Mid- to Late-Holocene Mediterranean climate variability: Contribution of multi-proxy and multi-sequence comparison using wavelet analysis in the northwestern Mediterranean basin

Abstract

Forcings and mechanisms underlying Holocene climate variability still remain poorly. This work review already published paleoclimatic time series and proposes an alternative way to compare them using spectral analysis. Such an approach may emphasize joint features between different signals and lead us closer to the causes of climate changes. Ten paleoclimatic proxy records from 5 sequences from the Gulf of Lions and surrounding areas were compiled. These paleoclimate time-series were supplemented with proxies of the North Atlantic Oscillations (NAO), El Niño-Southern Oscillations (ENSO) and the Intertropical Convergence Zone (ITCZ) variability. A comparison of their frequency content is proposed using wavelet analysis for unevenly sampled time series. A new algorithm is used in order to propagate the age model errors within wavelet power spectra. Three main groups of shared features specific to the Mid- and Late Holocene (after 7000 yrs cal BP) can be defined on the basis of the results of these analyses, an Atlantic cyclic period, solar cyclic periods and tropical cyclic periods. The Atlantic cyclic period is probably related to fluctuations of the Atlantic thermohaline circulation which would induce changes in the storm track extension and position thereby impacting upon precipitation and storminess over a millennial scale. The centennial scale solar variability might induce a NAO-like variability of the atmospheric circulation thereby influencing storminess in Western Europe and Mediterranean. Finally, tropical cyclic periods are possibly registered in of the Gulf of Lions and Atlantic climate proxies, potentially highlighting the influence of ENSO variability over the western Mediterranean.