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UNM team studies climate change in Belizean cave

ALBUQUERQUE, N.M. — In the jungles of southernmost Belize, close to Guatemala and Honduras, there’s a cave the locals call Yok Balum, which means the Jaguar’s Paw.

It’s a cave ripe with riches but, like all respectable treasure caves, it’s difficult to reach. From the nearest village, it’s a 90-minute trek along muddy, overgrown trails favored by venomous snakes. And there’s a river, the Rio Blanco, that must be forded.

Sometimes crossing the river is inconvenient, sometimes it’s perilous and sometimes it’s impossible.

“I’ve seen the river when it was ankle deep, I’ve crossed it when it was up to my neck and I’ve seen it when it was 20 feet deep,” said Keith Prufer, associate professor of anthropology at the University of New Mexico. “It can rise within hours.”

Like Prufer, Yemane Asmerom, UNM professor of earth and planetary sciences, has been up to his neck in the treacherous waters of the Rio Blanco, surrendering his usual sound reasoning to overconfidence in his determination to reach the cave and the prizes it holds.

The lure is not gold, silver or jade, but scientific revelation.

UNM scientists Yemane Asmerom, left, and Keith Prufer, right, cross Belize's Rio Blanco with the help of a local guide in June 2010 on the way to the Jaguar's Paw cave. Getting to the cave is not easy, but the scientific treasures found there make the hardships worthwhile. (Courtesy of Douglas Kennett)

UNM scientists Yemane Asmerom, left, and Keith Prufer, right, cross Belize’s Rio Blanco with the help of a local guide in June 2010 on the way to the Jaguar’s Paw cave. Getting to the cave is not easy, but the scientific treasures found there make the hardships worthwhile. (Courtesy of Douglas Kennett)

Vital information

“One of the best places to study climate is the archive in this cave,” Asmerom said. “It has wonderful stalagmites. For some reason, the stalagmites in this particular area have a lot of (mineral) aragonite, a lot of uranium.”

That composition makes the stalagmites especially good for analysis. Recently, Yemane, Prufer and a couple of UNM associates used uranium thorium dating on a stalagmite sample collected in the cave to produce a rainfall record reaching back 450 years.

That record strongly suggests that man-made industrial emissions have contributed to a decrease in rainfall in the northern tropics. This is vital information not only for understanding the past, but also for preparing for the future.

Getting to the cave doesn’t get easier after crossing the river.

The final 10 minutes is a steep climb over rocks, mud and roots up to the cave’s mouth. Near the entrance is the unusual stalactite formation – shaped like a big cat’s paw – that earned the cave its name.

The cave is about a half-mile long, but it’s a tight squeeze to get in and it’s necessary to crawl 20 feet before reaching an area where it’s possible to stand up and look around. Stalactites form columns that are impressive to see and that divide the cave into chambers.

Keys to a mystery

“As caves go, it is very beautiful due to the amount of flowstone and the formations,” said Prufer, who has made more than 30 trips to the cave over the years.

Evidence gathered in the Jaguar’s Paw may be useful to UNM scientists in studying the relationship between climate and culture, and the ways climate volatility affects political strategy.

The cave provides data from the past while Prufer works with the contemporary population of the area to get a better understanding of human responses to changes in the ecosystem.

Considered together, information from the cave and the people living near it may provide insights into what role climate change played in the collapse of the great Mayan civilization that existed in this part of Belize hundreds of years ago.

“The Maya went from these great cities to blending back into the forest,” Prufer said. “What is the role of climate change in the political undoing that occurred?”

The keys to unlocking that answer are the stalagmites in the cave.

Using UNM’s state-of-the-art, multicollector inductively coupled plasma mass spectrometer, which measures isotope values – negative values indicating wet conditions and more positive values indicating dry conditions – it is possible to map out the region’s climatic history over hundreds of years by analyzing subtle changes in the chemistry of the aragonite in the cave’s stalagmites.

UNM professor Yemane Asmerom, left, and UNM senior research scientist Victor Polyak use the university's mass spectrometer to analyze stalagmite samples collected from the Jaguar Paw's cave in Belize. (Courtesy of the University of New Mexico)

UNM professor Yemane Asmerom, left, and UNM senior research scientist Victor Polyak use the university’s mass spectrometer to analyze stalagmite samples collected from the Jaguar Paw’s cave in Belize. (Courtesy of the University of New Mexico)

Crucial contribution

That’s just what UNM’s team – Asmerom; Prufer; Victor Polyak, a senior research scientist in the earth and planetary sciences department; and Valorie Aquino, a graduate student in anthropology – did in producing the record linking man-made industrial emissions to reduced rainfall.

UNM’s crucial contribution was part of an international study that also included Durham University in the United Kingdom, Pennsylvania State University, Northern Arizona University, and several other universities and institutes.

Analysis of the stalagmite samples indicate a substantial drying trend from 1850 onwards, a period that matches up with the steady rise of sulphate aerosols in the atmosphere due to the burning of fossil fuels to feed industrial growth in Europe and North America.

Interestingly enough, the record also showed short-lived drier spells in the northern tropics since 1550, following large volcanic eruptions that produced emissions similar to those caused by burning fossil fuels.

From whatever source, these emissions moderated temperatures in the Northern Hemisphere by reflecting the sun’s radiation. The cooler temperatures forced the tropical rainbelt, known as the Intertropical Convergence Zone, to shift toward the warmer Southern Hemisphere and, as a result, deprive the northern tropics of rainfall.

‘Truly important’

“The reason why this is truly important – not only in the climate in the tropics, but also globally – is because moisture transport across Central America from the Atlantic and Pacific is one of the key relays that modulates ocean currents and long-term climate variability,” Asmerom said. “The tropics are an important engine of climate.”

And while this rainfall record gives scientists like Prufer material to consider in pondering the past, it also provides a warning worth heeding.

“The fact it is getting drier has great implications for food security,” Prufer said. “We need to be making plans.”

The Jaguar’s Paw holds answers to the past and, hopefully, solutions for the future.

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