Physical and biochemical aspects of the flow across the Mascarene Plateau in the Indian Ocean.

This paper presents results from a detailed hydrographic survey of the Mascarene Plateau and surrounding area undertaken by the RRS Charles Darwin in June-July 2002. We examine how the westward-flowing South Equatorial Current (SEC) crosses the plateau, and how the structure of the flow determines the supply of nutrients to the surface waters. We find that the flow of the SEC across the plateau is highly dependent on the complex structure of the banks which make up the plateau, and that a large part of the flow is channelled between the Saya de Malha and Nazareth Banks. Furthermore, the SEC forms a sharp boundary between subtropical water masses from further south, which are low in nutrients, and waters from further north, which are relatively nutrient rich. Overall, the SEC delivers relatively high levels of nutrients to the near-surface waters of the central and northern regions of the plateau, compared with the southern regions of the plateau. This is partly due to uplifting of density surfaces through Ekman suction on the northern side of the SEC, and partly due to the higher levels of nutrients on those density surfaces on the northern side of the SEC. This may drive increased production of phytoplankton in these areas, which would in turn be expected to fuel increased abundances of zooplankton and higher levels of the food chain.

Effect of 2-hydroxyacids on guinea-pig footpad stratum corneum: mechanical properties and binding studies.

Synopsis The effect of aqueous solutions of 2-hydroxyacids of chain length C(3) to C(10) on the extensibility of undamaged and solvent-damaged guinea-pig footpad stratum corneum has been studied. The increase in extensibility of solvent-damaged corneum, caused by treatment with hydroxyacid, reached a maximum with 2-hydroxycaprylic acid (C(8)); on undamaged corneum, 2-hydroxycaprylic acid was the only hydroxyacid studied to give a significant effect. The increase in corneum extensibility produced by 2-hydroxyacids decreases when the pH is raised from 3 to 4. This loss of effect correlates with the ionization of the hydroxyacid (pK 3.85). The binding of radiolabelled 2-hydroxycaproic (C(6)) and 2-hydroxycaprylic acids to stratum corneum has been studied. 2-Hydroxycaprylic acid binds much more strongly than 2-hydroxycaproic acid, the difference in the binding being consistent with the hydrophobic binding energy of two methylene groups. Raising the pH above 3.5 results in a large decrease in the binding of 2-hydroxycaprylic acid in line with the corresponding reduction in extensibility. Treatment with 2-hydroxyacids results in a small increase in the water-binding capacity of solvent-damaged stratum corneum, but in a decrease in the water-binding capacity of undamaged stratum corneum. These data are discussed in terms of a possible mechanism for the plasticizing of stratum corneum.