Pleistocene stratigraphy in the Devils Hole Area,Central North Sea: Foraminiferal and amino-acid evidence

A detailed study of the foraminiferal assemblages from the 229.1-m-deep core 81/34 in the central North Sea has been combined with a series of measurements of the isoleucine epimerisation of foraminiferal tests. A total of 17 foraminiferal zones have been established and both the faunal compositions and the amino-acid values suggest that a major part of the sequence represents deposits of early and middle Pleistocene age. Only the uppermost zone is referred to the late Pleistocene. The sequence mainly comprises a series of marine zones from cold periods, but with some barren, possibly non-marine intervals in between. Only two of the foraminiferal zones can be referred to interglacial periods. The oldest one of these, defined here as the Devils Hole Interglacial, may belong to the latter part of the Cromerian Complex, while the upper warm interval is correlated with the Holsteinian of northwest Europe on the basis of its amino-acid values. A detailed stratigraphical correlation between core 81/34 and the neighbouring core 81/29 is suggested on the basis of their foraminiferal content, palaeomagnetic evidence and amino-acid measurements from both cores. A characteristic feature of both sequences is that most of the Quaternary record is missing. Similar episodic patterns of deposition and erosion have been reported previously from the North Sea area.     

Palaeontology and taphonomy of Late Quaternary fossil assemblages at Somersham,Cambridgeshire, England,and the problem of reworking

Assemblages of foraminifers, ostracods and molluscs from temperate Ipswichian Stage (last temperate stage) sediments and overlying cold Devensian Stage (last cold stage) sediments at Somersham in the southern Fenland of Cambridgeshire have been analysed. The Ipswichian sediments contain faunas consistent with temperate brackish water conditions under tidal influence. The Devensian assemblages were recovered from a series of sands and gravels laterally accreting in a channel cutting into Ipswichian sediments. In contrast to the Ipswichian faunas, the faunas of particular Devensian samples show a complex mixture of temperate freshwater, brackish and marine taxa. The molluscs are mainly freshwater, with few land snails; they occur together with foraminifers and ostracods. Freshwater, brackish water and marine ostracods are present with foraminifers. A sample of Devensian fine laminated sediment in the channel was analysed for pollen; only abundant pre-Quaternary spores were present, with abundant foraminifers in the same sample. The taphonomy of the assemblages and the difficulties of their interpretation in environmental terms are discussed. The importance of taphonomy in assessing environments, climate, range of taxa and dating is stressed.     

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.     

Dynamics of the Venus ionosphere: A two-dimensional model study

A two-dimensional model of the ionosphere of Venus which simulates ionospheric dynamics by self-consistently solving the plasma equations of motion, including the inertial term, in finite difference form has been constructed. The model, which is applied over the solar zenith angle range extending from 60 to 140° and the altitude range 100 to 480 km, simulates the measured horizontal velocity field quite satisfactorily. The ion density field is somewhat overestimated on the dayside because of the choice model neutral atmosphere and underestimated on the nightside because of setting the ionopause height at too low an altitude. It is concluded that solar photoionization on the dayside and ion recombination on the nightside are the processes mainly responsible for accelerating the plasma to the observed velocities. The plasma flow appears to be sufficient to maintain the nightside ionosphere at or near the observed median level of ion densities.     

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.     

Multi-satellite ocean tide modelling—the K1 constituent

All major ocean tide constituents are aliased into signals with periods less than 90 days from TOPEX/POSEIDON altimetry, except the K₁ constituent. The aliased K₁ has a period of 173 days. Consequently, it might be confounded with height variations caused by the semiannual cycle having a period of 183 days.The correlation between K₁ and the semiannual signal has been investigated both locally and globally using combinations of T/P, ERS-1 and GEOSAT observations. Subsequently, two empirical methods have been investigated to improve the mapping of K₁ from multiple satellites.At high latitudes, where the presence of crossing tracks cannot separate K₁ from the semiannual signal from TOPEX/POSEIDON, the importance of including ERS-1 and GEOSAT observations was demonstrated. A comparison with 29 pelagic and coastal tide gauges in the Southern Ocean south of 50°S gave 5.59 (M₂), 2.27 (S₂) and 5.04 (K₁) cm RMS agreement for FES95.1 ocean tide model. The same comparison for the best empirical estimated constituents based on TOPEX/POSEIDON + ERS-1 + GEOSAT gave 4.32, 2.21, and 4.29 cm for M₂, S₂ and K₁, respectively.