Das Faziesgesetz der vorquartären Vulkaneruptionen

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Burdigal- und Helvettransgression im Rheintalgraben

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Effect of fluid column dynamics on longitudinal vibrations of an ultra deepwater riser covered by an orifice plug

The paper studies longitudinal vibrations of an ultra-deepwater drilling riser whose bottom end is disconnected from the sea floor and covered by a plug (a blind one or the one with a hole). An elastic shell is used as a model of a riser pipe. The fluid column motion in the riser is described by the Navier–Stokes equation for a compressible fluid. Losses of fluid pressure during its flowing through a hole in the plug are taken into account. Solution of the riser equations is carried out in the frequency domain. Analysis of the effect which the riser length, wave period and height, and the plug-hole diameter on the amplitude of the riser's tension vibrations is conducted. A riser manufactured of strong aluminium alloys, some of prospective materials for ultra deepwater drilling, was considered as a prototype. It has been shown that risers 2000–4000 m long, plug-hole, and a riser 6000 m long with plug-hole of 0.087 m in diameter can withstand wave height of >15 m throughout the frequency range.     

A large late pleistocene blocky debris flow on the central scotian slope

A SeaMARC I side-scan sonar survey on the central Scotian Slope shows a blocky debris flow with high surface roughness between the 1,000 and 2,000 m isobaths, covering an area of about 1,000 km². The flow is at least 20 m thick, occuring as lenses within channels and as sheets on intervalley areas. The surface reflectivity is variable, with blocks and depressions 50 to 200 m wide and relief of 5 to 20 m. The source zone lies within two canyons on the upper slope and has relatively smooth surface reflectivity, in contrast to the gullied slope to either side.     

Fluxes of iron and manganese across the sediment–water interface under various redox conditions

Fluxes of dissolved forms of iron and manganese across the sediment–water interface were studied in situ in the Gulf of Finland and the Vistula Lagoon (Baltic Sea), and in the Golubaya Bay (Black Sea) from 2001 to 2005. Fluxes were measured using chamber incubations, and sediment cores were collected and sliced to assess the porewater and solid phase metal distribution at different depths. Measured and calculated benthic fluxes of manganese and iron were directed out of sediment for all sites and were found to vary between 70–4450 and 5–1000 µmole m^− 2 day^− 1 for manganese and iron, respectively. The behavior of the studied metals at various redox conditions in the near-bottom water and in the sediment was the main focus in this study. Our results show the importance of bottom water redox conditions for iron fluxes. We measured no fluxes at oxic conditions, intermediate fluxes at anoxic conditions (up to 200 μmole m^− 2 day^− 1) and high fluxes at suboxic conditions (up to 1000 μmole m^− 2 day^− 1). Total dissolved iron fluxes were generally dominated by iron(II). Contribution of iron(III) to the total iron flux did not exceed 20%. Obtained fluxes of manganese at all studied regions showed a linear correlation (r² = 0.97) to its concentration in the porewater of the top sediment layer (0–5 mm) and did not depend on dissolved oxygen concentrations of bottom water. Organically complexed iron and manganese were in most cases not involved in the benthic exchange processes.     

Toxicity assessment of sediment cores from Santa Monica Bay,California

During the summer of 1997, sediment core samples were taken at 25 stations in Santa Monica Bay. Toxicity testing was performed on 4-cm sections of the entire length of each core using purple sea urchin fertilization and amphipod survival tests. The sea urchin test identified sections as being toxic at six stations, all located near current or former Hyperion Treatment Plant (HTP) wastewater outfall locations. The amphipod test identified sections from 17 stations as having toxic sediments. The stations having toxic sediments were scattered throughout the bay and toxicity was identified at numerous core depths. Spatial and temporal patterns indicated that toxicity was most strongly associated with the historical disposal of municipal wastewater sludge. Many of the sections toxic to the amphipods did not have chemical levels expected to cause toxicity and were in locations where a source of toxicity was not apparent.     

Drifter Observations of Anticyclonic Eddies near Bussol' Strait, the Kuril Islands

Hydrographic surveys and satellite imaging reveal that mesoscale anticyclonic (AC) eddies are common features of the area south of Bussol' Strait, the deepest of the Kuril straits connecting the western North Pacific and Sea of Okhotsk. To examine the velocity structure of these eddies, we deployed groups of 15-m drogued satellite-tracked surface drifters over the Kuril-Kamchatka Trench in the fall of 1990 and late summer of 1993. Drifters in both groups entered large AC eddies centered over the axis of the trench seaward of Bussol' Strait and subsequently underwent a slow northeastward translation. One drifter (Drifter 1315) deployed near the center of the “Bussol' eddy” in 1990, remained in the eddy for roughly 45 days and made five loops at successively greater distances from the eddy center. Large-amplitude (80–100 cm/s) storm-generated inertial oscillations were observed during the first two loops. The vorticity field associated with the eddy resulted in a Doppler “red-shift” of inertial frequency motions such that the “effective” inertial period of 21 hours was roughly 4 hours greater than the nominal inertial period for the drifter latitude (45°N). In 1993, a second drifter (Drifter 15371) was retained in the Bussol' eddy for about 40 days. This eddy had characteristics similar to those of the 1990 eddy but was devoid of significant high-frequency motions until the drifter's final half loop. The observed spatial scales, persistence, and slow poleward translation of the eddies suggests that they play an important role in the dynamics of the East Kamchatka and Oyashio current systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lunar fortnightly modulation of tidal mixing near Kashevarov Bank, Sea of Okhotsk, and its impacts on biota and sea ice

Here we examine the consequences of strong tidal mixing on spatial and temporal distributions of biota and sea ice above Kashevarov Bank, Sea of Okhotsk, using data from field surveys (hydrography, pressure gauge and current meter moorings, and bio-acoustic soundings) and remote sensing (NOAA AVHRR). Fortnightly variations in the amplitude of diurnal tidal currents, primarily resulting from the K₁–O₁ interaction, are shown to dominate water motion over the bank. These currents (with maximum velocities 2 m s⁻¹) create a sharp tidally-mixed front that separates well-mixed water above the bank from stratified water along its flanks. Such mixing draws water upward from the cold dichothermal layer (100–150 m) into the surface layer, and thus serves to ventilate the intermediate layers of the Sea of Okhotsk. In summer, fortnightly modulation of the tidal mixing creates temporal variations in water column stratification, a critical factor in the joint supply of nutrients and light required to sustain phytoplankton growth. As such, chlorophyll-a and oxygen values vary in response to the fortnightly cycle, and zooplankton likewise form dense aggregations within the tidally-mixed front in response to the phytoplankton production. It is further noted that the brood cycle of dominant zooplankton species on the bank matches the fortnightly modulation of the tidal currents. In winter, tidal mixing draws relatively warm water upward from mid-depth to maintain a polynya that cyclically opens and closes in response to fortnightly variation in vertical heat flux.