Näslandsfjärden Bay

Radiographs of sediment cores

The coastal bay Näslandsfjärden is part of the waterway connecting the Lake Mälaren region with the Baltic Sea, and is situated north-northwest of and connected with the bay Himmerfjärden by the narrow passage Skanssundet.

Radiographic comparison between the upper part of cores 633 and 915 from a depth of 38 and 39 m respectively in Näslandsfjärden.

These rather gas-rich cores expanded after sampling. The expansion of core 915 amounted to 2.5 cm about one day after sampling (increase in core length from 41.9 to 44.4 cm = 6 %). As shown by the core-to-core correlation above 3 new annual varves were formed between 1980 and 1983. At coring site 633 the border between the upper laminated and the lower bioturbated deposits probably corresponds to the year 1963.

The core-to-core correlation in this bay is based on radiographs of 8 sediment cores, cores 632 - 633 sampled on 6 August 1980, core 681 sampled on 18 June 1981, cores 914 - 916 sampled on 28 June 1983, core 1115 sampled on 26 June 1985, and core 1208 sampled on 15 November 1986. The coring sites were situated at water depths between 21 and 39 m.

Radiographs of the upper part of sediment core 1208 from a depth of 39 m in Näslandsfjärden. The lead letters (O, X, etc.) mark corresponding levels on the partly overlapping radiographs. The curve, showing the downcore variation in dry bulk density, is based on film-density values, recorded along the centerline of the left radiograph.

The rate of sedimentation was rather high at this coring site. For the 10-year period 1975 - 1985 the annual mean mass sedimentation rate (salt-free) amounted to 2.6 kg/m² and the annual mean linear sedimentation rate to 15 mm. The given mean linear sedimentation rate is based on the prevailing overburden pressure in 1986. However, it must be stressed that given linear sedimentation rates for modern deposits will generally decrease with time and especially with increasing overburden pressure due to gravitational compaction.

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