We present a case study of multi-coil frequency-domain electromagnetic (FD-EMI) prospection of a wooden ship wreckage from the 17th century. The wreckage is buried in a sandbar in the German part of the tidal flat area of the North Sea. Furthermore, the wreckage was excavated in advance and covered again after investigation. This ground truthing background and the position of the wreckage makes it a unique investigation object to test the feasibility of FD-EMI for prospecting wooden archaeological objects in the high conductive sediments of tidal flat areas. Our results reveal the shape and position of the wreckage in terms of conductivity maps. The resulting signal change caused by the wreckage in conductivity is only 10% of the value of the water-saturated sandy background, respectively, making a cautious process necessary, including a precise height correction. The data, furthermore, reveals a sensitivity to the vertical shape of the wreckage and thus sufficient depth sensitivity, but with reduced sensing depth. The study highlights the great potential of EMI for both in situ heritage management and archaeological research in the Wadden Sea.

Along the southern North Sea coast from the Netherlands to Denmark, human cultivation efforts have created a unique cultural landscape. Since the Middle Ages, these interactions between humans and natural forces have induced major coastal changes. In North Frisia (Germany), storm floods in 1362 AD and 1634 AD turned wide areas of embanked cultural land into tidal flats. Systematic geoarchaeological investigations between Nordstrand and Hallig Südfall comprise coring, trenching, sedimentary, geochemical and microfaunal palaeoenvironmental parameter analyses and radiocarbon dating. Together with geophysical prospection results and archaeological surveys, they give insights into the landscape’s development and causes for land losses. Results reveal that fens and bogs dominated from c. 800 BC to 1000 AD but are mostly missing in the stratigraphy. Instead, we found 12th to 14th cent. AD settlement remains directly on top of a pre-800 BC fossil marsh. This hiatus of c. 2000 years combined with local ‘Hufen’ settlements implies an extensive removal of peat during cultivation eventually resulting in the use of underlying marshland for agricultural purposes. Fifteenth cent. AD tidal flat deposits on top of the cultivated marsh prove that human impact lowered the ground surface below the mean high water of that time, clearly increasing the coastal vulnerability. We consider these intensive human–environment interactions as a decisive trigger for the massive loss of land and establishment of the tidal flats in North Frisia that are currently part of the UNESCO World Heritage “Wadden Sea”.

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.

We present a case study on the applicability of geophysical methods to map shipwrecks in the coastal zone. We present results of magnetic gradiometry, electromagnetic induction, and photogrammetry.

Zusammenfassung: Das im Jahr 1920 entdeckte Prunkgrab von Hoby ist ein zentraler Befund der älterkaiserzeitlichen Archäologie. Es ist eines der reichsten Gräber der „Lübsow-Gruppe“ und barg qualitätsvolle Gegenstände römischer Herkunft und nicht minder qualitätsvolle Artefakte einheimischer Produktion. Zu Beginn des 21. Jahrhunderts wurden knapp 250 Meter entfernt von der Bestattungsstelle durch Hobbyarchäologen älterkaiserzeitliche Keramik und mehrere Metallfunde entdeckt, die von einem mit dem Grab zeitgleichen Siedlungsplatz stammen. Dieser wurde seit 2005 ausgegraben. Im Rahmen eines dänisch-deutschen Kooperationsprojektes werden diese Befunde ausgewertet. Zugleich wird auch das Inventar des Prunkgrabes neu bearbeitet – die Ergebnisse der separat vorgenommenen antiquarischen Untersuchungen zu den einheimischen Gegenständen aus dem Grab können hier präsentiert werden. Die Untersuchungen zu den Fibeln und der Schnalle sowie die vergleichende Analyse der Importgefäßzusammensetzung verweisen gänzlich auf eine Datierung des Grabes von Hoby in claudische Zeit, relativchronologisch in die Subphase B1b.

The publication at hand are the proceedings of the 15th International Conference on Archaeological Prospection held between March 28 and April 1, 2023, in Kiel, Germany. The content of the articles ranges from local to large-scale case studies all over the world and from various archaeological times, over methodological improvements, new processing and visualization techniques to a special session on marine and wetland prospection. Thus, the collection of articles summarizes the state of the art of prospection methods for on- and offshore archaeological investigations.