Implementing a cave and climate monitoring system across the Swabian Alb, southwestern Germany

Monitoring studies of cave systems are essential for understanding the hydrological and microclimatic processes that control the isotopic signatures preserved in speleothems and for improving the interpretation of paleoclimate records. Despite increasing efforts in recent years, many aspects of karst system responses to climate variability and change remain poorly constrained.

In 2023, a comprehensive cave and climate monitoring network was established across the Swabian Alb (N 48°30'60''; E 9°24'15''), a karstic region in southwestern Germany, covering both the Neckar and Danube catchments. Four caves were chosen for a monitoring infrastructure based on their location and accessibility: Bärenhöhle, Nebelhöhle, Schertelshöhle, and Hohle Fels. Continuous measurements of relative humidity, temperature and water dripping rates were conducted inside the caves. Measurements of cave air CO₂ concentrations and dripping water samples were taken during periodic site visits. Dripping and spring water samples were analyzed for triple oxygen (δ¹⁸O and δ¹⁷O) and hydrogen (δD). External climate monitoring included temperature and precipitation measurements, as well as the isotopic analysis of rainfall and the calculation of δ¹⁷O-excess and δD-excess from rainwater collected at multiple locations on and around the Swabian Alb.

Preliminary results from the first year of monitoring indicate: (1) seasonal fluctuations in the concentration of CO₂ in cave air due to winter ventilation and cave-air stagnation in summer, indicative of buoyancy-driven airflow between the surface and the cave; (2) a uniform air moisture source feeding the rainfall over the Swabian Alb; (3) caves and springs appear to be decoupled from short-term weather signals, implying integration over longer-term climatic conditions; and (4) the isotopic composition of rainwater seems to be related to the rainfall amount and temperature at the monitoring sites. By combining multiple-site and cave monitoring at different elevations and two basins of the Swabian Alb, this study provides new insights into the environmental factors controlling the isotopic signal and airflow dynamics in caves. These findings are essential for improving the interpretation of speleothem-based climate proxies and the sensitivity of karst systems to ongoing future climate change.