By Penelope Gardner
Medill Reports, Dec. 13, 2023
On a hot July day, Alexzander Roman once more sets out in search of boulders on the Wind River Range. He has been trekking up and down these Wyoming moraines for weeks seeking suitable rocks to sample that act as time machines to reveal the retreat of the glaciers.
Once he’s found a boulder that looks to have been undisturbed for the last few millennia, he takes measurements and location information before collecting his sample. Roman drills a hole into the boulder, places a charge and a nail in the hole and hits the nail on its head to set off the charge. This tiny explosion sounds like a gunshot and takes off the top few centimeters of the boulder.
Roman repeated this with a team of up to five other researchers over 130 times during the summer months of 2021 and 2022, all while sleeping in a tent on campgrounds along the border of Boulder Lake. The huge fists of glacial ice collected the boulders as they moved southward in the last ice age and tossed them aside as the glaciers receded in warming times.
“The area out there is a gold mine for glacial geology,” Roman said. “We were able to be so picky with the kind of samples we would take due to the absolute abundance of glacial boulders.”
Once back at the University of Maine, where he is a Ph.D. candidate, he can determine the age of the boulder samples using Beryllium-10 dating. Beryllium-10 accumulates near the surface of the boulders as cosmic rays strike the rock once it is shed from the ice. The isotope collects at predictable rates so he can compare the dates when the glaciers advanced and retreated in the Northern Hemisphere to those in the Southern Hemisphere.
Roman and his Ph.D. advisor Aaron Putnam have found that New Zealand, which is the same distance from the equator as the Wind River Range, shows similar timing to the waxing and waning of glaciers in the North. They’ve dubbed this Mercer’s paradox as glaciologist John Mercer was the first to recognize the anomaly in 1984. It flies in the face of previous hypotheses that ice ages in the Northern and Southern Hemispheres did not synchronize.
“Mercer did radiocarbon dating in the Chilean Lake District in South America and found that those glaciers advanced nearly synchronously with the Laurentide Ice Sheet during the last glacial maximum which completely defied any explanation [within the earlier hypothesis],” Roman said. The Laurentide Ice Sheet once covered North America, which means that Mercer’s discovery of the nearly identical movement of glaciers on continents on either side of the equator was revolutionary to his and Roman’s field.
These new findings could have significant implications for paleoclimate research and for current and future climate change as a synchronized global impact.
“They are getting some interesting preliminary results that suggest the glaciers were on really fine time scales, operating simultaneously which, if correct, would require these rapid changes to be global in scope and require a change to the energy budget of the planet,” Putnam said.
“The more we can understand what affects our climate [naturally] and what pushes it between these two extreme states of glacial and interglacial, the more we can understand how we are affecting it [through human interventions],” Roman said.
Roman presented these findings at the annual Comer Climate Conference, an international gathering of climate scientists that met in southern Wisconsin this October.
Photo at top: (Alexzander Roman)