Description: A sediment core, collected from the western part of the continental slope of the Ross Sea at 2380 m water depth, records events of the last two climatic cycles (250 kyr). A Full-size image (〈1 K)-based chronology was obtained and boundaries of the isotope stages were set assuming that biological productivity was enhanced during periods of less ice cover. Then, Full-size image (〈1 K), organic carbon, biogenic silica and biogenic Ba distributions were compared to the glacial–interglacial stage boundaries and corresponding ages of the Full-size image (〈1 K) record of Martinson et al. [Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C., Jr., Shackleton, N.J, 1987. Age dating and the orbital theory of the ice ages: development of a high-resolution 0 to 300,000-year chronostratigraphy. Quaternary Research, 27: 1–29]. Sediment accumulation rates ranged between 1.2 cm kyr−1 in the isotope stage 6 and 3.8 cm kyr−1 during the Holocene. Variations in the concentrations and fluxes of organic carbon, biogenic Ba, biogenic silica and Mn gave information on palaeoclimate changes. Processes of sediment redistribution in the Ross Sea margin were enlightened from a comparison of the measured and expected fluxes of Full-size image (〈1 K). Calculation of the focusing-corrected accumulation rates of biogenic Ba enabled us to evaluate the export palaeoproductivity. Corrected accumulation rates of biogenic components and calculated palaeoproductivities were low, compared to the Antarctic Polar Front in the Atlantic sector, throughout the last two climatic cycles. Glacial–interglacial changes of sea ice cover and ventilation of the Ross Sea were probably major causes of variations in biogenic particle flux and distribution of redox-sensitive elements within the sediment column.

Description: Surface exposure dating requires the knowledge of cosmogenic nuclide production rates. When determining time-integrated production rates the exposure ages of the calibration samples need to be accurately known. The landslide of Köfels (Austria) is very well suited for this purpose. It is the largest landslide in the crystalline Alps of Austria dating back to 7800±100 years BC (AMS 14C dating of buried wood), which is well within the 14C dendro calibration curve. Exposed quartz veins were sampled from the tops of large boulders from the toe of the landslide for analysis of 10Be and 26Al. To calculate sea level, high geomagnetic latitude (≥60°), open sky radionuclide production rates, corrections were applied for altitude and latitude, for shielding by surrounding mountains, for sample geometry, vegetation and snow cover, and for sample thickness. The production rates for an exposure age of 10,000 years are 5.75±0.24 10Be atoms/yr g SiO2 and 37.4±1.9 26Al atoms/yr g SiO2. A 26Al/10Be ratio of 6.52±0.43 can be calculated. The influence of the geomagnetic field on these production rates has been estimated using two different geomagnetic field records. Our production rates should be a good approximation for the use of surface exposure dating between about 5000 and 13,000 years BP.

Description: Two ferromanganese crusts from the Indian Ocean and one from the Atlantic Ocean have been analysed for 10Be/9Be, 143Nd/144Nd and 208,207,206Pb/204Pb ratios as a function of depth beneath their growth surfaces. 10Be/9Be ratios provide growth rate estimates for these crusts between 1.55 and 2.82 mm Ma−1 and further suggest that 87Sr/86Sr in crusts do not in any case examined so far provide reliable estimates for growth rates. A crust ALV-539 from 35°N in the western N. Atlantic has ϵNd and Pb-isotope variations indistinguishable from crust BM-1969.05 from 39°N in the N. Atlantic [K.W. Burton, H.-F. Ling, R.K. O'Nions, Closure of the central American isthmus and its impact on North Atlantic deepwater circulation, Nature (London) 386 (1997) 382–385] when 10Be/10Be ratios are used to estimate growth rates. Both crusts provide evidence for a marked change in deepwater composition in the western N. Atlantic with a reduction in ϵNd and an increase in 206Pb/204Pb from ∼8 Ma ago towards the present day. The two crusts from the Indian Ocean show comparatively small variations in ϵNd between −8.0 and −7.0 over the last 20 Ma and do not show the large shift in ϵNd seen in the Atlantic crusts. Comparison of ϵNd in the crusts analysed here with those published previously [H.-F. Ling, K.W. Burton, R.K. O'Nions, B.S. Kamber, F. von Blanckenburg, A.J. Gibb, J.R. Hein, Evolution of Nd and Pb isotopes in central Pacific seawater from ferromanganese crusts, Earth Planet. Sci. Lett. 146 (1997) 1–12; K.W. Burton, H-F. Ling, R.K. O'Nions, Closure of the central American isthmus and its impact on North Atlantic deepwater circulation, Nature (London) 386 (1997) 382–385] shows that provinciality in the present-day ϵNd structure of the Pacific, Atlantic and Indian Oceans has been maintained over ∼20 Ma or more despite the palaeogeographic changes that have occurred within this period. These include the closure of the Panama gateway and the uplift of the Himalayas. Superimposed on this broad inter-ocean structure are changes in ϵNd of the western N. Atlantic which may relate to the Panama gateway closure and shifts in the ϵNd of equatorial Pacific deepwater from 3–5 Ma ago. The absence of any such structure in ϵNd of the southwest and central Indian Ocean suggests that Himalayan erosion products such as preserved in the Bengal Fan sediments have not contributed significantly to Indian Ocean deepwater over the last 20 Ma. There is no straightforward relationship between records of 87Sr/86Sr in the global ocean and ϵNd in ocean deepwater as would be expected if inputs of radiogenic Sr and unradiogenic Nd were coupled.

