Underground Weather Reports

  • October 19th, 2004

Caverns Provide Geologists Insight Into Global Warming

by Linda Hill

UA graduate student Michael Rasbury returns from a hidden chamber in DeSoto Caverns. (photo: Joe Lambert)
UA graduate student Michael Rasbury returns from a hidden chamber in DeSoto Caverns. (photo: Joe Lambert)

One of Alabama’s popular spots under the ground is helping University of Alabama scientists understand more about global warming on top of the ground.

A team of UA geologists is conducting research deep in the underground caves of DeSoto Caverns Park, a state attraction visited by more than 100,000 people annually, located on the outskirts of Childersburg, a small town in Talladega County.

By studying carbonate deposits — stalactites and stalagmites — that have formed in the caves, the UA scientists are able to learn how the outside climate has changed over time. They hope to date the climate changes back to the time the caves were actually discovered by the Spanish explorer Hernando DeSoto in 1540 and beyond.

The team is led by Dr. Paul Aharon, UA professor of geology and holder of the Ray E. Loper Endowed Chair in Geological Sciences. Aharon is working on the project with UA doctoral students Joe Lambert of Cullman and Michael Rasbury of Sulligent.

Stalactites (from above) and stalagmites (from below) are plentiful in DeSoto Caverns
Stalactites (from above) and stalagmites (from below) are plentiful in DeSoto Caverns

Aharon says the DeSoto Caverns research project is designed to look at current issues scientists are debating concerning global warming. For example, the Southeast is in a 10-year cycle of drought, and scientists are asking if this is related to global climate data measuring some 2 degrees warmer than 50 years ago.

“Are the extreme events we see today linked to a trend in global warming, or are they part of a natural cycle that tends to come and go?” Aharon asks.

The professor and his students will use what nature has left behind to unravel the past climate and environment of the

A dental drill is used to micro-sample growth bands
A dental drill is used to micro-sample growth bands

area. Stalactites and stalagmites are formed when rainfall drips through the soil and bedrock, depositing in caves over long time periods.

By using “radio-isotope” dating (similar to Carbon 14 dating) of samples from stalagmites in DeSoto Caverns — in conjunction with isotopes of oxygen and carbon that serve as climate indicators — the scientists are gathering data that can be plotted using the age against the isotopic compositions as related to the weather that would have caused the isotopes to reach a particular value.

The stalagmites contain growth increments, shown in bands, that the UA team is able to measure and use in the interpretation of the climatology and history of the environment.

Annual growth bands of a stalagmite. (photos: Joe Lambert)
Annual growth bands of a stalagmite. (photos: Joe Lambert)

Enclosed, underground caves — where the stalactites and stalagmites grow — have provided a steady annual temperature with no seasonal fluctuation, Aharon notes. So, any changes in the formations are direct results of external climate changes, he explains.

The UA team has already taken samples from stalactites and stalagmites in DeSoto Caverns. “Our aim is to use the stalagmites as a proxy record — like an archive of the rainfall and outside annual air temperature means. Any changes in temperature could be related to the global climate,” Aharon says.

This stalagmite cross-section contains about 400 years of climate data.
This stalagmite cross-section contains about 400 years of climate data.

The scientists are using recorded historic climate data to track through time with the data they collect from the cave samples for cross calibration purposes.

In addition to studying samples, the research team is using data-collecting sensors placed near the stalactites and stalagmites in DeSoto Caverns to monitor temperature, relative humidity and carbon dioxide. They have chosen a remote cave area undisturbed by the site’s many visitors.

Being close to home was a compelling reason to study the formations in DeSoto Caverns, but the researchers add that the caves are among the oldest in the United States explored by human beings. DeSoto Caverns has an interesting history: the Native Americans

This stalagmite was collected from DeSoto Caverns in 2002.
This stalagmite was collected from DeSoto Caverns in 2002.

inhabited the caves at one time, they were used for mining salt peter to make ammunition in the Civil War, during the Prohibition Era the site was frequented by moonshiners, and later the site was used for mining the semi-precious onyx stone. Today, DeSoto Caverns is owned by Allen Mathis III whose family has owned the place since 1925; this third generation owner turned the site into a popular family attraction and has welcomed the UA research team.

The UA research site is in a hidden area of the caves not accessible to tourists. “We have identified stalagmites large enough to date back in time many thousands of years,” Aharon noted.

Based on initial research results, Aharon says they have observed a climate shift toward warmer temperatures around 1850. This could indicate global warming caused by the Industrial Revolution, the clearing of forests, or it could be part of a natural climate cycle.

Older stalagmites such as this may extend climate records thousands of years into the past. (photos: Michael Rasbury)
Older stalagmites such as this may extend climate records thousands of years into the past. (photos: Michael Rasbury)

“The bottom line is that the study of stalagmites and stalactites is providing a good way to solve some of the controversies about global warming that exist today,”Aharon says.

This UA research project is also being conducted in a special laboratory on campus, funded by the National Science Foundation, that has been built, designed and tested over the past two years by the scientific team and is dedicated for this kind of research.

Further Reading

The University of Alabama, part of The University of Alabama System, is the state’s flagship university. UA shapes a better world through its teaching, research and service. With a global reputation for excellence, UA provides an inclusive, forward-thinking environment and nearly 200 degree programs on a beautiful, student-centered campus. A leader in cutting-edge research, UA advances discovery, creative inquiry and knowledge through more than 30 research centers. As the state’s largest higher education institution, UA drives economic growth in Alabama and beyond.