ALBERT

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: 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: Porewaters in volcanogenic sediments from the Mariana Back-arc riftzone near 18°N were investigated in order to characterize their chemical composition, reveal the reaction processes which determine their composition and examine differences in fluid chemistry in relation to their distance from the spreading axis. Extensive hydrothermal activity has recently been observed along the spreading axis near 18°N, therefore an important aim of this investigation was to identify any hydrothermal component in the porewaters. The samples are from 11 sediment cores taken along two profiles crossing the NNW-SSE orientated spreading axis at 18°02'N and 18°13'N. Sediment samples were investigated with regard to their lithological, mineralogical and chemical composition. The fluid samples were analyzed for dissolved nutrients ([PO4]3·, NH 3, [SO4]2-, SiO2), trace metals (Fe, Mn, Cu, Cd, Zn), chloride, alkali and alkali earth elements (Li+, K+, Mg2+, Ca2+), total alkalinity, pH, dD, d180 and 87/86Sr. From their crystalline mineral composition, high proportion of volcanic glass, and bulk geochemistry, we conclude that the young 520,000 year old sediments of the Mariana Trough near 18°N are primarily a product of local volcanic activity. The mineralogical composition (mainly plagioclase and clinopyroxene) reflects the phenocrysts of the Mariana Back-arc and Island-arc Basalts. Only minor amounts of detrital and biogenic components are present in the sediments. The minor content of authigenic minerals, as smectites and analcite, and the abundant well-preserved glass particles show that the sediment is primarily unaltered, with alteration processes having only a minor effect on the mineral composition. The degree of sediment alteration increases with the distance from the spreading axis. Statistical evaluation of the chemical composition of the leached surface sediments show that bathymetry, distance from the Mariana island-arc, and distance from the spreading axis all have a strong influence on recent sedimentation processes in the area investigated. These parameters are principally responsible for differences in the chemical composition of the surface sediments. Only diagenetic reactions were found to control the chemical composition of the porewaters in the investigation area. These reactions include the alteration of volcanoclastic material, forming authigenic minerals (smectite and zeolite) and hydrated glass and clay minerals, the dissolution of siliceous and carbonaceous biogenic particles, and the decomposition of organic matter. The chemical compositions of the pore fluids are influenced by the following processes: * hydration of volcanic ash, causing a passive increase in elemental concentrations in the porewater; * alteration of volcanic material, causing a decrease in the 8180-value and the 87/86 Sr-ratio of the seawater-derived fluid; * dissolution of volcanic minerals such as plagioclase and clinopyroxene, releasing Ca into the porewaters; * formation of Mg- and Fe-rich silicates such as saponite, nontronite and zeolites, causing a decrease in Mg-, Fe- and Si-concentrations in the porewaters; * decomposition of organic matter dividing the sediment column into oxic (upper -10 cm) and into suboxic (below -10 cm) zones. In the oxic zone trace metals such as Cd, Cu and Zn are released from the organic matter into the porewater. In the suboxic zone trace metals are removed from the porewater, probably being precipitated as sulfides or adsorbed onto particulate matter; * formation of anoxic environments in areas of formerly high organic matter content such as station 35 GKG. At this location the decomposition of organic matter leads to a significant [PO4]3- increase in the porewater; and * dissolution of siliceous minerals, siliceous biogenic particles such as diatoms and radiolaria, and carbonaceous biogenic particles such as foraminiferas, leading to an increase in the Ca- and Si-concentrations of the porewaters. Although the intensive hydrothermal activity observed in 1985 may have been responsible for the formation of authigenic quartz and nontronite in the sediment samples, at the time of sampling in 1990 there was no evidence for the influence of hydrothermal activity on porewater compositions in the investigated sediment cores.

Description: Der Schutz und die Erhaltung natürlicher und/oder naturnaher Moorökosysteme sowie die Umwandlung bewirtschafteter und entwässerter - ungenutzt gebliebener - Moorstandorte oder Moorteile in Feuchtgebiete mit Moorcharakter sind in den vergangenen 20 Jahren ein wichtiges Thema für den Naturschutz geworden, was mit dem allgemeinen Rückgang wüchsiger, torfbildender Vegetation an ihren originären Standorten und deren ökologischen Besonderheiten zusammenhängt. Mit einer Ausnahme, bezeichnenderweise den Verlandungsmooren, betrifft dieser Rückgang auch alle Moortypen in Mecklenburg-Vorpommern (SUCCOW 1988), Damit ist ein wesentlicher, natürlicher Bestandteil der Landschaft der unwiederbringlichen Vernichtung durch den Menschen anheim gefallen.

Description: Recent benthic foraminifera from the Gulf of Guinea (West Africa) were investigated as part of the NOSOFO project (North South Foraminiferal Transect), which concerns the latitudinal distribution of foraminifera in the eastern Atlantic Ocean. The Gulf of Guinea is particularly interesting because of the local confluence of fluvial waters with both coastal and equatorial upwelling systems. The distribution of the samples along 11 transects from Guinea to Gabun enables the determination of the effect of the spatial variation in the input of organic material to the benthic ecosystem. Thus, the benthic foraminiferal fauna is of interest for its modern ecological response and for its potential use as an indicator of the shifting, waxing and waning, and interacting of these systems through time. The material consists of 53 surface sediment grab samples from water depths of 27 to 560 m taken during the METEOR cruise 6-5, Dakar - Libreville in January and February, 1988. Bioceonoses from of the uppermost centimeter of the sediment were investigated, using the 63 - 250 µm grain fraction; thanatocoenoses were analyzed from 22 of these samples. In addition, biocoenoses from 10 sediment cores which represent the first 1 - 6 cm underlying the grab samples were analyzed. Living specimens were stained with Rose Bengal and seperated from the unstained tests.

Description: Recent benthic foraminifera in surface sediments from the continental slope in the Gulf of Guinea (West Africa) were studied in order to determine the utility of foraminiferal species and assemblages as environmental and bathymetric indicators. In the study 67 samples, ranging in water depth from 631 to 4970 m, collected during the "METEOR" expedition M6-5 were needed. Based on their depth range and geographic distribution the dominant species of the living (stained) and the dead assemblage of the 63-250 µm grain size fraction were divided (“stacking by eye”) into three bathymetric groups: The Upper Bathyal Fauna. the Lower Bathyal Fauna and the Abyssal Fawia. These faunal associations have partly overlapping depth ranges. A comparison of the depth ranges of the faunal groups in the Gulf of Guinea with results of investigations of other authors show that similar bathymetric divisions of foraminiferal faunas also occur in the lower and middle latitude (47° N to 30° NS) East Atlantic.

Description: Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic d13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic d13C by 0.4-0.5 per mil. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.