Reconstruction of the provenance of detrital sediments in the Skagerrak region over the past 150 years

The Skagerrak basin represents the main sink area for fine-grained sediments transported through the North Sea region. To trace the provenance of Skagerrak sediments and reconstruct the main sedimentary processes in the North Sea, radiogenic Sr, Nd, and Hf isotope signatures, as well as clay mineral compositions of the detrital clay fraction of surface sediment samples from the North Sea, the Scandinavian fjords, and the Baltic Sea, were measured. Additionally, to investigate the temporal variability in sediment supply from the predominant source areas and the changes in sedimentation over the past 150 years, Skagerrak sediment cores were analyzed using a time series of radiogenic isotopes, clay mineral compositions, grain-size distributions, and X-ray fluorescence (XRF) core scans.

The spatial distribution of the geochemical characterization identifies the northern North Sea, southern North Sea, and Scandinavian fjords as the main sources of fine-grained sediments deposited in the central part of the Skagerrak. Seabed erosion at the Fladen Ground, located in the northern North Sea, supplies the Skagerrak with large amounts of clay-sized sediments, primarily controlled by the inflow of the Atlantic Current into this region. Contributions from mid-European rivers, such as the Elbe, Weser, and Ems, as well as the Baltic Sea, are only minor. Radiogenic isotope ratios and XRF data from Skagerrak sediment records indicate a shift since the second half of the 20th century, with reduced sediment supply from the southern North Sea and increased contributions from the northern North Sea. This shift is caused by an increase in storm frequency and intensity in the 1980s and 1990s, which amplified hydrodynamic conditions in the North Sea region. Strong westerly winds intensified the Atlantic inflow into the northern North Sea and Skagerrak Basin, enhancing seabed erosion in the Fladen Ground and increasing sediment supply from the northern North Sea.

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