Time dependence of organic matter decay and mixing processes in Framvaren, a permanently anoxic fjord in South Norway

Three different layers have been identified in Framvaren, which has a maximum water depth of 184 m. One oxic layer above the redoxcline at 18–20 m. One anoxic layer from 20 to 100 m which is occasionally ventilated by a flow over the sill (which has a depth of 2.5 m), and finally a stagnant layer below 100 m. Using the release rate of silica from the bottom and measurements of the concentration of HTO it is possible to make some calculations on the annual volume of interleaving in the layers 25–50 m, 50–75 m, and 75–100 m together with the advective flows. Reliable values of the sulfide concentration were obtained by precipitating and weighing HgS together with careful protection of all anoxic water samples with argon. The light yellow color of the precipitate in the depth range 25 to 80 m indicates that the occasional ventilation will cause such reactions as 0.50₂ + H₂S S(colloidal) + H₂O. The elemental sulfur, being stabilized with HS^–, is set free upon the precipitation of HgS. The new data for the concentration of sulfide give an acceptable stoichiometry for the decay reaction of organic matter. This is not the case with the data of Yao and Millero. The mean values for the concentrations of ammonium and phosphate agree with the new data of Yao and Millero. The mol/mol C/N ratio of 10.1 found in trapped material by Naess and coworkers (1988) agrees with the stoichiometry of the dissolved constituents, i.e. C/N = 9.92 ± 0.45. A denitrification reaction is suggested to explain the high values of C/N. The vertical diffusion coefficient at 100 m calculated from the depth profile of silica was 0.92 × 10^–6 m² s^–1 which lies in the range of values given by Fröyland. Finally, the ¹⁴C age of the total dissolved inorganic carbon (Ct) in the water below 90 m was about 1600 years indicating a bioproduction in the period 8000 years B.P. to A.D. 1853 when a channel was opened between the fjord outside (Helvikfjord) and Framvaren.     

Magnetic susceptibility in sediment records of Lake Ådran,eastern Sweden: correlation among cores and interpretation

Magnetic susceptibility was used to test the representativity of the lithostratigraphy of a master sediment sequence from Lake Ådran, eastern Sweden. Five further sediment cores from the same lake were correlated and compared with the master sequence using magnetic susceptibility records. Mineral magnetic correlations are generally based on matching prominent susceptibility features but may be significantly improved by using slot sequence analyses. The result of these analyses show that the sediment in the Lake Ådran master sequence can be considered representative for the basin. The variations in the magnetic susceptibility in relation to pollen and diatom analyses also seem to reflect water level changes and shore displacement in the Baltic between 9900 ¹⁴C years B.P. and the isolation at 5900 ¹⁴C years B.P. The first emergence of scattered non-vegetated islands is characterised by high susceptibility values. Along with a continuous water lowering and the development of the vegetation during the Ancylus fresh water stage, susceptibility values gradually decrease. A rapid phase of the Ancylus regression between 9200 and 9000 ¹⁴C years B.P. is seen as an increase in magnetic susceptibility. During the following Baltic brackish water stage, the Litorina stage, susceptibility values are at their lowest, followed by higher values at the isolation from the Baltic with a maximum around 5000 ¹⁴C years B.P.Shore displacement between 9900 and 5900 ¹⁴C years B.P. is discussed based on the magnetic susceptibility measurements and their relationship to the pollen and diatom analyses.     

Behaviour of rubble-mound breakwater in directional and uni-directional waves

The application of directional waves in design processes has clearly received much interest during recent years. Thus, in model testing with moored ships and offshore structures, significant deviations have been revealed between results obtained in traditional uni-directional wave trains and those obtained in directional wave fields. Whether the same tendency is valid in connection with the design of rubble mound breakwaters is studied in the present project. A breakwater with a front slope of 1:2 is tested at the scale 1:40. The weight and diameter of the stones in the core, filter and armour layers were carefully selected, and the sources of scatter in repeated tests were minimized. Furthermore, the incident wave energy was accurately adjusted to keep the same level in both uni-directional and directional waves. For the actual rubble-mound breakwater unambiguous results were obtained. When uni-directional waves were applied, the damage increased by 30–50% relative to the directional wave situation.     

