Publications

Comparison of stone detecting strategies in terms of scientific and stakeholder purposes

The demand for efficient stone detection techniques of stony areas (reefs) in the marine environment increased in the last years. This is especially important for seafloor areas with a patchy distribution of stones in an otherwise sand-dominated milieu. These hard substrates are hotspots of marine biodiversity; especially for benthic communities. For fishes, marine mammals and birds stony areas are important breeding and feeding places. Current research projects are dealing with the stone distribution and density to investigate e.g. species-habitat interactions. On the political level detailed distribution maps are relevant for resource assessments, coastal management and protection conventions. The detection of stony habitats in sublittoral environments is still a considerable challenge in spite of modern high resolution hydroacoustic techniques. Object detection on the seafloor is commonly done on the basis of hydroacoustic backscatter intensities recorded with e.g. sidescan sonar and multibeam echo sounder. Single objects such as stones can generally be recognized by the acoustic shadow behind the object. For small areas single objects can be easily identified manually; for large scale mapping automated techniques are required which are still under development. We collected a set of hydroacoustic data on the German continental shelf to compare and discuss the following approaches to detect and demarcate stony habitats: • manual detection on backscatter mosaics • automated detection on backscatter mosaics using machine learning techniques • seismo-acoustic approach (sediment echo sounder, sidescan sonar)

Seitensichtsonar-Kartierung der Abrasionsplattform seewärts des Brodtener Ufers (Lübecker Bucht)

Die geologisch / sedimentologische Ausbildung des Meeresbodens bestimmt neben der Exposition eines Kustenabschnittes und der Nahrstoffzufuhr masgeblich die Abundanz von Zoo- und Phytobenthos. Die Zielsetzung dieses Projektes war es, die sedimentologische Beschaffenheit des Meeresbodens seewarts des Brodtener Ufers mittels hydroakustischer Messsysteme in einem ausgewahlten Areal flachendeckend zu erfassen und die Ergebnisse in einer Karte darzustellen. Weiterhin sollte eine Zusammenstellung von bereits im Institut fur Geowissenschaften der Christian-Albrechts-Universitat zu Kiel (IfG) vorhandener Seitensichtsonar-Daten aus der Lubecker Bucht erfolgen.

Evolution of and processes acting on inner continental shelf areas

Shallow seas are influenced by a magnitude of processes, acting on- and offshore. Therefore, most inner continental shelf areas have a unique appearance. Sediments and morphological features preserve information both about the geologic history and recent processes. In this study, extensive hydroacoustic surveys, including side scan sonar, multibeam echo sounder, and reflection seismic measurements, as well as sedimentological analyses were carried out in the Fehmarn Belt (SW Baltic Sea, Germany) and offshore Khao Lak (Andaman Sea, Thailand) between 2007 and 2011. The geologic evolution of a drowned river system since the last glacial as well as recent sediment dynamics of a subaqueous dune field were investigated in Fehmarn Belt. Offshore Khao Lak, the impact of the 2004 Indian Ocean Tsunami was evaluated.

Genesis and sediment dy-namics in a subaqueous dune field in Fehmarn Belt (south-western Baltic Sea)

No abstract is provided for this article.

The Agadir Slide offshore NW Africa: Morphology, emplacement dynamics, and potential contribution to the Moroccan Turbidite System

A newly identified large-scale submarine landslide on the NW African margin (Agadir Slide) is investigated in terms of its morphology, internal architecture, timing, and emplacement processes using high-resolution multibeam bathymetry data, 2D seismic profiles, and gravity cores. The Agadir Slide is located south of the Agadir Canyon at a water depth ranging from 500 m to 3,500 m, showing an estimated affected area of approximately 5,500 km2. The analysis of the Agadir Slide's complex morphology reveals the presence of two headwall areas and two slide fairways (the Western and Central slide fairways). Volume calculations indicate that ∼340 km3 of sediment were accumulated downslope along the slide fairways (∼270 km3) and inside the Agadir Canyon (∼70 km3). Stratigraphic correlations based on five gravity cores indicate an emplacement age of 142 ± 1 ka for the Agadir Slide. However, its emplacement dynamics suggest that the slide was developed in two distinct, successive stages. The presence of two weak layers (glide planes) is a major preconditioning factor for the occurrence of slope instability in the study area, and local seismicity related to fault activity and halokinesis likely triggered the Agadir Slide. Importantly, the Agadir Slide neither disintegrated into sediment blocks nor was transformed into turbidity currents. The emplacement timing of the Agadir Slide does not correlate with any turbidites cored downslope across the Moroccan Turbidite System.

