Dating a tropical ice core by time–frequency analysis of ion concentration depth profiles

Michel Gay 1, 2 M De Angelis 3 Jean-Louis Lacoume 2
1 GIPSA-Services - GIPSA-Services
GIPSA-lab - Grenoble Images Parole Signal Automatique
2 GIPSA-SIGMAPHY - SIGMAPHY
GIPSA-DIS - Département Images et Signal
Abstract : Ice core dating is a key parameter for the inter-pretation of the ice archives. However, the relationship be-tween ice depth and ice age generally cannot be easily es-tablished and requires the combination of numerous investi-gations and/or modelling efforts. This paper presents a new approach to ice core dating based on time–frequency anal-ysis of chemical profiles at a site where seasonal patterns may be significantly distorted by sporadic events of regional importance, specifically at the summit area of Nevado Illi-mani (6350 m a.s.l.), located in the eastern Bolivian Andes (16 37 0 S, 67 46 0 W). We used ion concentration depth pro-files collected along a 100 m deep ice core. The results of Fourier time–frequency and wavelet transforms were first compared. Both methods were applied to a nitrate concentra-tion depth profile. The resulting chronologies were checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points. With this first experiment, we demonstrated the effi-ciency of Fourier time–frequency analysis when tracking the nitrate natural variability. In addition, we were able to show spectrum aliasing due to under-sampling below 70 m. In this article, we propose a method of de-aliasing which signifi-cantly improves the core dating in comparison with annual layer manual counting. Fourier time–frequency analysis was applied to concentration depth profiles of seven other ions, providing information on the suitability of each of them for the dating of tropical Andean ice cores.
Keywords : Signal Datation Ice core
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Michel Gay, M De Angelis, Jean-Louis Lacoume. Dating a tropical ice core by time–frequency analysis of ion concentration depth profiles. Climate of the Past Discussions, European Geosciences Union (EGU), 2014, 10, pp.1 - 15. <10.5194/cp-10-1-2014>. <hal-01118398>

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