Climate scientist Alexzander “Zander” Roman knows his rocks.
Roman, a Ph.D. candidate in Earth and climate sciences at the University of Maine, is hunting rocks for clues to construct a timeline of the Little Ice Age. The Little Ice Age is estimated to have lasted from the 1300s through the mid-1800s, causing infamous famines in the Northern Hemisphere.
By studying natural climate shifts of the past, scientists are able to predict how climate change may be accelerated by current human activities. Scientists such as Roman study the Little Ice Age because it is the most recent natural abrupt climate change in the Earth’s history. Roman is constructing chronologies of glacial fluctuations in Southern New Zealand to understand whether the region was impacted by the same climate changes seen in the Northern Hemisphere. Roman presented his research on Sept. 30, 2025 at the annual Comer Climate Conference, which gathers veteran scientists Ph.D. candidates from across disciplines in southwestern Wisconsin each fall.
Open questions
There is debate within the scientific community about whether the Little Ice Age, which was previously believed to be limited to the Northern Hemisphere, was actually a global event. Fewer universities exist in the Southern Hemisphere, so research has historically been limited.
Scientists also disagree on the cause of the Little Ice Age. Theories include cooling from volcanic output, sunspots, and the positions of winds. Understanding the timing and spatial extent of the Little Ice Age is crucial to determining its cause. Glaciers are very sensitive to climate changes. A wind system occurring around one mountain range might impact one glacier, without causing a global fluctuation in the climate system. “Being able to expand the data set and confidently say if it was global or not, will help us weed out some of the other forcings that wouldn’t be able to account for a global response,” Roman said.
Reviewing rock samples
Roman fills in his chronology through analyzing rock samples from his field site in the Southern Alps of New Zealand. These rocks were deposited in their current locations as the glaciers melted. Because he is obtaining data from the Holocene era, the period in the Earth’s history from about 12,000 years ago until present day, he needs to take samples of relatively more newly deposited rocks. Over time, he has honed his ability to identify good candidates by sight.
The color is also revealing: if a moraine is pink rather than gray, the iron of the rock has had enough exposure to the elements that it has begun oxidizing.
Finally, younger rock deposits have not had time to embed into the soil they sit on, and depending on where they sit on the moraine, they may have been moved by the elements. Roman needs samples that have not moved, so he looks for rocks that sit on the crest, or highest point, of the moraine. He can be confident that rocks that have maintained their position on the crest have not been moved, because if so, gravity would have pushed them to lower elevations. Other, smaller rocks leaning against them also prove that a rock hasn’t moved.
Analyzing the samples
After samples are obtained, Roman’s team collects quartz and, back at the lab in Maine, conducts a beryllium-10 count, a surface-exposure dating process to determine when the rocks were freed from the ice. Beryllium-10 collects in rocks at predictable levels that correlates to a time machine for dating. Here’s how that works:
First, the team must isolate the quartz from the rock. The team minimizes the rock sample at the lab into the size of a cobblestone, then pulverizes it into fine sand grain.
Next, in what is called hydrofluoric leeching, the rock is boiled in phosphoric acid to chemically separate quartz from organic material.
When the only material remaining is quartz, the beryllium-10 can be targeted. The sample is sent to the Lawrence Livermore National Laboratory for mass spectrometry. At Livermore, a machine the size of a football field accelerates the particles, allowing the amount of beryllium-10 to be tallied and for the team to determine the rock’s age. The entire process can take between one and four months, depending on the age of the sample.
Constructing a timeline
Roman uses the ages of the rocks to better understand the retreat path of the glaciers over time, which will help scientists understand whether the Little Ice Age impacted the Southern Hemisphere. He is one of many researchers currently studying this topic. “I would love to see a more comprehensive glacial chronology from the Holocene through present for the Southern Hemisphere,” he said. The search continues!
[Credit: Kimberly Henrickson]