Drip water δ18O variability in the northeastern Yucatan Peninsula, Mexico: Implications for tropical cyclone detection and rainfall reconstruction from speleothems

This study examines the oxygen isotopic composition (delta O-18 values) of drip water, rainfall, and groundwater in the Rio Secreto cave system, located in the Yucatan Peninsula, Mexico. The main motivation of this study was to determine the impli-cations of drip water hydrology for the reconstruction of rainfall, droughts and tropical cyclone activity from stalagmite delta O-18 records. Monitoring of environmental and isotopic conditions was conducted for two years, from June 2017 to April 2019. This study provides the first instrumental evidence of an amount effect on interannual timescales in the Yucatan Peninsula. Observed bi-weekly to interannual variability in drip water delta O-18 values can be explained for individual drips by different inte-grations of rainfall amount in the time domain. Drip sites in two chambers (Stations A and B) integrate 4-15 months of rain-fall accumulation. In a third chamber (Station LF) one drip site reflects the annual rainfall isotopic cycle with a positive offset and another, the largest rainfall events. During epikarst infiltration, the integration of rainfall amount by drip water source reservoirs determines the degree to which they dilute a tropical cyclone (TC) isotopic signature. TCs can be detected par-ticularly when: (1) the water volume of the reservoir is low, such as during a persistent meteorological drought, and; (2) TCs have a sufficiently distinct isotopic signal relative to that of the reservoir prior to the event. TC isotopic signals can be masked or attenuated when drip water samples integrate more than a week and if significant rainfall events proceed the TC. In Rio Secreto cave, reconstructing precipitation amount and detecting the TC isotopic signatures from stalagmite delta O-18 records is possible. Our analysis shows that stalagmite delta O-18 records are more likely to underestimate the magnitude of annual-scale droughts following normal hydroclimate conditions and more likely to record TCs during multiyear droughts than during normal or wet periods. Drip water monitoring results suggest that available stalagmite delta O-18 records from the Maya lowlands might be underestimating the intensity of paleo-drought events, such as the Terminal Classic droughts associated with the disintegration of the Maya civilization. This study complements the results from Lases-Hernandez et al. (2019) comparing two different sampling protocols of drip water collection. This study shows that a discrete sampling protocol is expected to approximate the amount-weighted isotopic composition of a drip, as long as it is conducted at a temporal resolution higher than the rainfall integration time by the drip reservoir. We highlight the importance of conducting multiyear monitoring of drip water and rainfall in order to interpret stalagmite delta O-18 as a paleoclimate proxy. (C) 2020 Elsevier Ltd. All rights reserved.