Transmission of Hydrogen and Oxygen Isotopic Variability from Precipitation to Dripwater at Rio Secreto Cave in the Yucatan Peninsula: Implications for Speleothem Rainfall Reconstruction.
Abstract
The interpretation of stalagmite δ18O records from tropical regions requires an understanding of the time integration of rainfall amount and its isotopic composition by drip waters that form stalagmites. This study presents oxygen (δ18O) and hydrogen (δD) isotopic results from over 1200 groundwater, rainfall and drip water samples, collected at weekly time intervals, over three hydrological years at Rio Secreto Cave, in the Yucatan Peninsula, Mexico. Cave environment and drip isotopic composition were monitored in three chambers with different degrees of air ventilation, along with temperature and relative humidity conditions at the surface. We examined 16 drips and observed annual δD and δ18O variability reflects the isotopic variability of rainfall. The observed drip water annual isotopic amplitude represents 5 to 95% that of rainfall, reflecting epikarst water reservoir size and complexity of flow paths. Drips that closely reflect the isotopic variability of rainfall and therefore best preserve the isotopic signal of individual rainfall events are observed, but uncommon: only 2 drips out of 16 were found to have potential to record rainfall isotopic shifts associated with tropical cyclones if sampled at weekly resolution. The relationship between δD and δ18O in drip water suggests the recharge is biased toward the rainy season (June to November) which represents up to 80% of total annual precipitation. We find that over the course of a year most drips reflect the δ18O composition of rainfall, in support of quantitative precipitation records from stalagmite δ18O values. We find evidence that stalagmite δ18O variability almost never represents seasonal rainfall isotopic variability because of isotopic inertia associated with each unique drip water reservoir. Isotopic inertia associated with most drips, furthermore, would result in stalagmite d18O records to underestimate the magnitude of a drought during year one, and to record a multiyear drought with a delay of at least one year. Lastly, we provide evidence that the effective recharge in this cave system is controlled by precipitation amount and not limited to the months when precipitation exceeds evaporation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP12B..06L
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 1041 Stable isotope geochemistry;
- GEOCHEMISTRYDE: 1655 Water cycles;
- GLOBAL CHANGEDE: 1833 Hydroclimatology;
- HYDROLOGY