『Abstract
　We determined ¹⁵N/¹⁴N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand (δ¹⁵N=5‰) and the imprint of river-borne nitrogen input into the SE North Sea (δ¹⁵N up to 12‰ in estuaries of the SE North Sea) on the other hand. we compare the results with δ¹⁵N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of δ¹⁵N in cores from the Skagerrak - the largest sediment sink for nitrogen in the entire North Sea - was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow-water sediments before reaching the main sedimentary basin of the North Sea.

Keywords: North Sea; Skagerrak; Kategat; eutrophication; nitrogen isotopes; sediments』

1. Introduction
2. Working area
3. Materials and methods
　3.1. Surface sediments
　3.2. Multicores and gravity cores
　3.3. Chemical and isotopic analyses of sediment samples
　3.4. Dating
4. Results
　4.1. Regional patterns of δ¹⁵N in surface sediments and multicores
　4.2. The pre-industrial situation: gravity cores
5. Discussion
　5.1 Isotopic composition of N-sources: relation to surface sediments
　5.2. A view to the past? The sediment record
　　5.2.1. Isotopic enrichment in the Kattegat
　　5.2.2. Isotopic uniformity in the Skagerrak
6. Conclusions
Acknowledgements
References