Turbulent Airflow and Wave-Induced Stress Over the Ocean

We examine the structure of turbulent airflow over ocean waves. Based on an analysis of wind and wave observations derived from a moored and floating Air–Sea Interaction Spar buoy during the Shoaling Waves Experiment field campaign, we show that the cospectra of momentum flux for wind–sea conditions follow established universal scaling laws. Under swell-dominant conditions, the wave boundary layer is extended and the universal cospectral scaling breaks down, as demonstrated previously. On the other hand, the use of peak wave frequency to reproduce the universal cospectra successfully explains the structure of the turbulent flow field. We quantify the wave-coherent component of the airflow and this clarifies how ocean waves affect momentum transfer through the wave boundary layer. In fact, the estimated wave-induced stresses for swell-dominant conditions explain the anomalous cospectral shapes observed near the peak wave frequency.     

Floodplain sedimentation: Quantities,patterns and processes

This paper presents the result of measurements of floodplain sedimentation using sediment traps. The study was carried out on two embanked floodplains along the Rivers Rhine and Meuse in The Netherlands during a 3 day flood in January 1993. Raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging. The sediment maps show clear patterns in sediment accumulation, together with the estimated interpolation errors. Average sediment accumulation ranges between 0·57 and 1·0 kg m^?2. High sediment accumulation is found on the levees (4 kg m^?2 or more) and on low lying areas (1·6 kg m^?2); sediment accumulation decreases with distance from the main channel. The sedimentation patterns are related to floodplain topography and sediment transporting mechanisms. Sediment transport by turbulent diffusion as well as by convection can be recognized. Also, flood duration and the process of sediment settling out in ponding water in closed depressions are important. The applied method allows comparison of the results with raster-based sedimentation models.     

Mercury levels in fish,invertebrates and sediment in a recently recorded polluted area (Nissum Broad,western Limfjord,Denmark)

High concentrations of mercury were measured in sediment and animals collected in the immediate vicinity of a closed-down chemical factory. Sediment contained up to 22 ppm (dry wt) of mercury, deposit-feeding bivalves between 1.4 and 4.4 ppm (wet wt), suspension-feeding bivalves between 0.9 and 1.9 ppm and predatory fish between 0.3 and 0.8 ppm. Outside the ‘hot spot’ area, the mercury concentration in sediment and mussels (Mytilus edulis) rapidly decreased with increasing distance from the former factory. Mercury concentration in flounders (Platichthys flesus) also decreased with distance from the source; the decline was, however, much less marked.     

Relations between submarine fissures,internal breccias and mass flows during Triassic and earlier rifting periods

Deep fissures in shallow-water limestones filled with deep-water sediments are described from many places especially in the Triassic and Jurassic of the Tethys and in the Middle to Upper Devonian of the Variscian Mountains. Mass flows occur in the same formations and areas. On the island of Hydra (Greece) it was possible to show that both phenomena are linked by internal breccias of well-fitted limestone fragments. They are indicative of slope or near-slope positions and are very probably caused by flexure-like deformations of shallow-burial limestones. Seismic shocks producing overpressure may be instrumental in the disintegration of the semi-lithified limestones thus providing the material for mass flows. These events are associated with a tectonical subsidence as shown by deep-water matrix in the brecciated shallow-water limestones. They occur in areas and periods of submarine rifting, especially in late Devonian and Triassic time. At least four Triassic brecciation events can be traced from Greece to the Alps and correspond presumably to major transgressions in the cratonic basin of middle Europe.     

Alterations of cretaceous siltstones and sandstones near basalt contacts (Nûgssuaq,Greenland)

The influence of the intrusion of basaltic dykes and sills was investigated on sandstones and siltstones of the Atane Formation (Turonian-Coniacian) from the Sarqaq area (Nûgssuaq peninsula, central West Greenland).In the unaltered rock sequence, the siltstones are dominated by kaolinite, quartz and feldspar. No cementation was observed. The sandstones which are prevalent in this formation are arkoses and lithic arkoses with quartz/feldspar ratios of about 1, with variable contents of rock fragments and with minor amounts of matrix. The matrix consists mainly of kaolinite, less frequently of illite-muscovite and smectite or interstratified illite-smectite. Cement minerals include calcite, Fe-calcite, both mainly in concretions, and subordinate Fe-oxide hydrates.The porosity of the sandstones and siltstones indicates a former maximum depth of burial of 1000 m in the Sarqaq region.Adjacent to thin dykes and sills (1–2 m) the above-described rocks are altered as follows. In sandstones albite (fibrous), quartzine, smectite, goethite were all formed at the expense of kaolinitic matrix, and aragonite cement. In siltstones, interstratified illite-smectite, illite, smectite and low-cristobalite replaced kaolinite. These minerals, especially smectite, exclude temperatures above 200°C; they were probably formed during a cooling period.Adjacent to thicker basalt intrusions—only sills, over 5 m thick, and no dykes are known from this area—the following alterations are observed. In sandstones two textural types of albite were formed in addition to: (1) fibrous albite mentioned above; (2) undulose lath-shaped albite; (3) coarse-twinned non-undulose replacement albite. Moreover, brownish luminescing undulose quartz, muscovite, chlorite, epidote, nontronite and anatase occur. In siltstones the mineral association muscovite-chlorite-pyrophyllite-albite occurs, suggesting temperatures in the range of 250–500°C. Additionally a 22–26 Å mixed-layer mineral (chlorite-muscovite?) formed. At the contacts of thick as well as thin basalt intrusions the detrital grains directly adjoining the basalt are partly fractured; potassium feldspar grains show also a chemical disintegration.The temperatures calculated by application of a cooling model are higher than those indicated by the mineral alterations observed. Convective heat transfer by pore water is suggested as an explanation.     

Pigmente phototropher Bakterien in Seesedimenten und ihre Bedeutung für die Seenforschung

Sediments of shallow lakes contain besides plankton pigments as well pigments of purple non-sulfur and purple sulfur bacteria. A thin-layer chromatographic method was developed for the separation of the most important pigments of purple bacteria beside plankton pigments. The new method was examined in three different lakes for a stratigraphic analysis of bacteria pigments beside plankton pigments and the results were discussed subsequently.