Effects of using inclined parametric echosounding on sub-bottom acoustic imaging and advances in buried object detection

This study reports an adaptation of a parametric echosounder system using 15 kHz as secondary frequency to investigate the angular response of sub-bottom backscatter strength of layered mud, providing a new method for enhanced acoustic detection of buried targets. Adaptions to achieve both vertical (0°) and non-vertical inclination (1–15°, 30°, 45° and 60°) comprise mechanical tilting of the acoustic transducer and electronic beam steering. Data were acquired at 18 m water depth at a study site characterized by a flat, muddy seafloor where a 0.1 m diameter power cable lies 1–2 m below the seafloor. Surveying the cable with vertical incidence revealed that the buried cable can hardly be discriminated against the backscatter strength of the layered mud. However, the backscatter strength of layered mud decreases strongly at >3±0.5° incidence and the layered mud echo pattern vanishes beyond 5°. As a consequence, the backscatter pattern of the buried cable is very pronounced in acoustic images gathered at 15°, 30°, 45° and 60° incidence. The size of the cable echo pattern increases linearly with incidence. These effects are attributed to reflection loss from layered mud at larger incidence and to the scattering of the 0.1 m diameter buried cable. Data analyses support the visual impression of superior detection of the cable with an up to 2.6-fold increase of the signal-to-noise ratio at 40° incidence compared to the vertical incidence case.

The Panarea natural CO2 seeps: fate and impact of the leaking gas (PaCO2)

No abstract is provided for this article.

Investigating the Norse Harbour of Igaliku (Southern Greenland) Using an Integrated System of Side-Scan Sonar and High-Resolution Reflection Seismics

This study presents the results of a marine geophysical survey performed in the Igaliku fjord in southern Greenland in order to understand the harbour setting of the former Norse settlement Garðar (modern Igaliku). The aims of the survey were (a) to reconstruct the former coastline during the first centuries of the Norse settlement period (c. 11/12th centuries) and (b) to search for archaeological remains on the seabed connected to maritime traffic and trade. In order to approach these goals, we used an integrated marine survey system consisting of a side-scan sonar and a reflection seismic system. The system was designed for lightweight transport, allowing measurements in areas that are logistically difficult to access. The side-scan sonar data revealed no remains of clear archaeological origin. Bathymetric data from seismic seabed reflection and additional Differential GPS height measurements yielded a high-resolution bathymetric map. Based on estimates of Holocene relative sea level change, our bathymetry model was used to reconstruct the shift of the high and low-water line since the early Norse period. The reconstructed coastline shows that a small island, which hosts the ruins of a tentative Norse warehouse at the mouth of the present harbour, was connected to the shore at low tide during the early Norse period. In addition, reflection seismics and side-scan sonar images reveal a sheltered inlet with steep slopes on one side of the island, which may have functioned as a landing bridge used to load ships. We also show that the loss of fertile land due to sea level rise until the end of the Norse settlement was insignificant compared to the available fertile land in the Igaliku fjord and is thus not the reason for the collapse of the colony.

Subsea salt flows in the Atlantis II Deep and Tethis Deep, Red Sea

In the area of today’s Red Sea, evaporites were widely deposited during the Miocene. Due to the ongoing rifting and seafloor spreading, the evaporites have lost their lateral constraint and started to move downslope. High sediment temperatures near the Red Sea graben and the weak rheology of halite may also favour evaporite movement. However, the deformation mechanism as well as the velocity of these flows is largely unknown. New high-resolution multibeam and seismic data were recorded in March 2011 (P408-2 cruise) within the framework of the project “The Jeddah Transect”, a cooperation between King Abdulaziz University, Saudi-Arabia and GEOMAR, Germany. The data give new insights into evaporite flows in the area of the Atlantis II Deep. This ~400 m deep seafloor depression is located at about 21°N in the central Red Sea graben and is partly filled with hot saline brine (T~68°C, S~270h. The brine-seawater interface at about 2050 mbsl coincides with the depth of a subseafloor salt layer in the seismic reflection data. The rough seafloor morphology of the Atlantis II Deep area is dominated by a sequence of normal faults showing vertical offsets of several hundred meters. However, SW-NE directed lineaments parallel to the seafloor gradient in the south east and possibly north-west of the deep, with typical heights between 20 and 40 m, widths between 300 and 1000 m and lengths exceeding 10 km in places, are interpreted as surface indications of subsurface evaporite flow. The fronts of some of these flows are well rounded, and their occurrence is limited to areas of low seafloor gradients. Generally, the appearance of evaporite flows in the Atlantis II Deep is comparable to salt flows in the Thetis Deep at ~23°N (Mitchell et al., 2010). Furthermore, deformed hemipelagic layers deposited on top of the Miocene evaporites indicate salt movement 60 km off the central rift axis. A second research cruise is planned in March 2012 (RV Pelagia) to obtain more high-resolution seismic data on the morphological structures related to the evaporite flows at 21°N. Additionally, repeated multibeam measurements in the Thetis Deep will constrain the maximum movement rate of the evaporites. Mitchell, N. C. ; Ligi, M. ; Ferrante, V. ; Bonatti, E. ; Rutter, E.: Submarine salt flows in the central Red Sea. In: Geological Society of America Bulletin vol. 122 (2010), Nr. 5-6, pp. 701–713

