ALBERT

Description: The aim of the sedimentological program of Leg ANT-X/2 was to densify the existing sample network in the area of the Weddell Sea and the Lazarev Sea, or fill the gaps in previous geological investigation sections due to bad weather conditions, unfavorable ice conditions or technical failures. The planned survey of Leg ANT-X/2 from the southwestern Weddell Sea to the eastern Lazarev Sea was only slightly affected by ice conditions. In particular, two stations were successfully conducted on the Polarstern Seamount, an area which had been previously surveyed in 1991 during R/V Polarstern Leg ANT-IX/3.

Description: A high-resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents, has been performed on undisturbed near-surface (0-40 cm) sediment sequences taken in the eastern Arctic Ocean during the international Arctic 91 Expedition. Based on the oxygen stable isotope records measured on Neogloboquadrina pachyderma (sin.) and AMS 14C dating, the upper 10 to 20 cm of the sediment sequences represent isotope stage 1, and the base of Termination I (15.7 ka) can be identified very well. Stage 1 sedimentation rates vary between 0.4 and 〉2.0 cm/kyr. In general, glacial stage 2 sedimentation rates are probably lower and vary between 0.4 and 0.7 cm/kyr. The glacial-interglacial shifts in delta18O values of N. pachyderma sin. may reach values of 1.3 to 2.5 per mil indicating (1) that, in addition to the glacial-interglacial global ice-volume signal, changes in surface-water salinity have effected the isotope records and (2) that these salinity changes have varied laterally. Glacial-interglacial differences in salinity were small in the Lomonosov Ridge area (0-0.4 per mil) and relatively high in the Morris-Jesup-Rise area (up to 1.4 per mil). This implies that the supply of low-saline waters onto the Eurasian shelves and its further transport into the central Arctic Ocean via the Transpolar Drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central Arctic. On the Morris-Jesup-Rise, on the other hand, the glacial low-saline-water signal at that time was strongly reduced in comparison to the modern situation. At the glacial-interglacial stage 1/2 boundary, a strong meltwater signal is recorded in a sharp depletion in delta18O as well as delta13C. This central Arctic Ocean meltwater event can be correlated from the Makarov Basin through the Lomonosov Ridge and Amundsen Basin to the eastern Gakkel Ridge. The beginning of this event is AMS 14C dated at 15.7 ka, i.e., significantly older than the major decrease in the global ice-volume signal which occurs between 9 and 13.5 ka. Large amounts of freshwater/meltwater were probably supplied from the Eurasian continent due to the decay of the Barents-Sea-Ice-Sheet, causing this distinct early meltwater anomaly in the central Arctic Ocean. The extension of a well-oxygenated surface-near water mass in the Arctic Ocean and (at least seasonal) open-ice conditions and some increased bioproductivity were probably established at the end of Termination I, as indicated by the increase in delta13C to modern values as well as increased carbonate (i.e., foraminifers, coccoliths, ostracodes) and total organic carbon contents.

Description: The research cruise SO79 with RV SONNE (April 18 to June 09 1992) aimed to assess the impact of a potential mining activity on the sensitive deep-sea ecosystem of the Peru Basin. Up to now only results of reconnaissance surveys of the extended manganese nodule field discovered in 1978 in the Peru Basin are available. The hydroacoustic, sedimentological, and geochemical studies on data and sample material of SO79 came to the following results: a small-scaled variation in thickness respectively type of surface sediments shown by the sediment echosounder respectively the side-scan-sonar is assumably due to variations in deposition or erosion. The composition of sediments is controlled by climatic cycles of different length which were caused by the variable influence of glaciation of the northern hemisphere. We think that during the quaternary a deep-water circulation reduced in intensity and O2-content may have produced a suboxic diagenetic environment which led to a remobilization and redeposition of Mn forming manganese nodules in the oxic surface sediments. Near the distinct redox boundary at about 10 cm depth the growth conditions for nodules are extremely favourable. Due to the great variability of sediments the impact of deep-sea mining will be highly variable and the disturbance of the seafloor will change the ecosystem considerably.

Description: We have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the Ontong Java Plateau (western equatorial Pacific) and on the northern Emperor Seamounts (northwest Pacific). Each of these locations is several hundred miles from the nearest Geochemical Ocean Sections Study (GEOSECS) stations, and the observed delta13C values at each site differ substantially from regionally averaged GEOSECS delta13C profiles. We discuss the possible causes of these differences, including horizontal variability, near-bottom effects, and problems with the Pacific GEOSECS delta13C data. We also measured the isotopic composition (C and O) of core top C. wuellerstorfi from a depth transect of cores at each location. The delta18O data are used to verify that our samples are Holocene. Comparison of foraminiferal and bottom water delta13C values shows that this species faithfully records bottom water delta13C at both sites and demonstrates that there is no depth-related artifact in the dissolved inorganic carbon-C. wuellerstorfi delta13C relationship at these sites.

