Edsviken Bay

Modern sedimentary structures and rates of sedimentation.

The Edsviken Bay, situated just north of Stockholm, is a small, elongated area with a narrow and shallow connection to the Baltic Sea. The bay has an area of 3.6 km2, a length of 8.5 km, a maximum depth of 20 m, and an average depth of 8 m. About one-third of the water volume is situated below the sill depth, 6.5 m.

Radiographic comparison between the upper part of cores 445, 804, and 1003 from a depth of 14, 14, and 13 m respectively in Edsviken.

By comparing stereoradiographs of the uppermost part of 28 sediment cores from different locations in this bay, sampled in 1978, 1981, 1982, 1983, and 1984, and by studying the newly formed sedimentary structures, it proved possible to base core chronologies on varve counts, and to determine temporal and spatial variations in sediment accumulation.

Locations of the 21 cores in the main, inner basin of Edsviken Bay, used for the calculation of sediment accumulation.

  

Accumulated amount of solids down to a sediment depth of 17.5 cm in core 445. The hardness index, hi, = the accumulated amount of solids down to a sediment depth of 10 cm.

Sediment focusing is the dominant explanation of the spatial variations in sedimentation rate in Edsviken Bay. The present rate of sedimentation in the deepest part of the bay is about three times higher than the average annual value for the bay, which amounts to 30 mg/cm2. About half of the present sediment accumulation in the bay is probably due to the sediment yield from the drainage area.

Mean annual sedimentation rate in percentage of predicted (1950-1977) at 21 coring stations in the Edsviken Bay.

The measured mean annual sedimentation rates have been compared with values predicted according to the relationship of mean annual sedimentation rate to water depth. As is obvious from this figure, the variations in sedimentation rate in this bay are not a function of the distance from the bay head. According to the statistical analyses, more than 70% of the variations in sedimentation rate are explained by the variations in water depth. About 10% of the variations are probably due to methodological errors. Most of the remaining variations are probably caused by local conditions at the coring stations. (See further Axelsson, V., and El-Daoushy, F., 1989: Sedimentation in the Edsviken Bay - studied by the X-ray radiographic and the Pb-210 methods. Geogr. Ann. 71 A).

File in Swedish.

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