The Ice Plant Cometh
In July 2004, nearly 5,760 meters sky-high in Peru’s Andes Mountains, the Science Bulletins film crew trailed a pair of glaciologists hiking the summit of Quelccaya, the largest tropical ice cap in the world. Cameras and sound booms in hand, we aimed to film the Ohio State University team drilling an ice core from the top of this 44-square-kilometer layer cake of accumulated snow and ice. But then Lonnie Thompson, the lead researcher on the National Science Foundation-funded project, took a detour. He headed toward a glacial lake pooling in a valley three kilometers away. Had we followed him, we may have caught on video a discovery of some importance. The find has profound implications for the fate of this ice cap and its kin that dot high-elevation sites at similar latitudes.
Frozen in Time?
Thompson’s eureka was a clump of brittle vegetation rooted near boulders flanking the ice-littered lake. It resembled a cow patty more than a plant. Thompson’s colleague Benjamin Vicenio scooped several plants into a plastic baggie, noting their proximity to the abrupt edge of the ice cap looming nearby.
Upon return to the United States, Thompson mailed a portion of the plant to the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, for carbon-dating. The verdict: more than 48,000 years old. “There had to be a mistake, I thought,” said Thompson. “They’ve got too many digits. It’s supposed to be 4,800 years old.” Thompson’s shock is understandable. After all, three previous samples of ancient plants near Quelccaya’s edge turned up dates near 5,000 years old. But a second carbon-dating at Lawrence Livermore National Laboratory confirmed that the “new” plant was indeed extremely old; according to Livermore’s method, it was more than 55,500 years old.
Like the 5,200-year-old “ice man” found in the Austrian Alps in 1991, the plant had been cryo-preserved in ice. Thompson suspects it was exposed only in the last few years as the 0 degree C ice cap shrinks in the 3 degree C air.
Plants at Quelccaya are often rooted in soil-filled depressions in the bedrock. Thus, Thompson suspects the plant was preserved as the cap advanced over such a depression. This left a chamber of trapped air that spared the plant from being scoured to tatters by the slow-flowing glacier.
To identify the plant, Thompson called on Blanca Léon, a botanist from the University of Texas at Austin. Looking at the plant under a microscope, Léon observed the cell walls of a fragile moss that was remarkably well preserved. “It looks like a plant that was taken recently from the field,” she says. “It is amazing.” Called Scorpidium, the moss still grows today along the edges of lakes in the Andes, but at warmer elevations no higher than 4,600 meters. The ancient plant was collected from Quelccaya at 5,000 meters. Léon concluded that “the plant must have existed at a time with warm conditions, enough to allow its establishment at such a high altitude.”
Thompson knows, however, that paleoclimate records derived from Antarctic ice cores show that no warm period occurred 50,000 years ago. Also, current carbon-dating technology cannot date objects older than 55,000 years or so. Therefore, Thompson suspects the plant is actually much older. Around 125,000 years ago, temperatures were about 2 degrees warmer than they are today,” he says. “I think that’s when these plants were actually growing. Then a cooling cycle began and the glaciers grew and buried the plant.” The plant was exposed and discovered in the current warming period.
Thompson has witnessed our current warming first-hand. Since 1978, he has snapped near-yearly terrestrial photographs of the cap’s largest outlet glacier, Qori Kalis. (Click here to watch Qori Kalis melt.) During each expedition, he spots more bedrock that has been exposed and lakes swelling or appearing out of nowhere. He sees newly freed boulders perched on crests of gravelly moraines, the piles of rocky debris left behind by the retreating wall of ice. The soundtrack to every trip is the constant drip, splash, trickle, and rush as ice turns quickly into water.
From his data, Thompson has determined that 20 percent of the ice he measured at Qori Kalis and Quelccaya as a whole in 1978 has since melted. “In the first measurement period, which was from the first aerial photographs of 1963 until our photographs in 1978, the terminus of Qori Kalis was retreating at a rate of about 4.7 meters per year,” he says. “From about 2000 to 2002, that rate had increased to over 200 meters per year, or over 40 times faster.”
It appears that global warming is shrinking every last tropical glacier, including those at the summits of Kilimanjaro, Mount Kenya, and the Himalayasall sites that Thompson has surveyed and cored in the past two decades. “Quelccaya will take 50 years or so to disappear completely given the current climate conditions,” he says. “And of course, the predictions are that things will get warmer over the next 50 years.” This summer, Thompson plans to return to Peru to drill more cores and sample more plants to better reconstruct the ice cap’s historybefore there’s no ice cap left to study.
If all the ice on, say, Greenland melted, it would raise global sea levels by about 6 meters. But the melting of tropical glaciers would contribute just a fraction to sea-level rise. Instead, Thompson considers the retreat of tropical glaciers ominous because they’re the proverbial “canary in a coal mine”: a bird taken into mines to test for the buildup of dangerous gases. “You have two choices,” says Thompson. “Either you take the warning and get out of the mine or you choose not to take any action. To me, the tropical glaciers are our canaries. And they're telling us the system is changing.”
50,000-year-old-plant May Warn of the Death of Tropical Ice Caps
Ohio State University's original press release for Thompson's 2004 plant find.
All About Glaciers: National Snow and Ice Data Center
USGS: world glacier volume and sea level rise potential
National Science Foundation
More About This Resource...
Supplement a study of geology with a classroom activity drawn from this Science Bulletin essay.
- Have students read the essay (either online or a printed copy).
- Have them write a one-page reaction to the article, explaining in their own words why Lonnie Thompson sees his discovery as a "canary in a coal mine."