Wavelet analysis of delta18O and delta13C time-series from an Holocene speleothem record from Corchia Cave [central Italy]: insights for the recurrence of dry-wet periods in the Central Mediterranean

In this work, the continuous wavelet transform [CWT] is used to analyse stable isotope [delta 18O and delta 13C] 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. delta 18O and delta 13C time-series show very coherent response to lower frequencies, but delta 18O time-series show the presence of higher frequencies, that are not reported in the delta 13C record. This can be related to a different response of the soil-karst system compared to variability in the delta 18O of precipitation and their recharge of the karst. A Matlab® code has been implemented to compute the wavelet trans form and to generate all the results presented in this work.