No abstract is provided for this article.
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.
High-resolution 2D seismic reflection profiles were examined to explore the stratigraphic architecture of the late Quaternary sediments deposited in the Beibu Gulf (SW off the Hainan Island, South China Sea). Two discontinuities identified in previous research by seismic reflectors R1 (top) and R2 (bottom) allowed to infer the presence of a paleodelta offshore Hainan Island. A detailed analysis of all discontinuities determined the extension of delta body, its thickness and spatial pattern of deltaic clinoforms. Analysis of data obtained by interpretation of seismic records allowed also to depict the relief of lower and upper delta surfaces identified by major erosional discontinuities. The seismic cross-sections provided tools with which to discern all the erosional incisions representing paleo-distributary channels of the delta on both surfaces. In addition, the delta geometry and clinoform dip angles were determined. Analyses have provided information on the direction of sediment transport and sources of deltaic sedimentary material. Distribution of vectors indicating the direction of delta progradation revealed the sediment transport from Hainan Island to be generally southwards to Yinggehai Basin and further towards the shelf edge, thus supporting the hypothesis of Hainan Island as the main source of sediment supply. The vector distribution is unclear in the westernmost part of delta body only, mainly because of an insufficient coverage of this part of the Gulf with seismic tracks and disturbances related to other sediment sources reaching Beibu Gulf in the north, which significantly contributed to the sediment supply.
The physical properties of biologically impacted seafloor are poorly known, including the effects of biology on local roughness. We present an in-situ laser line scanning method to determine the impact of macrofauna on seafloor microtopography and roughness. The local microtopography was determined with mm-level accuracy for the sand mason Lanice conchilega offshore of the island of Sylt in the German Bight (south-eastern North Sea). Ground truthing was done using underwater video data. Two stations were populated by tubeworm colonies of different population densities, and one station showed a hydrodynamically rippled seafloor. Tubeworms caused an increased skewness of the microtopography height distribution and an increased root mean square roughness at short spatial wavelengths compared with hydrodynamic bedforms. Spectral analysis of the 2D Fourier transformed microtopography showed that the roughness magnitude increased at spatial wavelengths between 0.020 and 0.003 m, eventually independent of the tubeworm density. This effect was not detected by commonly used 1D roughness profiles but required consideration of the complete spectrum. The microroughness of different blue mussel and oyster shells were determined in the laboratory. The potential impact of roughness on high-frequency acoustic scatter – widely used for marine remote sensing and strongly influenced by seafloor roughness – is discussed based on an extensive multi-frequency multibeam echo sounder dataset recorded in shallow water (< 3m) offshore Sylt Island. The results indicate that new indicator variables for benthic organisms may be developed based on the microroughness of benthic organisms.
The worldwide implementation of Marine Protected Areas (MPAs) has been used as a conservation measure to preserve marine biodiversity. Due to technological limitations, many early designated MPAs often neglected the distribution of marine habitats. Marine remote-sensing techniques development represents an opportunity to reshape and rethink MPA designs. This study focuses on the Vila Franca do Campo MPA (established in 1983) on São Miguel Island, Azores, using advanced acoustic remote-sensing techniques (MBES, SSS). Mapping of approximately 394 ha revealed a 1-3 ratio between rock and sediment habitats within the MPA, while the adjacent unprotected area showed a ratio of less than 1-2, with significant black coral gardens observed below 40 m depth. According to these results and the ecological importance of the organisms detected, we recommend remodeling the MPA. Furthermore, identifying readily accessible black coral communities provides an opportunity for comprehensive assessments of their contribution to marine biodiversity and conservation resources.
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.
The Baltic Ice Lake, Yoldia Sea, Ancylus Lake and Littorina Sea stages of regression and transgression controlled the history of the Baltic Sea since the last glacial period. Many details regarding their development remain unknown, including the question whether the regression of the Ancylus Lake (between 10,700 and 10,200calyr BP) took place west of the Darss Sill, or elsewhere. This study addresses whether a drowned river system in Fehmarn Belt (SW Baltic Sea) can be related to the drainage of the Ancylus Lake. The river channel is cut into glacial till in the western part of Fehmarn Belt. Here, the channel reaches an incision depth of up to 12m at a base level of 40m b.s.l. (below sea level). Near Mecklenburg Bay, the buried channel is incised down to 60m b.s.l. and widens rapidly from several hundred meters to more than 1km, fading towards east. It was mainly shaped as part of a glacial meltwater system at a maximum water level of 30m b.s.l., and is therefore not related to the Ancylus Lake drainage. During the lowstand of the Baltic Ice Lake, local shallow water bodies covered the study area. A previously reported westward directed drainage of a lake in the eastern Fehmarn Belt could be restricted to a time interval between the highstand of the Ancylus Lake and prior to the Littorina Transgression. Timing, water level and potential water discharge of this event suggest a connection to a partial drainage of the Ancylus Lake. It is concluded that the threshold separating the Ancylus Lake from the North Sea needs to be located west of Fehmarn Belt.