Highly dynamic biological seabed alterations revealed by side scan sonar tracking of Lanice conchilega beds offshore the island of Sylt (German Bight)

Hydroacoustic surveys are common tools for habitat investigation and monitoring that aid in the realisation of the aims of the EU Marine Directives. Howeve

Short-term anthropogenic impact of mobile bottom-contact fishing on the biogeochemistry of coastal sediments and its long-term effects on mineral distribution

<p>The research project MGF-Ostsee deals with the consequences of the exclusion of mobile bottom-contact fishing in the southern Baltic Sea, specifically to assess its effects on the biogeochemistry of surface sediments and across the benthic-pelagic food chain. In Summer 2021, an in-situ monitored experiment was conducted at a coastal site in the region of Warnemünde/Rostock to investigate the short-term impacts of bottom trawling. Herein, we present first results on how this anthropogenic intervention affects biogeochemical processes and associated elemental cycling, as well as the resulting changes in geochemical mineral tracers. We analyzed porewater and sediment, as well as the water column for major, minor and trace elements, and the stable isotope composition (C, S, O) of dissolved and solid carbon and sulfur species. Porewater gradients are combined with lander-based oxygen-consumption- and radiotracer-based microbial sulfate reduction rates to elucidate how the disturbances by the fishing gear affect element (C, P, Mn, Fe, S) and mineral (re)distribution.</p><p>The controlled trawling experiment generated a re-suspension plume that reached up to 2 m above the sea floor, with 4 NTU in the lowermost portion. In the central trawled area, short cores were taken with a MUC prior and one to two hours after the experiment, and on the following day. In addition, sediment cores were recovered by divers from furrows and mounds of recent trawl marks. First results suggest that in the trawled area, the coupled Fe-Mn-P cycle reacts most sensitively, as expressed by altered porewater gradients and element diffusion. In the trawl marks, pore waters are affected differently whether sediments are removed, as in trawl furrows (erosion), or added/topped, as in trawl mounds (burial). In general, the tentative results point towards a Mn loss in the trawling area and in the furrows, whereas in the mounds Mn becomes enriched. The observed short-term changes in geochemical patterns from the experiment in the Warnemünde region are compared to data from a monitored region in the Fehmarn Belt. There, the observed patterns are tentatively associated to meso-scale areas with a history of low or high trawling impact.</p>

Influence of submerged peat deposits on methane production in shallow coastal regions by submarine groundwater discharge - controlled carbon release

No abstract is provided for this article.

Impact of Sparse Benthic Life on Seafloor Roughness and High-Frequency Acoustic Scatter

Quantitative acoustic marine habitat mapping needs to consider the impact of macrobenthic organisms on backscatter data. However, the sensitivity of hydroacoustic systems to epibenthic life is poorly constrained. This study explores the impact of a benthic community with sparse abundance on seafloor microroughness and acoustic backscatter at a sandy seafloor in the German North Sea. A multibeam echo sounder survey was ground-truthed by lander measurements combining a laser line scanner with sub-mm resolution and broad-band acoustic transducers. Biotic and abiotic features and spatial roughness parameters were determined by the laser line scanner. At the same locations, acoustic backscatter was measured and compared with an acoustic scatter model utilizing the small-roughness perturbation approximation. Results of the lander experiments show that a coverage with epibenthic features of 1.6% increases seafloor roughness at spatial wavelengths between 0.005–0.03 m, increasing both spectral slope and intercept. Despite the fact that a strong impact on backscatter was predicted by the acoustic model based on measured roughness parameters, only a minor (1.1 dB) change of backscatter was actually observed during both the lander experiments and the ship-based acoustic survey. The results of this study indicate that benthic coverage of less than 1.6% is insufficient to be detected by current acoustic remote sensing.

