Cyclone and bioturbation effects on sediments from coral reef lagoons

Despite the severity of tropical cyclone ‘Winifred’, which crossed the Great Barrier Reef on 1 February 1986, there were little long-term effects on lagoon surface sediments from reefs in its path. Short-term effects were apparent only at one particularly exposed area. These were: an increase in proportion of the coarse fraction, the establishment of sand ripples, and the destruction of the mounds produced by callianassid shrimps (normally the dominant topographic feature). Within six weeks this area was indistinguishable from a typical reef lagoon. This is probably the result of sediment reworking by callianassid shrimp, involving selective burial of the coarse fragments and transport to the surface of finer particles. Sediment turnover rates by callianassids are commensurate with change to the sediment within the relatively short period observed. The sediment fauna responded quickly to the changes in sediment type. Immediately after the cyclone the disturbed area supported a fauna typical of the coarse sediments on the shallow reef flat, as the sediment reverted to a more normal type so the fauna changed back to that typical of a reef lagoon.     

Effects of benzene and dimethylnaphthalene on homeostatic processes in two species of crabs

Long-term exposure of animals to sub-lethal doses of toxicants such as benzene (B) and dimethylnaphthalene (DMN) may result in subtle changes in their physiology and biochemistry. In crustaceans such changes include decreased rate of limb regeneration, extended time to molt and decreased growth increment at molt.^1,2 These processes depend upon an adequate supply of stored nutrients in the tissues and appropriate release of neuroendocrine substances from the central nervous system.^3,4 We are examining the effects of sub-lethal doses of B and DMN on osmotic and ionic regulation and on nutrient storage in the blue crab, Callinectes sapidus, and the green crab, Carcinus maenas. Disturbances in these physiological processes may reflect alterations in neuroendocrine functions brought about by the presence of toxicants. We find that exposure of C. maenas to B or DMN, followed by transfer to a dilute medium, results in impaired osmoregulatory capacity, while addition of these compounds to a dilute medium to which the animal is already acclimated does not affect their regulatory ability. Storage of carbohydrate in the midgut gland (hepatopancreas) is decreased by B or DMN, while the accessory storage tissues (gill, muscle) are not significantly affected.     

Submarine-fan facies associations of the Upper Cretaceous and Paleocene Gottero Sandstone,Ligurian Apennines,Italy

The Upper Cretaceous and Paleocene Gottero Sandstone was deposited as a small deep-sea fan on ophiolitic crust in a trench-slope basin. It was thrust northeastward as an allochthonous sheet in Early and Middle Cenozoic time. The Gottero, as thick as 1500 m, was probably derived from erosion of Hercynian granites and associated metamorphic rocks in northern Corsica. Outcrops of inner-fan channel, middle-fan channel and interchannel, outer-fan lobe, fan-fringe, and basin-plain facies associations indicate that the depositional model of Mutti and Ricci Lucchi for mixed-sediment deep-sea fans can be used. The original fan had a radius of 30 to 50 km.     

Null broadening with snapshot-deficient covariance matrices in passive sonar

Adaptive-array beamforming achieves high resolution and sidelobe suppression by producing sharp s in the adaptive beampattern. Large-aperture sonar arrays with many elements have small resolution cells; interferers may move through many resolution cells in the time required for accumulating a full-rank sample covariance matrix. This leads to "snapshot-deficient" processing. In this paper, the -broadening technique originally developed for an ideal stationary problem is extended to the snapshot-deficient problem combined with white-noise constraint (WNC) adaptive processing. Null broadening allows the strong interferers to move through resolution cells and increases the number of degrees of freedom, thereby improving the detection of weak stationary signals.     

Dissolved carbon and 33-133-133-1anomalies in the water column caused by hydrocarbon seeps on the northwestern Gulf of Mexico slope

Alkalinity, dissolved inorganic carbon (DIC), and ¹³C profiles from seep sites on the northwestern Gulf of Mexico upper slope show anomalously negative ¹³C values of up to –4.5 PDB, increased levels of DIC of up to 2.45 mmole/liter, and slight alkalinity rises of up to 2.54 meq/liter, relative to water column profiles from a seep-free site (0.63, 2.04 mmole/liter, and 2.39 meq/liter). The observed DIC enrichments coupled with the¹³C-depletions are attributed to the release of CO₂ by microbial oxidation of crude oil in the seep environment, and its migration into the water column. The ¹³C composition of the migrating CO₂ is estimated to be –26.0 on the basis of dissolved carbon inventory. Manifestation of DIC and ¹³C anomalies in the water column caused by hydrocarbon seepage holds promise to be useful for hydrocarbon reconnaissance surveys over large offshore tracts on account of the simplicity of sampling acquisition, and rapidity of analytical techniques in the laboratory.     

Sensitivity to stress of the estuarine bivalve Macoma balthica from areas between the Netherlands and its southern limits (Gironde)

Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress.     

Risk of dike failure due to flow slides

Flow slides may affect the stability of dikes. A flow slide is an instability of a submerged slope caused by liquefaction of loose, (medium) fine sand. Whether a flow slide will occur depends on the properties of the sand, which are a function of its density, and the geometry of the slope, as determined by wave and current induced scour and sedimentation. The influence of sand properties and the geometry parameters on the risk of flow slides are discussed. The application of a flow slide prediction method to an example and a risk analysis is briefly discussed.     

On the structural evolution of the Central Trough in the Norwegian and Danish sectors of the North Sea

The Central Trough of the North Sea is not a simple rift graben. It is an elongated area of regional subsidence which was initiated in mid Cretaceous times and continued to subside through to the late Tertiary. Its form is not representative of pre-mid Cretaceous tectonics.In Late Permian times the North Sea was divided into a northern and southern Zechstein basin by the E-W trending Mid North Sea-Ringkøbing-Fyn High. The latter was dissected by a narrow graben trending NNW through the Tail End Graben and the Søgne Basin. The Feda Graben was a minor basin on the northern flank of the Mid North Sea High at this time. This structural configuration persisted until end Middle Jurassic times when a new WNW trend separated the Tail End Graben from the Søgne Basin. Right lateral wrench movement on this new trend caused excessive subsudence in the Tail End and Feda Grabens while the Søgne Basin became inactive.Upper Jurassic subsidence trends continued during the Early Cretaceous causing the deposition of large thicknesses of sediments in local areas along the trend. From mid Cretaceous times the regional subsidence of the Central Trough was dominant but significant structural inversions occurred in those areas of maximum Early Cretaceous and Late Jurassic subsidence.