Sediments and bedform mapping of the Lower Saxony Wadden Sea and North Sea (Germany)

Seafloor mapping is the subject of several worldwide research programs dealing with the growing awareness that changes of the marine environmental conditions have to be accurately monitored. The monitoring requirements strongly stimulate the scientific interest in innovative mapping methods and tools, which should be exploitable within the extensive mapping programs carried out by governmental agencies and institutes.

The Coastal Research Station within the NLWKN is carrying out a long-term program to map subtidal areas of the Lower Saxony coastal and marine waters, adopting a methodological approach aimed to increase objectivity and repeatability of results.

The study area is one of the world’s largest tidal system encompassing a multitude of transitional zones between land, marine, and estuarine environments. The geological and geomorphological setting is closely related to the Late Quaternary evolution of the North Sea and the actual morphodynamic processes. The seabed is made of Holocene sand to silt deposits and peat layers. They overlay Pleistocene fluvioglacial deposits, made of sands, rocks, and boulders, which locally outcrop in small areas of the North Sea and in the deepest sectors of the Wadden Sea tidal inlets.

Even though existing maps provide a good broad-scaled representation of the sediments distribution, they were produced by the interpolation of grab-samples therefore lacking of spatial resolution and bedforms characterization. The ongoing mapping program provides full-coverage detailed sedimentological and geomorphological data, by means of swath-bathymetrical systems, subbottom profiler, and validation samples. The methodological approach integrates bathymetric, backscatter, and stratigraphic information to characterize bedforms and substrates. Bathymetry and seabed images are interpreted using geomorphometric as well as object-based image analysis, to increase the objectivity and generate reproducible results.

Maps outline common sedimentological and geomorphological features across all the observed Wadden Sea tidal inlets, which are made of fine sandy sediments and narrow outcrops of peat layers on the main tidal channels slopes. Both erosive and depositional geomorphological processes are present, represented by several orders of scarps, mainly connected to alternations of hard-substrates and unconsolidated sands, and medium to very large sand waves. Moreover, data reveal high-resolution information about hard-substrate outcrops in the North Sea area.

The mapping program provides new detailed geological-geomorphological features of a very dynamic coastal area, using repeatable and objective methods. The combination of different datasets and tools allows the quantitative analysis of the complex subtidal morphology, the correlation of bedforms and substrates. Resulting products will be further developed for habitat mapping purposes and morphological and hydro-dynamical modelling.