Accurate Method to Date Tropical Glaciers May Impact Global Warming Studies

Dating glaciers and their moraines is crucial for understanding climate change. Now, scientists have discovered a more accurate method to determine the ages of the boulders deposited by tropical glaciers. The findings could influence previous research of how climate change has impacted ice masses around the equator.

Moraines are sedimentary deposits that mark the extent of glaciers. Since glaciers respond sensitively to climate, especially at high latitudes and high altitudes, the timing of glacial fluctuations marked by moraines can help scientists better understand past climactic variations and how glaciers may respond to future changes. In order to date these moraines, though, researchers use a variety of techniques. Yet this new method could prove to be far more accurate.

In the tropics, glacial scientists commonly use beryllium-10 surface exposure dating. Beryllium-10 is produced when cosmic rays strike bedrock that's exposed to air. Elevation, latitude and other factors impact the rate at which beryllium-10 is produced. Scientists use rates taken from sites scattered across the globe rather than rates locally calibrated at sites being studied, though. This means that readings aren't necessarily accurate.

That's why researchers decided to take a closer look at the Quelccaya Ice Cap. This glacier, which is located in the Peruvian Andes, has retreated significantly in recent decades. The researchers managed to determine a new locally calibrated production rate that's at least 11 to 15 percent lower than the traditional global production rate.

"The use of our locally calibrated beryllium-10 production rate will change the surface exposure ages reported in previously published studies at low latitude, high altitude sites and may alter prior paleoclimate interpretations," said Meredith Kelly, one of the researchers, in a news release.

In fact, the new ages are older than previously recorded, which means that the boulders were exposed for longer than previously estimated. This means that glaciers in the Peruvian Andes advanced during early Holocene time about 8,000 to 10,000 years ago. Previously, scientists thought this time was both warm and wet in the Andes.

The findings reveal a little bit more about the past climate. This, in turn, will inform research on future climate predictions.

The findings are published in the journal Quaternary Geochronology.