133 publications from this institution
The NW African continental margin is well known for the occurrence of large-scale but infrequent submarine landslides. The aim of this paper is to synthesize the current knowledge on submarine mass wasting off NW Africa with a special focus on the distribution and timing of large landslides. The described area reaches from southern Senegal to the Agadir Canyon. The largest landslides from south to north are the Dakar Slide, the Mauritania Slide, the Cap Blanc Slide, the Sahara Slide and the Agadir Slide. Volumes of individual slides reach several hundreds of cubic kilometres; run-outs are up to 900 km. In addition, giant volcanic debris avalanches are widespread on the flanks of the Canary Islands. All headwall areas are complex with clear indications of multiple failures. The most prominent similarity between all investigated landsides is the existence of widespread glide planes that follow the stratigraphy, which points to weak layers as most important preconditioning factor for the failures. Landslides with volumes larger than 100 m 3 are close to being evenly distributed over time, contradicting previous suggestions that landslides off NW Africa occur at periods of low or rising sea level. The risk associated with the landslides off NW Africa, however, is relatively low due to their long recurrence rates.
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.  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 bathymetric data were collected on the 27<sup>th</sup> of June 2020 as underway research data on a 1.5 km track during the cruise EMB239 with the German research vessel Elisabeth Mann Borgese. The objective of the data acquisition was to survey seafloor scars resulting from the controlled detonation of ground mines. For data acquisition, the ship’s hull-mounted Sonic 2024 (R2Sonic Inc.) multibeam echosounder was used. The raw sonar data were loaded in Qimera v2.4.3 (Quality Positioning Services B.V.) and automatically processed to compute sounding footprint location under consideration of sound velocity, position, motion, and heading information. To make the data usable without any specific software, the georeferenced soundings were exported without any bathymetric data cleaning as comma-separated ASCII file in the coordinate reference system EPSG: 32632 - WGS84 / UTM zone 32N. For more details please refer to Papenmeier, S., Darr, A., Feldens, P. (in prep): Geomorphological data from detonation craters in the Fehmarnbelt, German Baltic Sea.
