ALBERT

Description: A considerable number of samples recently obtained from the collections of the German research vessels "Meteor" and "Valdivia" in the eastern North Atlantic have been evaluated for their planktonic foraminiferal composition. The new data enabled a quantitative and qualitative improvement of the data base for a statistical analysis of planktonic foraminiferal fauna using the transfer function technique of IMBRIE & KIPP (1971). 134 modern sediment samples from the eastern North Atlantic were selected according to their excellent preservation of foraminifera and treated by a principle component analysis. The resultant six factors account for 96.7% of the variance of the original data comprising 15 major species and species groups. A multiple regression analysis between these factors and the actual mean sea-surface temperatures and salinities resulted in a set of equations. They can be applied for estimating past sea-surface winter and summer temperatures and salinities from planktonic foraminiferal assemblages for approximately the last 500,000 years. The new functions have a standard error of 1.2° C for winter and summer temperature and 0.4‰ for annual salinity.

Description: To reconstruct the deep-water circulation for the last 3.5 Ma from deep-sea sediments of the eastern equatorial Atlantic, sea floor morphology, sub-bottom reflectors and the echo character have been mapped on the basis of 3.5 kHz records and sediment cores. Physical properties of sediments and synthetic seismograms derived from them enable us to decipher reflector sequences in environments of pelagic, currentresuspended and turbidity sedimentation. The individual reflectors originate from carbonate dissolution, hiatuses, coarse sand layers and interferences. Those which are related to carbonate dissolution and hiatuses provide evidence of water-mass boundaries by their distribution. Five phases of different deep-water circulation can be seen in the record of the last 3.5 Ma, and these are related to climate history: 1. Between 3.7 Ma and 2.2 Ma a strong deep-water circulation indicates a northward flow of bottom water below 4200 m (AABW = Antarctic - Bottom Water) and a southward flow of deep-water above 4200 m (NADW = North-Atlantic Deep Water). 2. Between 1.6 and 1.4 Ma a southward flow of bottom water below 4500 m and a diminished southward flow above 4500 m can be detected. This water-mass geometry can be interpreted by an expansion of the NADW-masses and a displacement of the AABW-masses during the same time. 3. Since 1.4 Ma a northward flow of a bottom-water current developed again. This current flow created a leeside sediment ridge in the southern part of the Kane Gap and furrows in the northern part of it. 4. Beetween 400,000 and 200,000 yrs B. P. the oceanic and atmospheric circulation increased. The strengthened oceanic circulation caused an increase in carbonate dissolution, which is documented by a traceable reflector from 2800 m to 4500 m water depth. At the same time an increase of the atmospheric circulation caused a drastic rise in the pelagic sediment accumulation (〉 100%) through an intensification of upwelling. This runs parallel with a higher oceanic productivity in the northern equatorial divergence zone and an enhanced supply of fluvial and probably eolian sediments from Senegal and Guinea. 5. Before 10,000 yrs B.P. an erosive northward flowing bottom-water current prevailed below 4500 m water depth. After 10,000 yrs B.P. the bottom-water flow was sluggish and non erosive.

Description: Sedimentological and geotechnical analyses were carried out on two undisturbed large diameter deep sea cores from the Antarctic sector of the Atlantic ocean. One core, from a silled basin within the Bransfield Strait is characterized by fine grained hemipelagic material and turbidite layers. The other core, from the continental slope of the Weddell Sea represents a typical glacial marine environment. The variations of physical properties as related to both an increasing overburden pressure (or depth below top of core) and/or to lithological changes are discussed. With increasing overburden pressure only small variations of physical properties were observed. In core 14882-2 the porosity decreases 0.7% per meter, the natural water content 6% per meter. The wet bulk density and the shear strength increase with rates of 0.015 g/cm3 and 0.5 KPa per meter. Compared to small variations in consolidation, the changes of the lithology cause more extreme variations of physical properties: e.g. decreases the natural water content by 100%, the porosity by 14%, and the wet bulk density increases by 0.23 g/cm3 due to a turbidite layer in the core from the Bransfield Strait (core 14882-2). In the core from the continental slope of the Weddell Sea (core 14875-1) two major unconformities have been detected. The ice-rafted debris of this core causes a generally lower porosity (64%), a lower natural water content (75%), a higher wet bulk density (1.55 g/cm3) and specific grain density (2.62 g/cm3), compared to the core from the Bransfield Strait (porosity 77% , natural water content 151% , wet bulk density 1.34 g/cm3, specific grain density 2.47 g/cm3).

