Cave clues reveal droughts that shaped Maya civilization
Chloe Baul
(CN) — A stalagmite deep inside a cave in Mexico has revealed just how long and severe droughts were during one of the most turbulent chapters in Maya history — including one dry spell that lasted 13 years.
A team led by the University of Cambridge analyzed chemical fingerprints, specifically oxygen isotopes, in the cave formation, allowing them to estimate rainfall during individual wet and dry seasons between 871 and 1021 CE.
That time span overlaps with the Terminal Classic period, when many southern Maya cities were abandoned and the civilization’s political power shifted north.
The findings were published Wednesday in the journal Science Advances and supported by the National Geographic Society and the Leverhulme Trust.
“It hasn’t been possible to directly compare the history of individual Maya sites with what we previously knew about the climate record,” said lead author Daniel H. James, who conducted the work while a Ph.D. student at Cambridge, in a press release. “Lake sediment is great when you want to look at the big picture, but stalagmites allow us to access the fine-grained detail that we’ve been missing.”
The stalagmite came from a cave in the Yucatán Peninsula and, according to researchers, recorded eight wet-season droughts lasting at least three years each. The longest stretched for more than a decade — a span that would have tested even the most sophisticated water management systems the Maya had in place.
This is the first time researchers say they have been able to isolate rainfall conditions for wet and dry seasons separately during the Terminal Classic, an important detail for understanding how climate stress affected crops.
Previous studies could only estimate annual averages, which don’t capture whether the rainy season failed.
“Knowing the annual average rainfall doesn’t tell you as much as knowing what each individual wet season was like,” James said. “Being able to isolate the wet season allows us to accurately track the duration of wet-season drought, which is what determines if crops succeed or fail.”
Researchers say the climate record lines up with changes in the archaeological record. At Chichén Itzá and other major Maya sites, monument building and political activity appear to have stopped during some of the most intense dry periods.
“This doesn’t necessarily mean that the Maya abandoned Chichén Itzá during these periods of severe drought, but it’s likely they had more immediate things to worry about than constructing monuments,” James said.
The stalagmite’s layers, each about a millimeter thick, built up over centuries as mineral-rich water dripped from the cave ceiling.
According to researchers, the ratios of oxygen isotopes in each layer reflect how much rain fell, particularly during the wet season. Earlier research using lake sediment offered broader climate trends but lacked this year-by-year precision.
James and colleagues from the U.K., U.S. and Mexico say this fine-scale data can now be used alongside inscriptions and other archaeological evidence to better understand how climate shaped Maya society during its decline.
“This period in Maya history has been a cause of fascination for centuries,” James said. “There have been multiple theories as to what caused the collapse, such as changing trade routes, war or severe drought. In the past few decades, we’ve started to learn quite a lot about what happened to the Maya and why, by combining the archaeological data with quantifiable climate evidence,” he said.
Findings also suggest that stalagmites could offer more than drought records. Researchers say they might hold signs of past tropical storms or other weather extremes, opening the door to richer reconstructions of ancient climate.
“As a case study for fine-grained comparisons between climate and historical data, it’s exciting being able to apply methods usually associated with the deeper past to relatively recent history,” James said.