Nutrient (P, N) dynamics in the southwestern Kattegat, Scandinavia: sedimentation and resuspension effects

 The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000 tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m^–2 yr^–1) and 477 ton of P (on average 0.9 g m^–2 yr^–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity (56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively. Received: 10 July 1995 · Accepted: 19 January 1996     

A new method of initial orbit determination

Up to now we have been dealing with the construction of entirely analytical planetary theories such as VSOP82 (Bretagnon, 1982) and TOP82 (Simon, 1983). These theories take into account the whole of the Newtonian perturbations of nine point masses: the Sun, the Earth-Moon barycentre, the planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. They also take into account perturbations due to some minor planets, to the action of the Moon and the relativistic effects. The perturbations of these last three types are in a very simple way under analytical form but they considerably increase the computations when introduced in the numerical integration programs.In the present paper we thus study a solution in which the Newtonian perturbations for the ten point masses are treated through numerical integration, the other perturbations being analytically added.     

Theoretical properties of radio-galaxies

We present optical photometric observations of the cataclysmic variables AO Psc and V 1223 Sgr, both of which are believed to contain slowly-rotating white-dwarf pulsars. These objectes belong to the new class of intermediate polars in which the magnetized-white-dwarf rotation period lies in between synchrous and extremely fast rotation periods. The observations reported here were carried out from the Kavalur Observatory using a 1 m reflector. High-time resolution light curves depicting a rich variety of flicker phenomena are presented. Results of a periodic analysis to search for coherent periodic modulations in the light curves are also presented. We have also derived the optical pulse profile of AO Psc and point out its similarities to the X-ray pulse profile.     

Application of beam forming techniques to measurements of acoustic scattering from the ocean bottom

Signals from an explosive source backscattered from the seafloor and received at long range by hydrophones of a towed array are processed to estimate the directional distribution of energy for a given time increment. As assembly of these data shows the time and amplitude of scattering features, and after conversion to distance, the geographic location of the return. A frequency-domain beam-forming procedure is used in which beam levels are averaged over a given band of a broad-band source. The processing is applied to experimental data obtained in the southern Tyrrhenian Sea. The major backscattering occurred at the Baconi Seamounts and the coastal margin of Sardinia.     

The three-dimensional geometry of the heliospheric current sheet

The three-dimensional geometry of the heliospheric current sheet seen from fixed points in interplanetary space is constructed for idealized (sinusoidal) magnetic neutral lines (equators) and for an observed magnetic equator on the basis of the “kinematic method” developed by Hakamada and Akasofu (1982). The cross-sections of the wavy current sheet at distances 1, 2 and 5 a.u. are also constructed for the idealized magnetic neutral lines.     

FORWARD MODELING IN THE FREQUENCY-SPACE DOMAIN*

Forward modeling of zero-offset data is performed in the frequency-space domain using a one-way extrapolation equation. The use of the frequency domain offers several advantages over conventional time domain methods. The greatest advantage of the frequency domain is that all time derivatives are evaluated exactly by a simple multiplication. Synthetic zero-offset sections are computed with a high degree of accuracy for arbitrary velocity and reflectivity structures. Examples are shown for realistic complicated models and compared with results from physical modeling.