Why the once great Maya civilization withered away is still a matter of debate among historians, archaeologists, and geoscientists. The leading theory is that the Maya suffered a series of severe droughts around 800–1100. New evidence suggests there may have been another reason: severe tropical storms.
Researchers studying past climate records in the Caribbean found that storm activity was weak and predictable up to about 900. At that point, storms became more intense and unpredictable. The stress of dealing with the highly variable and intense storms, in addition to battling drought, may have pushed the Maya over the edge, according to research published in Scientific Reports in July.
Reconstructing Past Climate
Atlantic hurricane activity, which includes the Caribbean, and how it varies over the long term are often attributed to the behavior of ocean and atmospheric systems like the Atlantic Multidecadal Oscillation (AMO) and the El Niño–Southern Oscillation (ENSO). “But without long-term observations of storm behavior, it’s hard to speak to these relationships conclusively,” said Richard Sullivan, who studies paleoclimatology at Texas A&M University at Galveston and was not part of the new study.
Historical or instrumental records of hurricanes and tropical storms go back only a little more than a century. To peer further back in time, scientists often decipher telltale signatures left in sand and mud deposited by ancient storms.
One source for finding undisturbed sediments is blue holes, marine sinkholes into which sediments are continually deposited. Generally, the sediments in deposition layers are smooth. But when a large storm passes by, it rakes up and deposits coarse particles. Because of the structure of a blue hole, material can be deposited but cannot get out, allowing the feature to act as a near-perfect record of ancient storms.
Now Dominik Schmitt of Goethe University in Frankfurt, Germany, and colleagues have reconstructed past storms in the region going back 2,000 years. The researchers recovered and studied an 8.5-meter-long sediment core from the Great Blue Hole on Lighthouse Reef off the coast of Belize.
Upon analyzing the results, Schmitt’s team found evidence of the AMO going back to 300. According to Schmitt, this provides statistical proof that the AMO, along with ENSO, modulates hurricane activity in the southwestern Caribbean.
When the Weather Changed
The sediments also revealed something else. “The tropical cyclone activity of the southwestern Caribbean generally shifted from a less active (100–900 CE) to a more active state (900 CE to modern),” said Schmitt. The shift happened right around the time when the Maya civilization was in decline.
The Classic Maya civilization, which once occupied most of the Yucatán Peninsula, began to wane starting in the late 800s. During the next century, great Maya cities like Copán (in what is now Honduras) and Tikal (in what is now Guatemala) were abandoned.
Climate change is thought to have been a primary driver of this collapse. The leading theory suggests that a series of severe and prolonged droughts plagued the Yucatán Peninsula, which may have reduced the availability of fresh water and decreased agricultural productivity.
In addition to drought, the Maya may have had to contend with increased and more unpredictable Caribbean cyclones. The Great Blue Hole sediment core showed five exceptionally thick layers—15 to 30 centimeters—deposited between 700 and 1150. These layers suggest extremely intense cyclones; for comparison, the deposition layer left by Hurricane Hattie, a Category 5 hurricane that passed over the same area in 1961, was just 4 centimeters thick.
Two of the ancient cyclones struck during drought periods, and the others struck just before and after severe droughts. It’s likely these cyclone landfalls destroyed Maya infrastructure, caused coastal flooding and crop failures, and added to the environmental stress of the intensive drought phases.
The increased storm activity around 900 is similar to what Sullivan found in his study of sediment cores from a sinkhole south of Tulum, Mexico, near the Maya site of Muyil. Still, he is cautious in interpreting the results, saying they do not necessarily mean that an increase in storm frequency definitely contributed to the Classic Maya collapse.
However, “it’s not hard to imagine that a culture contending with severe drought and already in decline would have been stressed further by persistent, devastating storms,” Sullivan added. “It is certainly possible that increasing hurricane frequency factored into the collapse of the Mayan empire, but the extent of that contribution is something we may never know conclusively.”
—Lakshmi Supriya ([email protected]), Science Writer