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RESEARCH PRODUCT

Geoarchaeological evidence of marshland destruction in the area of Rungholt, present-day Wadden Sea around Hallig Südfall (North Frisia, Germany), by the Grote Mandrenke in 1362 AD

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Abstract Geophysical and geoarchaeological investigations were carried out in the Wadden Sea of North Frisia (Schleswig-Holstein, Germany) to elucidate major environmental changes that considerably altered the coastal landscape since medieval times. Between the 12 th and 14 th cent. AD, the present-day tidal flats around the marsh island Hallig Sudfall belonged to the historical Edomsharde district and its main settlement Rungholt . For North Frisia, it is well known that during medieval and early modern times, extreme storm surges caused major land losses associated with a massive landward shift of the coastline. Today, cultural traces like remains of dikes, drainage ditches, terps or even plough marks are still visible in the Wadden Sea and provide evidence of the once cultivated marshland. Based on a multi-proxy analysis of sediment cores retrieved from the tidal flat zone around Hallig Sudfall and from the Hallig itself, we identified a late medieval paleosol associated with the formerly cultivated marshland most probably belonging to the Edomsharde and local trade centre of Rungholt. Around Hallig Sudfall, remains of medieval marsh deposits were found partly eroded and covered by a coarse-grained high-energy deposit including abundant shell debris and artefacts. Based on sedimentological, micropaleontological, geochemical and geochronological data, we conclude that these deposits are associated with the 1 st Grote Mandrenke (or St. Marcellus’ flood ), an extreme storm surge event in 1362 AD. Our results, for the first time, provide geological evidence of this 1362 AD storm surge for the Wadden Sea of North Frisia. Moreover, marshland on Hallig Sudfall dating to the 17 th -18 th cent. AD was found covered by a thick layer of storm surge sand and shell debris which seems to be associated with one of the major storm event that hit the German North Sea coast in modern times, e.g. the 2 nd Grote Mandrenke (or Burchardi flood ) in 1634 AD or the Christmas flood in 1717 AD.