50,000-year-old plant may warn of the death of tropical ice caps

A simple stroll after a full day of field research near a high Andean glacier in Peru led glaciologist Lonnie Thompson to discover a bed of previously hidden plants that date back at least 50,000 years.

And while that discovery is novel enough to please any scientist, it’s the implication that those perfectly preserved plants may suggest that really excites him.

Thompson, a professor of geological sciences at Ohio State University and a world-class glaciologist, has made nearly annual pilgrimages to Peru’s Quelccaya ice cap to monitor its slow demise, a probably victim of recent global climate change. The glacier is retreating 40 times faster now than it was when the first aerial photographs were taken in 1963.

He told this story today as part of his Emiliani Lecture presentation at the annual meeting of the American Geophysical Union in San Francisco.

In 2002, he and his colleagues from the Byrd Polar Research Center had found a small bed of plants that had, until then, been buried by the ice cap. Carbon dating on those plants suggested that they had been buried nearly 5,000 years ago. “We were surprised by those dates and had the plant tissue dated four times by two separate institutions,” Thompson said, “but the dates remained the same.”

This time, Thompson decided to look up a different valley, some 1.8 miles (3 kilometers) from the initial plant find. “But about a quarter-mile from there, I found yet another area of uncovered plants.” When Thompson returned to his campus lab, he packaged the three new samples and sent them off for carbon-dating as well. The first two yielded dates similar to the 2002 plant find — about 5,200 years ago.

But the date for the third plant sample seemed radically skewed. “We had the samples dated at the National AMS Facility at Woods Hole Oceanographic Institute (NOSAMS) and later sent other samples to the Lawrence Livermore National Laboratory (LLNL),” he explained. And when the dates on the third sample returned from both institutions, Thompson was shocked. “The tests showed that the samples of the third plant patch were greater than 48,000 years old, according to NOSAMS, and greater than 55,500 years old, according to LLNL – more than 10 times older than the earlier finds.”

But, Thompson pointed out that carbon-dating is unreliable for samples older than 50,000 years, so all he can accurately say at this point is that they are at least that old. He cautiously admits that they might be older but adds that there are no good methods to confirm that. “I want to stay conservative in my estimates as we continue to investigate this find,” he explains.

Blanca Leon, a researcher with the Plant Resources Center at the University of Texas at Austin, tentatively identified the plants as part of the genus Breutelia and they have similar modern descendents. There is a strong possibility that researchers can retrieve DNA from the samples.

Aside from the novelty of the find, Thompson is focusing on its potential implications: The plant had to have remained covered and protected for most of that time, which means that the ice cap most likely has not deteriorated to its current size for any length of time in more than 50,000 years.

That suggests that the global climate change he and others blame for the shrinkage also was less during that long period.

Tropical glaciers are major resources in the Andes for hydroelectric power production, crop irrigation, municipal water supplies and tourism. As these glaciers shrink, water supplies are reduced during the annual dry season and during future droughts, they will be seriously diminished, Thompson said. “The latest find is just one in a series pointing to the continued loss of mountain glaciers and hence the loss of the Earth’s ‘crown jewels,’” he said.

The National Science Foundation supported this work in part.