Mining the Ice Age to Predict our Future

In response to global warming, scientists across the world are working to better understand how climate changes affect the planet’s ecosystems, and, in particular, how glaciers and ice caps melt and contribute to sea level rise. While studying current examples of these phenomena is important, looking to the past is vital: more data about prior periods of warming and deglaciation may hold the key to predicting—and possibly mitigating—the worst effects of future climate changes.

Bentley Professor of Natural and Applied Sciences P. Thompson (“Thom”) Davis has been researching the history of deglaciation in Canada and New England for decades.  Recently, he and two colleagues (Asst. Prof. Jeremy Shakun at Boston College and Professor Paul Bierman at The University of Vermont) were awarded a three-year, $265,117 grant from the National Science Foundation (NSF) to study the timing and rate of the thinning of the southeastern Laurentide Ice Sheet (LIS) during the last major period of deglaciation after the Pleistocene epoch, or the “Ice Age.

Influential Ice

The LIS was the largest of the Ice Age ice masses, covering—and shaping—millions of square miles of present day Canada and much of the northern United States, gouging out the Great Lakes and molding all of New England as the ice sheet advanced and retreated and ultimately thinned out. The changes in the LIS over time influenced the jet stream, major ocean currents, and local climates throughout North America.

But the ice sheet’s most significant impact during its melting period may have been on sea levels. Understanding how the LIS affected sea levels may be crucial to understanding the challenges of present-day global warming.  

As Davis and his colleagues explain in their abstract, “The largest, but also most uncertain, control on the pace and magnitude of future sea level rise is how the Greenland and Antarctic Ice Sheets will respond to continued warming. The end of the last Ice Age provides an outstanding opportunity to probe this question since it featured the collapse of major ice sheets and abrupt multi-meter jumps in sea level that remain to be fully explained.”

Cosmic Rays and Dipsticks

In order to delineate the vertical thinning of the LIS, the researchers will use an ingenious “dipstick” method, first developed by glacial geologists in Antarctica, that measures the exposure of glacial boulders and glacially eroded bedrock to cosmic rays, which produces cosmogenic nuclides—a particular kind of atom—that can be measured on tandem mass accelerators, at places such as Lawrence Livermore National Laboratory in California. By identifying the presence of nuclides and age of exposure at various elevations on mountains throughout the study area, Davis and colleagues will be able to trace the rate at which the LIS thinned vertically. As their abstract puts it, the presence of the nuclides reveals “when the ice sheet surface lowered below various elevations, much like rings in a bathtub.” From summits to valleys, the exposure ages revealed by the nuclides will paint a picture of the vertical rate of thinning of the LIS.

The researchers will combine these data with what is already known about the horizontal margins of the LIS to ultimately create a three-dimensional model of the thinning of the largest ice sheet of the Ice Age. With this new model in hand, researchers can compare it to current models being applied to today’s thinning ice sheets in Antarctica and Greenland to assess their predictive accuracy.

Mysteries of the Last Melting

Davis and colleagues also seek to answer some key questions about the last Ice Age, including:

• When specifically did the LIS thin out, and did it do so during known periods of warming?
• How fast did the ice surface lower vertically?
• How did the thinning rate relate to known cycles and changes in sea level, such as the well-dated global Meltwater Pulse IA, whose glacial source is still unidentified?
• How well do current mathematical models simulate LIS deglaciation?

Davis, who is starting his 30^th year teaching at Bentley, reports that this current research project was submitted to the NSF’s Geosciences division about 18 months ago; there is a roughly 15% acceptance rate for any given proposal in this division.

He’s intrigued by the mysteries that he and his colleagues may be able to unravel, saying, “We know there was a period when sea levels rose very rapidly—we think that there should be a corresponding time when ice sheets around the globe thinned dramatically. The modern equivalent might be seen in anthropogenic changes to climate, so we might gather useful information on how fast modern sea level will rise in the future.” Davis notes that melting periods during prior epochs didn’t produce what current models are projecting for contemporary sea level rise. “And, these pre-historic meltwater pulses may turn out to be small compared to what we will see over the next 100 years.”

Turning Environmental Research into Sustainable Business Practices

Davis has introduced Bentley students to these fields of study through courses he teaches on weather and climate, and another on water cycles and the environment. For the Bentley International Education program, he and his colleague Robert Ackert at Harvard have led five separate groups of students to New Zealand in the January term and three groups of students to Iceland during May term to study glacial geology and climate change in those areas.  Bentley students have also accompanied him to Baffin Island in the Canadian Arctic where he did some of his earliest research on Ice Age dynamics. “Business students respond well to the overall umbrella of environmental sustainability—and see these environmental concerns as a likely part of their future employers’ sustainability efforts,” reports Davis. “They can take the data and the knowledge that we give them and influence corporate and government policies.”