On the influence of submarine ridges on translation and stability of Agulhas rings

A series of experiments with a quasi‐geostrophic model have been carried out to investigate the influence of topographic obstacles on the translatory movement of Agulhas rings. The rings were initialized as Gaussian‐shaped anomalies in the stream function field of a two‐layer ocean at rest. Bottom topography consisted of a meridional ridge of constant height in the middle of the quadratic model domain. The vertical ring structure, the initial ring position, and the height of the ridge were varied. The general northwestward movement of the model eddies has been shown to be modified toward a more equatorward direction by encountering the upslope of the ridge. Sufficient topographic heights and strong slopes can even block the eddies and force them toward a pure meridional movement. During their translation the eddies lose their vertical coherence. After about 150 days the eddy can only be detected by the surface signal, while the lower layer eddy is dispersed by the radiation of Rossby waves. The passage of “young” (regarding the time between their initialization and their contact with the ridge) and energetic eddies is accompanied by the observation of along‐slope currents of significant strength. These may be due to the rectification of radiated Rossby waves at the topographic slope. Only eddies with a significant dynamic signal in the lower layer are influenced by the bottom topography. Strong, shallow eddies over deep lower layers can cross the ridge without strong modification of their translatory movement

AFLP analysis sheds light on distribution of two Salix species and their hybrid along a natural gradient

Amplified fragment length polymorphism (AFLP) analysis of 26 trees of three Salix taxa: Salix alba L. (White Willow), S. fragilis L. (Crack Willow) and their hybrid S. x rubens Schrank, across an example of their habitat range in south-west Germany, supported the distribution previously determined using morphological characterization. UPGMA and principal coordinates analysis of the AFLP data revealed three distinct clusters corresponding to the three taxa. In addition, AFLP analysis on individuals which were difficult to identify morphologically revealed that they were either the hybrid S. nr rubens or S. fragilis. Four specimens of S. fragilis were indistinguishable with three primer combinations suggesting they are members of one clone

Biomechanics of the giant reed Arundo donax

The quantitative description of local buckling of hollow plant stems requires the knowledge of Young's modulus in the longitudinal and tangential directions for the different tissues of which the stem is composed. For thick-walled stems the shear modulus for the radial-tangential plane is needed for an advanced treatment of the process of ovalization. The primary causes of failure can be predicted if critical compressive strains in the longitudinal direction and critical tensile strains in the tangential direction are known. All of these mechanical properties and their variation along the length of the stem can be measured in Arundo donax