In light of rising sea levels and increased storm surge hazards, detailed information on relative sea-level (RSL) histories and local controlling mechanisms is required to support future projections and to better prepare for future coastal-protection challenges. This study contributes to deciphering Holocene RSL changes at the German North Sea coast in high resolution by developing a transfer function for RSL change. Recent associations of Foraminifera and Ostracoda from low intertidal to supratidal settings of the barrier island of Spiekeroog in combination with environmental parameters (granulometry, C/N, TOC, salinity) were investigated and quantified in elevation steps of 15 cm in order to generate a first transfer function (TF) of Holocene RSL change. In a future step, the TF can be applied to the stratigraphic record. Our data show a clear vertical zonation of foraminifer and ostracod taxa between the middle salt marsh and the tidal flat with very few individuals in the sand flat area, suggesting removal by the tidal current or poor preservation. Multivariate statistics identify the elevation, i.e. the inundation frequency, as main driving factor. The smallest vertical error (49 cm) is associated with an entirely new approach of combining Foraminifera and Ostracoda for a TF. Advantages of the TF over classical RSL indicators such as basal and intercalated peat – beside the relatively narrow indicative meaning – include the possible application to a wide range of intertidal facies and that it does not depend on compaction-prone peat.

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Palaeolandscape reconstructions at the German North Sea coast are essential for the understanding of coastal changes and dynamic landscape-forming processes. This study contributes to reconstructing Holocene coastal changes in the back-barrier area of the East Frisian island of Norderney and draws conclusions on the local palaeogeography. Five sediment cores were analysed in terms of sedimentology (grain-size distribution), geochemistry (TOC, TIC, N, C/N), microfauna (foraminifers and ostracods) and 13 radiocarbon dates. In order to identify driving environmental factors and support the facies interpretation, multivariate statistics (PCA) were carried out. Additional cores from the surrounding area (WASA Project and ‘Landesamt für Bergbau, Energie und Geologie’ (LBEG) Hannover) enabled correlation of the investigated cores over a transect of ~6 km, showing six depositional environments, which can be used for landscape reconstruction. Deposition starts with periglacial (aeolian and glaciofluvial) Pleistocene sediments, with subsequent pedogenesis followed by swamp conditions that develop into a salt marsh. The overlying tidal-flat sediments are partially cut by (fossil and recent) channel deposits. A hiatus at the base of the tidal-flat deposits that spans some 3000 years hints at their reworking caused by a combination of antrophogenic coastal protection measures and the impact of storms. Furthermore, based on the profile correlation and the age data, a widespread salt-marsh area with a minimum age of ~4000 cal BP is defined for the ‘Hohes Riff’ in the southwestern back-barrier of Norderney Island.

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In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ≙ ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal BP. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal BP. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.