ALBERT

Description: Analyses of Pb from mid-ocean ridge basalts obtained from DSDP Leg 37 lie on a line of near-zero-age slope. The data seem consistent with an evolutionary model of three stages, the beginning of the second stage being at about 600 m.y. - the model age obtained for the least radiogenic Pb. The beginning of the third stage of evolution at the time of formation of the rocks apparently did not change the average Th/U ratio since measured values are consistent with the ratio deduced from Pb isotope ratios. Ratios of U/Pb are not consistent with Pb isotope ratios, however, thus ruling out a simple two-stage evolutionary model.

Description: Oxygen isotopic and microfaunal analyses and shell size variations of Orbulina universa in two Indian Ocean cores indicate that the position of the Subtropical Convergence has fluctuated between a northern limit north of 31°S during glacial stages and its present, maximum southern limit. The northward displacement of the Subtropical Convergence to a position off Durban, South Africa, reflects the general weakness of the Agulhas Current during glacial stages and parts of interglacial stages, representing about 65 percent of the past 540,000 years.

Description: research

Description: Samples of algae and sediment were taken between July 1973 and May 1975 at intervals of 2-5 weeks from a number of depths at the entrance of Eckernförder Bay (Western Baltic Seal. The purpose was to ascertain the correlation between the settlement of foraminifera and ecofactors, and to determine the annual carbonate production by foraminifera. Produection data were compared with the foraminifera content of the sediments. Information on the extend and place of dissolution could be gained by measuring the saturation of the water with mineral carbonates. The exact area of colonisation (=sediment surfaee, in the sediment or on algae, Fig. 6) was determined for the most important speeies of the Western Baltie. Reproductions were not regulated by one environmental factor, but rather by a number of these. Here the abiotic parameters appear to play the more important part. The conditions necessary for the start of a reproduction can, however, also be fulfilled by the presence of symbiotic algae or increased food avai1ability (Fig. 6). The growth of the foraminifera lasts 3 to 5 months. Carbonate production by foraminifera amounts to between 0.1 and 0.04 g CaC03/m**2 pa in the residual sediment area and up to 3.12 g CaCO3/m**2 pa in the basins. The species living on algae only produce up to 0.003 g CaCO3/m**2 pa (Tab. 9, Fig. 9). The carbonate production figures are only 1-3 % of those reached by the large foraminifera in tropical latitudes, however, similar values were found in the Adriatic. Only 0-3 % of the carbonate produced by the foraminifera is preserved (Tab. 11). In the residual sediment area all foraminiferal carbonate produced is destroyed or washed out. The highest preservation was found in the deepest basins; here, not only is more produced, but also more is preserved. In the sha1lower part of the area of investigation the tests are destroyed by the continual restratification of the sediment and also through being washed out and transported away. In the deeper areas dissolution and predation are major faetors. For some months of the year the water column is under-saturated with mineral carbonates, while there is over-saturation in the interstitial water below a sediment depth of about 1 cm. Therefore tests must be dissolved on the surface or in the uppermost millimetres of the sediment. The quantity of calcareous foraminifera in the sediments is regulated by the following factors: a) intensity of water movement, b) oxygen content of the bottom water (regulates settlement of macrobenthos and bacterial growth), e) rate of sedimentation, d) grain size composition of the sediment. A far more important part than previously assumed is played by the burrowing macrobenthos. The animals transport some foraminifera tests from the sediment surface, where they are exposed to dissolution, into the deeper parts of the sediment, where they can be preserved. On the other hand high colonisation density of macroorganisms feeding on substrate and foraminifera can, in extreme cases, lead to the total destruction of the tests.

Description: research