Description: The "Meteor" cores 22M36 and 22M37 are situated on the eastern rim of the Mediterranean Ridge SW of the Peloponnesus at 3200 and 3350 m water depth. Core 22M37 contains a breccia consisting mainly of Upper Serravallian/Lower Tortonian claystone clasts. They are characterized by smectite-dominated clay mineral assemblages. The breccia contains displaced benthic foraminifers of neritic character and bryozoan debris. At the top of the breccia follows a chaotic stratigraphic sequence including Serravallian (?), Tortonian, Messinian, Pliocene and Pleistocene sediments. The deposits of Upper Tortonian to Pleistocene age are characterized by illite-dominated clay mineral assemblages. The smectite-dominated assemblages are very similar to that of the surface sediments from the extreme eastern part of the Levantine Basin which represent Nile-derived terrigenous material. It is speculated, that during Upper Serravallian/Lower Tortonian time mineral detritus derived from an early "Nile" may have been transported into the Ionian Sea. This would implicite a seafloor morphology different from today's (the Mediterranean Ridge prevents sediment transport into the Ionian Sea) and considerable tectonic movements since that time. The termination of the smectitedominated sedimentation in the considered area SW of the Peloponnesus would indicate the beginning of the barrier function of the Mediterranean Ridge. Such movements have to be inferred also from the neritic components of the breccia. They have to be explained by turbiditic influx. However, in the present morphology, turbidity currents starting from a shallow water region could not reach the core positions. Core 22M36, situated close to core 22M37, represents a Quaternary sequence (upper part of nannoplankton zone NN 19 to base of NN 21) with conglomeratic layers and unconformities. They point to tectonic movements within this time. The origin of the breccia as well as of the chaotic sequence in core 22M37 may have happened near the boundary of nannoplankton zones NN 19/20.

Description: Based on the faunal record of planktonic foraminifers in three long gravity sediment cores from the eastern equatorial Atlantic, the sea-surface temperature history over the last 750,000 years was studied at a resolution of 3,000 to 10,000 years. Detailed oxygen-isotope and paleomagnetic stratigraphy helped to identify the following major faunal events: Globorotaloides hexagonus and Globorotalia tumida flexuosa became extinct in the eastern tropical Atlantic at the isotope stage 4/5 boundary, now dated at 68,000 years B.P. The persistent occurrence of the pink variety of Globigerinoides ntber started during the late stage 12 at 410,000 years B.P. CARTUNE-age. This datum may provide an easily detectible fauna! stratigraphic marker for the mid-Brunhes Chron. The updated scheme of the Ericson zones helped the recognition of a hiatus at the northwestern slope of the Sierra Leone Basin covering oxygen-isotope stages 10 to 12. Classifying the planktonic foraminifer counts into six faunal assemblages, according to the factor analysis derived model of PFLAUMANN (1985), the tropical and the tropical-upwelling communities account for 57% at Site 16415, and 86% at Site 13519, respectively of the variance of the faunal record. A largely continuous paleotemperature record for both winter and summer seasons was obtained from the top of the Sierra Leone Rise with the winter temperatures ranging between 20 and 25° C, and the summer ones between 24 and 30° C. The record of cores from greater water depths is frequently interrupted by samples with no-analogue faun al communities and/or poor preservation. Based on the seasonality signal, during cold periods the thermal equator shifted to a geographically more asymmetrical northern position. Dissolution altering the faunal communities becomes stronger with greater water depth, the estimated mean minimum loss of specimens increases from 70% to 80% between 2,860 and 3,850 m water depth although some species will be more susceptible than others. Enhanced dissolution occurred during stage 4 but also during cold phases in the warm stages 7 and 9. Correlations between the Foraminiferal Dissolution Index and the estimated sea-surface temperatures are insignificant. Foraminiferal flux rates, negatively correlated to the flux rates of organic carbon and of diatoms, may be a result of enhanced dissolution during cold stages, destroying still more of the faunal signal than indicated by the calculated minimum loss. The fluctuations of the oxygen-isotope curves and the hibernal sea-surface temperatures are fairly coherent. During warm oxygen-isotope stages the temperature maxima lag often by 5 to 15 ka behind the respective isotope minima. during cold stages, sea-surface temperature changes are partly out of phase and contain additional fluctuations.