Investigation of submarine landforms in Potter Cove, King George Island, Antarctic Peninsula

Using Fourier Transform Infrared (FTIR) to Characterize Tsunami Deposits in Near-Shore and Coastal Waters of Thailand

Understanding the tsunami cycle requires a simple method for identification of tsunami backwash deposits. This study investigates Fourier transform infrared (FTIR) spectroscopy followed by careful analysis of variance (ANOVA), Gaussian distribution, hierarchical cluster analysis (HCA) and principal component analysis (PCA) for the discrimination of typical marine sediments and tsunami backwash deposits. In order to test the suitability of FTIR spectra as innovative methods for classifications of tsunami deposits, typical marine sediments and terrestrial soils were classified into three zones, namely zone-1 (i.e. typical marine sediments), zone-2 (i.e. including tsunami backwash deposits) and zone-3 (i.e. coastal terrestrial soils). HCA was performed to group the spectra according to their spectral similarity in a dendrogram and successfully separate FTIR spectra of all three sampling zones into two main clusters with five sub-clusters. The simplicifolious (i.e. single-leafed) type of dendrogram was observed with the strong dissimilarity of terrestrial components in subcluster-5. Graphical displays of PC1 vs PC2 highlight the prominent features of zone-1, which is explicitly different from those of zone-2 and zone-3. The acceptable discrimination of typical marine sediments and tsunami backwash deposits, even six years after the tsunami on Boxing Day 2004, dramatically demonstrates the potential of the method for the identification of paleotsunami.

Laboratory Measurements to Image Endobenthos and Bioturbation with a High-Frequency 3D Seismic Lander

The presented 3D seismic system operates three transducers (130 kHz) from a stationary lander and allows non-destructive imaging of small-scale objects within the top decimeters of silty sediments, covering a surface area of 0.2 m2. In laboratory experiments, samples such as shells, stones, and gummy worms of varied sizes (down to approx. 1 cm diameter) could be located in the 3D seismic cube to a depth of more than 20 cm and differentiated by a reflected amplitude intensity and spatial orientation. In addition, simulated bioturbation structures could be imaged. In a practical application, the system allows to determine the abundance of endobenthos and its dynamic in muddy deposits in-situ and thus identify the intensity of local bioturbation.

What AIS misses and Acoustics reveal: Monitoring seafloor disturbance and recovery from bottom trawling in the southern Baltic Sea over five years

This study evaluates bottom trawling intensity and its ecological effects in the Fehmarn Belt (southern Baltic Sea) between 2020 and 2024. The region is dominated by small-scale fishing vessels ( < 12 m length) and therefore conventional Vessel Monitoring System (VMS) data are unavailable. We compare changes in seafloor integrity caused by bottom trawling with fishing activity inferred from Automatic Identification System (AIS) tracking. Trawling intensity was quantified using a previously developed trawling index (TI) based on furrow volume derived from multibeam echosounder (MBES) data. A pronounced alteration in seafloor integrity was observed between 2021 and 2022, with furrow volumes decreasing from 5067 m 3 to 1108 m 3 over an area of 3.4 km 2 . This trend was not recorded by AIS-derived fishing activity, which showed only slight changes in vessel track counts. Spatial and temporal fluctuations in abundance, biomass and community structure were revealed through repeated macrofauna sampling. The fluctuations are likely linked to shifting trawling pressure related to the ban of a fishery targeting cod in the Western Baltic. These biological responses did not follow a linear trend but suggest a dynamic equilibrium may be reached over time. Although MBES data cannot replace AIS for tracking fishing effort, it can supplement and improve the AIS information, providing insights into physical impacts and benthic responses in regions of interest. Integrating MBES-derived indicators identifies the spatial extent of the seabed affected by bottom trawling, thereby strengthening ecological monitoring frameworks and supporting sustainable seabed management, including in marine spatial planning. • Trawling intensity from multibeam surveys improves spatial and ecological monitoring. • In Fehmarn Belt, trawl-induced furrows declined fivefold between 2021 and 2022. • Publicly available AIS data fails to reflect trends in bottom trawling activity. • Over five years, macrofauna response fluctuated non-linearly with trawling pressure. • EEA Reference grid and objective method support alignment across data platforms.

Ship wake-induced water column mixing and meter-scale seabed erosion in the Baltic Sea