The Trendermarsch sunken in the Wadden Sea (North Frisia, Germany) : reconstructing a drowned medieval cultural landscape with geoarchaeological and geophysical investigations
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Abstract
Located in the North Frisian Wadden Sea, today's tidal flat sediments cover a formerly cultivated area outside the present-day sea dike of Nordstrand that had been occupied by settlers since the Middle Ages. The intensive cultivation increased the coast's vulnerability to storm floods. Especially the medieval storm surges of the first Grote Mandränke (St Marcellus flood) in 1362 CE and the second Grote Mandränke (Burchardi flood) in 1634 CE destroyed large parts of the diked marshland.
This study focusses on the investigation of the drowned part of the medieval Trendermarsch outside the modern sea dike of Nordstrand.
We combine different geophysical and geoarchaeological methods to estimate how and to what extent anthropogenic impact has shaped the coastline of Nordstrand since the Middle Ages. Guided by the evaluation and georeferencing of historical sources and embankment plans, the geophysical prospection was initially carried out in equidistant search grids and then intensified in areas of detected anomalies. The coring locations were selected accordingly to these results.
Sedimentary, geochemical and microfaunal analyses of sediment samples of 22 sediment cores were carried out to calibrate the geophysical results and to establish a local stratigraphy of landscape evolution. Radiocarbon dating together with historical reports provides a geochronological framing.
Using magnetic gradiometry, we found imprints of at least three settlement sites and a dike segment preserved in the recent tidal flats. Reconstruction of the natural local depositional environment, based on 13 stratigraphic units, initially shows sedimentation under lagoon-like brackish–marine shallow water conditions (unit A), followed by salt marsh formation (units C.1, C.2) and subsequent development of fenlands at around ca. 800 BCE (unit D).
A hiatus between a younger marsh formation (unit C.3) at around ca. 650 CE and recent tidal flat deposition (unit G) reveals that evidence of colonisation in the High Middle Ages is mostly preserved as a “footprint”. Still, we found distinct evidence of terp enlargement that indicates different phases of settlement, presumably in response to the threats induced by storm flood events. Using brick-like ashes (unit F.1), we provide the first evidence of some type of (salt) peat processing on a local scale after the second Grote Mandränke and thus after the drowning of parts of the Trendermarsch in 1634 CE.
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Quaternary science journal, 74, Copernicus, Göttingen, 2025, https://doi.org/10.5194/egqsj-74-37-2025