The World Today
MADRID, 14 (EUROPA PRESS)
A 13-year drought and several others, each lasting more than three years, may have contributed to the collapse of the Classic period of Mayan civilization.
A detailed analysis of oxygen isotopes in a stalagmite from a Mexican cave allowed a team of researchers, led by the University of Cambridge, to determine precipitation levels for individual wet and dry seasons between 871 and 1021 AD, coinciding with the Terminal Classic period of the Maya civilization. The results are published in the journal Science Advances.
This is the first time it has been possible to isolate precipitation conditions for individual wet and dry seasons during the Terminal Classic, the period of social decline historically known as the Maya collapse.
During the Terminal Classic, the southern limestone Maya cities were abandoned and dynasties came to an end, as one of the great civilizations of the ancient world shifted northward and lost much of its political and economic power.
Data from the stalagmite, found in a cave in Yucatán, showed that there were eight rainy-season droughts lasting at least three years during this period, with the longest drought lasting 13 consecutive years.
These climate data are consistent with existing historical and archaeological evidence: monument construction and political activity at several important northern Maya sites, including the famous city of Chichén Itzá, halted at different times during this period of climatic stress.
DETAILED CHRONOLOGY
Precisely and accurately dated, droughts provide a new framework for detailed analysis of the chronology and dynamics of human-climate interactions in the region.
"This period of Maya history has been a source of fascination for centuries," said lead author Dr. Daniel H. James, who conducted the research while a PhD student in Cambridge's Department of Earth Sciences, in a statement.
There have been multiple theories about the causes of the collapse, such as changes in trade routes, wars, or severe droughts, based on the archaeological evidence left behind by the Maya. But in recent decades, we have begun to learn a lot about what happened to the Maya and why, combining archaeological data with quantifiable climate evidence.
Beginning in the 1990s, researchers began combining climate records with those left by the Maya, such as dates they recorded on key monuments, to show that a series of droughts during the Terminal Classic likely contributed to the massive sociopolitical upheaval in Maya society.
Now, James and his co-authors from the United Kingdom, the United States, and Mexico have used the chemical fingerprints contained in stalagmites from a cave in northern Yucatán to shed more light on these droughts.
Stalagmites form when water drips from a cave ceiling and the minerals it contains accumulate on the cave floor. By dating and analyzing the oxygen isotope layers within the stalagmite, researchers gleaned highly detailed information about the climate during the Late Classic period.
Previous research has measured oxygen isotopes in lake sediments to determine drought severity, but these sediments do not contain enough detail to identify climate conditions in a given year at a particular site.
"It hasn't been possible to directly compare the history of individual Maya sites with what we previously knew about the climate record," said James, who is currently a postdoctoral researcher at University College London (UCL).
"Lake sediments are great for getting a big-picture view, but stalagmites allow us to access the finer details we were missing."
Previous research on stalagmites determined average annual precipitation amounts during the Terminal Classic, but the Cambridge-led team has now been able to go further and isolate information from individual wet and dry seasons, thanks to the relatively thick annual layers (approximately 1 mm) in the stalagmite used in this study. The specific oxygen isotopes in each layer are an indicator of dryness during the wet season.
"Knowing the average annual rainfall doesn't reveal as much as knowing what each rainy season was like," James said. "Being able to isolate the rainy season allows us to accurately track the duration of the drought, which is what determines the success or failure of crops."
EIGHT DROUGHTS OF AT LEAST THREE YEARS
According to the information contained in the stalagmite, there were eight rainy season droughts lasting at least three years between 871 and 1021 AD. The longest drought of the period lasted 13 years. Even with the water management techniques the Maya possessed, such a prolonged drought would have had a significant impact on society.
The climatic information contained in the stalagmite matches the dates inscribed by the Maya on their monuments. During periods of prolonged and severe drought, date inscriptions at sites like Chichén Itzá ceased to appear altogether.
"This doesn't necessarily mean that the Maya abandoned Chichén Itzá during these periods of severe drought, but they likely had more immediate concerns than building monuments, such as whether the crops they depended on would thrive," James said.