Description: Over 100 samples of recent surface sediments from the bottom of the Atlantic Ocean offshore of NW Africa between 34° and 6° N have been analysed palynologically. The objective of this study was to reveal the relation between source areas, transport systems, and resulting distribution patterns of pollen and spores in marine sediments off NW Africa, in order to lay a sound foundation for the interpretation of pollen records of marine cores from this area. The clear zonation of the NW-African vegetation (due to the distinct climatic gradient) is helpful in determining main source areas, and the presence of some major wind belts facilitates the registration of the average course of wind trajectories. The present circulation pattern is driven by the intertropical front (ITCZ) which shifts over the continent between c. 22° N (summer position) and c. 4° N (winter position) in the course of the year. Determination of the period of main pollen release and the average atmospheric circulation pattern effective at that time of the year is of prime importance. The distribution patterns in recent marine sediments of pollen of a series of genera and families appear to record climatological/ecological variables, such as the trajectory of the NE trade, January trades, African Easterly Jet (Saharan Air Layer), the northernmost and southernmost positions of the intertropical convergence zone, and the extent and latitudinal situation of the NW-African vegetation belts. Pollen analysis of a series of dated deep-sea cores taken between c. 35° N and the equator off NW Africa enable the construction of palaeo-distribution maps for time slices of the past, forming a register of palaeoclimatological/palaeoecological information.

Description: Molybdenum and vanadium were analysed in 9 sediment cores recovered from the continental slope and rise off NW Africa. additional chemical and sedimentological parameters as well as isotope stage boundaries were available for the same core profiles from other investigations. Molybdenum, ranging between 〈 1 and 10 ppm, occurs in two associations, either with organic carbon and sulphides in sediments with reducing conditions or with Mn oxides in oxidized near-surface core sections. Highest values (between 4 and 10 ppm Mo) are found in sulphide-rich core sections deposited during glacial times in a core from 200 m water depth. The possibility of anoxic near-bottom water conditions prevailing at this site during certain glacial intervals is discussed. In oxidized near-surface core sections, the diagenetic mobility of Mo becomes evident from strong Mo enrichment together with Mn oxides (values up to 4 ppm Mo). This enrichment is probably due to coprecipitation and/or adsorption of Mo from interstitial water to the diagenetically forming Mn oxides. The close relation between Mo and Corg results in strongly covarying sedimentation rates in both components reaching up to 10 times the rates in glacial compared to interglacial core sections. Vanadium (values between 20 and 100 ppm) does not show clear relations to climate and near-bottom or sediment milieu. It occurs mainly bound to the fine grained terrigenous fraction, associated with aluminium silicates (clay minerals) and iron oxides. Additionally positive covariation of vanadium with phosphorus in most core profiles suggest that some V may be bound to phosphates.

Description: A statistical analysis of 15 deep sea cores in the eastern North Atlantic off NW Africa revealed the typical fluctuation pattern of distinct species groups as has been described from various parts of the world ocean. Only the "WBF-group" appears to be correlated with global climatic changes, i.e. warmer periods as the Eemian and the Atlanticum. A partly antagonistic "High Productivity group" (HPR-group) is in general not linked with global changes but times of increased fertility in the surface water and the resulting flux of organic matter reaching the bottom. The groups were extracted from cluster analysis of more than 150 surface samples (HPR-group, LuTZE & CouLBOURN 1984) and a factor analysis of selected cores (WBF-group). In contrast to previous studies the observed fluctuations can not be explained by drastic changes in bottom water masses, but by the pulsation of a distinct "High Productivity Patch" in space and time. At present, this patch is located below the well known upwelling area between 22° and 12° northern latitude. It shifted to the north (up to 27° N) during the latest glacial period (18 ky), indicating an equivalent shift of upwelling productivity caused by advection of nutrient rich upwelling SACW-waters, probably during most of isotopic stages 2 and 3.