ALBERT

Description: High-resolution color reflectance records of KC01 and KC01B (Calabrian Ridge, Ionian Sea) are presented and compared with a modified spliced high-resolution color reflectance record of Ocean Drilling Program (ODP) Site 964. This comparison revealed that KC01B is characterized by intensive deformation between ~27 and 28.5 m piston depth and that some sapropels are tectonically reduced in thickness. Moreover, the piston coring has caused considerable stretching in the top of KC01 and KC01B. Using a new splice of ODP Site 964 as guide, previous astronomical tuned timescales of KC01B and ODP Site 964 were evaluated. This evaluation resulted in a new sapropel-based astronomical timescale for the last 1.1 Myr. The new timescale implies a much more uniform change in sedimentation rate for the Ionian Sea cores. Two prominent excursions to lighter values in the d18O record of the planktonic foraminiferal species Globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale. These shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle. They are absent in global ice volume records and are interpreted as reflecting a (summer) low-salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods. All biostratigraphic and magnetostratigraphic events found in KC01B and ODP Site 964 were re-dated according to the new timescale, and the ages of 33 tephra layers were reviewed. The new ages for the Calabrian Ridge 2 and 3 magnetic events in the Brunhes are concordant with minima in the global Sint800 composite record, derived from worldwide deep-sea records of relative paleointensity and have been attributed to the Big Lost and La Palma excursions, respectively.

Description: The evolution of the Solar System has been shown to be chaotic (Laskar, 1990, doi:10.1016/0019-1035(90)90084-M), which limits our ability to retrace the orbital and precessional motion of the Earth over more than 35-50 Myr (Laskar, 1999, doi:10.1098/rsta.1999.0399). Moreover, the precession, obliquity and insolation parameters (Laskar et al., 1993; Quinn et al., 1991) can also be influenced by secular variations in the tidal dissipation and dynamical ellipticity of the Earth induced by glacial cyclicity (Laskar et al., 1993; Dehant et al., 1990, doi:10.1029/JD095iD06p07573; Tushingham et al., 1991, doi:10.1029/90JB01583; Peltier and Jiang, 1994, doi:10.1029/94GL02058; Mitrovica and Forte, 1995, doi:10.1111/j.1365-246X.1995.tb03508.x, Mitrovica et al., 1997, doi:10.1111/j.1365-246X.1997.tb01554.x) and mantle convection (Forte and Mitrovica, 1997, doi:10.1038/37769). Here we determine the average values of these dissipative effects over the past three million years. We have computed the optimal fit between an exceptional palaeoclimate record from the eastern Mediterranean Sea and a model of the astronomical and insolation history3 by testing a number of values for the tidal dissipation and dynamical ellipticity parameters. We find that the combined effects of dynamical ellipticity and tidal dissipation were, on average, significantly lower over the past three million years, compared to their present-day values (determined from artificial satellite data and lunar ranging (Laskar et al., 1993; Quinn et al., 1991; Stephenson and Morrison, 1995). This secular variation associated with the Plio-Pleistocene ice load history has caused an average acceleration in the Earth's rotation over the past 3 Myr, which needs to be considered in the construction of astronomical timescales and in research into the stationarity of phase relations in the ocean-climate system through time.