Intraseasonal Hydroclimate Variability in the Yucatán Peninsula During the Maya Terminal Classic Period: A Proxy Record of Paleo-MJO?

Waves in the tropical atmosphere modulate rainfall and water vapor at the intraseasonal scale, including equatorial Rossby waves, Kelvin waves, and tropical disturbances organized by the planetary-scale Madden-Julien Oscillation (MJO). The MJO's regions of enhanced and suppressed convection travel slowly eastward, resulting in a characteristic 30-60 day rainfall cycle at tropical sites. The MJO's pace and intensity vary over time and by location, influencing monsoons, El Niño-Southern Oscillation (ENSO) events, and tropical cyclone genesis/intensification. MJO-induced teleconnections influence extratropical weather anomalies, i.e. as atmospheric rivers. Despite forecast challenges, modeling studies indicate MJO sensitivity to anthropogenic climate forcing.

Records of pre-instrumental MJO behavior would contribute to assessment of tropical paleoclimate and hydroclimate sensitivity to climate forcing factors. Paleoclimate records of intraseasonal variability was prevented due to the relatively fast pace of MJO vs. proxy resolution. We report a possible late Holocene paleo-MJO signal in a ~weekly stalagmite oxygen isotope (δ¹⁸O value) record from Cueva Tzabnah, Yucatán, Mexico.

We re-sampled a well-studied stalagmite Chaac across the Maya Terminal Classic Period (c. 800-950 C.E.) and instrumental era. With continuous micromilling at 6.5 µm spacing and stable isotope analysis (Kiel IV+MAT253), we reached ~50 samples/year. The Chaac record reveals expected interannual-decadal hydroclimate signals and better resolves short-term variability. A recurrent pattern of δ¹⁸O value oscillations over about 4-12 samples (representing approx. 1-3 months). The amplitude of these intraseasonal-scale oscillations is around 0.3 - 0.5‰, smaller than annual/interannual variations. The intraseasonal pattern varies in amplitude, clarity, and frequency over time, similar to the modern MJO.

Intraseasonal oscillations in Chaac most likely reflect local intraseasonal hydroclimate variability during the Maya Terminal Classic Period. Because this scale of rainfall variations is driven primarily by the MJO, we are investigating this pattern as a possible paleo-MJO record. We will present the new Chaac record and wavelet analysis results, with discussion including regional cave dripwater data.