Description: Summary: The stratigraphy of the Shackleton Range established by Stephenson (1966) and Clarkson (1972) was revised by results of the German Expedition GEISHA 1987/88. The "Turnpike Bluff Group" does not form a stratigraphic unit. The stratigraphic correlation of its formations is still a matter of discussion. The following four formations are presumed to belong to different units: The Stephenson Bastion Formation and Wyeth Heights Formation are probably of Late Precambrian age. The Late Precambrian Watts Needle Formation, which lies unconformably on the Read Group, is an independant unit which has to be separated from the "Turnpike Bluff Group". The Mount Wegener Formation has been thrusted over the Watts Needle Formation. Early Cambrian fossils (Oldhamia sp., Epiphyton sp., Botomaella (?) sp. and echinoderms) were found in the Mt. Wegener Formation in the Read Mountains. The Middle Cambrian trilobite shales on Mount Provender, which form the Haskard Highlands Formation, are possibly in faulted contact with the basement complex (Pioneers and Stratton Groups). They are overlain by the Blaiklock Glacier Group, for which an Ordovician age is indicated by trilobite tracks and trails, low inclination of the paleomagnetic field and the similarity to the basal units of the Table Mountain Quartzite in South Africa. The Watts Needle Formation represents epicontinental shelf sediments, the Mount Wegener Formation was deposited in a (continental) back-arc environment, and the Blaiklock Glacier Group is a typical molasse sediment of the Ross Orogen.

Description: The Recent distribution of living and dead benthic foraminifera of the Arctic Ocean proper has been examined in surface sediments that were sampled during the International Arctic Ocean Expedition 1991 (Arctic 91). The samples represent the Amundsen and Nansen Basins, the Morris Jesup Rise, and the Yermak Plateau from 90°N to 79°42.4'N, 05°15.6'E. Due to the technical difficulties of deep-sea drilling in the Arctic Ocean these areas have, until now, been investigated only in very low density sampling. The Arctic 91 sites of this study cover a water depth range between 552 and 4375 m and represent three sites which are seasonally ice-free, although not yearly, while the other sites are characterized by permanent sea-ice. There is a Recent production of benthic foraminifera in the whole investigation area and all surface samples contain both benthic and planktonic foraminifera. Abyssal assemblages are recorded in the Amundsen and Nansen Basins where Stetsonia arctica dominates with high abundances. It is, however, also possible to distinguish these two basins by the use of diagnostic species. At intermediate water depths (500 to 2000-2500 m) the faunas show higher diversities and higher abundances of Atlantic species than the deep-sea sites. Mixing of North Atlantic water down to approximately 2500 m, is suggested to explain the influx of Atlantic species on the Yermak Plateau and the Morris Jesup Rise. The foraminiferal tests are well preserved within the investigation area and dissolution does not seem to be very obvious in the deeper areas. There is no evidence from the Recent foraminiferal faunas that the bottom waters of the eastern, central Arctic Ocean are undersaturated with respect to calcium carbonate and the deep-sea areas appear, therefore, to lie above the present CCD.

Description: The neodymium isotopic composition of the silicate fraction of Holocene pelagic sediments from the North Pacific define two provinces: a central North Pacific province characterized by unradiogenic and remarkably homogeneous end (-10.2 +/- 0.5) and a narrow circum-Pacific marginal province characterized by more radiogenic and variable end (-4.2 +/- 3.8). The silicate fraction in the central North Pacific is exclusively eolian; based on prevailing wind patterns, meteorological data, and neodymium isotopic data, the only significant sediment source is Chinese loess. Leaching experiments on Chinese loess confirm that leachable Nd is isotopically indistinguishable from bulk and residual silicate Nd. Silicates in the circum-North Pacific marginal province comprise eolian loess, volcanic ash, and hemipelagic sediments derived from volcanic arcs. A compilation of Pacific seawater and Mn nodule epsilon-Nd data shows no clear spatial variation except for a general decrease from surface to deep waters from -3 to -4 and slightly lower epsilon-Nd in bottom waters along the western North Pacific due to the incursion of Antarctic Bottom Water. The relative homogeneity of bottom water epsilon-Nd, which contrasts sharply with the distinctive variation in sediment epsilon-Nd, plus the large difference between the average end of bottom waters and the central North Pacific eolian silicates (-4 vs. -10), suggests that any contribution of REE to seawater from eolian materials is insignificant. Furthermore, leaching of REE from eolian particles as they sink though the water column must be insignificant because Nd in shallow waters is more radiogenic than Nd in deeper waters. That there is no contrast in the Nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from Pacific rim volcanic arcs also contribute minimal REE to seawater. The elimination of eolian, ash, and hemipelagic sediments leaves only near-shore riverine particulates as a possibly significant particulate source of REE to seawater.

