Description: Am Meeresgrund und vereinzelt in Dauerfrostböden liegt eine schier unerschöpfliche Energiequelle verborgen: Methanhydrat — eine Einschlussverbindung aus Wasser und Methan, in der das Methangas in Eiskäfigen eingeschlossen wird. Makroskopisch nimmt Methanhydrat eine eisähnliche Gestalt an. In reiner Form ist es schneeweiß und zersetzt sich bei Raumtemperatur und Atmosphärendruck. Dabei wird Methangas frei, dessen Menge ausreicht, um eine dauerhafte Flamme bis zur vollständigen Zersetzung eines Gashydratbrockens zu erzeugen — daher rührt auch der Name „Brennendes Eis”. Die mikroskopische Struktur und Dynamik von Methanhydrat waren bislang noch weitgehend unerforscht. Neutronenstreuexperimente ergaben jetzt erste Einsichten.

Description: In a core from the outer Skagerrak, the content of biogenic opal is higher in Late Pleistocene (Younger Dryas) than in Holocene deposits. In terms of opal accumulation, rates are 1 g/cm2/1,000 y during the Holocene and five to ten times larger during the Younger Dryas. Intensive dissolution has greatly reduced the Holocene opal content and does not allow calculation of paleoproductivity. The intensity of opal dissolution is reflected by dissolution stages of both the diatomParalia sulcata and sponge spicules. The intensity of dissolution is negatively correlated to the sedimentation rate and appears to be controlled by silica-undersaturated environment on the sea floor and the uppermost sediment layer.

Description: Highlights • Dextral strike-slip faulting occurs offshore E Sicily above a lateral slab tear fault. • Proposed dextral Ionian Fault becomes sinistral to the south, in external wedge. • Compressional (folding and thrusting) tectonics occur throughout the wedge. • Morpho-tectonics indicate ongoing subduction and advance of Calabrian backstop. The detailed morphology and internal structure of the Calabrian accretionary wedge and adjacent Eastern Sicily margin are imaged in unprecedented detail by a combined dataset of multi-beam bathymetry and high-resolution seismic profiles. The bathymetric data represent the results of 6 recent marine geophysical surveys since 2010 as well as a compilation of earlier surveys presented as a 2 arc-sec (60 m) grid. Several distinct morpho-tectonic provinces are identified including: the deeply incised Malta–Hyblean Escarpment, numerous submarine canyons, broad regions of relatively flat seafloor dominated by fields of sediment waves, the gently undulating anticlinal fold-and-thrust belts of the external Calabrian accretionary wedge and the adjacent portion of the Western Mediterranean Ridge. The Calabrian arc can be divided into 4 domains (from SE to NW): 1) the undeformed Ionian abyssal plain, 2) the external evaporitic wedge, 3) the internal clastic wedge, 4) the Calabrian backstop (Variscan crystalline basement). The Calabrian accretionary wedge can also be divided laterally into two major lobes, the NE- and the SW lobes, and two minor lobes. The kinematics of the limit between the two major lobes is investigated and shown to be sinistral in the external (evaporitic) wedge. A network of radial slip lines within the southernmost external wedge unequivocally demonstrate ongoing dextral displacement of a rigid indenter (representing the corner of the clastic wedge) into the evaporitic wedge thereby confirming the geodynamic model of an active lateral slab tear fault here off eastern Sicily. The slab tear produces a series of major sub-parallel dextral strike-slip faults offshore Mt. Etna and south of the Straits of Messina consistent with the relative motions between Calabria and the Peloritan domain (NE Sicily). Abundant strike-slip faulting, and wide-spread folding and thrusting observed throughout the entire accretionary wedge, indicate regional shortening between the Ionian abyssal plain (foreland) and the Calabrian–Peloritan backstop caused by active subduction.

Description: Condensed pelagic deposits characterize the uppermost sediment sequence of the Maud Rise in the eastern Weddell Sea. The comparison of subbottom profiling data with the sediments drilled at two ODP sites shows that Lithologic Unit Ib deposited during late Miocene to late Pliocene times is generally characterized by acoustic transparency. A prominent reflector with strongly increased amplitude (called Reflector “Pc”) occurs within this mainly homogeneous diatom ooze unit and is correlated with the porcellanite horizon found at ODP Site 689. As evidenced by sediment findings, Reflector “Pc” marks a distinct stratigraphic layer of early Pliocene age. The development of the Reflector “Pc” and its amplitude of reflection in the echosounding records is most likely caused by the silica cementation of porcellanite within this layer. The analyses of the sediment echosounder profiles from five R.V. Polarstern cruises make it possible to map the regional distribution of Reflector “Pc”. In large areas of the central Maud Rise, a patchy but also continuous distribution of Reflector “Pc” was found. The reflector does not occur in sediments below 3000 meters of water. On average Reflector “Pc” is detected around 11 and 12 meters below seafloor, but depth occurrence is highly variable within the range of 8 m to more than 18 m. The apparent amplitude of Reflector “Pc” is higher in those areas where the diatom ooze Unit Ib reaches greater thicknesses, which may be caused by local enhanced tectonic subsidence. In general a good correlation of Reflector “Pc” amplitude and thickness of lithologic Unit Ib is observed. This may imply that the diatom ooze Unit Ib serves as a silica source, since the extent of silica cementation of the porcellanite layer is controlled by the amount of dissolved silica supply. Other possible interpretations for silica sources include silica-rich interstitial water ascending from deeper sediment levels using tectonic structures for migration.

Description: A porcellanite layer, probably younger than 0.6-0.4 Ma, of a nearly monomineralic composition of opal-CT was sampled on the Southwest Indian Ridge during Polarstern cruise ANT-VI/3. The intense cementation of the rock, together with recent findings by the Ocean Drilling Program (Legs 113 and 120) and the occurrence of a unique older porcellanite from Eltanin Core 47-15, provides evidence of very early silica precipitation in pure diatom oozes of the Southern Ocean. Such porcellanites occur in shallowly buried young sediments and provide a contrast to the established concepts of porcellanite formation.

Description: The geochemistry of seep gases is useful for an understanding of the local petroleum system. Here it was tested whether individual light hydrocarbons in seep gases are representatively entrapped in authigenic carbonates that formed near active seep sites. If applicable, it would be possible to extract geochemical information not only on the origin but also on the thermal maturity of the hydrocarbon source rocks from the gases entrapped in carbonates in the past. Respective data could be used for a better understanding of paleoenvironments and might directly serve as calibration point for, amongst others, petroleum system modeling. For this approach, (sub)-recent seep carbonates from the Black Sea (Paleodnjepr region and Batumi seep area), two sites of the Campeche Knoll region in the Gulf of Mexico, and the Venere mud volcano (Mediterranean Sea) were selected. These seep carbonates derive from sites for which geochemical data on the currently seeping gases exist. During treatment with phosphoric acid, methane and higher hydrocarbons were released from all carbonates, but in low concentrations. Compositional studies demonstrate that the ratio of methane to the sum of higher hydrocarbons (C1/(C2+C3)) is (partly strongly) positively biased in the entrapped gas fraction. δ13C values of C1 were determined for all samples and, for the samples from the Gulf of Mexico and the Mediterranean Sea, also of C2 and C3. The present dataset from six seep sites indicates that information on the seeped methane can be—although with a scatter of several permil—recorded in seep carbonate matrices, but other valuable information like the composition and δ13C of ethane and propane appears to be modified or lost during, for example, enclosure or at an early stage of diagenesis.