Presented at a symposium on 'Physico-chemical aspects of penetration through plant cuticle', organised by the Physicochemical and Biophysical Panel on 2 April, 1968.

The cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing. We investigated this cascade along the Hawaiian Ridge using observations and numerical models. A divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models. Large internal tidal waves with peak-to-peak amplitudes of up to 300 meters occur on the ridge. Internal-wave energy is enhanced, and turbulent dissipation in the region near the ridge is 10 times larger than open-ocean values. Given these major elements in the tides-to-turbulence cascade, an energy budget approaches closure.

No abstract

[1] A primitive equation model is used to examine the structure and energetics of M 2 internal tides generated at the Hawaiian Ridge. Recent estimates based on altimeter data suggest that 20 GW of barotropic tidal dissipation occurs at the ridge, with conversion to internal tides believed to be the dominant dissipation mechanism. The model simulates an internal tide that accounts for 9.7 GW of radiated energy away from the ridge in the northeast and southwest directions. The strongest generation occurs at three sites where enhanced barotropic currents flow across elongated topographic features. The depthintegrated baroclinic energy flux and energy densities at these sites are on the order of 10 4 W m À1 and 10 4 J m À2 , respectively. A modal decomposition indicates that 62% of the outgoing energy flux is accounted for by the first internal mode, 15% is accounted for by the second mode, and less than 5% is accounted for by each subsequent higher mode. The tidal dissipation due to bottom friction along the ridge is estimated to be 0.1 GW. The level of turbulent dissipation near the ridge owing to tidal energy conversion remains to be determined to assess fully the barotropic-baroclinic energy budget. INDEX TERMS: 4544

No abstract

Abstract. A numerical investigation is made into the generation of semidiurnal internal tides by tidal flow over steep topographic features in the deep ocean. A fully three-dimensional, free surface, nonlinear, hydrostatic model (the Princeton Ocean Model) is used with real stratification, representative tidal forcing, and Gaussian-shaped seamounts, ridges, and islands for the topography. The eificiencies of the different topographies in extracting energy from the barotropic tide and in generating an internal tide are considered. Each topography produces an internal tide characterized by signals propagating away from the feature as beams that follow internal wave characteristic paths. The strength of the signals, however, varies markedly for different topographies. This is largely attributed to the way in which the barotropic tide interacts with the three-dimensional topography. Internal wave generation requires a significant vertical displacement of stratified water by the barotropic tide as it flows over topography. It is found that for symmetric seamounts and islands the barotropic flow tends to go around the feature, producing only a weak internal tide. When elongated into a ridge, barotropic flow is forced across isobaths, generating an energetic internal tide. Changing the horizontal aspect ratio of the topography from 1:1 (a seamount) to 3:1 (a ridge) increases the resulting baroclinic energy flux by nearly an order of magnitude. The slope of the topography relative to that of the internal wave characteristics is also shown to be important with strongest generation occurring at regions of critical or supercritical topographic slope.

No abstract

SUMMARY A wick feed method was used to recrystallize a range of different plant epicuticular waxes from solutions in organic solvents. Using the scanning electron microscope the ultrastructure of the recrystallized wax from each species was compared with that of the wax on the corresponding intact plant surface and in many cases was found to be similar. It is concluded that the crystal structure of epicuticular waxes is greatly influenced by their inherent chemical and physical properties rather than by properties of the underlying cuticular membrane or by any mechanism of extrusion or transport of the wax to the plant surface.