Physical and chemical properties, 14C ages and palynology of sediment cores from the Western Baltic Sea

Sea level related radiocarbon, palynological and stratigraphical data from sediment cores in the Western Baltic have been tested against the existing sea level curves for the region. The relative sea level rise curves for the beginning of the Holocene show no significant deviations between the Kiel, Mecklenburg und Lübeck Bays and hence do not support the previously reported differences in the averaged regional subsidence rates for this time interval. Local subsidence and upheaval due to salt tectonics probably played a greater role than previously suspected in the region. The sea level possibly stagnated around -28 m during the early Holocene before rising very rapidly to -14 m. The submarine terraces at -30 m and perhaps also at -27 m were formed during the lacustrine phase of the Western Baltic when the water levels were controlled by the main thresholds in the Great Belt.

Investigation of Manganese nodules in the southern Baltic Sea

Die Genese von Mangan-Eisen-Akkumulaten der Kieler Bucht wurde durch In-situ-Experimente vor allem in Tauchgängen unter Berücksichtigung der hydrographischen und sedimentologischen Gegebenheiten sowie natürlicher Akkumulatvorkommen und Krusten auf künstlichen Substraten untersucht. An den diagenetisch gebildeten Akkumulaten wurden chemische Zusammensetzung, Mineralogie, physikalische Parameter, Morphologie und Internstrukturen untersucht. Wichtige Faktoren für die Entstehung der Mangan-Eisen-Akkumulate sind geringe Sedimentationsraten am Entstehungsort, das Vorhandensein geeigneter Anlagerungskerne sowie ausreichende Zufuhr von gelöstem Mangan und anderen Metallen durch Diffusion aus dem Sediment und durch lateralen Transport im freien Wasser vor allem im Sommer und Frühherbst infolge absinkender Sauerstoffgehalte im Bodenwasser der Rinnen. Die Experimente ergaben eine saisonale Abscheidungscharakteristik der Mangan-Eisen-Oxide in Abhängigkeit von der hydrographischen Jahresentwicklung mit niedrigen Zuwachsraten im Winter und Frühjahr und hohen Werten im Sommer und Herbst. Die 1981 experimentell ermittelte Wachstumsrate liegt im Bereich der südlichen Kieler Bucht (Boknis Eck) bei ca. 20 mm/1000 a. Für das Vorkommen vor Schleimünde wurden in Anlehnung an SUESS & DJAFARI (1977) 30-50 mm/1000 a berechnet. Unter reduzierenden Bedingungen infolge Sedimentüberdeckung können Mangan-Eisen-Akkumulate partiell oder vollständig wieder aufgelöst werden. Für den Verbleib der Akkumulate an der Sedimentoberfläche wird die Bedeutung der Seenelke Metridium senile nachgewiesen.

(Table1) Frequency of well defined bioturbation in sediments of the Eckernförder Bay, Western Baltic Sea

The lamination and burrowing patterns in 17 box cores were analyzed with the aid of X-ray photographs and thin sections. A standardized method of log plotting made statistical analysis of the data possible. Several 'structure types' were established, although it was realized that the boundaries are purely arbitrary divisions in what can sometimes be a continuous sequence. In the transition zone between marginal sand facies and fine-grained basin facies, muddy sediment is found which contains particularly well differentiated, alternating laminae. This zone is also characterized by layers rich in plant remains. The alternation of laminae shows a high degree of statistical scattering. Even though a small degree of cyclic periodicity could be defined, it was impossible to correlate individual layers from core to core across the bay. However, through a statistical handling of the plots, zones could be separated on the basis of the number of sand layers they contained. These more or minder sandy zones clarified the bottom reflections seen in the records of the echograph from the area. The manner of facies change across the bay, suggests that no strong bottom currents are effective in the Eckernförde Bay. The marked asymmetry between the north and south flanks of the profile can be attributed to the stronger action of waves on the more exposed areas. Grain size analyses were made from the more homogeneous units found in a core from the transition-facies zone. The results indicate that the most pronounced differences between layers appear in the silt range, and although the differences are slight, they are statistically significant. Layers rich in plant remains were wet-sieved in order to separate the plant detritus. This was than analyzed in a sediment settling balance and found to be hydrodynamically equivalent to a well-sorted, finegrained sand. A special, rhythmic cross-bedding type with dimensions in the millimeter range, has been named 'Crypto-cross-lamination' and is thought to represent rapid sedimentation in an area where only very weak bottom currents are present. It is found only in the deepest part of the basin. Relatively large sand grains, scattered within layers of clayey-silty matrix, seem to be transported by flotation. Thin section examination showed that the inner part of Eckernförder Bay carbonate grains (e. g. Foraminifera shells) were preserved throughout the cores, while in the outer part of the bay they were not present. Well defined tracks and burrows are relatively rare in all of the facies in comparision to the generally strongly developed deformation burrowing. The application of special measures for the deformation burrowing allowed to plot their intensity in profile for each core. A degree of regularity could be found in these burrowing intensity plots, with higher values appearing in the sandy facies, but with no clear differences between sand and silt layers in the transition facies. Small sections in the profiles of the deepest part of the bay show no bioturbation at all.