Investigation of the role of gas hydrates in continental slope stability west of Fiordland, New Zealand

Sediment weakening due to increased local pore fluid pressure is interpreted to be the cause of a submarine landslide that has been seismically imaged off the southwest coast of New Zealand. Data show a distinct and continuous bottom‐simulating reflection (BSR)—a seismic phenomena indicative of the presence of marine gas hydrate—below the continental shelf from water depths of c. 2400 m to c. 750 m, where it intersects the seafloor. Excess pore fluid pressure (EPP) generated in a free gas zone below the base of gas hydrate stability is interpreted as being a major factor in the slope's destabilisation. Representative sediment strength characteristics have been applied to limit‐equilibrium methods of slope stability analysis with respect to the Mohr‐Coulomb failure criterion to develop an understanding of the feature's sensitivity to EPP. EPP has been modelled with representative material properties (internal angle of friction, bulk soil unit weight and cohesion) to show the considerable effect it has on stability. The best estimate of average EPP being solely responsible for failure is 1700 kPa, assuming a perfectly elastic body above a pre‐defined failure surface in a static environment

Gas Hydrates on the Hikurangi and Fiordland Margins, New Zealand

The presence of gas hydrates offshore New Zealand has been inferred from bottom simulating reflections (BSRs) for over two decades (Katz, 1981). BSRs are widespread on the Hikurangi margin east of the North Island and on the Fiordland margin southwest of the South Island. New Zealand’s largest conventional gas field may be depleted in a few years and hence, there is increasing interest in the resource potential of gas hydrates. Most of our studies are currently focusing on the Hikurangi margin, mainly because of its proximity to major population centers, making it attractive for possible future gas production. For this margin, we have performed first estimates of the resource potential in gas hydrates (Pecher and Henrys, 2003). Because of a paucity of adequate seismic data and lack of drilling and coring of gas hydrates, our estimates are highly uncertain. However, based on the distribution of BSRs, we were able to constrain the gas hydrate province to an area of about 50,000 km 2 (Fig. 1). Using conservative values for an average gas hydrate saturation of 2 % of the pore space, the volume of gas locked in gas hydrates in this area is estimated to be over 20,000 km 3 at standard temperature and pressure conditions. However, for economic extraction of gas it may be essential to identify potential gas hydrate “sweet spots”, i.e., areas of high gas hydrate concentration. Ga

Test of a ring imaging Cherenkov counter

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Resuspension and particle transport in the Benthic Nepheloid Layer in and near Fram Strait in relation to faunal abundances and 234Th depletion

The West Spitsbergen Current, flowing northward through Fram Strait, causes a benthic nepheloid layer (BNL) on the western slope of the Yermak Plateau. This BNL is weaker on the eastern side of the Plateau and absent on the Greenland side of the Fram Strait where the East Greenland Current flows south. In this BNL we find throughout a depletion of 234Th relative to its parent 238U, and we use this to study the particle dynamics in the BNL. The export flux from the ice-covered surface ocean and from a young bloom found in the ice-free waters off NE Greenland is shown to be negligible, allowing us to explain the 234Th depletion by interaction with the sediment alone. The depletion, balanced by a similar excess in the surface layer of the sediment, implies the existence of a settling-resuspension loop with an average particle residence time of 1-2 months.The asymmetry with a stronger resuspension loop on the western (80-120 mg m-2 d-1) than on the eastern side of the Yermak Plateau (1-15 mg m-2 d-1) is reflected in the numbers of species and individuals of suspension feeders in box core samples, and in epifauna abundance as has been estimated from video observations. The suspension feeders thus contribute to deposit the particles that are advected from more productive ice-free regions. This explanation is in agreement with the east-west asymmetry in the input of organic material to the sediments of the Yermak Plateau, which has been concluded by Soltwedel et al. (2000) from the distribution of pigments, bacterial activity and meiofauna abundances, observed in a concurrent study at the same stations.On the West Spitsbergen shelf, a very intensive BNL was monitored over one month with a moored filtration system. A part of the sustained high suspended load may be advected over long distances.This study gives an example how the tracer 234Th can help to determine to what extent suspended particles are in continuous exchange with the seafloor, and where biological mediation and chemical modification can be expected

Kooperativer Gewaesserschutz in Nordrhein-Westfalen - Sachstand, Trends, Strategien Fachkolloquium

SIGLEAvailable from TIB Hannover: RO 7208(19) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Wasserentnahmeentgelt in Nordrhein-Westfalen?

Available from TIB Hannover: RO 7208(21) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman