Brunnsviken Bay

Radiographic analysis of sediment cores.

This bay in the northern part of the city of Stockholm has an area of 1.5 km² and a maximum depth of 14 m. The core-to-core correlation in Brunnsviken is based on radiographs of 13 sediment cores, sampled in the bay during the period 1976 - 1984. The coring sites are shown on the map further down.

Radiographic comparison between the upper part of cores 741 and 1007 from a depth of 13 and 12 m respectively in Brunnsviken. The distance between these two coring sites amounted only to barely 50 m.

As shown by the radiographs the content of gas (the black spots) was high in these cores. After sampling, the cores increased in length (and volume) due to the formation and expansion of gas bubbles as a result of decreased hydrostatic pressure and temperature rise. Therefore the core data are recalculated to represent in situ values. The length of core 741 increased from 51.5 to 55.2 cm in about twenty-four hours, that is with 7 %.

In core 1007 the organic content was highest at a core depth of 15 - 20 cm, where the mean value, determined as the loss on ignition, amounted to 33.6 %. At this coring site the mean annual rate of sedimentation probably amounted to about 0.51 kg/m² during the 20-year period 1964-1984, corresponding to a linear annual sedimentation rate of 8 mm.

In core 13 an event type of stratification was found at a core depth of 51 cm, probably corresponding to the year 1863, when Brunnsviken, a former lake, was connected to the Baltic by a channel at Ålkistan, and a lowering of the water level by about 1.25 m took place. This also means that the mean annual sedimentation rate during the period 1863 - 1976 probably amounted to about 4.5 mm at that coring site (including compaction due to increasing effective overburden pressure).

Coring sites in Brunnsviken.

File in Swedish.

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