Abstract:

A 12-year study (2000–2012) of the stable isotopes of recent fluvial tufas has been performed in the Monasterio de Piedra Natural Park (River Piedra, NE Iberian Peninsula), an area of Mediterranean climate with intense tufa deposition since the Pleistocene. The biannual monitoring of the tufa calcite δ13C and δ18O signatures and of the water δ18O value has demonstrated a clear seasonal pattern for the tufa-calcite oxygen isotope composition, with less negative values for cool periods, which is consistent with regional temperature oscillations. The tufa calcite δ13C values only occasionally exhibit a pattern, which is inconclusive and opposite to the δ18O clear pattern. The water δ18O signature has a distinct seasonal pattern, also opposite to the tufa-calcite δ18O clear pattern. The temperature calculations from the tufa-calcite δ18O values and average water δ18O values agree with the seasonal pattern of measured water temperatures, with a mean difference of 2.3 °C between the calculated and measured temperatures.

The anomalous values recorded for both the water and the tufa-calcite oxygen isotope composition during a two-year period are characterized by smoothing of the seasonal variations of the tufa calcite and by reversal of the water pattern. There is also an increase in the differences between the measured and estimated temperatures. The detected anomaly is roughly synchronous with a change in the isotopic signature of the regional precipitation δ18O values.

This contribution demonstrates that tufas in this depositional and climatic context are good indicators of seasonal temperature oscillations, and that tufas can also record other interannual environmental changes such as variations in the isotopic composition of precipitation. These results can be extrapolated to ancient tufa systems developed in similar contexts, which would expand the potential of tufas as high-resolution records of paleoenvironmental conditions.

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