The Potential for Abiotic Methane in Arctic Gas Hydrates

Most methane enclosed in gas hydrates is biotic in origin, formed by microbial degradation of sedimentary organic matter. Increasingly, there is evidence that substantial gas hydrate may also be sourced from thermogenic decomposition of organic matter and subsequent migration of this gas into the gas hydrate stability zone. In addition, there is a third potential source of methane that does not involve organic matter at all— abiotic methane, which can be generated by magmatic processes or gaswater- rock reactions in the crust and upper mantle

Unsicherheit im Lehrerberuf als Ursache mangelnder Lehrerkooperation? Eine Systematisierung des aktuellen Forschungsstandes auf Basis des transaktionalen Stressmodells

Der vielfach beklagte Mangel an Lehrerkooperation in deutschen Schulen wird in der Forschungsliteratur u.a. mit der sog. Unsicherheit des Lehrerberufes erklärt. Dieser Artikel systematisiert die bisherigen Befunde der schulbezogenen Unsicherheitsforschung mittels des transaktionalen Stressmodells nach Lazarus (1991) und bietet so einen Einstieg in dieses, in der deutschsprachigen Forschung bislang unterrepräsentierte Themengebiet. Die Nützlichkeit dieses Unsicherheitsmodells für die Formulierung von komplexen Forschungshypothesen und die Interpretation von empirischen Daten wird an einer Reanalyse des PISA-2003 l PLUS Datensatzes exemplarisch aufgezeigt. (DIPF/Orig.)In research literature, the often lamented lack of teacher cooperation at German schools is explained by the so-called uncertainty of the teaching profession. The authors develop a systematization of the present results of school-related research on uncertainty on the basis of the transactional model of stress according to Lazarus (1991), thus providing a gateway to this topic, which has so far been underrepresented in German-language research. The usefulness of this model of uncertainty for the formulation of complex research hypotheses and for the interpretation of empirical data is illustrated on the basis of a re-analysis of the record of PISA-2003 l Plus. (DIPF/Orig.

Relationship between Density and Biogenic Opal in Sediments from Sites 658 and 660

At Site 658, and especially at Site 660, sediments rich in biogenic opal were recovered. The fractions of biogenic silica, biogenic carbonate, and terrigenous material vary throughout the entire sequence at these sites (see chapters for Sites 658 and 660, this volume). At Site 660, biogenic-opal contents up to 100% are common in Eocene sediments. In studying these opal-rich sediments, a rapid method for estimating biogenic opal published by Mann and Muller (1980) was found useful. These authors applied an X-ray method which measures the height of a broad, diffuse reflection band of opal extending from about 15° to 32° 20, with a maximum at about 22° 20 (i.e., 4.04A) (Fig. 1, IB). Furthermore, this paper describes another method for estimating variations in the biogenic-opal content by using grain density. Grain density (p) can easily be determined by measuring the weight (G) and the volume (V) of the dry sediment, where p = G/P7g/cm3)

Role of tectonic stress in seepage evolution along the gas hydrate‐charged Vestnesa Ridge, Fram Strait

Methane expulsion from the world ocean floor is a broadly observed phenomenon known to be episodic. Yet the processes that modulate seepage remain elusive. In the Arctic offshore west Svalbard, for instance, seepage at 200–400 m water depth may be explained by ocean temperature‐controlled gas hydrate instabilities at the shelf break, but additional processes are required to explain seepage in permanently cold waters at depths \u3e1000 m. We discuss the influence of tectonic stress on seepage evolution along the ~100 km long hydrate‐bearing Vestnesa Ridge in Fram Strait. High‐resolution P‐Cable 3‐D seismic data revealed fine‐scale (\u3e10 m width) near‐vertical faults and fractures controlling seepage distribution. Gas chimneys record multiple seepage events coinciding with glacial intensification and active faulting. The faults document the influence of nearby tectonic stress fields in seepage evolution along this deepwater gas hydrate system for at least the last ~2.7 Ma

Norwegian margin outer shelf cracking: a consequence of climate-induced gas hydrate dissociation?

A series of en echelon cracks run nearly parallel to the outer shelf edge of the mid-Norwegian margin. The features can be followed in a *60-km-long and *5-km-wide zone in which up to 10-m-deep cracks developed in the seabed at 400–550 m water depth. The time of the seabed cracking has been dated to 7350 14C years BP (8180 cal years BP), which corresponds with the main Storegga Slide event (8100 ± 250 cal. years BP). Reflection seismic data suggest that the cracks do not appear to result from deep-seated faults, but it cannot be ruled out completely that tension crevices were created in relation to past movements on the headwall of the Storegga slide. The cracking zone corresponds well to the zone where the base of the hydrate stability zone (BHSZ) outcrops. Evidence of fluid release in the BHSZ outcrop zone comes from an extensive pockmark field. We suggest that post-glacial ocean warming triggered the dissociation of gas hydrates while the interplay between dissociation, overpressure, and sediment fracturing on the outer shelf remains to be understood.publishedVersio

Ice-sheet-driven methane storage and release in the Arctic

It is established that late-twentieth and twenty-first century ocean warming has forced dissociation of gas hydrates with concomitant seabed methane release. However, recent dating of methane expulsion sites suggests that gas release has been ongoing over many millennia. Here we synthesize observations of B1,900 fluid escape features—pockmarks and active gas flares—across a previously glaciated Arctic margin with ice-sheet thermomechanical and gas hydrate stability zone modelling. Our results indicate that even under conservative estimates of ice thickness with temperate subglacial conditions, a 500-m thick gas hydrate stability zone—which could serve as a methane sink—existed beneath the ice sheet. Moreover, we reveal that in water depths 150–520 m methane release also per- sisted through a 20-km-wide window between the subsea and subglacial gas hydrate stability zone. This window expanded in response to post-glacial climate warming and deglaciation thereby opening the Arctic shelf for methane release