What was done
In the words of the authors, "sediment cores from Lakes Punta Laguna, Chichancanab, and Peten Itza on the Yucatan Peninsula were used to (1) investigate 'within-horizon' stable isotope variability (δ¹⁸O and δ¹³C) measured on multiple, single ostracod valves and gastropod shells, (2) determine the optimum number of individuals required to infer low-frequency climate changes, and (3) evaluate the potential for using intra-sample δ¹⁸O variability in ostracod and gastropod shells as a proxy measure for high-frequency climate variability."

What was learned
The five researchers report that their results "allow calculation of mean isotope values and thus provide a rough estimate of the low-frequency variability over the entire sediment sequence," and these results indicated that "relatively dry periods were persistently dry [italics added], whereas relatively wet periods were composed of wet and dry times."

What it means
Escobar et al. state that their findings "confirm the interpretations of Hodell et al. (1995, 2007) and Curtis et al. (1996) that there were persistent dry climate episodes associated with the Terminal Classic Maya Period." In fact, they find that "the Terminal Classic Period from ca. AD 910 to 990 was not only the driest period in the last 3,000 years, but also a persistently dry period [italics added]." And in further support of this interpretation, they note that "the core section encompassing the Classic Maya collapse has the lowest sedimentation rate among all layers and the lowest oxygen isotope variability."

We additionally note, in this regard, that the AD 910 to 990 time period falls very close to the central section of the frequency plot of the time-of-occurrence of the Medieval Warm Period for many of the locations where it has been detected (to date) throughout the entire world, as may be seen from the Interactive Map and Time Domain Plot of our Medieval Warm Period Project, which observation suggests that the climate of the Yucatan Peninsula during that time period likely was also persistently warm. And that "double whammy" of persistent warmth and persistent dryness appears to have been just a bit too much for the Mayans of that trying time to endure.

References
Curtis, J.H., Hodell, D.A. and Brenner, M. 1996. Climate variability on the Yucatan Peninsula (Mexico) during the past 3,500 years, and implications for Maya cultural evolution. Quaternary Research 46: 37-47.

Hodell, D.A., Brenner, M. and Curtis, J.H. 2007. Climate and cultural history of the Northeastern Yucatan Peninsula, Quintana Roo, Mexico. Climatic Change 83: 215-240.

Hodell, D.A., Curtis, J.H. and Brenner, M. 1995. Possible role of climate in the collapse of classic Maya civilization. Nature 375: 391-394.