Description: The sediments recovered on ODP Leg 104 have been reported to be characterized by hiatuses. The hiatuses were defined by biostratigraphy and were believed to be caused by erosion related to temporary changes of bottom current composition and velocity. They have been associated with major paleoenvironmental changes, reorganization of global deep water production, and increased bottom water flows. Because of the importance of hiatuses for ongoing research, we decided to closely investigate the sedimentation history for the most significant Pliocene and Miocene biostratigraphic hiatuses by sedimentologic and geochemical means. The sedimentologic studies include clay mineral distributions, grain size data, and organic carbon concentrations. The geochemical studies include determination of Full-size image (〈1 K)Sr ratios, 10Be and Ir concentrations. The results of the sedimentologic studies suggest either that paleoenvironmental changes associated with hiatuses are not represented in the preserved sediments, or that the hiatuses are an artifact of interpretation of the biostratigraphic data. Strontium isotopes indicate continuous sedimentation for the interval investigated at Site 642, an interpretation confirmed by the steady decline in 10Be. Full-size image (〈1 K)Sr ratios in the interval from above and below proposed hiatuses H Full-size image (〈1 K) and Full-size image (〈1 K) at Site 643 display stronger changes with depth than expected by steady sedimentation. Ir data for this same interval indicate reduced sedimentation rates. Combining both, sedimentologic and geochemical evidence, the proposed hiatuses could not be confirmed and may represent preservation artifacts.

Description: A new generation multiple collector plasma source mass spectrometer (PSMS) produced by Nu Instruments Ltd is evaluated. The instrument has a double-focusing Nier–Johnson analyser with laminated magnet and a novel variable dispersion ion optical arrangement, enabling all masses to be located in the centre of the Faraday collectors of a fixed static array. mThe performance of the instrument has been assessed through the analysis of NBS-981 Pb using a Tl doping technique with Faraday collector efficiencies and amplifier gains determined independently. A second method of analysis involves comparison of interspersed standard and sample Pb measurements with effective gains for each collector determined from the standards. In both cases the repetition of Pb isotope measurement is competetive with the thermal ionization mass spectrometry (TIMS) double-spike method

Description: A high resolution Pb isotope time-series for the last 26 Ma, dated by 10Be/9Be chronology, is reported for a north Indian Ocean ferromanganese crust. This record is compared with available Pb isotope time-series of six other crusts from the Atlantic, Indian and Pacific Oceans, each of which is based on 10Be/9Be chronology. The seven Pb isotope records reveal some remarkable features. In contrast to the Nd isotope time-series of these crusts which show a long-term (∼60 Ma) provinciality between the three main ocean basins, the Pb isotopes only show comparable provinciality over the last ∼5 Ma. Prior to about 15 Ma ago no distinct Indian Ocean Pb isotope signal existed. Within this established framework of Pb isotope distribution in the oceans the 208Pb/206Pb data for the north Indian Ocean crust reported here are anomalous. The 208Pb/206Pb ratio is particularly high and exceeds a value of 2.08 during the time interval from 20 to 8 Ma ago. Consideration of potential sources of Pb in the Indian Ocean which might provide such high 208Pb/206Pb ratios suggests that this crust most probably has recorded a time-varying erosional input of Pb from the Himalayas. The timing of the isotopic shift is in good agreement with maximum Himalayan exhumation rates deduced from crystallisation and cooling ages of synorogenic granites (20–14 Ma) and the sedimentation history of the Bengal Fan.