Description: Near Weissbach - Diessbach southeast of Lofer (Salzburg, Austria), at the western rim of the Steinernes Meer (Northern Calcareous Alps), the sedimentary sequence of a local Jurassic strike slip basin (pull apart basin) is exposed. This basin formed during the Hettangian (Lias) along E-W directed sinistral strike slip faults showing the structure of a halfgraben with a complex basin fill and asymmetric facies distribution. Along the scarp faults, some of which are still well exposed, different types of mass flows were deposited. In the more distal part red bedded liassic limestones with numerous turbidite and debris flow intercalations (Weissbach Formation) are developed. These slope sediments are overlain by large, up to several hundred meter thick synsedimentary Dachsteinkalk-blocks which slid into the basin and mark a phase of extreme high subsidence. The blocks are overlain by thin, grey and red liassic limestones with a hardground and manganese horizon on top. At places hardground and manganese horizon directly rest on top of the blocks and debris flows. The limestones of the slope facies contain a rich and interesting holothurian fauna, which differs significantly from that of the German Lias. Among the numerous holothurian sclerites there are some stratigraphically important and new species like Theelia liassica MOSTLER, Theelia multiundulata MOSTLER (Upper Hettangian-Lower Pliensbachian), Theelia loferensis MOSTLER (Pliensbachian) und Neomicroanlyx ingridae MOSTLER (Lower Toarcian). Laterally the slope facies interfingers with and is overlain by sediments of the Allgäu Formation, which also contains a manganese mineralization. Apart from the scarp faults the Liassic sequence is developed in a different facies: Dachsteinkalk is overlain by a thin sequence of red and grey, nodular cherty limestones, which upward grade into well bedded cherty limestones and into sediments of the Allgäu Formation. Within the sedimentary sequence of the basin manganese mineralisations occur in two different stratigraphic horizons: A manganese mineralization together with the hardground on top of the Dachsteinkalk-blocks and debris flows and overlying condensed limestones (Lower Toarcian), and a stratiform manganese mineralization within the Allgäu Formation (Aalenian-Bajocian). This stratiform mineralization should not be mixed up with manganese nodule mineralizations which are very common in the deep sea environment. Three different orefacies types have been recognized. Cu-, Ba- and SiO2 -content of the manganese ores and the occurring manganese ore sludges indicate a local source from hydrothermal solutions which ascended along a deep fault system.

Description: Over the past decade an increasing body of evidence has accumulated indicating that much, perhaps most, of the deep sea floor is an environment of substantial temporal variability (Smith and Baldwin, 1984 doi:10.1038/307624a0; Smith, 1987; Deuser and Ross, 1980 doi:10.1038/283364a0; Thiel et al., 1988). This variability is driven largely by seasonal changes of processes occurring in the surface waters (Smith, 1987; Deuser and Ross, 1980; Billett et al., 1983 doi:10.1038/302520a0). The coupling of the deep sea floor environment to the surface waters is the result of rapid vertical transport of particulate matter through the water column (Honjo, 1982 doi:10.1126/science.218.4575.883; Deuser et al., 1986 doi:10.1016/0198-0149(86)90120-2; Lampitt, 1985 doi:10.1016/0198-0149(85)90034-2), affording only limited time for degradation before arrival at the sea floor. Studies in the Pacific Ocean have indicated that temporal variations in particulate organic carbon fluxes to the sea floor are accompanied by temporal variability in sediment oxygen demand by as much as a factor of four (Smith and Baldwin, 1984; Smith, 1987). We report here time-series studies of oxygen fluxes into the sediments of the oligotrophic Atlantic near Bermuda which contrast sharply with these previous reports. At the Bermuda site, despite large seasonal variations in particulate organic carbon fluxes, in situ measured sediment oxygen consumption does not vary significantly. These results imply that large areas of the sea floor may be characterized by seasonally invariant sediment oxygen demand.

Description: Results of studies in two biogeochemically active zones of the Atlantic Ocean (the Benguela upwelling waters and the region influenced by the Congo River run-off) are reported in the book. A multidisciplinary approach included studies of the major elements of the ocean ecosystem: sea water, plankton, suspended matter, bottom sediments, interstitial waters, aerosols, as well as a wide complex of oceanographic studies carried out under a common program. Such an approach, as well as a use of new methodical solutions led to obtaining principally new information on different aspects of oceanology.