ALBERT

Description: Ice-rafted fossils of late Cretaceous and Tertiary age were detected in Pleistocene-Pliocene glacially influenced sediments of the Vdring Plateau, eastern Norwegian Sea. The ice-rafted associations contain frequent Inoceramus (Bivalvia) prisms and rare occurrences of both benthic and planktonic foraminifers of Miocene, Oligocene, and Maastrichtian to Campanian age. As source areas, shallow outcrops on the Norwegian Continental Shelf as well as the Greenland Shelf and the North and Baltic Seas have to be considered.

Description: Ocean Drilling Program Leg 104 recovered sediments containing calcareous nannofossils of latest Oligocene to Holocene age from the Voring Plateau in the Norwegian-Greenland Sea. The section drilled is virtually the most complete and detailed sedimentary sequence yet obtained from such a high latitude North Atlantic location. Due to unfavorable paleoclimatic conditions, the nannofossil assemblages observed are generally of low diversity and poorly preserved. A limited nannofossil biostratigraphy can still be formulated, although many of the standard low-latitude zonal markers are absent in the area of study. An important aspect of the Norwegian-Greenland Sea is the response of the sediments to the onset and variability of glaciation in the area. The sediments deposited since the onset of Northern Hemisphere glaciation consist of alternating carbonate- (and nannofossil-) rich interglacial sediments and carbonate-poor glacial sediments. The glacial sediments also contain ice-rafted debris, including reworked Cretaceous and older Cenozoic nannofossils. The reworked nannofossils were most likely deposited by ice-rafting from the area to the south with minor contributions of reworked material from exposed shelf areas near Norway and from fault-exposed outcrops of upthrust Cretaceous rocks in the area.

Description: Two foraminiferal assemblages are observed in surface sediments of the Elbe estuarv. an Elphidium excavatum assemblaae and an Ahmonia/Protelphidium assemblage. They are the result of test-size sorting in accordance to the grain size of the sediments. These assemblages of mainly empty tests differ basically from the living population, which is dominated exclusively by E. excavatum. The average test size is decreasing when advancing from the Open sea into the estuary and the living fauna disappears near the entrance of the Kiel Canal. In the dead assemblage the diversity is distinctively higher and the average test size varies with the grain size of the sediment. The assemblages found in plankton tows are nearly identical with those in corresponding bottom samples. This indicates the distribution pattern to be caused by transport in currents (mainly in suspension). This type of foraminiferal assemblages characterize macro- and mesotidal estuaries and might indicate a high tidal range when observed in sediments of fossil estuaries.

Description: Geothermal waters with maximum temperatures of 103°C emanate from two sublacustrine hot spring areas which are located in the northem part of Lake Tanganyika (East African Riftsystem). The hydrothermalism leads to the formation of crust- and stockwork-like massive sulfide bodies on the lake bottom to a maximum water depth of 46 m. These geothermal vent areas were investigated and sampled during the German-French TANGANYDRO-campaign in 1991. The aim of this work is to characterize the mineralogy and geochemistry of these sulfides and to reconstruct their genesis. Mineralogical methods that have been used inc1ude scatter electron microscopy (SEM), polarization microscopy, and X-ray diffraction analysis. The geochemical methods inc1ude electron microprobe analysis (EMP) and inductively coupled plasma mass spectrometry (ICP-MS) for the major and trace elements and sulfur isotope measurements in order to determine the d34S-values of the samples. The samples consist exc1usively of iron sulfides. The dominant minerals are marcasite and melnicovite with subordinate pyrite. All samples show collophorm textures indicating their origin from gel-like precursors. They are characterized by high contents of As (up to 3.4 wt%), Sb (up to 0.6 wt%) and Tl (up to 2.6 wt%). Low d34S-values in the range of -11.6 %0 to +2.4 %0 (rel. PDB) indicate bacterial sulfur fractionation. The crystallization of the gel-like precursor leads to the formation of marcasite and pyrite with melnicovite as a transitional phase. Pyrite is formed by the replacement of either melnicovite or marcasite. This mechanism accords to previously postulated models for the formation of iron sulfides in low temperature (〈100°C) hydrothermal systems. A significant sulfur isotope fractionation (increase of d34S) has been observed during the replace- ment of melnicovite by the mature phases marcasite and pyrite. Biogenie impact on the sulfide formation is indicated by low Co/Ni-ratios (〈1), the negative d34S-values and the occurrence of framboidal pyrite. The metabolism of sulfur oxidizing and sulphate reducing bacteria at the wall rock of the vents and in the spring waters is suggested to actively influence the setting of specific pH-values required for the formation of either marcasite or pyrite. The altemating pyrite-marcasite layers are the result of fluctuations in the productivity of those bacteria, which may depend on seasonal variations or changing nutrient support.

Description: Ein grosse Teil! ca. 10 - 15%, der Sedimentgesteine der Erdkruste wird von Karbonaten im wesentlichen Kalkstein und Dolomit, aufgebaut (FAIRBRIDGE et al. 1967). Lösungs- und Fällungsreaktione von Kalziumkarbonat spielen schon bei deren Genese (Frühdiagenese) (WALTE & MORSE 1985) und verstärkt bei der Verwitterung eine zentrale Rolle. Die chemische Wechselwirkung zwischen Karbonatgesteinen und Wasser beeinflusst deren Porosität und Permeabilität und damit wesentliche hydrodynamische Eigenschaften (HANSHAW & BACK 1979) und bestimmt weitgehend den Chemismus der Sicker- und Grundwasser.

