Abstract This study examines the oxygen isotopic composition (δ18O 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 implications of drip water hydrology for the reconstruction of rainfall, droughts and tropical cyclone activity from stalagmite δ18O 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 δ18O values can be explained for individual drips by different integrations of rainfall amount in the time domain. Drip sites in two chambers (Stations A and B) integrate 4 to 15 months of rainfall 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 particularly 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 δ18O records is possible. Our analysis shows that stalagmite δ18O 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 δ18O 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 δ18O as a paleoclimate proxy.

中文翻译：

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墨西哥尤卡坦半岛东北部的滴水 δ18O 变异性：对热带气旋探测和洞穴重建降雨的影响

摘要 本研究检测了位于墨西哥尤卡坦半岛的 Rio Secreto 洞穴系统中滴水、降雨和地下水的氧同位素组成（δ18O 值）。本研究的主要动机是确定滴水水文对从石笋 δ18O 记录重建降雨、干旱和热带气旋活动的影响。从 2017 年 6 月到 2019 年 4 月，对环境和同位素条件进行了两年的监测。这项研究提供了尤卡坦半岛年际时间尺度上“数量效应”的第一个工具证据。每两周观察到的滴水 δ18O 值的年际变化可以通过时域中降雨量的不同积分来解释单个滴水。两个房间（A 站和 B 站）的滴水点整合了 4 到 15 个月的降雨积累。在第三个室（LF 站）中，一个滴水点反映了年降雨同位素循环，具有正偏移，另一个反映了最大的降雨事件。在表层岩溶下渗过程中，滴水源水库对降雨量的整合决定了它们“稀释”热带气旋 (TC) 同位素特征的程度。特别是在以下情况下可以检测到 TC： (1) 水库水量低，例如在持续的气象干旱期间，以及；(2) 相对于事件发生前的储层，TC 具有足够明显的同位素信号。当滴水样本积分超过一周并且如果有明显的降雨事件发生时，TC 同位素信号可能会被掩盖或减弱。在 Rio Secreto 洞穴中，从石笋δ18O记录重建降水量和检测TC同位素特征是可能的。我们的分析表明，石笋 δ18O 记录更可能低估正常水文气候条件下年度尺度干旱的程度，并且在多年干旱期间比正常或潮湿时期更可能记录 TC。滴水监测结果表明，来自玛雅低地的可用石笋 δ18O 记录可能低估了古干旱事件的强度，例如与玛雅文明解体相关的终末经典干旱。这项研究补充了 Lases-Hernandez 等人的结果。(2019) 比较两种不同的滴水收集采样方案。这项研究表明，离散采样协议有望近似于滴水的数量加权同位素组成，只要它以高于滴水蓄水池降雨积分时间的时间分辨率进行。我们强调了对滴水和降雨进行多年监测的重要性，以便将石笋 δ18O 解释为古气候代理。