Global Speleothem Analysis Reveals State‐Dependent Hydrological Response to Orbital Forcing

Tropical and subtropical hydrological systems are important to water resource management. To improve understanding of these dynamical systems, it is useful to probe their relationship with relevant forcings. Historically, insolation is believed to be a major driver of these dynamics, testable using speleothem stable oxygen isotope () records, whose growth regions and precise chronologies enable detailed investigations of tropical/subtropical hydrology. Here we present a systematic analysis of long speleothem records examining the global relationship between and insolation across different timescales and regions. Our analysis reveals that the relationship between speleothem and insolation varies significantly by region, with no latitude, season, or periodicity of insolation bearing global relevance. We demonstrate that, when comparing speleothem to insolation curves, seasonal influence often cannot be distinguished from physical lags without additional constraints from modeling or theory. Most notably, we identify a previously unrecognized asymmetry whereby coherence in the precessional (19–23 kyr) band frequently collapses during glacial periods while maintaining power in the 100 kyr band. This suggests a fundamental reorganization of the hydrological cycle and its response to orbital forcing during glacial periods. Our results indicate that comparing speleothem to single insolation curves oversimplifies the complex relationship between orbital forcing and hydroclimate variability, highlighting our framework's utility for comprehensively exploring these interactions. These findings advance understanding of how mid‐to‐low latitude hydrology responds to external forcing–knowledge that may prove valuable as we face unprecedented ‐driven climate change.