Recherche et interprétation climatique des microcycles du concrétionnement travertineux de l'aqueduc romain de Fréjus (Var, France)

• Published in: Quaternaire
• Main Author: Dubar, Michel
• Format: Article in Journal/Newspaper
• Language: French
• Published: Association française pour l’étude du quaternaire 2009
• Subjects: aqueduc; climat; hydrologie; microcycles; Oscillation Nord-Atlantique; période antique; spéléothèmes; Antiquity; aqueduct; climate; hydrology; North Atlantic Oscillation; speleothems; Doublets; North Atlantic; North Atlantic oscillation
• Online Access: http://journals.openedition.org/quaternaire/800

The drain of the ancient aqueduct of Fréjus is in part clogged by a laminated travertine concretion. The hydrology of the springs indicates that the lamination is seasonal and that the dark lamina doublet is annual. 102 doublets have been recorded. With the aim of deciphering possible climatic microcycles, a specific spectral analysis was applied to the chronological series of the thickness of laminae.The various spectrograms obtained revealed a high frequency robust peak at 7.1-7.3 years and a low frequency peak at 39-43 years. Such bipartition of frequencies characterizes the NAO which dominated the climate of Western Europe. As the two modes we present in the studied series, it is possible to infer that the mode of oscillation is not strictly determined. When using a Gaussian filter at 7.3 years, as was to be expected, a low frequency modulation was highlighted at 50+/-3 years. The considered period of 102 years which extended on the basis of the archaeological data from the mid-Ist century to the mid-IInd century, seems to offer alternative phases of active ONA with phases of less active ONA. It may be described as moderately wet with alternative dryer-colder phases. These results which demonstrate the quality and accuracy of the climatic records in laminated travertines lead us to project other future applications in earlier Holocene series. La canalisation de l’aqueduc antique de Fréjus est en partie colmatée par un concrétionnement travertineux laminé. L’hydrologie des sources montre que la lamination est saisonnière et que le doublet lamine claire-lamine sombre est annuel. Il y a 102 doublets. Dans le but de décrypter les éventuels microcycles climatiques, une analyse spectrale spécifique est appliquée sur la série chronologique de l’épaisseur des lamines.Les différents spectrogrammes obtenus font essentiellement apparaître un pic robuste de haute fréquence à 7,1-7,3 ans et un pic basse fréquence à 39-43 ans. Cette bipartition des fréquences caractérise l’ONA dont le rôle est prépondérant en Europe ...