Geology students travel the globe to examine climate change

William Harmon Norton Professor of Geology Rhawn Denniston has students working across the globe this summer on his long-running climate research.

For the past 10 years Denniston, along with Cornell geology and environmental studies students and fellow scientists, have studied the behavior of the Australian monsoon, the main source of rain in the Australian tropics. They do this by studying stalagmites from caves across northwest Australia, and they have discovered some surprises.

“It has generally been thought that over centuries the monsoon in Australia, which is connected with the monsoon in Southeast Asia as one big system, operated as a teeter-totter,” Denniston said. “When one side got wetter, the other side should be drier and vice versa. What we have discovered is it actually didn’t operate like a teeter-totter, it operated more like an accordion. Both sides got wetter or both sides got drier simultaneously. While monsoon rains in Australia impact a relatively small number of people, they impact billions of people in Southeast Asia, so figuring out this system is important.”

Chloe Martin, a junior who is part of the Cornell Summer Research Institute, traveled (along with junior geology major Paige Klug) with Denniston to Australia to visit the caves that are at the heart of their research. They downloaded information from data loggers positioned in and above three different caves. For her part, Martin is focusing her studies on how stalagmites react today to cave flooding during heavy rainfall events from the monsoon and hurricanes.

“We see mud layers within the stalagmites,” Martin said. “When the cave floods, it brings in sediment, which gets deposited on top of stalagmites. Then, when the water recedes, the stalagmites keep growing and that mud layer is trapped in there. We can see that when we cut them open.” 

Denniston says they’re determining how much rain is required to flood the caves, how long it takes floodwaters to fill the cave, and how long the floodwaters remain in the cave.

“By understanding these things and comparing them to our analyses of the stalagmites we get from the same cave, we can begin to interpret the stalagmites a little more clearly,” Denniston said. “By analyzing cave flooding in stalagmites, we now know that the frequency of extremely heavy rain events has varied a lot over the past 2,000 years, with medieval times being an interval with a particularly high number of heavy rains.”

On a related subject, Cali Pfleger, a senior and Cornell Fellow, is working on another piece of the research at Woods Hole Oceanographic Institution in Massachusetts. Her portion examines the impact large prehistoric volcanic eruptions had on the Australian monsoon.  Big eruptions can cool much of the planet for a few years and in the tropics, they can influence monsoon rainfall. 

To know exactly where in the stalagmite an eruption occurred, Pfleger is using the stalagmite’s chemistry. When volcanoes erupt, they spew sulfur. Pfleger is using specialized equipment at the lab to scan the stalagmite samples for layers with lots of sulfur.

“I’m studying the Australian monsoon response to large volcanic eruptions over the last millennium,” Pfleger said. “Volcanic eruptions induce a cooling, so we are trying to investigate, do all volcanoes cause the same response to the Australian monsoon or are there differences that we are going to find?”

Aside from the sulfur analysis, Pflger is working with complex computer models under the oversight of Caroline Ummenhofer in the Department of Physical Oceanography. These models allow Pfleger to investigate exactly how and where monsoon rains changed most profoundly after eruptions occurred.

This summer, Denniston also has students working on stalagmite projects at Ca’ Foscari University in Venice (Jamie Thompson, Macalester College), Iowa State University (sophomore Kat Armstrong), and with him in Portugal (junior Gabi Hiatt and senior Jace Bricker) as part of a cave study of prehistoric drought in southwestern Europe.

From volcanoes to floods to droughts, piecing together all of this information will give them the answers they need to understand climate change over periods of time much longer than the historical record. These are big projects that span the globe, but Denniston knows they help will put his students on the map when it comes to their futures.

“One of the things we always tell our students is that when you are applying to graduate schools or you are applying for jobs, there are going to be a lot of applicants that look very similar on paper,” Denniston said. “They are going to have had the same coursework, they are going to have had a lot of the same field experiences, and similar grades, but the things that make students stand out are these individualized research experiences.”