Description: Research on sediments recovered during Ocean Drilling Leg 160 has concentrated on two issues: the first concerned the stratigraphy of sapropel formation, the second was oriented to clarify specific processes that explain sapropel origin. Progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites. On the composites, initial work has resulted in the establishment of high-resolution and intermediate-resolution stratigraphies for three sites (963, 964, 967); correlation of sedimentary cycles to astronomical (insolation) cycles extends the stratigraphies to Sites 969 and 966. The sapropel occurrences in the marine and land sequences over the entire Eastern Mediterranean are correlated; with the resolution that can be obtained from isotope studies, groups of sapropels occurred simultaneously over the entire basin. In detail, however, the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins. The differences may be related to effects of water depth, diagenesis, and post-depositional tectonic attenuation of sequences. Studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels, caused the enrichment of trace metals associated with sapropels, and helped to preserve primary sedimentary structures. Besides, all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events.

Description: Pliocene core intervals from Ocean Drilling Program Site 1143 located in the southern part of the South China Sea were measured for their major and minor element composition at ~2-k.y. resolution. Changes in sediment composition parallel glacial-interglacial changes as indicated by the corresponding oxygen isotope record of benthic foraminifers. Carbonate contents are lower during glacial stages and higher during interglacial stages. This is attributed to dilution by a higher contribution of terrigenous detrital matter during glacial intervals and to enhanced biological productivity during interglacials as indicated by enrichments in barium. The terrigenous detrital matter fraction shows small but distinct changes in composition. These variations may be explained by multiple processes, including changes in provenance and weathering caused by monsoonal climate variability and sea level fluctuations. Gradual or long-term changes in sediment composition also occur during the investigated interval. There is a shift toward lower TiO2 (carbonate-free basis; cfb) values at around 2.9 Ma and an increase in Al2O3 (cfb) variations at around 2.55 Ma. These changes can be explained in both cases by an increasing contribution from the Mekong River, delivering material with low TiO2 (cfb)/Al2O3 (cfb) ratios, followed by a gradual increase in weathering, causing higher Al2O3 (cfb) (probably reflecting kaolinite) contents. Both may be the result of an enhanced summer monsoon. The manganese and phosphate geochemistry of Site 1143 sediments seem to be strongly dominated by biological productivity and a high burial flux of carbonate, which acts as an adsorbing agent and/or substrate. During strong interglacials and corresponding times of enhanced productivity, Mn may be remobilized from continental margin sediments deposited within an oxygen minimum zone and subsequently exported into the pelagic region, where it oxidizes and settles to form Mn-enriched layers in the sediment.

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.