By Jia You –
The Ice Ages created some of the most profound climate changes that Earth underwent over the past 2.5 million years. Now, geologists have uncovered new sites in Patagonia that reveal how climate changed during the most recent cold snap. The discovery could help scientists better understand how the climate system works and to better predict our planet’s future.
Geologist Mike Kaplan, of Columbia University, discovered the new sites. His research aims to nail down the chronology of glacial and climate changes in Patagonia, home to the largest Ice Age ice mass in the Southern Hemisphere outside of Antarctica.
At the Comer Abrupt Climate Change Conference held in southwestern Wisconsin this fall, Kaplan shared preliminary results from his research with other top climate scientists, pieces of a puzzle about how ice ages begin and end.
At its coldest during the last Ice Age, a period known as the Last Glacial Maximum, vast ice sheets covered much of North America and northern Europe. That was about 18,500 years ago. Later, the partial retreat of glaciers allowed ancient humans to migrate from Siberia to the Americas along the land bridge created at the Bering Straits. Ocean levels dropped dramatically, exposing the land bridge as the glaciers trapped so much water in their grip.
Then things started to heat up, an abrupt climate change heading out of the Ice Age. “It’s far bigger than anything we are going to experience in the next few decades,” Kaplan said.
Yet what exactly caused the Ice Age to start and end remains a puzzle for scientists. One important piece of it concerns whether the Ice Age occurred at the same in the Northern and the Southern Hemispheres. Initially, scientists thought that the Ice Age might have occurred at similar times in the two hemispheres. That would contradict the theory that explains Ice Ages, which states that the Ice Age should have occurred at different times because the amount of energy absorbed from the summer sun is different between the hemispheres. But findings over the last few decades suggest a much more nuanced picture than both the theory and earlier thoughts: Although there is some overlap in timing, the Ice Ages probably started and ended at slightly different times between the hemisphere.
So scientists now need to figure out what explains this timing. Finding the answer to this puzzle piece would help us understand how the climate system works, by using past climate changes as a natural experiment. It would also allow them to test current computer models on climate change with real climate data from the past, thus improving our ability to predict the planet’s future.
Kaplan and other scientists have embarked on research expeditions to New Zealand and Patagonia in order to find out when the last Ice Age started and ended in the South.
In order to do that, the scientists relied on trails of boulders and sediments tossed on the local landscape by glaciers. Like the rising and falling tides, a glacier advances and retreats as its surroundings freeze and warm in cyclical intervals of many thousands of years. As a glacier expands, it picks up rocks and sediments along the way and carries them forward. As the temperature rises and the glacier melts, it leaves behind trails of boulders and sediments on the landscape, which can be thousands of miles away from their places of origin.
As these abandoned rocks lie exposed to the air, they are bombarded by cosmic rays – high-energy subatomic particles that constantly bombard Earth from all directions. As cosmic rays hit the rocks on the ground, they change the rocks’ atomic structures, creating a new substance known as Beryllium-10. The longer the rocks have been exposed in the air, the more beryllium-10 they accumulate.
So. by measuring the amount of beryllium-10 in a rock sample, Kaplan and other scientists can deduce when a glacier melted and dropped the rock, and how far the glacier had advanced at that point. Progress in the technique over the past 10 years, pioneered by scientists including Joerg Schaefer, Kaplan’s colleague at Columbia, now allow researchers to precise date these glacial deposits, with an error margin of just 2 percent.
On a science expedition to Patagonia 10 years ago, one particular area caught Kaplan’s attention: the Tierra del Fuego, an island east of the Strait of Magellan that means “Island of Fire” in Spanish. At the time, scientists didn’t map out in detail glacial changes throughout the island, as they assumed that much of the area only contained records of glaciers during periods much earlier than the last Ice Age. But Kaplan suspected otherwise, and he had wanted to go back to the area ever since — so much so that he dubbed the place “the world’s end,” where prior studies had stopped.
“I always wondered what we would find if we went down the road,” he said.
In 2013, funded by the National Science Foundation, Kaplan and three Chilean colleagues finally embarked to the island. Right away, he was impressed by the amount of glacial deposits in the area.
“There were glacial deposits as far as the eyes could see,” he said while presenting the findings at the Comer conference.
Back at home, rock by rock, Kaplan, Schaefer and other team members measured the amount of Beryllium-10 contained in the glacial deposits they found, and began to piece together a map of changes in glaciers and temperatures on Tierra del Fuego.
They found that those glacial deposits were much younger than previously thought, at only 17,000 to 18,000 years old.
“It turns out … there is a much more complete record of the last Ice Age than we previously thought,” he said. That finding could provide crucial clues to when exactly the Ice Age started and ended in the Southern Hemisphere.
“What surprised me about Mike’s emerging chronology is how similar it is to our work in New Zealand,” said Aaron Putnam, a geoscientist at the University of Maine. Taken together, Putnam said, their results imply that the Southern Hemisphere was in a sustained glacial climate from at least 35,000 years ago to 18,000 years ago, after which the climate warmed up.
“It brings about the question of why and when the Southern Hemisphere was sitting so comfortably in a glacial mode for so long,” Putnam said. “Did it suddenly warm?”
Though the results are still preliminary, if they prove that Ice Age climate in Patagonia and New Zealand were indeed similar, then there would be a strong case that the Ice Age occurred at slightly different times in the Southern and Northern Hemispheres. In other words, the glaciers in New Zealand and Patagonia were retreating at the same time as the glaciers still covered much of North America, including much of the northern U.S. That would give scientists new insight into the mechanism of climate change, Kaplan said. This, in turn, would allow scientists to better understand how past climates have changed, which can be used to help them build more accurate computer models in predicting climate change in the future.
December 16, 2015
Photo on top: On a 2013 research expedition to Patagonia, Columbia University geologist Mike Kaplan uncovered new sites revealing clues to climate change during the last Ice Age. (Photo by Mike Kaplan)
