Wavelet analysis of δ18O and δ13C time-series from an Holocene speleothem record from Corchia Cave (central Italy): insights for the recurrence of dry-wet periods in the Central Mediterranean

Andrea Tognarelli (1), Giovanni Zanchetta (1,2), Eleonora Regattieri (1,3), Ilaria Isola (2), Russell N. Drysdale (5,6), Monica Bini (1,2) & John C. Hellstrom (7)
(1) Dipartimento di Scienze della Terra, University of Pisa, Via S. Maria 53, 56126, Pisa, Italy. (2) Istituto Nazionale Geofisica e Vulcanologia, Via della Faggiola, 56126, Pisa, Italy. (3) Istituto di Geoscienze e Georisorse, CNR, Via Moruzzi 1, 56126 Pisa, Italy. (4) School of Geography, University of Melbourne, Victoria, Australia. (5) Université de Savoie, Laboratoire EDYTEM, Pôle Montagne, Le Bourget du Lac, France. (6) School of Earth Sciences, University of Melbourne, Australia Corresponding author e-mail: andrea.tognarelli@unipi.it.

In this work, the continuous wavelet transform (CWT) is used to analyse stable isotope (δ18O and δ13C) time-series from a speleothem from Corchia Cave (Apuan Alps, Tuscany, central Italy). The record spans the ca. 13.3- 0.4 ka period. Both proxies are thought to represent changes in the amount of precipitation and in the hydrological recharge over the cave catchment, and to indicate alternating wetter and drier periods. The CWT shows the presence of different dominant frequency components, changing across the Middle-Holocene. This can be interpreted as mostly related to long term variations in summer and winter insolation, resulting from changes in orbital parameters. The lower frequencies (millennial scale) individuated may have different origin, not always obvious, and are rarely reported in others records. Instead, the short period components (multidecadal to centennial scale) could be in the range of frequencies considered as expression of the solar variability. δ18O and δ13C time-series show very coherent response to lower frequencies, but δ18O time-series show the presence of higher frequencies, that are not reported in the δ13C record. This can be related to a different response of the soil-karst system compared to variability in the δ18O of precipitation and their recharge of the karst. A Matlab® code has been implemented to compute the wavelet transform and to generate all the results presented in this work.

continuous wavelet transform analyses, speleothems, Mediterranean, stable isotopes, Holocene.