Composition of ocean suspended matter

Compositions of different types of ocean suspended matter are under consideration.

Isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) of sediment core SO188_342 from the Northern Bay of Bengal for the last 18 ka

The Indian Summer Monsoon (ISM) is a major global climatic phenomenon. Long-term precipitation proxy records of the ISM, however, are often fragmented and discontinuous, impeding an estimation of the magnitude of precipitation variability from the Last Glacial to the present. To improve our understanding of past ISM variability, we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower Ganges-Brahmaputra-Meghna catchment and the Indo-Burman ranges over the last 18,000 years (18 ka). The records derive from a marine sediment core from the northern Bay of Bengal (NBoB), and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the Bengal region. The isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) are compared to results from an isotope-enabled general atmospheric circulation model (IsoCAM) for selected time slices (pre-industrial, mid-Holocene and Heinrich Stadial 1). Comparison of proxy and model results indicate that past changes in the dD of precipitation and plant waxes were mainly driven by the amount effect, and strongly influenced by ISM rainfall. Maximum precipitation is detected for the Early Holocene Climatic Optimum (EHCO; 10.5-6 ka BP), whereas minimum precipitation occurred during the Heinrich Stadial 1 (HS1; 16.9-15.4 ka BP). The IsoCAM model results support the hypothesis of a constant moisture source (i.e. the NBoB) throughout the study period. Relative to the pre-industrial period the model reconstructions show 20% more rain during the mid-Holocene (6 ka BP) and 20% less rain during the Heinrich Stadial 1 (HS1), respectively. A shift from C4-plant dominated ecosystems during the glacial to subsequent C3/C4-mixed ones during the interglacial took place. Vegetation changes were predominantly driven by precipitation variability, as evidenced by the significant correlation between the dD and d13C alkane records. When compared to other records across the ISM domain, precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ISM from the Last Glacial to the present.

Benthic foraminiferal carbon isotopic records and the development of abyssal circulation at DSDP Sites 9-77, 12-119, 30-289, 82-563 and 94-608

The North Atlantic at present is ventilated by overflow of the Denmark Strait, Iceland-Faeroe Ridge, Faeroe Bank Channel, and Wyville-Thompson Ridge. The evolution of Cenozoic abyssal circulation of this region was related to tectonic opening and subsidence of these sills. We used d13C records of the benthic foraminifer Cibicidoides to decipher the timing of tectonically controlled changes in bottom-water circulation in the eastern basins (Biscay and Iberian) of the northern North Atlantic. Records from Site 608 (Kings Trough, northeastern North Atlantic) show that from about 24 to 15 Ma (early to early middle Miocene), d13C values in the Kings Trough area were depleted relative to western North Atlantic values and were more similar to Pacific d13C values. This reflects less ventilation of the Kings Trough region as compared to the well-oxygenated western North Atlantic. Comparison of Oligocene d13C records from Site 119 (Bay of Biscay) with western North Atlantic records suggests that the eastern basin was also relatively isolated prior to 24 Ma. At about 15 Ma, d13C values at Site 608 attained values similar to the western North Atlantic, indicating increased eastern basin ventilation in the middle Miocene. This increased advection into the eastern basin predated a major d18O increase which occurred at about 14.6 Ma. Subsidence estimates of the Greenland-Scotland Ridge indicate that the deepening of the Iceland-Faeroe Ridge was coincident with the marked change in eastern basin deep-water ventilation.

Paleomagnetism of DSDP Leg 80 holes

Paleomagnetic results from sediments acquired from the continental margin at DSDP Sites 548, 549, 550, and 551 are described. Where possible, the results were used to construct a polarity reversal stratigraphy for the sections sampled, thus enabling the biostratigraphic dating of the sediments to be refined. Several sections in this study were found to be suitable for magnetostratigraphic work, in particular the upper Paleocene to middle Eocene sediments from Site 549, which contained rich faunal assemblages. These sediments are underlain by a thick sequence of Cretaceous sediments that formed during the Long Cretaceous normal polarity interval. Sediments that formed during the later part of this magnetically quiet interval were also recovered at Site 550. Three short reverse polarity intervals were also recovered at this site; they lie directly over basement and are thought to represent a mixed-polarity interval of late Albian age. They may therefore provide important evidence concerning the age of the earliest sediments at this site. In addition, measurements of the magnetic susceptibility and intensity of remanent magnetism proved to be of interest. A significant decrease in the susceptibility and intensity values close to the early/middle Eocene boundary was noted at Sites 548 and 549. This decrease may be correlated with the results from Holes 400A and 401, which were drilled on DSDP Leg 48 in the northeast Bay of Biscay. The decrease may represent an abrupt reduction in the supply of terrigenous material at the end of the early Eocene, reflecting, perhaps, a change in sediment transport processes at that time