August 26, 2013
Last Glacial Maximum Peaked In Spain Much Earlier Than Elsewhere
Brett Smith for redOrbit.com - Your Universe Online
While it’s widely believed that the world’s massive ice sheets were at their greatest extent 20,000 years ago during the last glacial maximum, new research published in Scientific Reports suggested that the glacial peak was much earlier in modern-day Spain.
According to study researchers, their findings could inform more localized models of glacier activity and be used to calculate the effects of climate change.
“We wanted to unravel why and when glaciers grow and shrink,” said study co-author Jane Willenbring, a geologist at Pennsylvania State University.
While rings of boulders across the Spanish countryside indicate the extent of ancient glaciers, they don’t reveal what caused them to grow. To uncover the mechanisms behind glacier growth, the team examined the stalagmites and stalactites in an area cave that point to historical levels of precipitation since they grow as the result of dripping water.
“If you add the cave data to the data from the glaciers, it gives you a neat way of figuring out whether it was cold temperatures or higher precipitation that drove the glacier growth at the time,” Willenbring said.
Across three of Spain’s mountain ranges – the Bejár, Gredos and Guadarrama – and the proximate Eagle Cave, the research team tested boulders to date the extent of glacier activity and cave features to calculate precipitation activity during the last glacial maximum.
“Previously, people believe the last glacial maximum was somewhere in the range of 19,000 to 23,000 years ago,” Willenbring said. “Our chronology indicates that’s more in the range of 25,000 to 29,000 years ago in Spain.”
While local temperatures were fairly cool 19,000 to 23,000 years ago, conditions were also relatively dry, meaning glaciers were larger several thousand years earlier, when precipitation totals were higher. The researchers theorized that the increased precipitation was probably due to changes in the intensity of the sun’s radiation caused by a different tilt of the Earth’s axis. These changes can also affect wind patterns, temperatures and storms.
“That probably means there was a southward shift of the North Atlantic Polar Front, which caused storm tracks to move south, too,” Willenbring said. “Also, at this time there was a nice warm source of precipitation, unlike before and after when the ocean was colder.”
The Penn State geologist said her team’s findings will help give more context to the creation of global climate models on a more local scale.
“It’s important for global climate models to be able to test under what conditions precipitation changes and when sources for that precipitation change,” she said. “That’s particularly true in some of these arid regions, like the American Southwest and the Mediterranean.”
Research has shown that the American Southwest had conditions similar to those in the Mediterranean 26,000 years ago, with larger lakes and more overall moisture.
“Lakes in this area were really high for 5,000-10,000 years, and the cause for that has always been a mystery,” Willenbring said. “By looking at what was happening in the Mediterranean, we might eventually be able to say something about the conditions that led to these lakes in the Southwest, too.”