Submarine gravity flows are responsible for the largest sediment accumulations on the planet, but are notoriously difficult to measure in action. Giant flows transport 100s of km3 of sediment with run-out distances over 2000 km. Sediment concentration is a first order control on flow dynamics and deposit character. It has never been measured directly nor convincingly estimated in large submarine flows. Here we reconstruct the sediment concentration of a historic giant submarine flow, the 1929 "Grand Banks" event, using two independent approaches, each validated by estimates of flow speed from cable breaks. The calculated average bulk sediment concentration of the flow was 2.7-5.4% by volume. This is orders of magnitude higher than directly-measured smaller-volume flows in river deltas and submarine canyons. The new concentration estimate provides a test case for scaled experiments and numerical simulations, and a major step towards a quantitative understanding of these prodigious flows.
No abstract is provided for this article.
Anchoring activities exert significant physical pressure on seabed, altering benthic habitats through mechanical disturbances. The European Marine Strategy Framework Directive mandates the assessment of such anthropogenic impacts. Evaluating seabed integrity requires an understanding of both the spatial extent of disturbance and the rate of recovery. This study presents multibeam echosounder bathymetry and backscatter from a heavily impacted area in the Bay of Eckernförde, German Baltic Sea, a region with intensive tourist and naval shipping traffic. The data reveal a dense network of anchor tracks, characterized by elongated furrows flanked by mounds to both sides and extensive abrasion zones caused by the anchor chains. The profile of a fresh anchor track shows a depth of −0.3 m and a mound elevation of 0.2 m, both features diminishing by approximately half after 1 year. Its initial anchor impact crater reaches maximum depth of 0.7 m in the silty sediments. Seafloor disturbance extends approximately 3 m to both sides from anchor tracks, affecting approximately 20% of the surveyed area, excluding widespread abrasion zones. To analyze track degradation, a relative timeline was constructed using a topological sorting algorithm and compared with absolute dating based on AIS data. Results indicate slope measurements effectively capture anchor track degradation until morphological equilibrium is reached. Beyond this stage, tracks remain visible in backscatter data by increased intensity along former mounds. This suggests that anchor tracks have a more persistent impact on seabed integrity than bathymetric data indicate. The spatial extent and the long-lasting effect of the anchor tracks highlight the necessity for explicit spatial management strategies to mitigate cumulative impacts on seabed integrity.
Sediment echo sounder data are routinely collected during research cruises with a geophysical or geological programme. This has resulted in the accumulation of huge amounts of sub-bottom data over the last decades (more than 30,000 survey lines of variable length in the Baltic Sea for the IOW alone), which are often not further interpreted. On the other hand, the value of these datasets for research and industry is increasing, as new regulations (e.g. related to the establishment of marine protected areas) and offshore infrastructure (e.g. wind farms) often prohibit the collection of new survey data. Current topics of interest in the Baltic Sea include the reconstruction of the Late Pleistocene to Holocene palaeogeography of the Baltic Sea and the identification of fluid flow and free methane in the subsurface. The latter can be used to assess the potential release of methane from carbon-rich sediments accumulating in the Baltic Sea basins by identifying the extent, depth and temporal variation of free gas surfaces (e.g. due to seasonal effects and changing wind conditions) in sediment echosounder data. Free gas in the subsurface and water column is readily identified in sediment echosounder and low-frequency multibeam echosounder data due to the increase in acoustic impedance between water-saturated sediments and gas. &#160;Information on methane release is needed to assess the suitability of natural sediments in the Baltic Sea basins as a long-term carbon sink. The methane reservoirs in the southern Baltic Sea are related to various sedimentary and tectonic situations. The frequent generation of methane due to organic carbon accumulation, which is released into the water column and potentially the atmosphere, would have an antagonistic effect on carbon burial. Due to the large amount of data available, a deep learning model (U-Net) is trained on sediment echo sounder data from the Arkona Basin in the southern Baltic Sea to identify free gas surfaces and their depth below the surface. The parameters of the free gas surfaces are related to the thickness of the Late Pleistocene and Holocene sedimentary units (Baltic Ice Lake, Ancylus Lake and Littorina Sea). Repeated lines of sediment echo sounder data allow assessment of changes in spatial extent and depth of free gas through time.
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)
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.
