Phase relations between orbital forcing and climate response in the equatorial Atlantic between 9 and 10 Ma.

Abstract

The reconstruction of phase relations between orbital forcing and climate response in the Miocene is hampered by uncertainties in the values for the tidal dissipation and the dynamical ellipticity, which affect lags and leads calculated from paleoclimatic records. Here we aim to solve this problem by generating high resolution physical property data (magnetic susceptibility and color) and isotope data (δ18O and δ13C) of benthic foraminifera from Ceara Rise in the equatorial Atlantic (ODP Leg 154, Site 926) and using the sapropel bearing Monte dei Corvi section in Italy, for which a direct response can be assumed, to select the proper solution. The precession and obliquity phases of the Ceara Rise data relative to different orbital solutions are determined, and compared with existing younger datasets. Additionally, the effect of changing the tidal dissipation parameter on the phase relations for this time interval is explored. The main conclusions are that the tuning to the La2004(1,1.135) p-.5t maxima or to the La2004(1,1.16) p-.5t maxima gives the most reasonable phase relations for Ceara Rise and that slightly changing the tidal dissipation parameter does not have much effect on the determination of phase relations between 9 to 10 Ma. Also concluded is that the Ceara Rise data lag the Monte dei Corvi data by 57 ± 16 degree at the obliquity band. This lag is probably caused by deep water currents from the southern ocean containing a delayed obliquity signal. Furthermore, it seems that over time the phase between magnetic susceptibility and benthic δ18O remained relatively constant. However, the phase of the magnetic susceptibility as tuning target might have changed.