We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) S the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.

On the basis of stable oxygen isotopes (δO-18), the summer sea-surface salinity of the German Bight, southeastern North Sea, was determined for the past 800 years. In this near-coastal area, salinity is mainly dependent on the freshwater input of the Elbe River discharging its large catchment, which covers an area of 149 000 km(2) of central Europe. Therefore, a proxy for Elbe River discharge was reconstructed at the same time, and consequently the δO-18 record is also mirroring variations in precipitation within the entire drainage basin. Significant variations in these palaeoenvironmental variables are linked to climatic changes.

A high-resolution sediment core (sedimentation rate similar to2 mm/year) from the German Bight was analysed for its foraminiferal stable oxygen isotope (delta(18)O) composition. These data were correlated with instrumental summer sea-surface temperature and salinity data from the nearby island of Helgoland, reaching back 100 years. Comparing the isotope data with the instrumental records reveals a distinct delta(18)O-salinity relationship (delta(18)O=0.34xS-9.36; r=0.86) for the German Bight, where salinity is mainly driven by freshwater input from the Elbe River. Thus, these findings provide the possibility for future regional paleosalinity and paleodischarge reconstructions for times far beyond the instrumental timescale.