The radio–optical correlation in steep-spectrum quasars

Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation dependence (such as relativistic beaming), nor a by-product of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion on to a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio-luminous high-redshift galaxies.     

Estimation of sea surface topography in the Norwegian sea using gravimetry and Geosat altimetry

An analysis of the quasi-stationary sea surface topography (QSST) is carried out in the Norwegian Sea region (54°<ø<72°, -25°<<20°) using marine gravimetry and one year of Geosat ERM altimetry. As reference models the geopotential model OSU91A and the QSST model OSU89D were used. Two procedures to extract the QSST from mean sea surface heights and gravity anomalies were tested. Spherical FFT techniques were applied in both procedures. The results show that QSST associated with wavelength shorter than 4000 km exists. Relative to the OSU89D model the QSST was found to have a variance of (0.219 m)² and a correlation length of 1.105°. The circulation pattern recovered in this paper agree with results of oceanographic analysis.     

Reproduction of higher harmonics in irregular waves

The basic features of higher harmonic waves were originally presented by Stokes in 1847 who showed that a 2nd-order regular wave would attain a higher, sharper crest and a flatter trough than the basic linear one. In this paper, these characteristics are investigated for an irregular wave train. This was done to make it possible to reproduce in a laboratory flume a wave train which has the correct profile and rms according to 2nd-order theory. The 2nd-order wave heights and the overall horizontal asymmetries of the wave train were calculated for a 1st-order PM and a Jonswap spectrum. The theoretical predictions show that the traditional wave generation in a laboratory flume which is based on linear theory produces free 2nd-order waves in addition to the bound 2nd-order waves described by Stokes. These free, parasitic waves incorrectly distort the shape of the waves and produce a varying rms as a function of distance from the wave paddle. In the 2nd-order theory presented in this paper, these free (parasitic) waves are calculated for the entire spectrum. Knowing these, they can be eliminated by compensating for them by using a 2nd-order control signal on the wave paddle. This is verified by a series of model tests which show that realistic wave profiles can be generated only by means of 2nd-order control signals. The theory and corresponding paddle control are presented for any type of translating, rotating or combined wave generator.     

Group bounded long waves in physical models

During the last few years it has been shown that the results of model tests of harbour basins and moored ships are highly dependent on the correct reproduction of wave groups and the attached long waves. Although these bounded long waves are of second order and thus of a rather limited height, resonance and shoaling effects can increase their influence on the results of model investigations. In traditional first order wave generation, the boundary conditions at the wave board are not fulfilled for the bounded long waves, and consequently various spurious, free long waves are unintentionally produced. This paper outlines the general equations and the solution for a rotating and translating wave board. The translatory case is treated in detail, i.e. a physical interpretation of all the second order terms is given, and an approximate control signal for the suppression of spurious long waves for practical use is described. Finally, laboratory experiments successfully verify the various long wave terms and the effectiveness of the suppression terms.     

The stabilisation of wet sediment cores by means of a polyethylene glycol/freeze-drying treatment for display and permanent storage

A reversible method is presented to transform waterlogged sediment cores into dry and stable specimens which can go on exhibition or into permanent storage, needing no special precautions. Wet sediment core segments are bath-impregnated with polyethylene glycol of molecular weight 3,350 (PEG 3,350) dissolved in water. The samples are then subjected to a freeze-drying process, during which the PEG forms a stabilising and bonding porous network structure in the capillary system of the sediment. Standard sediment cores at least 1 m long become strong enough to stand upright. Sediment types ranging from muddy deep-sea sediments to very coarse littoral Halimeda sand were successfully stabilised. For standard cores of 10-cm diameters split length-wise, impregnation times vary from 2 weeks for coarse sand to 6–10 weeks for more compacted sediments. With regard to the stability of the samples and the visual clarity of detail, best results were obtained by impregnation with 25 to 60% solutions of PEG 3,350, coarse sediments needing more PEG than finer ones. Colour changes are systematic – the processed samples are lighter in appearance and the contrasts are enhanced, but there is no serious shift in colour tones. The PEG can easily be re-dissolved and washed out of the sediments. Display specimens can thus be made available for research again.