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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., Volkswagen Foundation http://dx.doi.org/10.13039/501100001663, Niedersächsisches Ministerium für Wissenschaft und Kultur http://dx.doi.org/10.13039/501100010570

Netherlands journal of geosciences : NJG 100, e4 (2021). doi:10.1017/njg.2020.16, Published by Cambridge Univ. Press, Cambridge

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.

After the deceleration of the postglacial marine transgression, the German North Sea coast was subject to deposition of a complex pattern of subtidal to terrestrial facies. This study aims at reconstructing these facies changes in the ‘Land Wursten’ region (Lower Saxony) by focussing on so-called dwog horizons (incipient soil horizons of the pre-engineered salt marshes). We explore their implications for relative sea-level reconstructions and their indication for early settlement activities. Archive drilling data (1960, provided by the ‘Landesamt fur Bergbau, Energie und Geologie’) were analysed to create five high-resolution stratigraphic cross sections. Three new drilling records were subjected to sedimentological and microfaunal investigations and interpreted to verify and calibrate the archive data. Two dwog horizons were found and 14C-AMS dated. We found basal salt marsh deposits inundated by a high-energy event and covered by tidal flat sediments. The thick tidal flat unit is again overlain by salt marsh deposits indicating the transition from a shallow marine to a terrestrial environment where dwogs were developed and covered by episodic marine incursions. The ages of the dwogs (1128–969 cal BC; cal AD 1426–1467) do not correlate with known layers of adjacent settlement sites and are critically discussed. However, we show that they correlate with phases of stagnant regional relative sea level (RSL) and can be used as RSL indicators. The combined archive and modern data provide valuable information for the RSL reconstruction and palaeoenvironmental changes. However, further research is recommended to accomplish more detailed information about coastal response during the Holocene sea-level changes and implications for settlement dynamics.

The Santo Andre lagoon is located on the southern west coast of Portugal, about 80 km south of Lisbon. Although the beach barrier separating the lagoon from the open sea was occasionally breached in the past and has artificially been opened on an annual basis for the last decades, the lagoon still represents an appropriate geo-bio-archive for reconstructing the Holocene palaeoenvironmental evolution. For this purpose, a 10-m-long sediment core was taken from the centre of the lagoon by using a floating platform. Sedimentological, geochemical and micropalaeontological analyses were performed in order to unravel past sedimentological, environmental and climatic conditions. Due to the lagoon's exposure to storms from the Atlantic and possible tsunamis triggered by earthquakes along the Eurasian-African plate boundary south of Portugal, it is of high interest to identify short-term high energy events that might have crossed or breached the shielding barrier, leaving their footprint in the sedimentary record of the lagoon. The sediment core archived the palaeoenvironmental evolution of the Santo Andre lagoon for at least the last eight millennia. The sandy deposits of the core's lowermost part most likely represent a former coastal flood plain that developed when the postglacial marine transgression had reached the area. The continued sea-level rise deposited alternating layers which indicate varying environmental conditions, characterized by peat growth, stagnant-water areas, as well as disconnections from and reconnections with the open sea. Since approximately 5000 BP, the longshore transport had formed a beach barrier, separating the marine embayment from the open sea and creating a lagoon. In addition, four sudden significant marine inundations between ~8500 and 6000 BP are indicated by the sedimentary and microfaunal analyses. Two of these layers can be correlated to extreme wave events (unit B-II), while for the other two layers an ingression caused by sea-level rise or extreme wave events remains debatable.

The coastal area of the southern North Sea passed through several stages of development during the Holocene starting with swamps and bogs on Pleistocene sands. These were covered due to the rising sea-level by brackish and intertidal sediments with intercalated peat layers indicating repeated shoreline replacements. Such sedimentary archives are excellent sources for environmental reconstructions and potentially suited to deliver a regional sea-level curve. We analysed a 4.6 m-long sediment core recovered south of the island of Norderney (East Frisia, Germany) using a multiproxy approach. The record comprises a vertical stack of changing sedimentary facies, including a basal peat and a second peat layer intercalated between marine sediments, which provides a sedimentological record of local coastal evolution since 7000 cal. BP. High-resolution stratigraphic, geochemical and paleobiological analyses enables reconstructing environmental variability in response to sea-level changes including a short-lived transgressive-regressive cycle. This took place around 6000 cal. BP and lasted only a few hundred years. Our multiproxy approach demonstrates that the combined analyses of geochemical and biological parameters in concert with statistical evaluation are indispensable for the reconstruction of coastal evolution and short-term sea-level fluctuations.