Recent and subrecent sedimentary conditions in the southern part of the North Sea–Baltic Sea transition

Abstract

The recent rate of net sedimentation (0–5mm/yr) in the southern Kattegat is to a high degree governed by resuspension. In shallow areas (10–25 m) there is no or very little sedimentation. Sediments here are sandy lag sediments with a low content of organic matter (0.5–3.0%), nitrogen (0–0.1%) and phosphorus (0.01–0.05%). In deep water (30–60 m) the sediments are clays or fine silts and generally have high contents of organic matter (3.0–10.8%), nitrogen (0.1–0.34%) and phosphorus (0.05–0.10%). Shallow water sediments are relatively well sorted because of resuspension of fine material, which is transported to deeper water. Here the sorting becomes poor because relatively coarser material is supplied during exceptional storm events. Discrimination on erosion/transport bottoms and on depositional bottoms was based on resuspension calculations, grain‐size parameters and Passegas (1964) CM diagrams. The IG/N ratio was an useful additional tool. From the sediment content of CaCO3 it is suggested that recent sedimentation in the deeper parts of southern Kattegat is less influenced by contributions from the North Sea than it was during the early Holocene.