Sea-floor dynamic processes as the possible cause of correlations between paleoclimatic and paleomagnetic indices in deep-sea sedimentary cores

Recent publications showing correlations between the variation of intensity of magnetization(J) and paleomagnetic inclinationI on the one hand, and diverse paleoclimatic indices on the other, have been interpreted to represent direct cause and effect relationships between climate and geomagnetism.It is proposed that several sea-floor dynamic processes, which are climatically variable, are at least equally feasible causes of the observed correlations. Thus, for variation inJ, it is a simple matter to invoke variations in such factors as the magnetic particle size fraction below 50 microns, carbonate content, or laminar flow layer thickness, all of which can change with climate. For variation inI, climatically related variation of the velocity gradient in the laminar flow layer can be employed to explain the correlation.Prior to accepting the suggested geomagnetic control of climate as real, it is recommended that simple measurements of the temporal and geographic variation in fabric and composition of the deep-sea sediments involved should be carried out, as a check for the effect of bottom dynamic processes.     

Mechanisms controlling summertime oxygen depletion in western Long Island Sound

Physical profile data (salinity, temperature, oxygen, and downwelling irradiance) and in situ incubations of light and dark bottles were used to characterize vertical structure and elucidate mechanisms controlling summertime hypoxia in western Long Island Sound. The period of oxygen depletion corresponded with the period of thermally-controlled stratification. Bulk density differences between surface and bottom waters were only 1.2 to 2.7 sigma-t units; but they were apparently sufficient to resist destratification by winds and tides. Thus oxygen depletion was a cumulative process through the summer. During the stratification period, net oxygen production (measured using light BOD bottles) was confined to a narrow surface zone of 1.8–4.5 m. Below this zone was an intermediate zone of high net oxygen uptake, beneath which was a subpycnoclinic zone where oxygen uptake was very low. Rates of total oxygen uptake (dark bottles) were greatest in the surface layer and diminished with depth. There was close coupling between physical conditions and metabolic structure. Vertical patterns of oxygen production and removal were strongest in calm weather. The location of the intermediate zone corresponded with that of the oxycline. The thickness of the zone and the steepness of the oxycline were determined by the depth and intensity of both physical stratification and biological production and respiration. The biological structure was weakened by physical mixing in the upper water column, and the intermediate zone disappeared with fall destratification. We hypothesize that biological uptake within the water column influences oxygen depletion through two mechanisms. (1) In bottom waters, uptake rates per unit volume are low, but bulk uptake is a significant factor in oxygen depletion because of the large volume of water involved. (2) The intermediate zone, where respiratory uptake is also significant, is strategically located between the surface zone of oxygen renewal and the bottom zone of depletion, where it constitutes an active filter which reinforces the pycnocline as a barrier to vertical oxygen dispersion. The magnitude of direct oxygen removal in the water column relative to removal by sediment oxygen demand and the potential effects of this biological filtering mechanism are important considerations for understanding eutrophication dynamics and managing Long Island Sound. Dynamic models which (1) underestimate the role of water column uptake and (2) incorporate only the two-zone characteristics of physical stratification will tend to (a) overestimate the contribution of sediments to summertime oxygen deficits and (b) overestimate rates of vertical dispersion and reventilation of bottom waters.     

Modeling subsurface flow in sedimentary basins

Groundwater flows that arise in sedimentary basins from the effects of topographic relief, buoyant convection, sediment compaction, erosional unloading, and combinations of these driving forces can be described using quantitative modeling techniques. Models can be constructed to consider the effects of heat and solute transport, petroleum migration, and the chemical interaction of water and rocks. The accuracy of model predictions, however, is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions, estimating past conditions such as topographic relief, and knowledge of how physical and chemical processes interact over gelogic time scales. Progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology, rock mechanics, and geochemistry.

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Zusammenfassung Grundwasserbewegungen in sedimentären Becken, die von dem topographischen Relief, konvektionsbedingtem Auftrieb, Sedimentkompaktion, isostatischen Ausgleichsbewegungen in Folge von Erosion und von Kombinationen dieser Kräfte gesteuert werden, können mit Hilfe quantitativ modellierender Techniken beschrieben werden. In diesen Modellen kann man die Auswirkungen des Transports von Wärme und gelösten Stoffen, Petroleum-Migration und die chemische Interaktion zwischen Wasser und dem grundwasserleitenden Gestein berücksichtigen.Die Genauigkeit der Modell-Voraussagen ist allerdings begrenzt wegen der Schwierigkeit, hydrologische Eigenschaften von Sedimenten in einem regionalen Rahmen vorauszusagen, dem Schätzen vergangener Bedingungen und dem Problem der Abschätzung von Wechselwirkungen physikalischer und chemischer Prozesse in geologischen Zeiträumen. Fortschritte für das Modellieren von Becken werden mit der Integration hydrologischer Forschungsanstrengungen in benachbarte Fachebiete wie Sedimentologie, Gesteinsmechanik und Geochemie zunehmen.

