Gunnar Kullenberg

Scattering of light by Sargasso Sea water

Abstract This experimental investigation deals with the problem of the scatterance of light by very clear ocean water. The forward scatterance was measured close to a laser beam using a new measuring device. The forward particle scatterance was found to be virtually independent of wavelength, whereas the backward scatterance was dependent on the wavelength. The water investigated has a high degree of clearness compared with other areas. The ratio of scatterance at 45° to total scatterance over all angles was found to vary within narrow limits for different oceanic areas.

Investigation of Small-Scale Vertical Mixing in Relation to the Temperature Structure in Stably Stratified Waters

Publisher Summary This chapter explores the connection between the temperature and dye distributions and compares the observations from the various areas. Thereafter, it interprets the observed formations of the dye layers in the light of various possible vertical mixing mechanisms. The profiles of salinity, temperature, and current are observed before and during the tracing period. The pulse-ford layers with an approximately homogeneous distribution are the most common ones. They are very persistent, and layers can, with a reasonable degree of certainty, be identified with increasing diffusion time. The sharp boundaries indicate the presence of shear, and by and large the same type of layered structure is found in the lake. The dye layers are clearly related to the temperature distribution. The remarkable persistency of the layers is proof enough of the weak current and the low turbulence intensity. There are significant differences between the distributions found in the lake and the sea; the lake layers are generally thicker and the multilayered structures are more common. The chapter concludes that a contaminant injected in a subsurface layer of stratified waters will become distributed in layers related to the current and density conditions in the water; because of trapping of layers they can be very persistent; and the vertical mixing rates are low. The observations favor the interpretation of the mixing as an intermittent process mainly governed by shear instabilities.

Light scattering observations in the northwest African upwelling region

Abstract Observations of suspended matter by a light scattering technique in the northwest African upwelling area are described. The distributions are compared with the temperature distributions and interpreted by considering upwelling dynamics. The observations suggest that there was upwelling over the shelf and slope, that the upwelling system reached depths of 300 to 400 m over the slope, and that the system prevailed to about 130 km from the coast. The scattering distributions indicate the frontal character of the upwelling zone and that this zone moved seawards during an upwelling event. Over the shelf and slope there was a turbid bottom boundary layer, generated on the shelf by the southgoing wind-driven current and related on the slope to the poleward undercurrent. At least part of the suspended matter in the layer was supplied by settling from the surface layer. The mean currents could not cause bottom erosion.

The Distribution of Particulate Matter in a Northwest African Coastal Upwelling Area

The particle distribution in the upper 200 m of the upwelling area oceanward of the northwest African coast has been investigated, using an in situ integrating light-scattering meter, with the twofold purpose of relating to the general conditions in the area regarding circulation, topography, biology, and chemistry, and investigating the possibility of defining and tracing water masses in such an area by their particle content. The investigation demonstrates that the particle content of water can serve as an indicator of physical and biological processes. Particle content very distinctly characterizes water-type. The great advance in using in situ lights cattering instruments combined with simultaneous temperature recording to study the oceanic particle distribution is apparent.

Note on the Role of Vertical Mixing in Relation to Effects of UV Radiation on the Marine Environment

Considering that the penetration depths of UV radiation into the sea are limited, and in particular as regards the levels at which UV radiation appears to be markedly harmful to marine organisms, the possible role of vertical mixing is discussed in relation to assessing harmful effects of UV radiation. The vertical mixing varies strongly in time and space, implying large variations of residence times of organisms in the near-surface layer. Periods of weak vertical mixing often coincide with periods of high biological activity.

Aspects of Bottom Boundary Layers in the Ocean

The dynamics of the “bottom” boundary layer in the ocean is influenced by the rotation of the earth, the mean oceanic circulation being in approximate geostrophic balance. An Ekman boundary layer is developed to match the interior flow, in which the velocity vector changes direction towards the bottom. Seen from above the change is clockwise in the northern hemisphere. Based on a Reynolds number criterion, the oceanic Ekman boundary layer is turbulent, the typical Reynolds number being at least an order of magnitude larger than the critical one (Wimbush and Munk 1971). However, the stability of the density stratification also influences the dynamics of the boundary layer.