Coring sites in the Baltic Sea

Most of the radiographs of sediment cores named in the frame to the left and on the map below are of cores sampled from the Finnish research vessel Aranda during the Baseline Study of Contaminants in the Baltic Sea in 1993. See further Axelsson, V., 1997: X-ray radiographic studies of sediment cores from the Baltic Sea. In Cato, I. & Klingberg, F. (eds.): Proceedings of the Fourth Marine Geological Conference: "The Baltic". Sveriges Geologiska Undersökning, Ser. Ca 86. For location of the coring stations named to the left, see the map below.

Locations of the selected coring stations in the Baltic Sea (and the former Yoldia Sea, core 223).

The gross amount of sediment that is deposited in the Baltic Sea is high in relation to the net amount and is estimated to be considerably higher than the inflow of sediment from the feeding rivers and from the productive surface layer, mainly due to erosion and redeposition of older deposits, which is favored by the land uplift. Areas where erosion often dominates over deposition and where newly deposited, fine-grained, more or less organic material therefore has a short residence time ("erosion-bottoms") are estimated to cover barely 1/3 of the Baltic Sea, while areas where the rate of sedimentation is positive and continious ("sedimentation-bottoms") reside over roughly half of the Baltic Sea. In the remaining roughly 1/4 of the BalticSea, the rate of sedimentation is probably also positiv, but discontinious due to erosion. See further the section "Tillförsel och omlagring av sediment" and the map showing "erosions- transport- och depositionsbottnar" by Valter Axelsson and John O Norrman in FRP (Fysisk Riksplanering) nr 4 1978.

Time gaps in the sedimentary sequence due to erosion are characteristic of high-energy environments. Erosion and resuspension of sediment along shallow and steep parts of a basin may be rather considerable in connection with heavy storms and bottom-seeking currents. Therefore, in shallow water, repeated reworking and redeposition of sediments tends to obliterate primary sedimentary stuctures. In deep water, the sediments can be completely mixed by bioturbation if the rate of sediment accumulation is low. Annually laminated modern sediments which reflect seasonal variations in the sedimentation rate as well as in the composition of settled particles are therefore most likely to be found in low-energy environments, where the rate of sediment accumulation is high or where the bottom water is permanently or periodically anoxic. This is the case in some areas of the Baltic Sea, especially in the deeper parts of several coastal bays.

See also the hardness index and the map of the 34 cores, X-rayed during the Baltic Sediment Baseline Study in 1993.

Back to the top.

Back to my front page.