CAT-scan analysis of sedimentary sequences: An ultrahigh-resolution paleoclimatic tool

Paleoclimate research is essential to determine the natural variability of climate and to place the current climate change into its natural context. The current need is to generate the highest temporal resolution paleoclimatic reconstructions possible in order to assess the natural variability of the climate system, but also to test the ability of numerical models to simulate conditions different from the ones observed with the relatively short instrumental records. In this paper, we show that CAT-scan analysis of sedimentary sequences, with its 1 mm downcore resolution, can be used to identify millennial to seasonal cycles in sedimentary sequences. In examples from the St. Lawrence Estuary, Eastern Canada, spectral analysis of the CAT-scan data from Holocene postglacial sediments revealed millennial- to centennial-scale oscillations possibly associated with either solar variability, changes in relative sea-level or tidal amplitude. Similarly, spectral analysis of Holocene and Sangamonian glaciomarine sequences revealed decadal- to annual-scale oscillations with periods close to the one previously associated with the North Atlantic Oscillation (NAO), whereas spectral analysis of the CAT-scan data from the Sangamonian rhythmites possibly revealed seasonal cycles.