ALBERT

Description: The Southern Ocean ecosystem at the Antarctic Peninsula has steep natural environmental gradients, e.g. in terms of water masses and ice cover, and experiences regional above global average climate change. An ecological macroepibenthic survey was conducted in three ecoregions in the north-western Weddell Sea, on the continental shelf of the Antarctic Peninsula in the Bransfield Strait and on the shelf of the South Shetland Islands in the Drake Passage, defined by their environmental envelop. The aim was to improve the so far poor knowledge of the structure of this component of the Southern Ocean ecosystem and its ecological driving forces. It can also provide a baseline to assess the impact of ongoing climate change to the benthic diversity, functioning and ecosystem services. Different intermediate-scaled topographic features such as canyon systems including the corresponding topographically defined habitats ‘bank’, ‘upper slope’, ‘slope’ and ‘canyon/deep’ were sampled. In addition, the physical and biological environmental factors such as sea-ice cover, chlorophyll-a concentration, small-scale bottom topography and water masses were analysed. Catches by Agassiz trawl showed high among-station variability in biomass of 96 higher systematic groups including ecological key taxa. Large-scale patterns separating the three ecoregions from each other could be correlated with the two environmental factors, sea-ice and depth. Attribution to habitats only poorly explained benthic composition, and small-scale bottom topography did not explain such patterns at all. The large-scale factors, sea-ice and depth, might have caused large-scale differences in pelagic benthic coupling, whilst small-scale variability, also affecting larger scales, seemed to be predominantly driven by unknown physical drivers or biological interactions.

Description: Bathymetric data reveal abundant submarine landslides along the deformation front of the northern Cascadia margin that might have significant tsunami potential. Radiocarbon age dating showed that slope failures are early to mid-Holocene. The aim of this study is the analysis of slope stability to investigate possible trigger mechanisms using the factor of safety analysis technique on two prominent frontal ridges. First-order values for the earthquake shaking required to generate instability are derived. These are compared to estimated ground accelerations for large (M=5 to 8) crustal earthquakes to giant (M=8 to 9) megathrust events. The results suggest that estimated earthquake accelerations are insufficient to destabilize the slopes, unless the normal sediment frictional resistance is significantly reduced by, for example, excess pore pressure. Elevated pore pressure (overpressure ratio of 0.4) should significantly lower the threshold for earthquake shaking, so that a medium-sized M=5 earthquake at 10 km distance may trigger submarine landslides. Preconditioning of the slopes must be limited primarily to the mid- to early Holocene as slope failures are constrained to this period. The most likely causes for excess pore pressures include rapid sedimentation at the time of glacial retreat, sediment tectonic deformation, and gas hydrate dissociation as result of ocean warming and sea level rise. No slope failures comparable in size and volume have occurred since that time. Megathrust earthquakes have occurred frequently since the most recent failures in the mid-Holocene, which emphasizes the importance of preconditioning for submarine slope stability.

Description: Die 72. Reise der FS Poseidon fand zwischen dem 9. und 13. März 1981 im Skagerrak statt.

Description: Definition Volcanogenic Massive Sulfides. Accumulations of dominantly sulfide minerals that form at sites of focused hydrothermal discharge on the seafloor. Also refers to a class of ore deposit mined from ancient oceanic crust that is now exposed on land.

Description: Seafloor massive sulfide (SMS) deposits are increasingly seen as important marine metal resources for the future. A growing number of industrialized nations are involved in the surveying and sampling of such deposits by drilling. Drill ships are expensive and their availability can be limited; seabed drill rigs are a cost-effective alternative and more suitable for obtaining cores for resource evaluation. In order to achieve the objectives of resource evaluations, details are required of the geological, mineralogical, and physical properties of the polymetallic deposits and their host rocks. Electrical properties of the deposits and their ore minerals are distinct from their unmineralized host rocks. Therefore, the use of electrical methods to detect SMS while drilling and recovering drill cores could decrease the costs and accelerate offshore operations by limiting the amount of drilling in unmineralized material. This paper presents new data regarding the electrical properties of SMS cores that can be used in that assessment. Frequency-dependent complex electrical resistivity in the frequency range between 0.002 and 100 Hz was examined in order to potentially discriminate between different types of fresh rocks, alteration and mineralization. Forty mini-cores of SMS and unmineralized host rocks were tested in the laboratory, originating from different tectonic settings such as the intermediate-spreading ridges of the Galapagos and Axial Seamount, and the Pacmanus back-arc basin. The results indicate that there is a clear potential to distinguish between mineralized and non-mineralized samples, with some evidence that even different types of mineralization can be discriminated. This could be achieved using resistivity magnitude alone with appropriate rig-mounted electrical sensors. Exploiting the frequency-dependent behavior of resistivity might amplify the differences and further improve the rock characterization.

Description: Three large plastic enclosures (3-4 m3) were anchored in the outer harbour of Helgoland (German Bight) and filled with natural seawater which was filtered free of algae. The enclosed water bodies were enriched with inorganic nutrients and inoculated with the diatom Thalassiosira rotula. During the growth of the algae diurnal changes in concentration of dissolved free amino acids (DFAA) occurred. The periodic concentration changes of individual amino acids with a low carbon to nitrogen ratio showed significant interrelationships with the partly synchronous devisions of the diatoms. From the exponential to the stationary phase the carbon to nitrogen ratio of DFAA shifted to higher values pointing at an adaptation of the organisms to the decreasing inorganic nitrogen source. During the bloom amino acids relatively rich in nitrogen were mainly excreted but by the end of the growth amino acids with a higher carbon content predominated. At phases of high photosynthetic activity the organisms probably reduced the high osmotic pressure by exudation of DFAA.

Description: Copepods are an important link in the marine food web, and, in particular, serve as food for fish larvae. Schizopera elatensis, a marine harpacticoid copepod, was reared in the laboratory, and the effect of various environmental factors, i.e., diet, temperature, salinity and height of water column on its growth was determined. Schizopera elatensis multiplies at a wide range of salinities, 10‰ to 70‰, and temperatures, from at least 18° C to an upper limit of 36° C, with an optimum of 25° C, and grows in high densities (300-400 individuals per ml): the lower the water column, the higher the density. The prospective use of S. elatensis as a live food organism in mariculture is discussed.

Description: The importance of bacteria in the feeding of marine bivalves has been demonstrated by several authors. Some examples of good growth of molluscs were noted on a bacterial diet only. But, while the intense filtration of bacteria by molluscs has been observed, the exact role of bacteria in the nutrition of bivalves was not completely known. The filtered particles were sometimes eliminated as pseudofaeces, without any intestinal transit. On the other hand, live cells could also pass through the gut without being degested. To study in detail the fate of bacterial cells distributed as food to young bivalves, we used a new method which combines histology and scanning electron microscopy. This made it possible to observe, on serial histological sections of whole animals, the gut content and the condition of the ingested cells at the different levels of the intestinal tract. The ingestion and digestion by young mussels (Mytilus edulis) of some marine bacterial strains belonging to different taxonomic groups were studied by this method. Thus, partially digested bacterial cells were observed in the stomach, when the hind gut contained undamaged cells, three hours after food distribution. The results obtained for all the strains we tested are presented and discussed in this paper.