Transport of clay minerals and anthropogenic compounds into the German Bight and the provenance of fine-grained sediments SE of Helgoland

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Abstract
A large mud body, 500 km 2 and up to 21 m thick, SE of Helgoland has been investigated using geochemical, mineralogical, and sedimentological methods. The analysis of 27 sediment cores from this area revealed that, overlying older fine-grained sediments, there is a 'cake' of muddy, polluted sediments, up to 3 m thick, which has accumulated over the last 100 years. It is assumed that human activities like dredging and dumping are responsible for this rapid rate of deposition. Generally it has been estimated that all of this mud has been supplied by rivers entering this part of the North Sea. But analyses of sediments from the Ems, Weser, and the Elbe rivers show that, under normal conditions, the river sediments do not enter the open sea but are trapped in the estuaries. It may, therefore be concluded that much of the underlying unpolluted sediments of the mud area were derived from elsewhere or were laid down during an earlier period. One possibility is that the lower sediments were deposited when the German Bight was a sheltered area, protected by a barrier of morainic sediments in the north between Helgoland and Schleswig Holstein. This barrier must have been breached more than 2000 years ago.