Cores from Idefjorden (Iddefjord)
This about 25 km long fjord is part of the border between Sweden and Norway. The core-to-core correlation in this fjord is based on radiographs of nine sediment cores (cores 948-956), see the map further down. The coring sites were situated at water depths between 26 and 37 m. Two of the (32) radiographs of these cores are shown below.
Radiographic comparison between the upper part of cores 952 and 955 from a depth of 37 and 28 m respectively, sampled on the same day and at a distance of about 1.3 km from each other in Idefjorden.
The harder (lighter), more minerogenic layer in the upper, anyhow partly annually laminated portion of these cores, was found in 4 (in cores 952 - 955) of the 9 cores (cores 948-956) sampled on the same day (1983-08-10) between Aleviken and Brattöya in Idefjorden. This layer was probably formed by deposition from a bottom-seeking turbidity current, presumably caused by the dumping of dredged material from the harbour at Halden around 1970 - 1971. However, this layer, that may be used as a time marker, was not found in cores 948 - 951 sampled south of core 952, nor in core 956 sampled northwest of core 955.
Vertical variation in dry bulk density in the upper 0.2 m of core 955.
The density of the upper, laminated part is low in relation to the lower, bioturbated. The amount of (salt-free) solids within the assumed annual varves has been used for the calculation of probable mass sedimentation rates. At this coring place the mean annual rate of sedimentation probably amounted to about 0.35 kg/m2 during the period 1970-1983, corresponding to a linear annual sedimentation rate of 5 mm. However, it must be stressed that these soft layers will decrease considerably in thickness with increasing depth of burial because of gravitational compaction.
Hardness index of cores 948 - 956 from Idefjorden.
The accumulated amount of solids, down to a sediment depth of 10 cm (= Hi), is used as a hardness index in order to compare the density of the upper part of the X-rayed sediment cores. As shown the difference in Hi between these cores is rather insignificant. The difference in the mean value of the organic content in the uppermost 0.1 m of these cores was also rather insignificant. When measured as the loss on ignition it varied between 29% (core 949) and 35% (core 955) of the (salt-free) dry weight.
Locations of the nine X-rayed sediment cores (948 - 956) from the central part of Idefjorden.
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