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Résumé Il est possible, par l'utilisation de techniques quantitatives de modélisation, de décrire les mouvements des eaux souterraines qui se manifestem dans les bassins sédimentaires, et qui résultent du relief topographique, de la convection, de la compaction des sédiments, de la décharge due à l'érosion et de la combinaison de ces divers facteurs. Dans ces modèles, on peut prendre en considération les effets des transferts de chaleur et de matières dissoutes lors de la migration du pétrole et ceux de l'interaction chimique de l'eau avec les roches. Toutefois la précision des prévisions que l'on peut en déduire est limitée par la difficulté d'estimer à l'echelle régionale les propriétés hydrologiques des sédiments, de reconstituer les conditions anciennes, et de connaître de quelle manière les processus physiques et chimiques interfèrent à l'échelle des temps géologiques. La modélisation des bassins progressera dans la mesure où la recherche hydrogéologique ser mieux intégrée à celles d'autres disciplines telles que la sédimentologie, la mécanique des roches et la géochimie.

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Intermediate-term,pre-earthquake phenomena in California, 1975–1986, and preliminary forecast of seismicity for the next decade

Intermediate-term observations preceding earthquakes of magnitude 5.7 or greater in California from 1975 through 1986 suggest that: (1) The sudden appearance of earthquakes in a previously inactive area indicates an increased likelihood of a significant earthquake in that area for a period from days to years; (2) these larger earthquakes tend to occur towards the ends of creeping fault segments; (3) one large earthquake in a region increases the likelihood of a subsequent significant event in the adjacent area; and (4) marginal evidence for the occurrence of a regional deformation event suggests that such events increase the probability of earthquake occurrence throughout the entire area. A common element in many of these observed patterns appears to be the transmission and amplification of tectonic stress changes by the mechanism of fault creep, and suggests that surface fault creep is a sensitive indicator of changes in stress. The preceding critieria are used to construct a preliminary forecast of the likely locations of significant earthquakes over the next decade.     

Final evolution of stars in the range 103–104 M ⊙

The final dynamical collapse of oxygen cores of 10³ and 10⁴ M which undergo the pair formation instability is computed. These cores are found to suffer complete collapse, presumably to form black holes, in contrast to cores of 100M which have previously been found to explode completely, leaving no remnant. These calculations represent a first attempt to ascertain the outcome of evolution over several decades of mass previously unexplored. The outcome may have some relevance to models of X-ray sources in globular clusters.     

Polyester mooring for the Mad Dog spar—design issues and other considerations

The Mad dog project will use a polyester mooring system on the drilling and production truss spar. This will be the first use of a permanent polyester mooring system on a Floating Production System (FPS) outside of Brazil and the first time polyester has been used on a spar. As such, there were many challenges, which include:

• Regulatory approval.

• Designing a mooring system which is dominated by current loadings.

• Largest polyester rope break load ever required.

• Rope design qualification and testing.

• Quality control and assurance.

• Inspection, Maintenance, Repair and Retirement (IMRR) of such a mooring system.

This paper will focus on the design issues, rope design, manufacturing, qualification and testing, and the IMRR plan that was developed to provide the assurance that the polyester mooring system could be safely operated over the 20-year field life.     

Prediction and observation of a model gravity platform on Drammen clay

The results of five centrifuge tests of a stiff circular model platform on overconsolidated undisturbed Drammen clay are reported from Manchester University together with predictions computed at the Norwegian Geotechnical Institute. Towards failure the models developed high shear strain and softening local to the base, accompanied by a permanent settlement or shakedown. A total stress transfer from edge to centre caused a rapid increase of excess pore pressure under the centre, having a high vertical gradient. These features, and failure values which decreased with increase in eccentricity of loading, conformed with previous observations on reconstituted clays. Comparison of observations with predictions highlights the sensitivity of the analytical method to the fineness of the finite element mesh just below the base. The predictions also indicated a sensitivity of the failure load to the degree of overconsolidation associated with a given undrained shear strength. The elastic type analysis did not predict the degree of shakedown which was associated with plastic displacement of clay from just under the base.