Discerning the interactions between environmental parameters reflected in δ13C and δ18O of recent fluvial tufas: Lessons from a Mediterranean climate region

• Recent tufa δ18O reveal seasonal and decadal climate changes in NE Iberia.
• δ18O calcite-derived Tw fit regional and local air temperature trends through time.
• Calculated Tw can be biased by discharge and rainfall isotopic composition changes.
• δ13C calcite reflects both exceptional discharge events and in-aquifer recharge.
• Together, this is relevant to climate inferences from isotopes in carbonate records.

δ13C and δ18O of recent, continuous tufa records, obtained during a monitoring period spanning 3 to 13 years, are compared with the corresponding, known environmental conditions. Three rivers in NE Iberia (located along a 200-km N–S transect) are used for this comparison. The isotopic variations through space and time are discussed in terms of the environmental and geological parameters that operate on different scales, focusing on discerning the interactions between these parameters and providing examples of possible misinterpretation of climatic conditions, which is important to past climate studies based on isotopic data.The calculation of the actual isotopic fractionation coefficients, and the comparison with the literature-derived coefficients, demonstrates that the studied tufa formation was close to isotopic equilibrium to reflect the water temperature. The difference between mean measured water temperature (Tw) and mean calculated Tw (based on δ18Ocalcite and measured δ18Owater) is less than 2.7 °C. Tendencies of these calculated Tw are similar to the regional air temperature (Tair) tendencies through time, in particular in the case of the 13-year record, although certain deviations exist over shorter time spans. The best agreement between measured and calculated Tw and between δ18Ocalcite-based Tw tendencies and Tair tendencies corresponds to the tufa stromatolite facies.Differences between the δ18Ocalcite records of the three rivers cannot be attributed to temperature changes, but to the varying influences of groundwater inputs and isotopic rainfall composition in each river. Without considering these parameters, δ18Ocalcite-based Tw calculations yield inaccurate results when comparing the study sites.δ13Ccalcite values do not exhibit distinct patterns over time, and δ13Ccalcite variations are likely caused by local processes that do not reflect general environmental changes.These findings underscore the significance of accounting for both groundwater behaviour and rainfall stable isotope composition when interpreting climate parameters in carbonate systems, particularly when differences between the isotopic signatures of deposits exist in the same region.