Objective: Here we propose to establish a refined astronomical-tuned time scale for the Neogene and late Paleogene by constraining exact values of dynamical ellipticity (ED) and tidal dissipation (TD) in the astronomical solution. The time scale will directly be applied to determine correct phase relations between astronomical forcing and climate response.
Background: The tuning of especially the late Neogene is well established and will not undergo significant changes anymore. However, this time scale still need to be fine-tuned by constraining the dynamical ellipticity (ED) and tidal dissipation (TD) values in the astronomical solution; both these parameters have a direct effect on precession and obliquity, and changing them will result in different astronomical (insolation) curves and, as a consequence, in different phase relations with the orbital parameters. Unfortunately the exact values cannot be calculated directly from the solution itself but have to come from a thorough comparison with the cyclostratigraphic record. The determination of these values is crucial if one aims to unravel phase relations between astronomical forcing and climate response.
Research strategy and methodology: High-resolution quantitative records (color, magnetic susceptibility, XRF and stable isotopes) of selected sites from ODP leg 154 in the equatorial Atlantic (925, 926 and 928) and ODP leg 199 in the equatorial Pacific (1218), and land-based sections in the Mediterranean (Tremiti, Monte dei Corvi) will be compared in detail with astronomical (insolation) target curves. These curves will be generated by modifying ED and TD values in the astronomical solution. Statistical methods to determine ED and TD values include (moving) cross-spectral and optimal fit (regression) analyses.
Feasibility: Previous studies have shown that deep marine sedimentary archives of ODP leg 154 and the Mediterranean are particularly suitable to accurately determine the values of dynamical ellipticity and tidal dissipation for the entire Neogene but the intervals studied were either to young or suffered from stratigraphic complications (Lourens et al., 2001; Pälike et al., 2000). At a later stage the approach will be extended to cover the entire Oligocene using similarly tuned records from ODP site 1218 in the equatorial Pacific (Pälike et al., 2006).
Innovative aspects and relevance: It will be for the first time that a refined Neogene astronomical time scale is established that will be used to determine the exact phase relations between astronomical forcing and climate response during the entire Neogene and possibly the Oligocene in the same way as has been done for the late Pleistocene.
Link with other projects: This project is directly linked to projects I.2 and I.3 because its other purpose is to confirm and where possible refine the astronomical time scale on which they rely on. It is also closely linked to the fundamental aspects of the tools project IV.1