Arctic glaciers grew rapidly in response to sudden climate change 8,200 years ago, a new study finds.
The study suggests that ice sheets such as those covering Greenland can quickly react to short-term climate shifts, said lead researcher Nicolás Young, a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory. "Ice sheets are very sensitive to modest changes in temperature," Young told LiveScience. "You don't need thousands of years of increasing or decreasing temperatures. A really quick temperature change will also trigger a response."
The climate switch investigated by Young and his co-authors is a brief cooling period that lasted only 150 years, with temperatures dropping 5.4 degrees Fahrenheit (3 degrees Celsius) in just 20 years.
During the cold snap, called the 8.2-ka event, galloping glaciers on Canada's Baffin Island descended from the mountains and extended tongues from remnants of the Laurentide ice sheet, report Young and his colleagues from the University at Buffalo in New York. [On Ice: Stunning Images of Canadian Arctic]
Despite the short time span, Baffin Island's glaciers grew larger during the 8.2-ka event than they did in a longer and colder climate shift called the Younger Dryas, the team found. The Younger Dryas was 10 times longer: It lasted from 12,900 to 11,700 years ago, with temperatures dropping 27 degrees Fahrenheit (15 degrees Celsius) below average.
Climate responses
The two cooling periods interest climate scientists, because they offer concrete evidence about how abrupt climate change affects the Arctic's ice sheets. The Younger Dryas is particularly perplexing, because a growing body of evidence, including Young's study, indicates Arctic glaciers did not advance during what was almost a mini-ice age. "When it gets cold, ice is supposed to grow," said Gifford Miller, of the University of Colorado, Boulder's Institute of Arctic and Alpine Research, who was not involved in the study.
Collecting data on the Arctic's response to past temperature swings will also help scientists more accurately predict the effects of global warming, through testing of climate models. "If the models are correct, they should get the past right," Miller told LiveScience. "What this study is saying is you have to be really careful about reconstructing ice behavior. Simple mean annual temperature change is not an ideal predictor for how ice will behave," he said.
Temperatures across the Arctic have been rising as a result of the buildup of greenhouse gases in Earth's atmosphere.
Sampling Baffin
Located just west of Greenland, Baffin Island is the fifth largest island in the world, with an area of 196,000 square miles (about 508,000 square kilometers). Baffin Island has both isolated mountain glaciers and an ice cap, a remnant of the massive Laurentide ice sheet that covered most of Canada during the last ice age. Working out of Clyde River (a small Inuit community on the island's eastern coast), the researchers tested both ice cap and mountain glaciers, to see if they responded differently to past climate change.
During spring, the team sampled rocks from moraines and collected shells – it was warm enough to work but cold enough to travel by snowmobile. Moraines are piles of glacially deposited sediment and debris. At the end of a cold phase, glaciers deposit a moraine before retreating.
Both the mountain glaciers and the ice cap, which are isolated from one another, increased in size at the same time, according to chemical-dating techniques. They had been shrinking before the sudden drop in temperature 8,200 years ago.
Based on the position of the moraines, the scientists concluded that advancing glaciers were larger during the 8.2-ka event than during the Younger Dryas.
Young said seasonal differences could account for the discrepancy. Some studies suggest that summers and winters were very cold during the 8.2-ka event, while summers were warmer during the Younger Dryas. "Ultimately, we don't really know why that is. I think a lot of work needs to be done on that front," Young said. Frigid summer temperatures would keep snow from melting, making the glaciers grow faster.
The findings are detailed in today's (Sept. 13) issue of the journal Science.
