| Summary: | The cave of Wintimdouine, located in a semi-arid context in Morocco, comprises the longest-known underground river in Africa. This cave system faces many challenges related to anthropogenic and climate forcing. Therefore, it has become necessary to understand the functioning of the aquifer system of Wintimdouine and how the regional climate affects its environment. Herein, we used different approaches based on a 4-year monitoring to shed light on the hydro-chemical behavior and stable isotopes contents of water samples, climate settings inside the cave, and moisture trajectory analyses. Chemical analyses show that groundwater is dominated by bicarbonate and calcite with an excellent chemical quality of cave water, suggesting an active recharge of the aquifer system which constitutes the main drinking source in the region. The stable isotope composition is consistent among rainwater, cave water and groundwater samples outside the cave. The evaporation effect is not significant, probably due to the rapid infiltration of surface water to the epikarst and vadose zone, which is favored by the abundance of exo-karstic forms above the cave. The cave monitoring indicates that periods of increased drip water flow induce an increase of temperature and humidity inside the cave, mainly during the spring-summer season. The high relative humidity and the relatively stable temperature favor the carbonate deposition under equilibrium conditions with drip water inside the cave. Furthermore, the moisture trajectory analysis confirms that the predominant air masses reach Wintimdouine cave from the North Atlantic Ocean, consistent with the mean deuterium-excess value of rainwater samples and the NAO-related westerly winds. Hence, we highlight the potential of Wintimdouine speleothem delta O-18 as a proxy of past climate variability at a regional scale.
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