ALBERT

Description: The boundaries of the mud area of the inner German Bight have been mapped w1th a subbottom echo sounder. The echo profiles reveal a uniform sediment body which is chararterized by the occurrence of mud (clayey silt) in separate layers. The western part of the area is dominated by mud showing fine-sand intercalations, the well-known storm sand layers. The eastern part consists of fine-sand /mud alternate bedding. Primary stratification may be altered by bioturbation, particularly in the western part. However, the echographic uniformity of the mud area is almost independent of the regional variations of facies. At the southern, western, and northern boundaries the mud-area sediment body wedges out above the adjacent, more sandy sedimems. The eastern boundary is a system of sand tongues and channels with fine-sand/mud alternate bedding. Here, interfingering of sand and sand/mud facies may be a typical pattern in the depositional sequence due to occasional shifting of both sand tongues and channels. Based on hydrographic data from the German Bight the origin of the mud was ascribed mainly to the suspension load of the river Elbe. The suspended matter is transported towards north by the "Elbe water mass" which is a particular water body with lower salinity, as compared with surrounding North Sea waters. Main part of the suspension load is, however, deposited in the inner German Bight. The limits of mud deposition are given by the western and eastern boundaries of the "Elbe water" body as well as by shallower sand ridges surrounding the mud area in the south, east, and west.

Description: Current and wind stress time series obtained from the F1-mooring are analysed with the aim of examining linear correspondences and testing the adequacy of linear coupling models at near-inertial frequencies. Significant linear correlations are found in the data set which are consistent with a linear winddriven model of the current system. The current in the mixed layer can be described by inertial oscillations directly forced by the local wind stress. A wind-driven simulation model of the mixed layer currents yields an energy input of 3.10-3 W/m2. The current in the thermocline can be described by a linear internal wave field of downward propagating wave groups driven via Ekman suction by the wind stress field. Internal waves are generated at a rate of 10-3 W/m2, consistently estimated from both kinematic and dynamic considerations.

Description: During a multi-institutional air-sea interaction experiment (GATE) in the central Atlantic North Equatorial Countercurrent in September 1974, vector-averaging current meter (VACM) measurements were made within the 30-m thick mixed layer from three different types of surface moorings. The moorings consisted of a single-point taut-line flexible mooring (E3), a spar-buoy (El), and a 2-legged mooring (Fl). Although the kinetic energy density spectral estimates of the E3, El, and Fl records in the low frequency range were equivalent with 95% confidence, the mean progressive vector diagrams differed by 6 % in length and 4 in direction. At frequencies above 1 cph the variances of the 7.2 m Fl current vectors were about 1.5 times larger than the 7.6 m E3 data and the spectral levels of the 20 m El and 21.4 m E3 record were equivalent, suggesting that VACM current vectors recorded near the surface beneath a surface-following buoy do not contain detectable amounts of aliased high-frequency mooring motion.

Description: Energy dispersive X-ray microanalysis was used to localize the two brominated natural products (aerothinonin and homoaerothionin) in the tissues of a marine demosponge, Aplysina fistularis. Virtually all of these compounds were localized within the spherules of the spherulous cells in the mesohyl. This is the first localization of any secondary metabolite at the cellular or sub-cellular level in any marine invertebrate. In Aplysina fistularis, as in other species of the same genus studied by Vacelet, the spherulous cells are concentrated just beneath the exopinacoderm and just beneath the endopinacoderm of the excurrent canals. Moreover, there is electron microscopic evidence for degeneration of some spherulous cells throughout the mesohyl. Presumably, this degeneration can release some aerothionin and homoaerothionin, which are known to have antibiotic properties. After release from the spherulous cells, these brominated natural products could function (1) within the mesohyl to exclude some types of bacteria or to aggregate ingested bacteria and/or (2) within the boundary layer of the surrounding seawater for defense or offense, as considered in the discussion section.

Description: The maximum counterillumination intensities of three species of mesopelagic squids and one species of mesopelagic fish were determined in a shipboard laboratory. The values were compared with the intensity of downwelling irradiance in the ocean measured off Oahu, Hawaii. The upper depth limits of the mesopelagic fauna were determined by mid-day and moonlit-night trawling. The data support the hypothesis that limits on concealment from predation through counterillumination determine the upper depth limits of this fauna during the day. At night near full moon, however, animals may be found at light levels higher than those at which counterillumination seems to be an effective strategy.

Description: The oligochaete fauna (mainly tubificids and naidids) of a freshwater tidal flat, the "Fiihrmannssand", in the freshwater part of the Elbe Estuary was investigated. The distribution patterns in relation to sediment structure and food availability are discussed. The population dynamics of tubificids and naidids differ significantly. The standing stock of tubificids remains fairly constant throughout the year. Breeding activities take place during the whole year. These data are discussed and compared with those of other surveys where seasonal reproduction activities of tubificids were reported. The naidid population fluctuates considerably in size throughout the year. Abundance maxima are mainly found in spring (Nais spp., Paranais frio). Two annual maxima, in early spring and autumn, are exhibited by Amphichaeta leydigii. Some data are presented on oligochaete endoparasites, especially on Caryophyllaeus laticeps (Cestoda).

Description: Horizontal velocity and temperature measurements observed from a two-dimensional array of moored instruments, mooring Fl, are analysed to describe the near-surface internal wave field in the GATE (GARP Atlantic Tropical Experiment) C-scale area. Spectral properties indicate strong deviations from the Garrett and Munk (1972, 1975) deep ocean internal wave models. The frequency spectrum in the upper pycnocline is dominated by three energetic bands centered at 0.0127 (inertial frequency), 0.08 (M2-tidal frequency) and 3 cph. The latter frequency band does not correspond to the local Brunt Väisälä frequency (〈 10 cph) and contains about one half of the total internal wave energy of fluctuations with periods less than 10 hours. Cross-spectral analysis of the high frequency internal waves yields corresponding wavelengths of order 1 km consistent with westward propagating first mode wave groups, if the effect of Doppler shift due to a strong mean current is taken into account