16 August 2013

Darrel and the caves

To learn about our planet’s paleoclimate, a MagLab scientist goes underground.

By KATHLEEN LAUFENBERG

It’s spooky inside the Dragon’s Tooth, an ancient cave in Marianna, Fla.

16august2013 tremaine cave1After a long day inside the Dragon’s Tooth, Darrel Tremaine takes a break near the opening of the cave.It’s so dark you can’t see your own hands, and the air is ripe with earthy decay. It’s eerily quiet, too — except for the breathing of 33-year-old Darrel Tremaine

Tremaine, a MagLab scientist, wants to understand what the climate was like in North Florida thousands of years ago. He’s especially interested in prehistoric rainfall patterns — info that could help predict future rain patterns. So for more than two years, he and several other Florida State University graduate students have regularly visited the Tooth, collecting data from natural earth formations called stalagmites that grow on the cave’s floor. Inside them is a treasure chest of climate information.

“We want to be able to predict what the rainfall patterns are going to look like in North Florida over the next 10, 50 or 100 years,” he says. “Our work with these stalagmites is really just one small piece of a much larger climate puzzle.”

The instruments he uses to decipher this climate puzzle are found in the MagLab, and they allow him to explore in a different way. By measuring the minute amounts of certain chemicals locked deep inside the stalagmites, he can discover what the environment was like.

Earth’s library

While stalagmites grow up from the floor, similar formations called stalactites also form on the ceiling. Stalagmites and stalactites can resemble boney fingers poking into the cavern or assume much thicker forms. A famous stalagmite at Marianna Caverns State Park resembles a wedding cake. A towering, 8-foot-tall stalagmite in Dragon’s Tooth resembles a giant tooth (hence the cave’s name).

16august2013 tremaine stalagmitesA look  inside a stalagmite that’s been growing for 50,000 years. Each “ring” is a cycle of growth.No matter their shape, though, all of the cave’s rock-hard stalagmites are thousands of years old. And locked inside them are trace elements and growth patterns that reveal what the weather was like in ancient times.

“If you know how to read it, a stalagmite is just like a weather book,” says Tremaine, a doctoral student in chemical oceanography. “There’s all kinds of information in there, but you need to know how to retrieve it.”

Rain creates these earth sculptures. As rainwater trickles through the earth, it dissolves the calcium carbonate in limestone. The calcium-rich water drips into underground caves. The dissolved calcium builds up on the ceiling where it’s dripping from, and on the floor beneath the drip. Over eons, the stalagmites and stalactites grow, forming new rings (just as trees do) with each cycle of growth.

Because they grow so slowly — adding perhaps a ring no thicker than a fingernail each year — they contain incredibly detailed chemical records of the planet’s environmental history. And while the same climate information is found in both stalagmites and stalactites, researchers say stalagmites reliably contain more detailed data. That’s why Tremaine, like many scientists, focuses his research exclusively on stalagmites.

The cave breathes

In order to explore these caves, though, Tremaine has to squirm through long, muddy passageways — called flatteners — that are barely a foot tall. It’s not for the faint of heart.

“I’ve been through passages so tight I had to breathe out to squeeze through,” the 155-pound Tremaine says. “I’ve had to take off my helmet and turn my head sideways just to snake through … I’m definitely braver than I was before doing this.”

But there’s beauty in caving, too. Once Tremaine slithers through the Tooth’s longest passage — a 20-foot flattener — he’s in the Dragon’s Belly. Inside this 20-foot tall, 100-foot wide room, he can stand up, stretch and use his bright, helmet-mounted, LED lights to scan the Belly’s impressive gallery of stalagmites.

16august2013 tremaine cavestuffSome of Tremaine’s must-haves: a helmet with a mounted light, a backpack, a map, his notebook and vials for sample collection.In order to understand the weather clues locked inside these mineralized crystals, Tremaine also needs to understand the environment they grew in.

“It’s sort of like, if you want to analyze a child, you have to go to the child’s house and figure out what kind of environment he grew up in,” he says. “Once we have an idea of what’s going on inside the cave, how the cave breathes in and out and its water chemistry, then we have an idea of how to interpret the records that are locked up inside the stalagmites.”

So inside the Tooth, he’s set up several small, battery-powered machines to track how the cave breathes. He monitors the cave’s carbon dioxide and radon levels, its temperature and humidity levels, and its barometric pressure and airflow velocity and direction. He also records the slow drip-drip-drip that forms the stalagmites.

“You measure as many things as you can and try to understand the changing drip chemistry, and the changing stalagmite chemistry, in terms of changing rainfall and changing ventilation,” he says. “Eventually, you do start to see patterns develop.”

Because the caves are pin-drop quiet, Tremaine sometimes calls his research “Zen science.” He’s even found a special meditation spot near an opening in one of the caves: At dusk, the light glows there in a mesmerizing way.

Back at the Lab

After more than a year of collecting cave data, Tremaine was ready to examine the stalagmites themselves. In order to do that, he had to remove them. It’s illegal to remove these prehistoric relics — which are beautiful eye candy in themselves — from public lands. Although scientists with legitimate goals can get permits to do so, Tremaine didn’t need any. The stalagmites he wanted were on privately owned land, and the owner gave him the necessary permission.

Tremaine chose to examine two: One is about 4,000 years old and 5 inches tall; the other, 50,000 years old and 10 inches tall. Once removed, he examined them in special labs in the MagLab's geochemistry department. He uses the geochem “clean labs,” which require you to take off your shoes or don special booties, wear a lab coat and even a hair net. The hypersensitive spectrometer machines inside these labs can detect barely-there traces of chemicals, and you don’t want to contaminate your samples with dust from your shoes, hair, hands or elsewhere.

Tremaine using mass spectrometerTremaine uses a mass spectrometer to analyze the powdery samples he’s removed from the stalagmites.

Tremaine carefully drills into places along each stalagmite and removes powdery samples. He analyzes these samples for infinitesimally tiny amounts of carbon and oxygen, as well as magnesium, calcium, barium strontium, lithium and uranium.

These trace elements are clues to the temperature inside the cave when the growth ring formed. Using this data, he can determine whether the weather was cold, warm or hot when the ring formed. And he can deduce what type of vegetation was growing on the earth above the stalagmite.

But teasing out the trace elements is also an art. He’s looking for a trace of, say, lithium in the range of one part per billion.

“That’s a very tricky measurement,” says Sambuddha Misra, a former MagLab scientist doing his postdoctoral work in chemical oceanography at the University of Cambridge in England. Misra helped Tremaine learn how to use the MagLab spectrometers, and he also explained to him why even talking to another scientist while working with some of the spectrometers can alter the readings.

“Your spit has a lot of sodium in it, and when you blink you give off potassium, and these machines are sensitive to one part per trillion,” Misra says.

To take such precise measurements, he adds, demands a special type of attention.

“You work on a flow bench, and you work with your hands away from your body. It’s essentially a ritual, and you try to make every step as perfect as possible.”

Two years into his data collection, Tremaine’s discovered that both of his stalagmites grew continuously during the last 4,000 years — which makes them perfect libraries of North Florida’s climate history. Preliminary data from one of the stalagmites also indicates that 2,200 years ago, something drastically changed, either in the weather, in the cave itself or on the land directly above the cave. Exactly what happened, though, remains a mystery until more data can be collected.

“To learn what our past was, we must look into nature’s archives, such as these stalagmites,” Misra says. “It’s very important work because we need a continental climate record.”