Geochemistry, carbon isotope ratio and radiocarbon ages of sediment core GIK1093-2 from Bornholm Basin, Baltic Sea

Concentrations of Cd, Pb, Zn, Cu, Co, Ni, Fe, and Al203, water content, the amounts of organic carbon, the ratio of 13C/12C and the 14C-activity of the organic fraction were determined with sediment depth from a 34 cm long box-core from the Bornholm Basin (Baltic Sea). The average sedimentation rate was 2.4 mm/yr. The upper portion of the core contained increasing amounts of 14C-inactive organic carbon, and above 3 cm depth, man-made 14C from atomic bomb tests. The concentrations of the heavy metals Cd, Pb, Zn, and Cu increase strongly towards the surface, while other metals, as Fe, Ni and Co remain almost unchanged. This phenomenon is attributed to anthropogenic influences. A comparison of the Kieler Bucht, the Bornholm and the Gotland Basins shows that today the anthropogenic addition of Zn is about 100 mg/m**2 yr in all three basins. The beginning of this excess of Zn, however, is delayed by about 20 years in, the Bornholm Basin and by about 40 years in the Gotland Basin. It is suggested that SW-NE transport of these anthropogenically mobilized metals may be related to periodic bottom water renewal in the Baltic Sea sedimentary basins.

Mesozooplankton in Bornholm Basin, Baltic Sea

The seasonal vertical distribution of mesozooplankton was investigated in the Bornholm Basin in October 1988, July 1991 and April 1992 by means of horizontal tows using a small net with a mesh size of 47 micrometers. This study shows that the vertical distribution of multivoltine copepods is linked with ontogeny and may also change seasonally, even in shallow areas such as the Baltic. Trends between copepod species, stages and seasons were discovered. Secondly, the correlation was investigated between the vertical mesozooplankton distribution on the one hand and chlorophyll a concentration and the density of medusae and fish larvae on the other hand. In several cases the comparison of the shape of the profiles led to greater differentiation than the coefficient of correlation. The abundances found allowed only scant statements about non-copepod taxa.

Clay mineral assemblages in the western Baltic Sea

Surface samples and nine cores from the western Baltic Sea and marginal water bodies were investigated for clay mineral composition. The clay mineral assemblages of recent sediments are rather homogeneous. Variations result mainly from the erosion of different glacial source deposits. High percentages of illite and low kaolinite/chlorite and quartz/feldspar ratios are characteristic for this glacial source. Advection of kaolinite-rich suspensions from the North Sea is believed to account for higher kaolinite/chlorite ratios in the Mecklenburg Bight. A contribution of the rivers Trave and Oder to the western Baltic Sea is indicated by increased smectite values in marginal water bodies. They correspond to increased kaolinite/chlorite and quartz/feldspar ratios. In the main basins the river signal is diluted beyond recognition. Cores from the Arkona, Bornholm and Gotland Basins penetrate through post-Littorina muds and sediments of the Ancylus Lake/Yoldia Sea into Late Glacial sediments of the Baltic Ice Lake. Clay mineral assemblages are characterized by an increase in kaolinite/chlorite ratios from Late Glacial to Holocene sediments, with a distinct shift at each facies change. This allows the distinction and core to core correlation of main lithological units with kaolinite/chlorite ratios. Kaolinite enrichment of Holocene muds corresponds to a brackish-marine facies and may reflect influx of kaolinite-rich suspensions from the North Sea. Cores from the lagoon of the Oderhaff show fluctuations in the contributions of the two main sediment sources: river suspension and glacial deposits during the Late Glacial and Postglacial sequence. Lacustrine sediments, which were deposited prior to 5500 years B.P. are characterized by smectite, kaolinite and quartz from the drainage area of the Oder river. Erosion of coastal and offshore glacial boulder clays with the Littorina transgression supplied a marine component rich in illite, chlorite and feldspars to the brackish muds of the Oderhaff.

(Table 2) Concentrations of dissolved Zn, Cd, Pb, and Cu in waters of the Baltic Sea

A method of determination of low concentrations of zinc, cadmium, lead, and copper dissolved in seawater and interstitial water with use of inversion voltammetry with AC solution conditions is described. The optimum conditions for measurements with accumulation on a mercury-film electrode with a silver substrate are presented. Detection limit is 0.2 ?g/l for zinc and 0.05 ?g/l for cadmium, lead, and copper. Large number of determinations can be carried out during expeditions at natural pH of seawater containing these four metals.