Frontiers

Frozen in Time

Jane Willenbring measures the rapid rate at which ice sheets are receding.
April 2012

Frigid temperatures, constant daylight and complete isolation from civilization—it doesn’t sound like a model camping trip. Welcome to Antarctica, home to the research of Jane Willenbring, Assistant Professor of Earth and Environmental Science. In her quest to understand long-term climate change, Willenbring charts the fluctuation of ice sheets. Using a method called “cosmogenic nuclide dating,” she is able to measure isotopic traces of radiation levels in rocks that have been exposed by receding glaciers. These findings help explain the consequences of increased deglaciation and its relation to global warming.

“The radiation process we study is kind of like a sun tan, except it is supernova radiation instead of sun radiation,” Willenbring says. “As something is exposed, it builds up a kind of cosmic ray tan you can use to figure out how long a rock or a boulder has been exposed.”

“The only way to prevent a catastrophic event is to stop temperatures from reaching the two to three-degree rise that we saw during the massive deglaciation of West Antarctica, which means drastically curbing carbon dioxide emissions.” – Jane Willenbring

The majority of Willenbring’s field work takes place in an area known as the Dry Valleys—reachable only by helicopter from a nearby military base—where the East Antarctic Ice Sheet butts up against the Transantarctic Mountains. The Dry Valleys was most likely carved by rivers some 50 million years ago, when Antarctica was still teeming with forests. Over time, as the continent transitioned to its frozen landscape, outlet glaciers formed between the peaks.

Because it is too cold for the glaciers to melt, they sublimate, leaving bathtub ring-like markings on rock called “moraines” which can be used to measure the rate at which the ice is receding. Once the underlying rock is exposed, the radiation-soaking process begins. Samples of the rock are then collected, which might involve anything from hacking off the top of a boulder, to happening upon a well-placed pebble. Samples are then sent to back to the lab at Penn to be analyzed using an accelerator mass spectrometer, which measures isotopes to provide an estimated timeline of exposure, which can then be used to chart ice sheet fluctuation.

Willenbring’s findings, paired with satellite observations, confirm what many scientists fear: glaciers are losing mass at an alarming, non-natural rate. Though carbon dioxide—a chemical compound long thought to be linked to global warming—is naturally absorbed by cold bodies of water like the Southern Ocean, it’s not a process that is sustainable, Willenbring says. The warmer the world’s oceans become, the less carbon dioxide they are able to soak up, creating a vicious cycle.

“If the World Trade center collapse caused a market crash, imagine what would happen if the whole low-lying New York City financial district suddenly looked like Venice,” says Willenbring. “The only way to prevent a catastrophic event is to stop temperatures from reaching the two to three-degree rise that we saw during the massive deglaciation of West Antarctica, which means drastically curbing carbon dioxide emissions.”


Outlet glaciers form between the peaks.

In addition to providing crucial information about climate change, the Dry Valleys also acts as a window into the past. Willenbring’s team, which at that time included researchers from North Dakota State University, discovered a freeze-dried lake bed housing fossilized insects and shells of mollusks. When placed in water, the artifacts fluffed up, even after being buried for millions of years. A preserved leaf, most likely from Antarctica’s ancient forests, was also found. Currently, the trees that produce this same leaf are found only in certain areas surrounding New Zealand. Through the study of these present-day habitats, Willenbring and her team can reconstruct the climate of the Antarctic valley when the leaf first fell.

“The Dry Valleys is an amazing place—otherworldly. Its closest analog is the surface of Mars,” says Willenbring. “What goes in rarely comes out. There’s a valley full of mummified seals that took a wrong turn. Initially, it’s creepy, but then you realize some of them are tens of thousands of years old—it’s fascinating.”