Description: Based on foraminiferal transfer-functions, the distribution patterns of early Holocene sea- surface temperatures (SST) were studied, using the information from 154 deep-sea sediment cores (92 Atlantic, 62 Indian Ocean and Western Pacific). For our reconstruction, we employed a uniform high-resolution, AMS 14C-calibrated d18O-chronology, converted to a calendar timescale, and the new SIMMAX-Transfer-Technique in the Atlantic Oceans (Pflaumann et al. in press). The short-term SST fluctuations during the last 30,000 years are not directly related to the relatively slow changes in insolation during this period, reaching maximum seasonal deviations from modern values at approximaterly 11,000 years B.P. Although seasonal changes in solar radiation must have triggered global warming to the modern, interglacial mode, there is little evidence for linear warming and heat transport by ocean currents. The SIMMAX-temperature estimates indicate an early and rapid warming in the Equatorial Atlantic, as well as in the eastern North Atlantic, where modern SSTs were reached for a short time between 20,000 to 16,000 kalendar-years B.P. On a core transect crossing the Island-Faroer Ridge, the history of high-latitude warming along the eastern margins of the big North Atlantic gyres was reconstructed. Prior to the Younger Dryas cold interval (12,000 kalendar years), SSTs of the Norwegian Greenland Sea were still at glacial levels. After the Younger Dryas, there was a rapid inflow of warm Atlantic surface waters into the Norwegian-Greenland basins. In the northern Indian Ocean, the SST-patterns were totally different from the Atlantic during the last 20,000 years. Temperature variations did not exeed 2-3°C in the open ocean. During the Last Glacial Maximum (18,000 years B.P.), temperatures were higher than today whereas they were lowest during the early Holocene. This was caused by changes in the monsoon-induced oceanic upwelling intensity. At this time trade winds off Northwest Africa were also stronger, related to the stronger seasonal constrasts in insolation. Perhaps, the atmospheric circulation was generally enhanced at 10,000 years B.P. High-resolution SST-records from the southern Ocean (Pichon et al. 1992) indicate a slight asymmetry between the two Hemispheres. At 10,000 years B.P, SSTs were 1-2°C higher than today in the southern Indian Ocean. At the same time, somewhat colder SSTs imply still cool, boreal conditions in the middle and high latitudes of the northern hemisphere. Although SSTs of both seasons are only little different from the modern patterns, differences in the direction and strength of the major ocean currents are indicated by internally consistent positive and negative temperature anomaly fields. They were found in both, in the lower and in the high latitudes. The distribution of the anomalies in the North Atlantic further suggests, that the remnants of the ice shields still had a strong impact on the SST distribution. The particulary stronger insolation in the high northern latitudes during summers had nearly no influence. Finally, many details in the SST fluctuations and in the distribution of temperature anomalies imply a more dynamic surface circulation than today which may be the most characteristic difference between the early Holocene and modern surface ocean.

Description: The abundance and composition of the upper Cenozoic terrigenous coarse-sand fraction (250 µm-2 mm) at ODP Sites 642, 643, and 644 were investigated to date the onset of significant ice-rafting in the Norwegian Sea, establish the regional chronology of ice-rafting, and determine the relative importance of global vs. regional controls on ice-rafting in this area. The first input of ice-rafted debris (IRD) occurs at approximately 2.9 Ma, with significant ice-rafting beginning at about 2.5 Ma. IRD abundances increase significantly in sediments younger than 0.9 Ma at all three holes, indicating climatic deterioration in the late Pleistocene. Differences in the timing of this IRD increase between holes result from regional patterns of IRD supply and surface circulation. Variations in IRD sources and dispersal patterns may also explain the slightly higher background level of IRD abundance at Hole 642B, a seaward site. Major peaks in the generalized IRD records from the Norwegian Sea are tentatively correlated to glacial stages or glacial-to-interglacial transitions in the globally defined oxygen isotope record. This correlation indicates the effect of global conditions on the regional climate of the Norwegian Sea, although the detailed IRD records at these sites are also affected by local/regional processes (e.g., circulation patterns and source area differences).

Description: Sediment composition and rate of deposition are the primary factors responsible for determining the spatial distribution of geotechnical properties on the Wring Plateau. Grain size and depth of burial have no significant influence. Vertical and lateral changes in geotechnical properties are associated with vertical and lateral composition changes in which biogenic silica is the most important variable. Anomalous trends of decreasing density and increasing porosity and water content with depth are associated with increasing silica content downsection. Void ratios, inferred in-situ permeability, and change in void ratio during consolidation testing are relatively high in siliceous sediments and tend to increase as the biogenic silica content increases. Portions of the section are overconsolidated, probably as a result of changes in sediment accumulation rates. However, the higher permeabilities of siliceous sediments may also be a factor influencing consolidation state.