By Lakshmi Chandrasekaran
Cosmic rays, hurling across the galaxy near light-speed, generate a time machine on Earth for us to measure the retreat of the glaciers and the pace of climate change.
Ph.D. student Peter Strand, at the University of Maine, drilled samples of quartz from boulders in Mongolia’s Altai Mountains this summer to tap this time machine. Cosmic rays strike the atmosphere and release showers of subatomic particles such as neutrons that collide with the rocks, creating a variant of the element beryllium that builds up once the ice retreats from the rock and leaves it exposed to the air. Scientists call this variant a cosmogenic nuclide – beryllium-10 (10Be). The surfaces of rocks and boulders contain 10Be and, what’s fascinating is that the 10Be can be used as a measure of when the glacial retreat began, anywhere from a hundred to tens of millions of years ago!
“Our goal in this research is to determine the character of ice retreat at the end of the last ice age in Mongolia by creating a 10Be surface-exposure age chronology. We can then compare this record to other paleoclimate records from around the world and tease apart the drivers of this last great climate warming” after the last ice age, says Strand.
So how will following the retreating glaciers in the Altai Mountains help us understand what is happening to the climate today? The motivation for the Mongolian research team has been to understand how sensitive Earth is to climate forcing. Scientists are interested in knowing how Earth’s system will be altered via human carbon emissions by following ‘past’ glacial retreat processes, creating a benchmark to evaluate future change.
You see, when glaciers cover the surfaces of rocks, it deflects the particles that produce 10Be. But once the ice retreats, rock surfaces are now like drawing boards where neutrons can etch 10Be. “Once the amount of 10Be in the sample is determined, we can estimate how long ago the rock surface was exposed. In this way we can learn about the movements of glaciers thousands of years ago!” remarks Strand. Longer the rock was exposed to cosmic rays, more 10Be was formed on its surface!
This summer, University of Maine climatologist Aaron Putnam led Strand and a group of other scientists and students on a field trip to the Altai Mountains to research the timing and rate of retreat of mountain glaciers since the Last Glacial Maximum. That’s when ice covered huge swaths of the planet at the height, or maximum of the last ice age, approximately 20,000 years ago.
The scientists presented preliminary results using the 10Be surface dating technique at the recently concluded Comer Abrupt Climate Change Conference in Wisconsin. They showed that Mongolia is an excellent place to apply the 10Be surface dating.
All over the globe, retreating glaciers are ticking clocks signaling the steady progression of climate change. This is causing a lot of alarm since melting glaciers are causing rising sea levels. But mountain glaciers also feed all major inland rivers. With the temperatures on Earth linked to increasing human use of fossil fuels, glacial ice has been melting at a faster rate. And a loss of inland glaciers could signal severe fresh water shortages. However, glaciers also have a natural cycle of advancing and retreating. Climate scientists have spent decades trying to understand the chronology of these geological events in terms of both natural and human activity.
The field research in Mongolia will help tell us how we are accelerating the processes of climate change by forcing it beyond the way nature impacted it previously. But according to the scientists, before we can understand how humans have impacted climate change, it’s critical to appreciate the natural cycles.
“We have to understand underlying natural sensitivity before making predictions about how human influence will fit on top of it as well,” Strand says.
The glacial fluctuations and deposits found in Europe, New Zealand and South America have been thoroughly studied by climate change experts. But not much is known about the glaciers in Asia, beckoning the University of Maine scientists to explore them.
“If you plotted some chronological studies of mountain glaciers all around the world, there is a huge hole in the middle of Asia,” says Strand, highlighting the lack of analyzable data from Asia.
Strand is particularly interested in isolating the quartz mineral in the rocks where 10Be is generated and captured. He conducted his experiments by taking samples of rock for analysis and testing. Samples are subjected to various chemical processes in the lab to isolate the element Beryllium, which was quantified at the Lawrence Livermore National Laboratory in California.
Glacial retreat takes place over vast areas of land. In addition to, 10Be dating technique, the scientists employ the latest new technology- drones, because this helps them determine where to collect samples and allows them to get a broader perspective on the geological landscape. And here is where Mariah Radue, a Master’s student at the University of Maine comes into the picture. She and others on the field team captured the drone video. Retreating ice sheds trails of rocks called moraines that become apparent from the bird’s eye view of a drone.
The researchers have benefited from seeing the glacial landforms as geological formations from the sky. “Drones are a relatively inexpensive tool that we can access,” Radue says adding that helicopter travel wasn’t an option and satellite imagery of Mongolia isn’t very good. “So Stephanie Comer bought a drone for us for research purposes,” says Radue. The Comer Family Foundation helped fund the expedition along with the National Science Foundation and Comer funding supported some of the seminal research identifying 10Be as a way to track retreating glaciers. Now, using drones, Radue has been able to view more large-scale details of the glacial landforms and how far the Altai glaciers have retreated.
This drone technology is relatively unique in glacial geomorphic mapping. “It’s pretty well used in archeology but is not as ubiquitous in geology,” comments Radue.
Their work with an isotope in the rock and vistas of the mountains highlights the zeal of the graduate students, a crucial workforce in determining the extent of climate change and its effect on our fragile ecosystem – the Earth!