Karst springs in the Main Range of the Crimean Mountains and the Crimean Piedmont show a restricted range of values (δ18O = -10.5 to -8.0 ‰, δ2H = -72 to -58 ‰), somewhat more negative than the weighted mean of meteoric precipitation. This suggests preferential recharge at higher elevations during winter months. Groundwater tapped by boreholes splits in three groups. A first group has isotopic properties similar to those of the springs. The second group shows significantly lower values (δ18O = -13.3 to -12.0 ‰, δ2H = -95 to -82 ‰), suggesting recharge during colder Pleistocene times. The third group has high isotope values (δ18O = -2.5 to +1.0 ‰, δ2H = -24 to -22 ‰); the data points are shifted to the right of the Local Meteoric Water Line, suggesting water-rock exchange processes in the aquifer. These boreholes are located in the Crimean Plains and discharge mineralized (ca. 25 g L-1) thermal (65°C) water from a depth of 1600-1800 m. Groundwater associated with mud volcanoes on the Kerch peninsula have distinct isotope characteristics (δ18O = -1.6 to +9.4 ‰, δ2H = -30 to -18 ‰). Restricted δ2H variability along with variable and high δ18O values suggest water-rock interactions at temperatures exceeding 95 °C.
Keywords: Crimea; groundwater; hydrogen-2; isotope hydrology; oxygen-18; recharge; water–rock interaction.