggests that temperature is the driving factor in shaping the size of Peru’s Quelccaya Ice Cap. The 17-square mile glacier in the Andes has been shrinking dramatically in the past few decades, making it a global warming symbol.
The findings support the idea that tropical glaciers are rapidly shrinking because of a warming climate — not because of a lack of snowfall. The study results will help scientists to better understand the natural variability of past and modern climate and to refine models that predict tropical glaciers’ response to future climate change.
“This is an important result since there has been debate about the causes of recent tropical glacial recession – for example, whether it is due to temperature, precipitation, humidity, solar irradiance or other factors,” said Dartmouth glacial geomorphologist Meredith Kelly, a co-author of the study.
Kelly’s team used field mapping combined with a sophisticated surface-dating technique to analyze how the Quelccaya Ice Cap has expanded and retreated over the past millennium. It is the first time that a record of past glacial extents has been compared directly with an annually dated ice core record from the same ice mass.
During the last millennium, a significant cooling event known as the Little Ice Age occurred, but scientists don’t know what caused the cooling or its geographic extent. The Dartmouth-led team was able to determine the age of glacial deposits of rock marking past positions of Qori Kalis, an outlet glacier that has been monitored by Thompson since he first visited Quelccaya in the early 1960s.
The results show that Qori Kalis advanced to its late Holocene maximum position prior to 520 years ago and subsequently retreated with only minor re-advances since that time. The comparison of the moraine record with the ice core record suggests that temperature was the driving force of glacial expansion and retreat, said Justin Stroup, lead author and a PhD candidate in Dartmouth’s Department of Earth Sciences.
Furthermore, the ebbs and flows of other glaciers in tropical South America are similar to the Qori Kalis extents, indicating a regionally consistent pattern of past climate conditions. On a global scale, the results suggest that glaciers were larger than present and depositing moraines in both northern and southern hemispheres at about the same time, indicating that the climate mechanisms which caused the late Holocene cooling likely influenced a globally synchronous pattern of cooling.
The study appears in the journal Geology.