Quasi - Continuous growth of speleothems on the Yucatan Peninsula and possible drought modulated hiatuses

The timing of drought occurrence on the Yucatán Peninsula has been a central focus of research linking Maya cultural evolution to regional hydroclimatic variability over the past several millennia. Climate proxy records that span periods of cultural decline and political instability are particularly valuable for constraining potential causal relationships. Numerous studies have proposed such links, most recently supported by sub-annual drought reconstructions (James et al. 2025, Science Advances). However, the precise and accurate determination of absolute ages for drought events and drought-related growth hiatuses remains a major challenge.

Advances in radiometric dating of speleothems, including ²³⁰Th/U and ¹⁴C methods, as well as independent stratigraphic approaches such as visual laminae counting and geochemical or isotopic proxy cycles, have substantially improved chronological resolution over the past decade. Nonetheless, combining independent dating techniques introduces important pitfalls related to systematic uncertainties. Corrections for initial ²³⁰Th can substantially degrade age accuracy, as they rely on the assumption of a single, well-characterized source rarely constrained by multiple measurements (e.g., isochrons). These corrections introduce systematic uncertainties that may exceed those associated with individual layer counts by up to two orders of magnitude. Conversely, layer counting alone provides absolute age control only when robust anchor points are available or when records are demonstrably continuous, and it requires independent constraints to interpret proxy-derived periodicities.

Here, we compile and assess available speleothem ²³⁰Th/U data from the Yucatán Peninsula to (i) evaluate the impact of variable initial ²³⁰Th on chronological precision and accuracy, (ii) identify pitfalls associated with combining radiometric dating and annual layer counting, and (iii) demonstrate quasi-continuous speleothem growth across the region over the past 3000 years. Our analysis reveals substantial geochemical variability in initial ²³⁰Th concentrations in drip waters from different cave systems, indicating a strong potential for underestimated systematic uncertainties, particularly at the onset of discontinuous chronologies. While annual layer counting based on geochemical proxies independent of water isotopic composition or vegetation changes can significantly reduce relative age uncertainties, systematic errors persist and require careful evaluation. Using more than 20 speleothem chronologies, we further document the frequency and regional coherence of growth hiatuses and their changes across the Terminal Classic Period. Integrating chronological data with soil-sensitive tracers allows assessment of critical thresholds in soil CO₂ concentration, drip-water availability, cave–drip water CO₂ gradients, and carbonate oversaturation.

Overall, our results highlight that accurately constraining drought timing from speleothem records remains challenging, underscoring the need for rigorous methodological integration and transparent quantification of systematic uncertainties.